1. CopyrightbyOchiagha Victor Ananaba 2007

2. Experimental Study On The Effect Of The Internal Design On The Performance Of Down hole Gas Separators by Ochiagha Victor Ananaba, B.Eng. Thesis Presented to the Faculty of the Graduate School ofThe University of Texas at Austinin Partial Fulfillment of the Requirementsfor the Degree ofMASTER OF SCIENCE IN ENGINEERING The University of Texas at AustinDecember 2007 3. Experimental Study On The Effect Of The Internal Design On The Performance Of Down hole Gas Separators Approved by Supervising Committee: Augusto L. Podio (Supervisor) Paul Bommer 4. DedicationTo God Almighty.To my loving and supporting parents Sir Emeka & Lady Nnenne Ananaba.To my siblings, Nnem, Ugochukwu, Ugwunwanyi, Ogbugo & Amah (Papa). To the woman that will be my wife. 5. AcknowledgementsI specifically want to thank my supervisor Dr. Augusto Podio for his continuoussupport and encouragement through this research project. Under his supervision I havegreatly improved my knowledge and skills in the areas of petroleum production engineeringand artificial lift systems. It is an honor to have him as my supervisor and to be his friend.I wish to thank Dr. Paul Bommer for the time that he took inside his very busyschedule to read and review my thesis.I will not forget to thank our Lab. Technician and my friend Tony Bermudez whosesupport in maintaining and constructing my laboratory models made certain that I finishedmy experiments in good time with high levels of accuracy.I wish to thank Glenn Banm, Harry Linnemeyer, Ehiwario M., Acholem K., OjifiniR., Elekwachi K. and Don Sorrell who were there to help whenever I needed assistance.My special thanks go to our amiable graduate coordinator Cheryl Kruzie. I would notbe in UT if not for her kind and honest counseling.Finally I would like to thank the companies that supported this research, EchometerCompany, ConocoPhillips, Yates Petroleum and Chevron. The comments and suggestionsfrom James McCoy, Lynn Rowland, John Patterson and Gabriel Diaz helped in shaping myresearch.I worked with Renato Bohorquez in the early days of this research and it was great. Ochiagha Victor Ananaba December 2007 v 6. ABSTRACTExperimental Study On The Effect Of The Internal Design On ThePerformance Of Down hole Gas SeparatorsOchiagha Victor Ananaba, M.S.E.The University of Texas at Austin, 2007 Supervisor: Augusto L. Podio The re-design of the internal geometry of static down hole gas separators directlyaffects the gas liquid separation performance. This thesis describes experimental results obtained after changing the dip tube designfrom the conventional straight design to a helical design. Typically, a static down hole gasseparator with a conventional straight dip tube design depends on gravity to induce densitydifference in the flowing wellbore fluid which causes gas liquid separation to occur. Thus,the device is known as a gravity driven down hole gas separator. vi 7. This research compared the experimental results and visual observations fromgravity driven down hole gas separators to that of static down hole gas separators withhelical dip tube designs known as static centrifugal down hole gas separators.The visual observations showed that not only did the driving mechanisms for gas liquid separation inside static centrifugal down hole separators include gravity it alsoincorporated other means such as induced centrifugal forces that greatly improved overallgas liquid separation. The 6 inch/second threshold downward superficial liquid velocitygenerally regarded as the industry rule of thumb for down hole gas separators wasincreased to 10 inch/second. In field units this is a 200 BPD increase in liquid production.This research also studied the effect of increasing outer diameter of gravity drivendown hole gas separators from 3inches (2.75 ID) to 4inches (3.75 ID). The resultsshowed that liquid handling capacity increased by over 90% due to favorable flow regimesobserved inside the separator. However, critical examination of gas liquid separationperformances of both 3 inch OD and 4 inch OD separators in terms of downward liquidsuperficial velocity reveal that gas liquid separation results are similar. It was concludedtherefore that downward superficial liquid velocity is a reliable parameter in the design ofdown hole gas separators and that all gravity driven separators regardless of separatorouter diameter will operate in similar fashion except at different liquid flow rates.Bubble rise experiment performed in this research project gave a range of 1 100 cpas region of applicability for the results discussed in this thesis.vii 8. Table of ContentsAcknowledgment vAbstract...viList of Tables ........................................................................................................ xiiList of Figures ...................................................................................................... xiiiCHAPTER 1 1Introduction ..............................................................................................................1 1.1 OBJECTIVE ..........................................................................................1 1.2 LITERATURE REVIEW ......................................................................3 1.2.1 PATENTED STATIC CENTRIFUGAL DOWN HOLE GAS SEPARATORS ...........................................................................15 1.2.1.1GAS ANCHOR - PATENT No 3128719.................................15 1.2.1.2Continuous Flow Down hole gas separator for Progressive Cavity Pumps - Patent No 5902378 .........................17 1.2.2 ACTIVE TYPE CENTRIFUGAL DOWN HOLE GAS SEPARATORS ...........................................................................20 1.2.2.1Liquid Gas Separator Unit - Patent No 3887342 .............20 1.2.2.2Liquid Gas Separator Apparatus - Patent No 4481020 ...21 1.2.2.4Apparatus for separating gas and solids from well fluids - Patent No 6382317 B1.................................................................24CHAPTER 2 28Experimental Facility And Procedure ....................................................................28 2.1 EXPERIMENTAL FACILITIES.........................................................28 2.2 DESCRIPTION OF EXPERIMENTAL FACILITIES .......................28 2.3 LABORATORY TEST WELL............................................................32 2.3.1 LABORATORY INSTRUMENTS ............................................34 2.3.1.1LIQUID FLOW MEASUREMENTS ................................34 2.3.1.2GAS FLOW MEASUREMENT ........................................35 viii 9. 2.3.2.2PRESSURE MEASUREMENT ........................................372.4EXPERIMENTAL PROCEDURE ......................................................382.5 SEPARATOR PERFORMANCE DISPLAY ......................................392.6DOWN HOLE GAS SEPARATOR DESIGNS ..................................44 2.6.1 ECHOMETER (3X1), ECHOMETER (3X1.5), ECHOMETER (4x1), ECHOMETER (4X1.5), ECHOMETER (4X1.75) ..........44 2.6.2 PATTERSON (3X1), PATTERSON (3X1.5), PATTERSON (4x1), PATTERSON (4X1.5), PATTERSON (4X2)..................47 2.6.3 TWISTER ...................................................................................48 2.6.3.1ECHOMETER-TWISTER ..........................................52 2.6.3.2PATTERSON TWISTER .........................................53CHAPTER 3 55Analysis Of Experimental Results .........................................................................553.1EFFECT OF HELICAL DIP TUBE DESIGN ....................................55 3.1.1 PERFORMANCE RESULTS FOR THE TWISTER SEPARATOR .............................................................................56 3.1.2 PERFORMANCE RESULTS FOR ECHOMETER TWISTER SEPARATOR .............................................................................58 3.1.3 PERFORMANCE RESULTS FOR PATTERSON TWISTER SEPARATOR .............................................................................613.2 COMPARISON OF PERFORMANCES OF HELICAL DIP TUBEGAS SEPARATORS TO STRAIGHT DIP TUBE GAS SEPARATOR63 3.2.1 COMPARISON OF ECHOMETER-TWISTER AND ECHOMETER (3X1) GAS SEPARATORS ..............................63 3.2.2 COMPARISON OF PATTERSON-TWISTER AND PATTERSON (3X1) GAS SEPARATORS ...............................73 3.2.3 EFFECT OF THE NUMBER OF DIP TUBE TWISTS ON STATIC CENTRIFUGAL SEPARATORS ...............................78 3.2.4 ANALYSIS OF STATIC CENTRIFUGAL SEPARATOR DESIGNS. ...................................................................................843.3 EFFECT OF INTERIOR AND EXTERIOR FLOW AREAS ONSEPARATOR PERFORMANCE........................................................88 3.3.1 EFFECT OF CHANGING INTERIOR AND EXTERIOR ANNULAR AREA FOR ECHOMETER GAS SEPARATORS90 ix 10. 3.3.2 EFFECT OF CHANGING INTERIOR AND EXTERIORANNULAR AREA FOR PATTERSON GAS SEPARATORS1033.4DIP TUBE LENGTH EFFECTS ..............................................1163.5 PERFORMANCE OF ECHOMETER (3X1) GAS SEPARATORWITH STANDING VALVE INCLUDED BETWEEN GASSEPARATOR AND TUBING RETURN LINE (PUMP INTAKE) .1193.5.1 ECHOMETER (3X1) AND ECHOMETER (3X1) WITHSTANDING VALVE COMPARED. .......................................1233.5.2 ANALYSIS OF PRESSURE DROP FOR ECHOMETER (3X1)AND ECHOMETER (3X1) WITH STANDING VALVE ......1253.6 FLOW REGIMES INSIDE THE DOWN HOLE GASSEPARATORS ..................................................................................126CHAPTER 4133Bubble Rise Experiments .....................................................................................1334.1 APPARATUS USED IN BUBBLE RISE EXPERIMENTS.............1344.2 PROPERTIES OF FLUIDS USED IN THE EXPERIMENT ...........1364.2.1 TEST FOR NEWTONIAN CHARACTERISTICS OF FLUIDS1364.2.2 DETERMINING THE VISCOSITY OF TEST FLUIDS INASSOCIATION WITH WATER AT ROOM TEMPERATURE1384.2.2.1TEST DATA FOR GLYCERIN IN ASSOCIATION WITHWATER ....................................................................................1394.2.2.2TEST DATA FOR CORN SYRUP IN ASSOCIATIONWITH WATER .........................................................................1404.3ANALYSIS OF RESULTS FROM BUBBLE RISE EXPERIMENTS141CHAPTER 5145Conclusions and Recommendations ....................................................................1455.1CONCLUSIONS...............................................................................1455.1.1 CONCLUSIONS FROM COMPARISONS OF GRAVITYDRIVEN SEPARATORS AND STATIC CENTRIFUGAL GASSEPARATORS .........................................................................1465.1.2 THE EFFECT OF INCREASING SEPARATOR OUTER DIAMETER FOR GRAVITY DRIVEN SEPARATORS .......1475.1.3 CONCLUSIONS FROM BUBBLE RISE EXPERIMENT ....149 x 11. 