Ministry of High Education and Scientific Research

Hayat Private University – Erbil

College of Engineering

Department of Petroleum Engineering

__________________________________

( Alkaline injection For Enhance Oil Recovery)A dissertation Submitted in Partial Fulfillment of the requirement of the

Bachelor Degree in Petroleum Engineering , Hayat Private University – Erbil

Prepared by : Supervised by :

1- ZanaMuhammedWasman Assistant lecturer :HunarKareem

2- Muhammad Bashar Akram

3- YusifWshiarJahfer

1

Abstract:

The world needs energy – and over the short and medium term it is clear that much of our global energy consumption will come from fossil sources such as oil, gas and coal. With the current growing demand for oil led by major energy consuming countries.

Enhanced Oil Recovery (EOR) processes; consists of methods aimed at increasing ultimate oil recovery by injecting appropriate agents not normally present in the reservoir, such as chemicals, solvents, oxidizers and heat carriers in order to induce new mechanisms for displacing oil.

Chemical flooding methods are now getting importance in enhanced oil recovery to recover the trapped oil after conventional recovery.

Alkaline flooding has great potential for enhancing the recovery of heavy oil, especially for reservoirs in which thermal methods are not suitable. In this study, alkaline flooding tests were performed in micromodels and sandpacks to investigate the microscopic displacement mechanisms for enhancing heavy oil recovery and the effect of the injection parameters on displacement efficiency. The micromodel tests indicate that the penetration of the alkaline solution into the crude oil and the subsequent formation of a water-in-oil (W/O) emulsion reduce the mobility of the water phase and divert the injected water into the unswept region, thereby improving the sweep efficiency. The sand packflood results show that the tertiary oil recovery can reach about 20% of the initial oil in place (IOIP) using 1.0% NaOH, and the tertiary oil recovery has been found to increase as the alkaline concentration increases. However, there is an optimum slug size and injection rate at which the highest tertiary oil recovery can be obtained during the alkaline flooding process. Continuous alkaline injection can provide a higher tertiary oil recovery compared with a cyclic alkaline injection pattern. These results show that the alkaline flooding, if properly designed and controlled, can lead to enhanced heavy oil recovery through the water-in-oil emulsification.

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Dedication:

I dedicate my work to my family , my colleagues , my teachers and anyone who

guide Me to do the best in my life. I would like to dedicate my work to workers and

Engineers who spend their lives to improve enhanced oil recovery science and sharpen

Our knowledge till today .

3

Acknowledgments:

Many thanks to my advisor Mr.Huner Kareem, for this continuous kind

Support throughout my research and always opened his door for any question at

any time. My special thanks to Dr.muhammedsaher and Dr.Falahand all other

Teachers for their continuous support and encouragement through out my study

life in petroleum engineering department at Hayat university for science and

Technology.

I would like to thank all my friends especially who helps me during my

studies life.

I would like to thank all my family especially my parents for believing in me and

praying for a huge success in my life.

4

Introduction

New discoveries of conventional oil fields are declining while demand for oil is estimated to increase approximately 1.5% per year.One of the most practical enhanced oil recovery techniques for recovering the residual oil left in the reservoir after water flooding is chemical flooding methods which play a significant role for those reservoirs where high-water-oil ratios have been reached as well.Middle East presents a significant opportunity to implement enhanced recovery methods on the fields with large remaining conventional oil resources and for future production growth.Water flood is commonly used as an economic and effective method in secondary recovery after primary methods have been exhausted. Many of sandstone or carbonate reservoirs have low primary and water flood recovery due to poor sweep efficiency as the result of bypassed or unswept oil. In general, water flood still leaves 50-70% oil in the formation and oil cannot be further removed without the use of chemical, thermal or gas injection processes. Chemical flooding was, up to 2000's, less common EOR method than thermal & gas but now, huge projects are initiated or revisited.