5.2GENERAL DESIGN GUIDE ...........................................................149 5.3RECOMMENDATIONS AND FUTURE WORK ..........................150Appendix A ..........................................................................................................152Schematics of the Echometer Separators .............................................................152Appendix B ..........................................................................................................155Schematics of the Patterson Separators ...............................................................155Appendix C ..........................................................................................................159Original data files .................................................................................................159Nomenclature .......................................................................................................160Abbreviations .......................................................................................................161References ............................................................................................................163Vita .165 xi 12. List of Tables Table 2-1 - Sample Excel Spreadsheet for continuous flow test.......................................... 41Table 2-2 Echometer gas separators configuration ............................................................ 44Table 2-3 Patterson Separator Configuration ...................................................................... 46Table 4-1 Dimensions of bubble rise experiment apparatus ........................................... 134Table 4-2 Fluid Properties used in bubble rise experiment ............................................. 135Table 4-3 Test data for glycerin in association with water............................................... 138Table 4-4 - Test data for corn syrup in association with water ....................................... 139xii 13. List of Figures Figure 1-1 - Centrifugal Separator(Kobylinski et al) ................................................................ 8 Figure 1-2 - Gas flow through centrifugal separator (Kobylinski et al) ................................ 9 Figure 1-3 - Reverse-flow separator (Kobylinski et al) .......................................................... 10 Figure 1-4 Collar-Size down hole gas separator (McCoy and Podio10)....................... 12 Figure 1-5- Down-hole gas separator (Patterson and Leonard11) ........................................ 14 Figure 1-6 - Jongbloed et al12 ..................................................................................................... 17 Figure 1-7 Static Centrifugal Separator by Obrejanu Marcel13 .......................................... 19 Figure 1-8 Invention by Bunnelle P14.................................................................................... 21 Figure 1-9 - Centrifugal Separator by Kobylnski et al ........................................................... 23 Figure 1-10 Invention by Powers Maston15 ......................................................................... 24 Figure 1-11 Invention by Delwin Cobb16 ............................................................................. 26 Figure 1-12 Cross section (3) in Figure 1-11 .................................................................... 26 Figure 2-1 Schematic of experimental test facility .............................................................. 30 Figure 2-2 Laboratory facility ................................................................................................. 30 Figure 2-3 Laboratory test well .............................................................................................. 31 Figure 2-4 Laboratory Well .................................................................................................... 32 Figure 2-5 Turbine flow meter and valve between pump and mixer ............................... 33 Figure 2-6 - - ITT Barton floco positive displacement meter .............................................. 34 Figure 2-7 - Fisher Porter Flow Rator tube............................................................................. 35 Figure 2-8 - Thermodynamic Omega Air Flow Meter .......................................................... 36 Figure 2-9 - Sample Performance plot for Patterson (3X1) in continuous flow ............... 42 Figure 2-10 Echometer (3 X1.5) gas separator design ....................................................... 45 Figure 2-11- Echometer entry port geometry ......................................................................... 45 Figure 2-12 Echometer (4X1.75) gas separator design ...................................................... 45 Figure 2-13 4 inch OD Patterson Separator Design .......................................................... 47 Figure 2-14 3 inch OD Patterson Separator Design .......................................................... 47 Figure 2-15 Twister Separator (Bohorquez) ........................................................................ 50 Figure 2-16 Twister Connection ............................................................................................ 50 xiii 14. Figure 2-17 Diagrammatic of the forces acting in a static centrifugal separator ............ 51 Figure 2-18 Echometer - Twister .......................................................................................... 52 Figure 2-19 Patterson - Twister ............................................................................................. 53 Figure 3-1- Twister results in field units .................................................................................. 56 Figure 3-2 - Twister result in terms of superficial velocities ................................................. 57 Figure 3-3 Echometer - Twister result in terms of superficial velocities ......................... 58 Figure 3-4 Echometer - Twister results in field units ......................................................... 59 Figure 3-5 - Patterson - Twister result in terms of superficial velocities ............................ 60 Figure 3-6 - Patterson - Twister results in field units............................................................. 61 Figure 3-7 Comparison of Echometer Twister and Echometer (3X1) results in terms of superficial velocity .................................................................................................................. 64 Figure 3-8- Comparison of Echometer Twister and Echometer (3X1) results in Field Units .............................................................................................................................................. 65 Figure 3-9 - Pressure Drop between the entry ports and pump intake for Echometer Twister and Echometer (3X1); Casing Pressure (Pc) = 10 13psi ...................................... 66 Figure 3-10 Pressure measurements during the tests ......................................................... 67 Figure 3-11 Pressure drop for Echometer-Twister and Echometer (3X1) at constant gas rates; Pc = 10 13 psi .......................................................................................................... 68 Figure 3-12- Pressure drop for Echometer-Twister and Echometer (3X1) at constant liquid rates; Pc = 10 13 psi ...................................................................................................... 71 Figure 3-13 - Comparison of Patterson Twister and Patterson (3X1) results in terms of superficial velocity ....................................................................................................................... 72 Figure 3-14 - Comparison of Echometer Twister and Echometer (3X1) results in Field Units .............................................................................................................................................. 73 Figure 3-15 - Pressure Drop between the entry ports and pump intake for Patterson Twister and Patterson (3X1) separators; Casing Pressure (Pc) = 10 13psi ...................... 74 Figure 3-16 Pressure drop for Patterson-Twister and Patterson (3X1) at constant gas rates; Pc = 10 13 psi ................................................................................................................. 75 xiv 15. Figure 3-17 - Pressure drop for Patterson-Twister and Patterson (3X1) at constant liquid rates; Pc = 10 13 psi ................................................................................................................. 76 Figure 3-18 Patterson-Twister (2 twits) ................................................................................. 77 Figure 3-19 - Patterson Twister (2 twists) results in terms of superficial velocities ....... 78 Figure 3-20 - Patterson Twister (2 twists) gas separator results in field units ................ 79 Figure 3-21 - Comparison of Patterson Twister (4 twists) and Patterson Twister (2 twists) results in superficial velocity terms ................................................................................ 80 Figure 3-22 - Comparison of Patterson Twister (4 twists) and Patterson Twister (2 twists) results in Field Units ........................................................................................................ 81 Figure 3-23 - Pressure drop between the entry ports and pump intake for Patterson Twister 2 twists and 4 twists gas separators; Casing Pressure (Pc) = 10 -13 psi.................... 82 Figure 3-24 Comparison of results for all static centrifugal separators in terms of superficial velocities .................................................................................................................... 84 Figure 3-25 - Comparison of results for all static centrifugal separators in field units ..... 85 Figure 3-26 - Pump Liquid Fraction for Static Centrifugal Separators at 10 in/sec ......... 86 Figure 3-27 - Echometer (4X1) and Echometer (3X1) results compared in field units ... 90 Figure 3-28 - Echometer (4X1.5) and Echometer (3X1.5) results compared in field units ........................................................................................................................................................ 91 Figure 3-29 - Echometer (4X1.75) results in field units ........................................................ 93 Figure 3-30 Comparison of results of all Echometer gas separators in terms of superficial velocity ....................................................................................................................... 94 Figure 3-31 - Pump Liquid Fraction for Echometer Separators at 6 in/sec ...................... 96 Figure 3-32 - Pump Liquid Fraction for Echometer Separators at 10in/sec ..................... 97 Figure 3-33 Comparison of all Echometer 4 inch OD separator results in field units . 98 Figure 3-34 - Pressure drop between the entry ports and pump intake for Echometer 4 inch OD gas separators for 2 phase gas liquid flow; Casing Pressure (Pc) = 10 -13 psi. 100 Figure 3-35 - Pressure drop between the entry ports and pump intake all tested Echometer gas separators; Casing Pressure (Pc) = 10 -13 psi ............................................ 101 Figure 3-36 - Patterson (4X1) and Patterson (3X1) results compared in field units ....... 103xv 16. Figure 3-37- Patterson (4X1.5) and Patterson (3X1.5) results compared in field units .. 104 Figure 3-38 Patterson (4X1.75) results in field units ........................................................ 105 Figure 3-39 - Patterson (4X2) results in field units .............................................................. 106 Figure 3-40 - Comparison of results for all Patterson 3 inch OD and 4 inch OD separators in superficial velocity terms .................................................................................. 107 Figure 3-41 - Pump Liquid Fraction for Patterson Separators at 6 in/sec ....................... 109 Figure 3-42 - Pump Liquid Fraction for Patterson Separators between 8 9 in/sec ..... 110 Figure 3-43 - Comparison of all Patterson 4 inch OD separator results in field units ... 112 Figure 3-44 Pressure Drop between the entry ports and pump intake for Patterson 4 inch OD gas separators; Casing Pressure (Pc) = 10 13psi ............................................... 113 Figure 3-45 - Pressure drop between the entry ports and pump intake for Patterson 4 inch OD gas separators at varying gas and liquid rates; Casing Pressure (Pc) = 10 -13psi ...................................................................................................................................................... 114 Figure 3-46 Comparison of results for Echometer (4X1.75) with 5dip tube and Echometer (4X1.75) with 2 dip tube in superficial velocity terms ................................................................. 116 Figure 3-47 - Comparison of results for Echometer (4X1.75) with 5dip tube and Echometer (4X1.75) with 2 dip tube in field units ...................................................................................... 117 Figure 3-48 Standing Valve Assembly ................................................................................ 119 Figure 3-49 SV joint Gas Separator Connection ........................................................... 119 Figure 3-50 Echometer (3X1) with SV result in terms of superficial velocities ........... 120 Figure 3-51 - Echometer (3X1) with SV result in field units .............................................. 121 Figure 3-52 Comparison of Echometer (3X1) with and without Standing Valve in terms of superficial velocities ............................................................................................................. 122 Figure 3-53 - Comparison of Echometer (3X1) with and without Standing Valve in field units ............................................................................................................................................. 123 Figure 3-54- Pressure drop between the entry ports and pump intake for Echometer (3X1) with and without Standing Valve .................................................................................... 124 Figure 3-55 - Pressure drop between the entry ports and pump intake for Echometer (3X1) with and without Standing Valve at varying gas and liquid rates; Pc = 10 -13 psi ... 125 xvi 17. Figure 3-56 Flow Regimes observed in the gas separator annular area (courtesy Renato Bohorquez7)................................................................................................. 126 Figure 3-57 Flow regime map for the annular space of 3 inch OD gravity driven gas separators7 127 Figure 3-58 Flow regime map for the annular space of 4 inch OD gravity driven gas separators .. 128 Figure 3-59 Flow regime map for the Twister separator annlus7 ................................... 130 Figure 3-60 Flow regime for Patterson Twister and Echometer Twister static centrifugal separators ................................................................................................................ 131 Figure 4-1 Schematic of Laboratory Constructed Apparatus for testing bubble rise velocity ......... 134 Figure 4-4 Glycerin Rheology test ....................................................................................... 136 Figure 4-5 Glycol Rheology test .......................................................................................... 136 Figure 4-6 Corn Syrup Rheology test.................................................................................. 137 Figure 4-7 Viscosity plot for Glycerin in association with water at room temperature ...................................................................................................................................................... 138 Figure 4-8 Viscosity plot for Corn Syrup in association with water at room temperature ...................................................................................................................................................... 139 Figure 4-9 Combined viscosity plots for glycerin and corn syrup in association with water at room temperature ...................................................................................................... 140 Figure 4-10 Examples of bubble diameter sizes measured.142 Figure 4-11 Mean bubble rise velocities in stationary liquid in an annulus ................... 143xvii 18. Chapter 1 Introduction1.1OBJECTIVE Most wells producing from mature reservoirs use artificial lift methods for oiland gas production. Common artificial lift methods include beam pumping,progressive cavity pumping and electric submersible pumping. All the mentionedartificial lift systems exhibit a common problem: Gas Interference The presence of free gas in beam pumps (sucker rod pumps) prevents thetraveling valve from opening at the appropriate time interval during the downstroke.This is caused by the high compressibility of gas in the pump barrel. The travelingvalve may eventually open when the gas inside the barrel has been compressedenough to overcome the fluid load on the plunger. In such a case fluid pound occurs.In extreme cases the peak pressure of the trapped gas on the downstroke isinsufficient to overcome the hydrostatic head of the traveling valve; then the pressureis not reduced enough on the upstroke to allow the standing valve to open and admitnew fluid. Both valves are essential stuck at a closed position and the pump refuses topump. This extreme case is known as gas locking.In progressive cavity pumps (PCP) the produced liquid lubricates the rotor andthe stator so as to reduce the heat caused by friction. The presence of free gas in the 1 19. produced fluid reduces the lubricating function of the produced fluid so that the rotorand stator are in direct contact. Temperature increase due to the direct contact causesdamage to the pump. In other cases gas in the produced fluid in PCP may change thechemical composition of the elastomer in the stator of the pump which furthercomplicates the problem. Electric submersible pumps (ESP) are typically used to handle high liquid flowrates. Significant volumes of gas entering the pump especially at low intake pressures degrade the pump performance, and dramatically reduce the head produced by the ESP.This may prevent the pumped liquid from reaching the surface. The ESP is composed ofa down hole motor which is connected to a seal section which in turn is connectedto a centrifugal pump. It is imperative that the motor be cooled by the produced fluidpassing the outer casing. In the event that large quantities of gas pass the motor, the heattransfer from the motor to the produced fluid will be drastically reduced, potentiallycausing motor damage by overheating. In all cases - beam pumps, PCP and ESP the pump volumetric efficiency isreduced by the presence of gas. To combat the problem of reduced volumetric efficiencyand system damage down hole gas separators are used in conjunction with down hole pumps. The sole purpose of down hole gas separators* is to prevent gas from entering into down hole pumps, or to at least reduce the quantity of gas entering into the pumpto permissible ranges where the pump efficiency is still acceptable. Unfortunately many gas separator designs have not yielded the desired efficiency.The widely used poorboy gas separator which depends on gravity segregation toseparate gas from liquids has become synonymous with inefficiency.* Down hole gas separators will mean the same thing as gas separators throughout this thesis 2 20. A thorough literature review on the subject of gas separator design was done tostudy previous designs and relevant applications. Sources of information includedpublished technical papers, patents and thesis reports by Lisguiski, Guzman andBohorquez. The scope of the present work emphasized the effect of the internal geometryand induction of centrifugal forces on gas separator performance. 1.2LITERATURE REVIEW Schome 1 in February 1953 reported a field test of a down-hole gas separator in awell in Utah. The pump volumetric efficiency obtained before the installation the down-hole gas separator ranged between 26 and 48%. Schome1 reported that the efficiency wasincreased to 70%; resulting in an increased production of 50BPD after the new gasseparator was installed. The author went on to describe some bottom-hole separator (asit was then referred) designs and their mode of operation. All the separator designsdescribed in his paper depended on gravity segregation as the controlling mechanism for efficient performance and were 30 40 ft long with 1inch suction tubes (dip tubes).Schome1 noted that operators often faced retrieval problems when the separators were plugged with formation debris. He attributed that to inconsistent installation techniquesand gas separator designs. Clegg2 did a thorough review of the different types of gas anchors (down-holegas separators) and the principles that govern most of their operation. He pointed outthat the desire of several gas separator inventors was to achieve a downward mixture3 21. velocity of 0.5ft/sec (6in/sec) inside the separator dip tube annular area. A downwardmixture velocity of 0.5ft/sec is generally accepted as being below the rising (slip) velocityof gas in low viscosity fluids. Clegg2 and McCoy3 et al described the reasons for the inefficiency of the commonest down-hole gas separator design the poorboy separator.The reasons for the inefficiency of the Poorboy gas separator according to the authorincluded the high downward liquid velocity inside the Poorboy separator and size of itsdip tube ID which the author considered as too small in diameter. The small ID dip tubeoften causes excessive pressure drop inside the separator. The Shell (Schmit Jongbloed)gas anchor formula:100gas anchor efficiency =(1 + C Pwf Vsl0.5 )0.66 1 Pwf= intake pressure at the anchor; Vsl=downward superficial velocity of liquids; C = gas anchorconstant (usually 0.2 based on laboratory data)described by Clegg1 showed that the performance of any given size and type of gasseparator is largely dependent on the intake pressure at the anchor and the downwardsuperficial velocity of the fluids in the anchor. An examination on the formula done bythe author reveled that at zero pressure and zero velocity the anchor/gas separatorefficiency is 100% and that at high velocities (greater than 0.5 ft/sec) inside the gasseparator the separation efficiency is poor. Pressures above 400psig also resulted in lowefficiencies. The author however cautioned that actual experiences indicate thatseparation may be significantly greater than what the formula predicts. The uncertainty inthe equation emerged from the use of the constant C which represented otherimportant variables