Chemical processes have been shown to be effective in recovering unswept oil by improving the mobility ratio (polymer flooding), or by reducing residual oil saturation (micellar or surfactant polymer flooding (SP), alkaline/surfactant/polymer (ASP)). Parameters such as mineralogy, permeability and viscosity ranges, temperature, salinity, have an impact on the feasibility of the process and also on the economics.Polymer flooding is the most important EOR process, improving the water-oil mobilityratio. The polymers act basically increasing the viscosity of the injected water and reducing the swept zone permeability, allowing an increase in the vertical and areal sweep efficiency of the water injection, and, consequently, increasing the oil recovery.

Chemical flooding methods aid a more desirable mobility ratio of the displacing flood and reducing the Another mobility ratio and capillary number by adjusting the interfacial tension between the displacing and the displaced phases in sequence. Wettability changes, relative permeability shifts, formation of precipitates and formation of macro- and micro emulsions are also other effects of these EOR techniques that must be carefully investigated in chemical and petroleum researches.

In the recent years, a great progress has been made either in laboratory studies or in pilot tests for alkali/surfactant/ polymer (ASP) and surfactant/alkali/polymer (SAP) combination flooding ASP flooding is a technique whichis developed out on the basis of alkali flooding, surfactant flooding and polymer floodingand oil recovery is enhanced gently by decreasing interfacial tension (IFT), increasing capillary number, enhancing microscopic displacing

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efficiency, improving mobility ration and increasing macroscopic sweep efficiency , Alkali forms soaps by reacting with naturally occurring organic acid in the crude oil, which interact synergistically with added surfactant to produce ultra-low IFT The ultra-low IFT is obtained by surfactant distribution between oil and water phase, and surfactant arrangement at interface of oil/water. This is controlled by pH value and ionic strength The alkali injected with surfactantcan reduce surfactant adsorption, play the role of ionicstrength and lower IFT Addition of polymer increases the viscosityof its aqueous phase sothat the mobility of aqueous phase decreases. Thus, the decrease in mobility ratio greatly increase sweep efficiency. Another main accepted mechanism of mobile residual oil after water flooding is that there must be a rather large viscous force perpendicular to the oil–water interface to push the residual oil. This force must overcome the capillary forces retaining the residual oil, move it, mobilize it, and recover it studied the viscoelastic effect of retained polymer molecules in porous media based on the pressure draw-down and buildup process. They proposed that the micro-scale displacement efficiency depends on the flow pattern and magnitude of the viscous force parallel to the oil–water interface. Under the same displacement efficiency as that of surfactant/ polymer flooding the main mechanisms of ASP flooding are interface producing, bridging between inner-pore and outer-pore and oil–water emulsion. In a vertical heterogeneous reservoir, ASP flooding increases displacing efficiency by displacing residual oil through decreasing IFT and improving sweep efficiency. ASP flooding is more effective for oil with high acid value. They showed that flooding system’s rheology and IFT between flooding system and oil with high acid value were the key factors effecting oil recovery investigated the fluid-flow mechanism of enhanced oil recovery (EOR) in porous media by ASP flooding. They have reported that ASP flooding displaces not only the residual oil in the high-permeability layer but also the remaining oil in the low- and middle permeability layers by increasing both swept volume and displacement efficiency. A critical step for the optimal design and control of ASP recovery processes is to find the relative contributions of design variables such as, slug size and chemical concentrations, in the variability of given performance measures (e.g., net present value, cumulative oil recovery), considering a heterogeneous and multiphase petroleum reservoir. In the present work, comprehensive studies have been done on ASP flooding varying the concentration and composition of different chemicals.

ASP flooding is an important technology for enhanced oil recovery. The production rates of the 100 largest oilfields in the world are all declining from plateau production. The challenge is to develop EOR methods that ensure an economical tail end production from these fields. Field practice has shown that more than 20% OOIP incremental recoveries can be obtained with the ASP process. Better ASP systems need to be developed with more cost-effective surfactants in weak alkaline systems.