such as viscosity, gas bubble size and dispersion. Laboratory resultsthat were not published indicated a constant of 0.2. The author warned that the 4 22. determination of accurate values of C is difficult for actual field conditions. Clegg2 strongly encouraged using a Natural gas anchor (installing the pump below the lowestperforation) whenever it is feasible as is gives the greatest down-pass area for the liquidthereby reducing the downward liquid velocity. The work by Campbell and Brimhall4 largely focused on developing an industrystandard for determining the down-hole gas separator area; the dip tube area and the diptube length to be used for different liquid and gas flow rates. The objective of theircomputer program was to aid in the design of a gas separator system and to evaluate thepressure drops within the system and thus the system efficiency. The major parameterswhich they noted were pivotal to gas separator design included the gas bubble velocity,diameter of the mud anchor (down-hole gas separator), length of dip tube and thepressure drops associated with the system. They agreed that the 0.5 ft/sec downwardliquid velocity inside the separator was a valid rule of thumb for low viscosity fluids.The design procedure began with using Stokes Law (see Equation 2) to determine theterminal rising velocity that a given gas bubble will achieve in a liquid for a given gasbubble radius, liquid viscosity and density difference between the two phases.2 g ( 1 2 ) Rb2U=92 Where U = terminal velocity, ft/sec; g = 32.17 ft/sec2; L = liquid density; Ib/ft3 g = gas density, Ib/ft3; = liquid viscosity; Ibm/(ft-sec); Rb = bubble radius (ft)The second step used the calculated terminal velocity to calculate the area of the gasseparator (also called Mud Anchor or MA) using equation 3. 5 23. 0.00935 QL AMA = U EVSTB Where AMA = area of mud anchor, in2, QL = liquid rate, ; EV = Pump efficiency D 3 These calculated values are inputted into the computer program explained intheir paper to generate relationships between (1) pressure effects on gas bubble velocityover constant viscosity and temperature (2) gas bubble velocity and diameter of the mudanchor over different liquid flow rates (3) dip tube diameter and pressure drop in the gasanchor over different liquid flow rates (4) pressure drop and dip tube length as afunction of liquid rate.The results showed that gas bubbles travelled faster in smaller OD mud anchorslarger dip tube diameters yielded the smallest pressure drop and longer dip tubes had thelargest pressure drops.Experimental results from Lisugurski5, Guzman6 and Bohorquez7 howeverdispute the orders of magnitude of the results from Campbell and Brimhall4. Field results9 based on Lisugurskis5 thesis have shown that a 6ft long gas separator canoperate efficiently at rates which would require longer gas separator lengths if Campbell4 and Brimhallsresults were practiced to the letter. Bohorquez7 in his work howeverconcluded that gas bubbles especially during the up - stroke of a sucker rod pumpingsystem coalesce more readily and rise faster in smaller separator annular areas comparedto larger annular areas.Kobylinski et al 8 described the design, development and laboratory testing of anew rotary gas separator, Figure 1-1 and Figure 1-2. The rotary gas separator is an active-6 24. type centrifugal separator. Laboratory and field comparison were conducted between theCentrifugal separator and the passive-type Reverse-flow separator, Figure 1-3.Laboratory tests were done using water and air as test fluids in continuous flowcondition. The Reverse-flow separator uses the gravity separation mechanism for gas liquid separation. The Centrifugal separator achieved separation of gas and liquid by theuse of cyclone and vortex technology. The characteristics of this method identified bythe authors were that the separated liquid is concentrated in the vicinity of the wall of theseparator while the gas phase concentrates at the center of the system. The authorsstated that dimensioning of the separator should be based on the equation of thetrajectory of the gas bubbles; they added that a general equation that would cover theturbulence arising in the process is not available. Kobylinski et al8 believe that since bothbubble dimensions and proportionality constant between gas and liquid velocities areunknown from Stokess law for laminar flow(1), reliance on experimental work fordesign optimization remains the only alternative. A detailed discussion on bubbledynamics is analyzed in the paper.The results from the field tests8 complemented the results from the laboratoryand led to a 95% average improvement in fluid production when results from the active- type centrifugal separators were compared to the passive-type reverse-flow separators intested wells. The dimensions of both the centrifugal and reverse-flow separators werenot given.7 25. Figure 1-1 Centrifugal Separator Kobylinski et al8 26. Figure 1-2 - Gas flow through centrifugal separator (Kobylinski et al) 9 27. Figure 1-3 - Reverse-flow separator (Kobylinski et al)McCoy and Podio10 gave a detailed description of the Collar Size gas separator, Figure 1-4. They emphasized a maximum pressure loss of PSI for friction loss in thedip tube. The authors also highlighted the need to allow for sufficient space in the gas 10 28. separator annular area. According to the authors sufficient flow area should exist so thatthe gas flow rate around the ports in the gas separator will allow liquid to flow or fallinto the gas separator annulus. The authors noted the necessity to balance the areaavailable for flow in the wellbore and that inside the gas separator. Decreasing the casingannulus will result in increased upward gas velocity which when above 10 ft/second willsuspend some of the liquid and allow mist flow to occur. Another consequence of casingannulus reduction and increase of gas velocity will be the prevention of liquid fromflowing into the gas separator annulus. The authors stressed the need for the use of largeports. Large ports allow liquid from the casing to fall by gravity force into the gasseparator because the pressures inside and outside the large ports are the same.Kobylinski et al8 in their paper also recommended that for a gas separator to operateefficiently, it must ingest the two phase mixture with minimal pressure drop. This isnecessary to prevent additional gas breakout inside the separator. The Collar Sizeseparator10 had a total port area which was approximately four times the area inside thegas separator. The gas separator length received special treatment by McCoy and Podio10they suggested that the dip tube length extend at least 18 inches below the gas separatorinlet perforations (separator ports). They based their calculation on a gas rise velocity of 6in/sec (0.5ft/sec) and an average pumping speed of 10 strokes per minute whichtranslates to a pumping cycle time of 6 seconds. The authors also looked at eccentricityof the separator. Earlier studies noted by the authors showed that liquid concentrateswhere tubing is placed against the casing wall and thus advised that gas separators outerdiameter should contact the casing wall, see Figure 1-4. In wells with some deviation McCoy and Podio10 advised that the separator should be allowed to rest on the low side of the casing since gas tends to flow up on the 11 29. high side of the casing annulus by installing any tubing anchors at a distance of 60 to 90feet shallower than the pump intake. Figure 1-4 Collar-Size down hole gas separator (McCoy and Podio10)Patterson and Leonard11 ran some field tests in coal-bed methane wells in Wyoming with some changes in the down hole pump setting depth interval and for anincrease in gas separator OD. The authors noted that while the modifications were notfully understood or tested with significant number of installations the improvementsobserved warranted some discussion. The tests were conducted in two wells and are fullydescribed in the paper. Patterson and Leonard11designed different gas separators used in the field tests in a bid to achieve greater pump efficiency. The gas separators used in the tests had smallerslot width and included vent holes and a baffle to facilitate the evolution of gas - Figure 12 30. 1-5 . The concept according to the authors assumes that a smaller slot width will reducethe amount of gas entering the gas separator and the vent holes will allow the gas thatenters to vent back to the casing. The slot sizes ranged from 0.3 wide by 6 long for the3.5 OD gas separator (2 in number) to a 3/16 wide by 10 long for the 5.5 OD gasseparator (8 in number). The 5.5 OD gas separators also had three diameter holesin the swedge (see Figure 1.1-5). Both separator designs had the same dip tube OD butdifferent dip tube lengths 2 inches difference. The 3.5 OD gas separator was 24 feetlong whereas the 5 OD gas separator was 26 feet long. The test well , 43-26, had a 3.5 OD 8 long gas separator installed with aProgressive Cavity Pump (PCP) at 1446 ft after a bucket test had been conducted.After some months a 5.5OD gas separator was attached to the PCP in test well 43-26.Although the well contained coal particles which got into the gas separator and starvedthe pump intake some useful evaluations on the effect of increase in gas separator crosssectional area were made from test well 43-26. Due to gas separator design changes the inlet area of the 5.5 OD gas separatordesign increased four times compared to the 3.5 OD gas separator design. The 5.5OD gas separator annular area (gas separator annular area = gas separator ID dip tubeOD) increased by approximately 3 times over the 3.5 OD gas separator. The field results11 showed that no gas was produced through the tubing when the5.5 OD separator was run with the PCP in test well 43-26. Patterson and Leonard11infer that the differences in inlet area and cross sectional area available for flow couldhave had an impact on gas separation and would appear that some combination of thesedifferences has a grater influence on gas separation than only increasing the cross sectional area. In another well test where a 4 OD gas separator with some modificationsto the entry slot area and separator length was compared to a 3.5 OD gas separator13 31. efficiency in the same well. The authors observed that whereas the 3.5 OD gasseparator produced gas through the tubing the 4 OD gas separator did not. The authorsobserved that the increase in annular area must have contributed to pump efficiencyimprovement. They however speculated that the increase in length of the 4 ODseparator or the baffle design of the gas separator might also have aided to theimprovement. The authors suggested that more field tests be done and visual modelingexperiments be evaluated with different geometries and configurations to betterunderstand the reason(s) behind the improvements. Patterson and Leonard11 made otherrelated conclusions in the paper which dealt with; downward liquid velocity, essence ofvent holes, position of the inlet of the gas separator relative to the perforations and theage old theory that placing the intake of the pump below the perforated interval createsan effective natural gas anchor (gas separator).Figure 1-5- Down-hole gas separator (Patterson and Leonard11) 14 32. Guzman6 experimentally determined that placing the gas separator inlet at about3feet below the lowest perforation results in natural separation that yields total gas liquid separation. A gas separator is not needed in such cases as long as the annular liquiddownward velocity is less than 6 inches per second.Guzman6 also suggested that the ports area should be equal the gas separatorannular area so that the superficial liquid velocity does not control the flow regime insidethe separator. The use of vent holes in the design of Patterson and Leonard11 in theexperiments conducted by in continuous flow Guzman6 showed that the vent holes donot improve gas separation. The author suggested the use of single row slots instead ofmultiple rows. He however noted that for the decentralized wells the results might bedifficult to predict due to well eccentricity10.Several centrifugal gas separators have been patented over the years. Most of thepatented arts require the invention have moving parts whereas some do not. The nextsections will initially describe the parts and mode of operation of patented staticcentrifugal separators and finally do same for active patented centrifugal separators1.2.1 PATENTED STATIC CENTRIFUGAL DOWN HOLE GASSEPARATORS1.2.1.1 GAS ANCHOR - PATENT No 3128719The invention (Figure 1-6) by Jongbloed et al12 in 1964 relates to a gas anchorconsisting of a cylindrical housing sealed at the bottom, at least one sheet metal helixaccommodated in the housing, and a tube (14), one side of which communicates withthe space underneath the sheet metal helix. According to the invention, a discharge15 33. conduit is centrally positioned in the housing, the conduit is provided with openings,preferably near the side of the sheet metal helix facing the bottom of the housing (19),the gas discharge conduit (17) and the sheet, communicates with the outside of thehousing through the opening (21) that is above the supply openings (20). In a reported experimental arrangement in which the outer diameter of thehelical channels was 7.5 cm (gas anchor ID = 3 inches), mixtures of varying gas/oilratios were supplied to a gas anchor according to the invention. The quantity of oilpassing the separator was from 1 1.5 cu. meters per hour (151 BPD 226 BPD). When fluid mixtures (dispersions) having gas oil ratios of between 5 and 20were supplied, the gas/oil ratio of the mixture flowing through conduit (14) was lessthan 0.01. This invention has no moving parts. 16 34. Figure 1-6 - Jongbloed et al12 1.2.1.2 Continuous Flow Down hole gas separator for Progressive Cavity Pumps - Patent No 5902378 This apparatus invented by Obrejanu Marcel13 in 1999 is a gas separator whichcan be attached to the suction of a down hole pump to remove gas from the liquidbeing pumped prior to the liquid entering the pump inlet. The separator has an elongate 17 35. housing having an annular chamber with guides which direct the liquid gas mixture toflow in an annular path from the inlet to the outlet end. During this flow centrifugalforces act to displace the gas content to the central region from which it is removed via aseparate central gas outlet so that liquid delivered to the pump inlet is greatly reduced inits gas content.In operation, the separator is attached in a coaxial fashion via sub (14) to thelower end of a progressive cavity pump. In a gaseous environment the liquid will containdissolved gases and will enter the chamber (15) under formation pressure through theinlet ports (16). When the pump is operated the reduction in pressure as a result of thepump suction will cause some of the dissolved gas to come out of solution. The gasliquid mixture is drawn upwardly within the tubular housing (12) and upon encounteringthe helical flights (20) is guided thereby to move in a helical path. The centrifugal forcescreated in the liquid as a result of the helical flow act to reduce the gas content of theperipherally outer region of the flow and increase the gas content of the central region ofthe flow. The angular momentum created in the liquid flow by the flights (20) ismaintained as the liquid moves upwardly into the expansion chamber (23). In thischamber the cross sectional area of the flow passage is expanded as a result of thetermination of the flights (20), the tapering and termination of the spindle (17), and theoutwards flare of the inner wall of the tubular housing (12), the combined effects ofthese resulting in a marked reduction in pressure of the liquid flow thus enhancing thegas separation effect. The centrifugal force in the rotating liquid is effective to confinethe separated gas to the axial region of the chamber which rises above the rounded topend (22) of the spindle. The separated gas flow through the axial exit passage (26) to theexterior of the sub (14) where they can be released into the well bore, or if so desireddelivered to the surface through a separate conduit.18 36. This separator has no moving parts within the separating chamber. To force theliquid into the chamber the separator depends on both hydrostatic head and the pressuredrawdown created by the action of the PCP mounted above. Another interesting featureabout the invention is that multiple separation chambers could be attached just below(18) for a two stage separation process before the liquid enters into the pump. This separator design is currently been manufactured in commercial quantity inCanada.Figure 1-7 Static Centrifugal Separator by Obrejanu Marcel1319 37. 1.2.2 ACTIVE TYPE CENTRIFUGAL DOWN HOLE GAS SEPARATORS1.2.2.1 Liquid Gas Separator Unit - Patent No 3887342The unit was invented by Bunnelle P14 in 1975. The inventor claims that the unitwhen tested in the laboratory could handle high liquid flow capacity of about 82 gallonsper minute (2730 BPD) at zero discharge pressure (pressure head generated by the unit)and that this rate is slightly reduced to 70 GPM when a 26 ft3/min (37440 CFD) gas isintroduced into the unit. The test fluids where air and water.The separator unit operates as follows. As motor shaft (58) revolves at a constantrate impeller shaft (26) and impeller (16) likewise revolve. The impeller draws a liquid gas mixture through intake openings (32a), into the chamber (12a). As this liquid gasmixture moves upwardly within chamber 12a, the revolving impeller vanes (20) impart acompound motion to it. Impeller vane segments (20b) impel the mixture primarilyupwardly through chamber (12a), while vane segments (20a) primarily impart circularmotion to the upwardly moving mixture, thereby centrifuging the liquid component ofthe mixture of the mixture outwardly away from the impeller hub (18) and causingundissolved gas present in the liquid to move inwardly toward the hub (18). Theseparated liquid flows up through discharge channels (100) into discharge elementchamber (72a). The separated gas forms a liquid free gas column around hub, thecolumn of gas moves upwardly into discharge element chamber 86a from where the gasflows into inlets (96b) and through gas conducting channels (96) to discharge outlets(96a) in nearly vertical, upward directions. The channel outlets discharge discrete highvelocity gas streams of separated gas that are substantially upwardly directed to promote 20 38. upward movement of the discharged gas within a wellbore where the separated unit issituated.Figure 1-8 Invention by Bunnelle P14 1.2.2.2 Liquid Gas Separator Apparatus - Patent No 4481020This centrifugal liquid-gas separator is same as described in earlier section (seeFigure 1-1). Here the mode of operation is briefly summarized with an explanatorypictorial shown in Figure 1-9.In operation the pump, separator apparatus (Figure 1-9) and motor aresubmerged down hole within a liquid gas well fluid mixture. The liquid - gas entersthe intake ports (54) of the intake head (18) through a perforated or slotted member 21 39. (100) which assists in filtering debris from the fluid mixture. From the intake ports, thefluid mixture enters the inducer (48) which pressurizes the fluid mixture and supplies itto the centrifugal separator (50) via transition region (52). The transition region, which isdesigned to provide a uniform rate of change through in flow direction and velocity tothe fluid mixture, conveys the fluid mixture smoothly to the centrifugal separator whileminimizing pressure loss. At the outlet end of the transition region, the tangentialvelocity of the fluid approaches angular velocity of the centrifugal separator vanes andthe axial velocity of the fluid approaches the flow through velocity of the apparatus.Liquid gas separation occurs at the inlet of the centrifugal separator region andcontinues throughout its length. The liquid section is supplied to the pump through (86),while the separated gas is vented via gas vents (90) into the space between the well casingand the separator.The rotary motion to the inducer and extending vanes are supplied by anattached motor (20)22 40. Figure 1-9 - Centrifugal Separator by Kobylnski et al 1.2.2.3 Recirculating Gas Separator for Electrical Submersible Pumps - PatentNo 4981175 This invention by Powers Maston15 in 1991(Figure 1-10) is a modification ofLee et al (Figure 1-9). The inventor claims that by including a recirculating means (56)for recirculating a portion of the discharged liquid from the discharge outlet (50) back tothe separator chamber (46) the gas oil ratio in the separator becomes substantiallylower than a gas to liquid ratio of well fluid entering the well fluid intakes (48). Therecirculating means includes all of the following:1. Extraction chamber (60) 23 41. 2. Liquid injection chamber (62)3. Conduit (64)A drive motor will be needed to extend an upward motion to drive all theseparator mechanisms.Figure 1-10 Invention by Powers Maston15 1.2.2.4 Apparatus for separating gas and solids from well fluids - Patent No6382317 B1The apparatus invented by Delwin E. Cobb16 Figure 1-11, is designed to separategas and solids from well fluids in a wellbore. 24 42. The gas and solids are removed from the well fluids in two separate steps by twoseparate spirals, one spiral for the gas (66) and a separate spiral for the solids (70). Anupper gas spiral is positioned below the openings (60) in the outer tubular housing (44)and a separate lower spiral spaced axially from the upper gas spiral is provided for thesolids. The spirals are positioned in the annulus between the outer tubular housing andthe inner flow tube (46). The spirals provide a helical flow and are spaced axially fromeach other at a distance. The gas accumulates in the swirl chamber (80) between thespirals and is librated from the liquid. The gas normally exists as large bubbles throughan inner gas annulus (72). The liquid flows downwardly in a helical path to the solidsspiral.The solids, such as sand are separated from the well fluid by the solids spiral andfall by gravity into the mud anchor or other suitable collection area. The liquid thenflows upwardly in the flow tube (46) to be pumped for flow to a surface location.This invention makes use of induced centrifugal motion and gravity to separategas and solids from wellbore fluids.The invention has no moving parts. 