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Contents :

Subjects : Page

Abstract 2

Dedication 3

Acknowledgments 4

Introduction 5

Contents 6

Chapter 1 : Enhace Oil Recovery ( EOR ) 9

1-1 History of the Technology 9

1-2 Enhace Oil Recovery ( EOR ) : 10

1-3 Types of EOR: 11

1-4 EOR chemical Flooding 13

1-5 Overview of Alkali 14

Chapter 2: Chemical structures and Characteristics : 15

2-1 Chemical structure of Alkalis 15

2-2 Alkaline materials used most commonly in EOR 15

2-3 Type of reservoir and it’s characteristic 16

2-4 Crude Oil Properties 18

Chapter 3: Mechanism of action and Operations 19

3-1 Alkaline flood operation 19

3-2 Mechanisms action of Alkali 20

3-3 Alkaline application in the oil industry 21

3-4 DISPLACEMENT MECHANISMS IN ALKALINE FLOODING 22

3-5 Effect of alkali and polymer on surface tension 22

3-6 Effect of alkali and surfactant on the viscosity of polymer solutions 237

3-7 Effect of alkali in ASP flooding 25

3-8 Alkaline conservation equation 25

3.9 Alkaline effect on water-oil surface tension 26

3.10 Alkaline effect on surfactant/polymer adsorption 26

Chapter 4 : Figures and Tables 27

Conclusion 32

References 33

8

Chapter 1:

Enhance Oil Recovery ( EOR )

9

Chapter 1: Enhance Oil Recovery ( EOR )

1-1 History of the Technology :

The history of alkaline flooding dates back- to the early 1920's, with roots in the combination of reservoir engineering and chemistry. Understanding, the interaction of the injected alkaline chemicals with the reservoir oil, water, and rock is a chemical problem, while using the interactions to improve oil recovery is a reservoir engineering problem. Alkaline oil recovery has been attributed to oil/alkali interaction (called "emulsification"), to alkali/rock interaction (called "wettability alteration"), and to chemical precipitation caused by mixing of the injected alkaline solution with the hardness ions in reservoir water. Any or all of these mechanisms can operate in a particular application. Because of the interplay of these mechanisms, alkaline flooding is ail extremely complex oil recovery process and tends to be site-specific in terms of process design and dominant recovery mechanism. Some of the apparent differences in the use of alkali cited in the literature result from the site-specific nature of a process that uses different mechanisms to improve oil recovery in different reservoirs. For this reason, most of the disagreement in the literature can be explained by differences in the recovery processes active in an individual reservoir, Recognition of the individual mechanisms should allow profitable application of alkaline flooding to a wide range of reservoir types. The first attempt to bring together what was known about alkaline flooding was made by Johnson' in 1975. He summarized Field data that had been published and the technology as it then was understood. From 1975 through 1979, when this paper was first written, the number of field tests concluded and described, begun, or planned grew as did research on the processes involved. It became evident that alkaline flooding was not a simplistic technique for enhancing oil recovery but rather a very complex one. From 1979 through mid-1982, the number of field tests planned and initiated increased markedly. This increase is attributed to the favorable economics created by the U.S. DOE's Tertiary Incentive Program. During the program's life from Aug. 1979 through Jan. 1981, 41 alkaline flood projects were certified.

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1-2 Enhance Oil Recovery ( EOR ) :

Enhanced oil recovery (abbreviated EOR) is the implementation of various techniques for increasing the amount of crude oil that can be extracted from an oil field. Enhanced oil recovery is also called improved oil recovery or tertiary recovery (as opposed to primary and secondary recovery). According to the US Department of Energy, there are three primary techniques for EOR: thermal recovery, gas injection, and chemical injection.Sometimes the term quaternary recovery is used to refer to more advanced, speculative, EOR techniques Using EOR, 30 to 60 percent, or more, of the reservoir's original oil can be extracted,[1] compared with 20 to 40 percent using primary and secondary recovery.