25 43. Figure 1-11 Invention by Delwin Cobb16 Figure 1-12 Cross section (3) in Figure 1-11 26 44. The research reported in this thesis extended the experiments of Kobylinski et al8and the theory behind the inventions of Jongbloed et al12 and Obrejanu13 in the sense ofusing gravity, agitation and centrifugal forces as physical mechanisms to obtain improvedgas liquid separation. The difference between this research and Kobylinski et al8 is inthe use of different experimental procedure, experimental facilities and most importantlythat the centrifugal down hole gas separator must have no moving parts; it must bestatic similar to the inventions of Jongbloed et al12 and Obrejanu13.This research also investigated experimentally the points raised by Patterson andLeonard11 in terms of the effect of the increase in the gas separator annular area andimprovement in pump efficiency. Visual observation as Patterson and Leonard11suggested was used to capture the separation mechanism(s) in the productionengineering laboratory at University of Texas at Austin as described in the next chapter.27 45. Chapter 2Experimental Facility and ProcedureThis chapter fully describes the facilities, equipment and procedure used inacquiring laboratory data used throughout this research. The down hole gas separatorsused for the purposes of this experimental study are described in detail.2.1 EXPERIMENTAL FACILITIESThe separator designs were installed in a laboratory well model and tested over arange of 120 900 BPD of water and air rates between 13 115 MSCFD. The inputinto the experimental test system was water and air at pre - determined rates Qg and Qw;the output from the system included the pressures at the entry ports, tubing pressure andthe gas flow-rate through the dip tube of the separator. The inputs and outputs arecombined in a mathematical model to calculate the pump liquid fraction (pumpefficiency) of the separator relative to particular input values.This chapter describes the facilities at The University of Texas ProductionLaboratory and the procedure used to input and acquire data.2.2 DESCRIPTION OF EXPERIMENTAL FACILITIESFigure 2-1 and Figure 2-2 show schematic and overview pictures of theproduction laboratory facility used for testing down-hole gas separator designs. The testfacility is a closed loop system with manually controlled valves for fluid flow control.Water was pumped in a loop into and out of a 3 - phase separator into the well (Figure 28 46. 2-3) Air was supplied to the system by a compressed air line. Water and air meet at themixer before entering into the well. The hoses lead the mixture from the manifoldthrough the casing perforations into the well. Water is returned to the 3 phaseseparator through a return a line. Air that passes through the dip tube is carried with thewater into the 3 phase separator and the rest rises up the casing. 29 47. Figure 2-1 Schematic of experimental test facility 30 48. Figure 2-2 Laboratory facility Figure 2-3 Laboratory test well31 49. 2.3 LABORATORY TEST WELLThe bottom parts of the well are made of clear acrylic pipe to allow observationof the gas and liquid phases inside the separator. Figure 2-3 shows close up pictures ofthe laboratory well. Figure 2-4 shows the full laboratory well picture, notice that thedown hole gas separator is placed below the down hole pump. All the laboratorytests were conducted with the gas separator situated in such position. The down-hole gasseparator components are positioned in the laboratory well as they would in a real well.The mud anchor is the outer barrel of the separator. The mud anchor entry ports orinlets allow water and some of the air to flow into the separator. The dip tube is thesmall diameter tube inside the separator. The water flows down in the separator annulararea to the dip tube suction. Then the water flows up through the dip tube to the tubingintake shown in Figure 2-4.The bottom part of the casing has an ID of 6 inches. The upper part is PVC pipethat extends to the rooftop of the Petroleum Engineering building at the University ofTexas, approximately 80ft. as seen in Figure 2-4. The bottom section of the casing hasseveral perforations, 31/64 inch in diameter, distributed at different positions. This wayit is possible to vary the relative location of the down-hole separator entry ports withrespect to the perforations.32 50. Tubing Pressuregauge (P3) Ports Pressure gauge (P2) Casing Pressure gaugeLocation of the (P1) separator Figure 2-4 Laboratory Well 33 51. 2.3.1 LABORATORY INSTRUMENTSThe instruments used in the conducting all the tests used for this research areshown below. The functions that they performed are also explained.2.3.1.1 LIQUID FLOW MEASUREMENTSFigure 2-5 is a photo of the Daniel MRT97 turbine flow meter, used to measurethe water flow rate, installed in the liquid loop before the mixer. The water flow wascontrolled by the valve in the same picture. Figure 2-5 Turbine flow meter and valve between pump and mixerThe ITT Barton Floco positive displacement meter (ITT Barton, model 308K)was used only for reference. It is installed between the turbine flow meter and the mixer.34 52. Figure 2-6 - - ITT Barton floco positive displacement meter2.3.1.2 GAS FLOW MEASUREMENTThe air flow into the mixer was controlled with the Fisher Porter flowrator tubeand the valve shown in Figure 2-7. The flowrator tube displays the airflow as apercentage of the maximum flow rate, 16416 CFD. The percentages used in the testswere 10, 20, 30, 60 and 90. The pressure in the compressed air line was measured by apressure transducer to convert the actual air flow rate to standard conditions using theideal gas law since working pressure of less than 100psi and laboratory temperature,allowed assuming a Z factor in the vicinity of 1.0. 35 53. Figure 2-7 - Fisher Porter Flow Rator tubeFigure 2-8 shows the Omega FMA-A2313 thermodynamic mass flow meterinstalled at the top outlet of the three - phase separator. This instrument gave the mostimportant reading in the tests, the amount of air that enters the pump. The units on the display are in standard liters per minute with accuracy of 1%.36 54. Figure 2-8 - Thermodynamic Omega Air Flow Meter2.3.2.2 PRESSURE MEASUREMENT The casing pressure (see Figure 2-4) was used as a control variable for the entiresystem. This pressure was set between 10 psig 13 psig for all experiments. Thesepressure values correspond to the maximum liquid volume in the casing that can bemanaged at the highest gas flow rates without overflowing at the top of the well model. This value was measured using an analog pressure gauge (Ashcroft, model Q-9047). An analog pressure gauge (Ashcroft, model Q-9047) determined the annularcasing pressure at the entry of the top ports of the down-hole gas separator Figure 2-4,P2. This pressure is measured within a foot from the ports and this value is used as areference value to determine the pressure drop inside the down-hole gas separator. The discharge pressure of the separator is considered to be equivalent to thepump intake pressure see Figure 2-4, P3. This pressure is equivalent to the pumpintake pressure. This pressure was measured using a pressure/ vacuum gauge, calibrated 37 55. in psig for positive values of pressure and in inches of mercury for vacuum. One of theapplications this pressure is to determine the pressure drop that occurs between theseparator in-take (P2) and the tubing pressure/discharge pressure (P3).2.4EXPERIMENTAL PROCEDURE Use Figure 2-1 to follow the step - by - step procedure shown next.Before beginning 1. Make sure that there is sufficient water in the separator using the level control. Add water if necessary2. Make sure that the desired ports in the manifold are open to inject flow from the desired position relative to the down-hole gas separator entry portsStarting the flow of fluids in the loop and setting the system in steady state 3. Turn on the pump 4. Use valve G to regulate the water flow rate. The gallons per minute read by the turbine flow meter should approximately result in the desired BPD. Valve G and the turbine flow meter are shown in Figure 2-5.5. Gradually open the air flow to the desired percentage. It is usually set at 0% for the first experiment. There are three valves involved in the airflow. First open valve D to let air in from the compressed air line. Then set the desired percentage with valve E (seen in Figure 2-7).38 56. 6. Finally open valve F to let air mix with the water. Valve F should beopened carefully. Otherwise the sudden injection of air can cause thewater to come out the top of the well. 7. By closing valve A, let water accumulate in the well until a desired bottom hole pressure is obtained. The pressure gauge labeled BHP in Figure 2-1indicates the bottom hole pressure. All the continuous flow tests wererun between 10 13 psi. Once the desired hydrostatic head is obtained,regulate the flow out of the well to match the flow entering the well usingvalve A. This way, the BHP and liquid level inside the three phaseseparator are kept constant. This control is done throughout the test. 2.5 SEPARATOR PERFORMANCE DISPLAYThe performance plots are displayed as three Dimensional graphs, Figure 2-9.The plots are presented both in terms of oil field units and in terms of superficialvelocities.In terms of oil filed units the x axis represents the input liquid flow rate inBPD entering into the well through the perforations; the y axis is the gas flow rate inMSCFD entering the laboratory well; the z axis is the gas rate through the separator inMSCFD. This represents the gas that would enter the pump in a real well having thedown hole gas separator installed immediately below the pump intake.In terms of superficial velocity the x axis is labeled the superficial liquidvelocity inside the separator in inch/second. The y axis represents the superficial gas39 57. velocity inside the casing annulus in inch/second and the z axis is the gas rate throughthe separator in MSCFD.The height of each dot (and/or the vertical bar) on the 3 D performance plotcorresponds to the gas rate through the separator for a given liquid and gas rate either interms of oil filed units or in terms of superficial velocity.The data used in plotting the performance plots are managed with an Excelspreadsheet, see a sample data set in Table 2-1. The inputs for the spreadsheet include the following:1. The actual start and end time for each conducted test 2. The casing, ports and tubing pressures (P1, P2 and P3) psi 3. The Floco meter reading (sec/0.1 bbl) 4. The input gas meter pressure (psi) 5. The measured gas rate through the separator (SLM).The spreadsheet calculates the following;1. The liquid input rate (BPD) 2. The gas rate (MSCFD) 3. The superficial velocities for both liquid and gas (inch/second) inside thecasing and inside the separator. 4. Gas rate through the separator (MSCFD)40 58. 