Enhanced oil recovery (EOR) is the process of obtaining stranded oil not recovered from an oil reservoir through certain extraction processes. EOR uses methods including thermal recovery, gas injection, chemical injection and low-salinity water flooding. Although these techniques are expensive and not always effective, scientists are particularly interested in EOR's potential to increase domestic oil production.

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1-3 Types of EOR:

1- Primary recovery

Primary oil recovery refers to simple pressure depletion where only reservoir energy, through different mechanisms, is used to extract the oil. These natural energy sources are; solution-gas drive, gas-cap drive, natural water drive, fluid and rock expansion, and gravity drainage. The particular mechanism of lifting oil to the surface, once it is in the wellbore is not a factor in the classification scheme [11] .The recovery factor after this depletion period is usually low, and normally, only 5-30 % of the original oil in place (OOIP) can be produced.

2 Secondary recovery

Secondary recovery is normally implemented when the reservoir natural energies are not sufficient to produce hydrocarbon. This involves injection of water or gas, either for pressure support or for displacement of oil towards the production wells. About 30-70 % of OOIP is left unproduced after the process Gas injection is either into a gas cap for pressure maintenance and gas-cap expansion or into oil column wells. In this process, oil is displaced immiscibly according to relative permeability and volumetric sweep out considerations.

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3- Tertiary recovery/EOR processes

Unfavorable reservoir characteristics such as heterogeneous rock properties (fractures, layers with large permeability contrasts, impermeable layers), unfavourable wettability conditions, or capillary trapped and bypassed oil, results in areas of the reservoir not flooded by the injected fluid. Approximately 30-70 % of OOIP in the reservoir is left after these conventional secondary oil recovery processes. It is the residual oil that is left in the reservoir after the secondary recovery that is the target for EOR processes. Thus, the purpose of initiating tertiary oil recovery processes is to extend lifetime of oil reservoirs which are approaching economical limit by support of water flooding or other conventional methods.Tertiary processes use miscible gases, chemicals, and/or thermal energy to mobilize and displace additional oil after the secondary recovery processes become uneconomical. EOR is defined by Bevier as: “EOR consists of methods aimed at increasing ultimate oil recovery by injecting appropriate agents not normally present in the reservoir, such as chemicals, solvents, oxidizers and heat carriers in order to induce new mechanisms for displacing oil”. Zhang also proposed the definition of EOR as any method, which is aiming to improve the fluid flow by means of changing physical property of the reservoir rock or fluids, including wet ability, interfacial tension, fluid density, viscosity, permeability, porosity, pore size, etc.

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1-4

14

1-5 Overview of Alkali

Alkali (from Arabic: Al-Qaly) is a basic, ionic salt of an alkali metal or alkaline earthmetal element. Alkalis are best known for being bases that dissolve in water. Bases arecompounds with a pH greater than 7. There is a vast uses of alkali like Sodium hydroxideis used to make paper, detergents and soap; Potassium hydroxide; Calcium carbonate isused as a building material; Magnesium hydroxide is used to help with stomach aches orindigestion. It makes the contents of a stomach less acidic.

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Chapter 2:

Chemical structures and Characteristics

16

Chapter 2: Chemical structures and Characteristics

2-1 Chemical structure of Alkalis : Alkalis are all Arrhenius bases, which form hydroxide ions (OH-) when dissolved in water. Common properties of alkaline aqueous solutions include: Moderately concentrated solutions (over 10−3 M) have a pH of 10 or greater. Concentrated solutions are caustic (causing chemical burns). Alkaline solutions are slippery or soapy to the touch, due to the saponification of the fatty acids on the surface of the skin.

Most basic salts are alkali salts, of which common examples are: sodium hydroxide(often called "caustic soda"), potassium hydroxide (commonly called "caustic potash"),lye, calcium carbonate, magnesium hydroxide is an example of an atypical alkali since it has low solubility in water. Nowadays, instead of sodium hydroxide (NaOH), sodium bicarbonate (NaHCO3) or sodium carbonate (Na2CO3) is used to reduce emulsion and scale problems.