5. The pump liquid fractionThe spreadsheet provides all the information needed to accurately study theperformance of each separator design. All the laboratory tests conducted were run under continuous flow condition. Inthis type of test the valve H is completely open so that there is constant liquid and gasrate throughout the system.41 59. Table 2-1 - Sample Excel Spreadsheet for continuous flow test 42 60. Figure 2-9 - Sample Performance plot for Patterson (3X1) in continuous flow 43 61. 2.6 DOWN HOLE GAS SEPARATOR DESIGNSSeven down hole gas separator designs were tested. Two of the four gravity drivenseparators were originally constructed in 2004 and 2005 and were used with minormodifications. The other two were constructed in 2007. The three static centrifugalseparators were constructed between summer 2006 and summer 2007.2.6.1 ECHOMETER (3X1), ECHOMETER (3X1.5), ECHOMETER (4x1),ECHOMETER (4X1.5), ECHOMETER (4X1.75)The naming procedure is given as: (separator name) (separator OD x dip tube OD). Continuous flow tests2 were run on these separators between spring 2006 andsummer 2007 for the purposes of:a. Comparing the performance of a gravity driven separator to that of a centrifugalseparatorb. Studying the effect of increasing the separator annular areac. Studying the pressure drop inside the separatord. Verifying the effect of port geometry Figure 2-10 and Figure 2-12 are pictures of the Echometer (3X1) and Echometer(4X1) design respectively. There are two sets of four slots. Each slot is 4 inches long and 2inches wide. The first set is located 11 inches below the separator thread and the second set2All the continuous flow tests were conducted with fluid entering from below the separator through the bottom four perforations located adjacent the separator see Figure 2-444 62. is 16 inches below the thread. There is a distance of 24 inches between the lower slots andthe dip tube suction and 44 inches between the upper slots and the dip tube suction. Both the 3inch and 4inch OD Echometer separators have a wall thickness of 0.125inch so that the IDs are 2.75 inch and 3.75 inch respectively. The dip tube wall thickness isalso 0.125 inch, making the ID of the dip tube a quarter of an inch less than the dip tubeOD. The 4 inch OD Echometer separators have the same design configurations as the 3inch OD Echometer separators, except for larger diameter. A summary of the Echometer separator design configurations is shown in Table 2-2below. Table 2-2 Echometer gas separators configurationArea of Area of Size of slotsSeparatorNumber of Total area ofseparatorcasing (WXL)type slots slots (in2) dip tube separator (inch) annulus (in2) annulus (in2) Echometer (3X1)42X432 5.15 21.20 Echometer (3X1.5)42X432 4.17 21.20 Echometer (4X1)42X43210.26 15.70 Echometer (4X1.5)42X432 9.28 15.70 Echometer (4X1.75) 42X432 8.64 15.70 45 63. Figure 2-10 Echometer (3 X1.5) gas separator designFigure 2-11- Echometer entry port geometry Figure 2-12 Echometer (4X1.75) gas separator design 46 64. 2.6.2 PATTERSON (3X1), PATTERSON (3X1.5), PATTERSON (4x1),PATTERSON (4X1.5), PATTERSON (4X2)The naming principle is same as the Echometer designs. Continuous flow tests wererun concurrently for both designs between spring 2006 and fall 2007. The purpose of thetests is same as listed for Echometer design.The Patterson design has 16 thin and long entry slots. The slots are 1/8 inch wideand 8 inch long. There are 0.5 in diameter vent holes. Table 2-3 is a summary of thePatterson separator configuration. Table 2-3 Patterson Separator ConfigurationArea ofArea ofSize ofNumberTotal areaseparator casing SeparatorNumberslots of inch of slotsdip tubeseparator type of slots(WXL) holes(in2)annulusannulus (inch) (in2)(in2) Patterson 16 4 1/8 X 8 165.1521.20 (3X1) Patterson 16 4 1/8 X 8 164.1721.20(3X1.5) Patterson 16 4 1/8 X 8 16 10.2615.70 (4X1) Patterson 16 4 1/8 X 8 169.2815.70(4X1.5) Patterson 16 4 1/8 X 8 168.6415.70 (4X1.75) Patterson 16 4 1/8 X 8 167.9015.70 (4X2) 47 65. Figure 2-13 4 inch OD Patterson Separator DesignFigure 2-14 3 inch OD Patterson Separator Design 2.6.3 TWISTERThe separator named The Twister is the first in the series of static centrifugalseparators constructed since summer 2006. The initial results of the performance of theTwister as reported by Bohorquez7 pointed to the need for more inquests into the 48 66. performance of static centrifugal separators based on the Echometer and Patterson separatorentry port designs. The twister design uses a wire reinforced PVC hose used as a dip tube. The hose hasa 1.028 in OD and a 0.75 in. ID. The reinforced PVC is spiraled four full turns inside thegas separator, Figure 2-15. The hose is twirled inside the gas separator and a plate is used tosecure the hose in place. The straight dip tubes (for example, Echometer (3X1)) used for gravity separatordesigns are directly connected to the wells tubing. But for the centrifugal design theconnection to the tubing is different. Figure 2-15 is a picture of the twister connection. Thearrows show the flow path for the gas through the gas vents and the liquid through the spiraltube connection. In operation the gas liquid mixture enters through the three circular entry ports ofthe Twister separator. The helical dip tube induces a centrifugal motion on the mixtureentering through the ports. Gas is evolved and a coalescing zone is formed. The length ofthe coalescing zone depends on the gas and liquid flow rates. The liquid mass is forced tothe inner walls of the separator by centrifugal forces and the gas mass accumulates at thecenter (coalescing zone). While the gas rises to the gas vents at the separator connection toescape into the casing annulus the liquid flows down towards the dip tube suction andthereafter into the pump by gravity forces. Figure 2-17 shows a diagrammatic of the forcesacting on the mixture as soon as it enters into the separator annulus. Laboratory observations show that the helical dip tube induces the centrifugalmotion by virtue of its design; a bubble coalescing zone is formed in the center of theseparator; the bubbles coalesce and become bigger bubbles in the coalescing zone and thusrise faster; the liquid momentum is reduced by the helical nature of the dip tube. This greatly The full construction detail for the Twister is covered in the thesis report by Bohorquez, 2006.49 67. improved the gas pathway through the core of the separator eliminating the need for a gasventing tube. The operation of the twister is similar to the invention by Jongbloed et al12 sinceboth are static type separators. The basic difference between the two is that the twister doesnot have a gas discharge conduit instead it has inclined gas vent holes at the connection head(Figure 2-16). The Twister design also has similarity with the invention by Obrejanu13. Apartfrom both separator designs been static by construction both separator designs depend onthe helical nature of the separator internal design to induce centrifugal motion and thuscentrifugal forces on the fluid flow inside the separator. The centrifugal forces inducedbecome the driving mechanism for gas liquid separation. The main differences betweenthe two are the entry port placement and gravity effects. The Twister has three entry portcircles at the top of the separator; the separator design by Obrejanu13 has the entry port atthe bottom part of the separator. The Twister depends to a significant extent on gravity forgas liquid separation as well as on hydrostatic head to flow the mixture through theseparator. The gas separator by Obrejanu13 depends on both hydrostatic head and pressuredrawdown created by the action of the PCP to operate efficiently. Whilst the advantages ofhaving the entry ports at the bottom part of the gas separator is founded by densitydifference; in the case of fines production the PCP rotor will erode at a faster pace causing pre mature pump damage.50 68. Figure 2-15 Twister Separator (Bohorquez)Gas VentSpiral Tube holes ConnectionFigure 2-16 Twister Connection51 69. coalescing zone Dip tube actsas baffleswhich reduce Inducedliquid centrifugalmomentum motion Improved gas path wayFigure 2-17 Diagrammatic of the forces acting in a static centrifugal separator 2.6.3.1 ECHOMETER TWISTERThe Echometer Twister is a static centrifugal separator. The design is very similarto the Twister as per the dip tube design which is helical. The major difference between thetwo separator designs is the entry port geometry. While the Echometer design has four 4X2slots the Twister has 3 circular entry ports and 4 half inch vent holes.The main objective of constructing the Echometer Twister is to study the effect ofcentrifugal forces on separation performance. A head to head comparison is madebetween Echometer (3X1) and Echometer Twister to understand the controllingmechanisms.52 70. Figure 2-18 is the picture of the laboratory constructed Echometer Twisterseparator. Figure 2-18 Echometer - Twister 2.6.3.2PATTERSON TWISTERThe Patterson Twister is the third in the series of static centrifugal separatorsconstructed. This separator design (Figure 2-19) has the same entry port geometry has thePatterson (3X1). Like the Echometer Twister it was constructed to comparatively studythe effect of centrifugal forces on the previously constructed Patterson (3X1) separatordesign. The Patterson Twister also has a dip tube with four full turns/twists with pitchlength of 12 14 inches lying at an angle of 45o on the inner walls of the separator. 53 71. Figure 2-19 Patterson - Twister54 72. Chapter 3 Analysis Of Experimental Results3.1EFFECT OF HELICAL DIP TUBE DESIGN These experiments studied the effect of changing the dip tube design from theconventional straight shape to a helical form. The designs experimentally tested include the following; The Echometer-Twister,Patterson-Twister (2 twists and 4 twists) and the Twister, which was previously tested byBohorquez7. The following parameters were examined during the experimental tests of theseparators: Liquid input rate: up to 600 BPD Gas flow rate: 0 MSCFD to 115 MSCFD Superficial liquid velocity in the separator: up to 14 in/sec Superficial gas velocity in the casing: up to 70 in/sec Casing pressure: between 10 and 13 psi55 73. The performance plots for each of the static centrifugal separators are presented inthe following sections and a comparative analysis is presented thereafter so that the effectsof the change in dip tube design are effectively captured.3.1.1 PERFORMANCE RESULTS FOR THE TWISTER SEPARATORFigure 3-1 and Figure 3-2 show the performance plots for the Twister separator incontinuous flow in both field units and in terms of superficial velocity. Notice that theTwister achieved a zero gas flow rate through the separator up to a downward superficialliquid velocity (Vsl) of 10 in/sec for all gas rates tested. This liquid rate is equivalent to 430BPD. The area highlighted in red represents the optimum performance for the Twisterseparator. Approximately no gas entered into the dip tube suction in this area for theseconditions of liquid and gas flow.56 74. Separator Type: TwisterOD Dip Tube = 1; Number of Slots = 3; Number of Twists = 4; Casing Pressure = 10 13 psi Dimension of Slots =2 1 holes & 1 1.5 hole; Position of the Separator = Above the PerforationsFigure 3-1- Twister results in field units 57 75. Separator Type: TwisterOD Dip Tube = 1; Number of Slots = 3; Number of Twists = 4; Casing Pressure = 10 13 psi Dimension of Slots =2 1 holes & 1 1.5 hole; Position of the Separator = Above the Perforations Figure 3-2 - Twister result in terms of superficial velocities 3.1.2 PERFORMANCE RESULTS FOR ECHOMETER TWISTERSEPARATORIn Figure 3-3 and Figure 3-4 the performance results for EchometerTwisterseparator are shown. 58 76. Separator Type: Echometer - TwisterOD Dip Tube = 1; Number of Slots = 4; Number of Twists = 4; Casing Pressure = 10 13 psi Dimension of Slots =2 X 4; Position of the Separator = Above the Perforations Figure 3-3 Echometer - Twister result in terms of superficial velocities 59 77. Separator Type: Echometer - TwisterOD Dip Tube = 1; Number of Slots = 4; Number of Twists = 4; Casing Pressure = 10 13 psi Dimension of Slots =2 X 4; Position of the Separator = Above the PerforationsFigure 3-4 Echometer - Twister results in field unitsThe region highlighted in red in both plots depicts areas where it was observed thatno gas entered into the dip tube suction of the EchometerTwister separator. Notice that inFigure 3-3 the no gas zone was established at a downward Vsl 10 inch/sec. 60 78. 3.1.3 PERFORMANCE RESULTS FOR PATTERSON TWISTERSEPARATORBoth Figure 3-5 and Figure 3-6 show the results for the PattersonTwister Separatorin continuous flow in terms of superficial velocities and in field units. Separator Type: Patterson - Twister OD Dip Tube = 1; Number of Slots = 16; Number of Twists = 4; Casing Pressure = 10 13 psiDimension of Slots =1/8 X 8; Position of the Separator = Above the Perforations Figure 3-5 - Patterson - Twister result in terms of superficial velocities61 79. Separator Type: Patterson - TwisterOD Dip Tube = 1; Number of Slots = 16; Number of Twists = 4; Casing Pressure = 10 13 psi Dimension of Slots =1/8 X 8; Position of the Separator = Above the Perforations Figure 3-6 - Patterson - Twister results in field units In the following sections a comparison is made between the separation performancesof EchometerTwister and Echometer (3X1) and then Patterson Twister and Patterson(3X1) in terms of both superficial velocity and field units. 62 80. 3.2 COMPARISON OF PERFORMANCES OF HELICAL DIP TUBE GAS SEPARATORS TO STRAIGHT DIP TUBE GAS SEPARATORThis section focuses on comparing the performances of gravity driven separators tostatic centrifugal separators in laboratory continuous flow experiments. For critical analysis,comparisons are made between gas separators that have the same entry port geometry andexact dip tube outer and inner diameters. Section 3.2 is organized as follows: Section 3.2.1 compares the performance of Echometer-Twister and Echometer (3X1) gas separators Section 3.2.2 compares the performance of Patterson-Twister and Patterson (3X1) gas separators Section 3.2.3 studies how the number of twists inside a static centrifugal separator affects performance. The performance of Patterson-Twister gas separator with 4 twists is compared to Patterson-Twister gas separator with 2 twists. Section 3.2.4 compares all the results for static centrifugal separators. 3.2.1 COMPARISON OF ECHOMETER-TWISTER AND ECHOMETER (3x1) GAS SEPARATORS The performance of the Echometer-Twister and Echometer (3X1) separators arecompared in terms of superficial velocities in Figure 3-7 in and in filed units in Figure 3-8.The test points in the performance plots are red for the Echometer-Twister and black forEchometer (3X1). As shown in the superficial velocity performance plot, Echometer (3X1)63 81. separates all the air entering the test well for downward superficial liquid velocities below 7in/sec, and the Echometer-Twister for downward superficial liquid velocities below 9.5in/sec.The plots in Figure 3-7 shows that the 6 inch/sec rule of thumb threshold fordownward superficial liquid velocity (Vsl) inside the separator for gravity driven separators(green highlighted region) is surpassed. The limiting downward Vsl for optimumperformance inside the Echometer Twister gas separator design is 9.5 inch/sec; a 58%increase over the conventional rule of thumb. In Figure 3-8, 9.5inch/sec optimumdownward Vsl for EchometerTwister gas separator design is equivalent to 480 BPD ofwater. This represents a 200BPD increase over the optimum operational area for theEchometer (3X1) gas separator design. The 7in/sec optimum downward liquid Vsl for theEchometer (3X1) design marginally exceeds the rule of the thumb. This is an additional 40BPD gas free liquid production. 64 82. Separator: Echometer- Twister & Echometer (3X1)Number of Slots = 4; Dimension of Slots = 4X 2; Position of Separator = Above Perforations: Test Type = Continuous Flow; Pc = 10psi Echometer TwisterEchometer (3X1)Figure 3-7 Comparison of Echometer Twister and Echometer (3X1) results in terms of superficial velocity 65 83. Separator Type: Echometer Twister; Echometer (3X1) OD Dip Tube = 1; Number of Slots = 4; Casing Pressure = 10 13 psiDimension of Slots =4 X 2; Position of the Separator = Above the Perforations Echometer Twister Echometer (3X1) Figure 3-8- Comparison of Echometer Twister and Echometer (3X1) results in Field Units The design of gas separators is a trade off between optimizing the separator annulararea and the pressure drop in the separator. Pressure drop analysis is performed on both gasseparator designs to determine the pressure difference between the entry ports, P1 and the66 84. pump intake, P2 shown in Figure 3-10. The difference P1 P2 is an approximation of thepressure drop inside the separator.An initial pressure drop comparison is performed with single phase liquid passingthrough the system in Figure 3-9 and thereafter the pressure difference is evaluated for two-phase, liquid and gas in the system at various gas-liquid rates.Pressure Drop for one phase liquid flow in Echometer (3X1) and Echometer-Twister765 Pressure Difference (psi) 43210 0100200300400500 600 700 800 Liquid Rate (BPD) Echometer-Twister Echometer 3X1Figure 3-9 - Pressure Drop between the entry ports and pump intake for Echometer Twister and Echometer (3X1); Casing Pressure (Pc) = 10 13psi67 85. Figure 3-10 Pressure measurements during the testsFigure 3-9 shows that the pressure difference for Echometer-Twister ranged from4.5 6.5psi. Echometer (3X1) pressure drop values ranged from 1.8 - 4.8psi. It is seen thatthe difference in pressure drop values are not vary significant between the two separators. 68 86. Figure 3-11 and Figure 3-12 studies the effect of 2 phase gas and liquid flow on thepressure drop values for the Echometer (3X1) and Echometer-Twister. Figure 3-11 presents the pressure drop values for varying liquid rates and severalconstant gas rates. The pressure drop values along constant gas rates are black forEchometer (3X1) and red for Echometer-Twister. The plot shows that the pressure dropacross the separator is liquid rate dependent for both gas separator designs. The pressuredrop increases as the liquid rate increases in both gas separators.Pressure Drop Analysis for Echometer (3X1) and Echometer-Twister at Constant Gas Rates 12 10E 14MSCFD Pressure Difference (psi) E 41MSCFD8 E 79MSCFD E 115MSCFD ET 14MSCFD6 ET 39MSCFD ET 76MSCFD ET 110MSCFD4 E = Echometer (3X1) ET = Echometer Twister 200 100 200 300400 500 600 700 Liquid Rate (BPD)Figure 3-11 Pressure drop for Echometer-Twister and Echometer (3X1) at constant gasrates; Pc = 10 13 psi It is usually expected that pressure drop values across the separator increase withincreasing dip tube length4,5. At 61, the dip tube length of Echometer-Twister is ft longer 69 87. than that of Echometer (3X1). Pressure drop analysis plot in Figure 3-10 agrees with theliterature but not in total. It is seen that between 450 BPD and 500 BPD the pressure dropvalues for the Echometer-Twister are lower than that of Echometer (3X1). A quickreference to Figure 3-8 will reveal that within the 450 500 BPD region, Echometer-Twister separates all the air entering into the test well, so that only liquid enters into thetubing return line3 .The presence of 1-phase liquid flow inside the separator reduced the pressure drop values.To explain this phenomenon a sketch of a section of a gravity driven separator under twophase flow conditions is shown belowSketch 1 Cross section of gas Separator under two phase flowThe sketch shows the liquid descending as the gas component rises upward due togravity. For gas to move from d to c in the sketch, the gas will have to overcome the drag3 Tubing return line is the pump intake in an actual case.70 88. forces posed by liquid resistance to upward gas flow. The drag forces are shown as tinyarrows pointing in the direction opposite to gas flow.Pressure increases as the work done to overcome drag forces increases. This causespressure drop across the gas separator to increase during two phase gas liquid flow.The additional pressure drop caused by phase interaction is absent for single phaseliquid flow conditions inside the separator. This is the basis for lower pressure drop valuesfor single phase liquid flow across the separator.This explains why Echometer-Twister had pressure drop values lower thanEchometer (3X1) at rates of 450 500 BPD where single phase liquid flow was thecontrolling flow regime inside the Echometer-Twister gas separator. At those rates thecontrolling flow regime inside Echometer (3X1) was two-phase gas-liquid flow. Figure 3-8distinguishes the single phase flow region for Echometer (3X1) as the green highlightedregion while the red highlighted area is the single phase flow regime for Echometer-Twister.Figure 3-11 shows the pressure drop plot for Echometer-Twister and Echometer(3X1) with respect to varying gas rates and constant liquid rates. The plot shows that thepressure drop values for Echometer (3X1) are independent of the gas rates into the system.Pressure drop in Echometer-Twister is independent of gas flow rates when one phase liquidflow exists inside the gas separator. When two phase gas-liquid flow exists, increasing gas rates increase the pressure drop across the gas separator. 71 89. Pressure Drop Analysis for Echometer (3X1) and Echometer-Twister at Constant Liquid Rates1210Pressure Difference (psi)8E 463BPD E 386BPD E 277BPD ET 644BPD6 ET 560BPD ET 434BPD E= Echometer (3X1) ET = EchometerTwister420 0 20 4060 80100120 140Gas flowrate (MSCFD)Figure 3-12- Pressure drop for Echometer-Twister and Echometer (3X1) at constant liquidrates; Pc = 10 13 psi72 90. 3.2.2COMPARISON OF PATTERSON-TWISTER AND PATTERSON (3x1) GAS SEPARATORS Figure 3-13 expresses the performance plot in velocity terms for the Patterson Twister and Patterson (3X1) gas separators. The performance plot in field units is given in Figure 3-14.Separator Type: Patterson Twister; Patterson (3X1) OD Dip Tube = 1; Number of Slots = 16; Casing Pressure = 10 13 psi Dimension of Slots =8 X 1/8; Position of the Separator = Above the Perforations Patterson TwisterPatterson (3X1) Figure 3-13 - Comparison of Patterson Twister and Patterson (3X1) results in terms of sup