2-2 Alkaline materials used most commonly in EOR :

Alkaline materials used most commonly in recent floodingsare :

Sodium hydroxide and Sodium orthosilicate.

Other Alkali material proposed studied include Sodium carconate , ammonium hydroxide , polyphodphate and hydroxyl amine .

A mixture of sodium hydroxide and sodium meta- silicate is also being used in operations because the reaction between these two yield s Sodium orthosilicate.

17

2-3 Type of reservoir and it’s characteristic :

Type of reservoir that Alkali uses Sandstone.

In addition, reservoirs that are not responsive water flooding are also not suitable for alkaline flooding. The major requirements and considerations are; the reservoir should not be very heterogeneous; otherwise some zones would be inaccessible.

There should be no extensive fractures or thief zones causing the alkali to bypass the bulk of the rock with little or no response to the injection. Highly faulted and or / fractured reservoirs are unsuitable

RESERVOIR SELECTION; It must be recognized that only a limited number of reservoirs may respond to alkaline flooding. After establishing such suitability, a comparative study must be done with other possible recovery techniques. General caustic flooring experience indicates that the basic criteria presented below may be useful in identifying reservoirs suitable for alkaline flooding.

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RESERVOIR characteristic:

1 ) The reservoir should not be very heterogeneous; otherwise some zones would be inaccessible.

2) Highly faulted and or / fractured reservoirs are unsuitable

3) Large degree of layering and shale barriers of large areal extent are detrimental to alkaline flooding. The net pay thickness should not be a small fraction of the gross formation thickness.

(4) The pay zone must be of a sizeable areal extend and sufficiently thick .

(5) An aquifer-connected water-drive reservoir is not suitable for alkaline flooding , particularly where a thin pay zone is underlain by a thick aquifer.

(6) The reservoir permeability and porosity should be will developed. An adequate injectivity must prevail, in view of the fact that the emulsions formed during alkaline flooding have lower mobility and some plugging always occurs due to formation damage and / or scale formation.

(7) The reservoir should not have a gas cap, because a sizeable amount of the mobilized oil could move up to resaturate the gas cap.

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2-4 Crude Oil Properties: The lowering of Oil –watering interfacial tension is a function of of the properties the crude oil . It is generalay accepted that reaction of alkali with components of the crude oil leads to the generation of low interfacial tension through the formation of surface-active agents. A multitude of crude components directly responsible have been identified these include :

(1) Carboxylic acids, (2) carbo-xyphenols, (3) porphyrins, and (4) asphaltenes .

Attempts have been made to characterize the crudes and correlate their properties to recovery efficiency. Some of the properties suggested by investigators are discussed here. A minimum acid number ( the number of milligrams of KOH required to neutralize one gram of the crude oil to pH=7 ) needed for successful alkaline flooding has been suggested by many researchers: a value of 0.5 or greater is generally considered very favorable. It is important to recognize that only organic acidity. Determined by subtracting the inorganic acidity due to mineral acids or acidic gas from the total acidity, is correlatable. Most oils have acid numbers less than 1 ,

Whereas the presence of acids in the crude a pears to be a necessary requirement, no direct correlation has been observed between the acid number of the crude and the interfacial activity or the magnitude of the enhanced oil.

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Chapter 3:

Mechanism of action and Operations

21

Chapter 3: Mechanism of action and Operations :

3-1 Alkaline flood operation

In general, an alkaline (caustic) flood is used only in a sandstone reservoir because of the abundance of calcium in a carbonate reservoir brine . Although the most common chemical used in caustic flooding is sodium hydroxide, sodium orthosilieate and sodium carbonate also are used . Other chemicals that have been used include ammonium hydroxide, potassium hydroxide, sodium silicate, trisodium phosphate, and polyethylenimine . The cost is important, e.g., a chemical such as sodium hydroxide costs less than potassium hydroxide . Ammonium hydroxide has been used in a carbonate reservoir according to ban et al . Divalent cations such as calcium and magnesium in the connate water can deplete a caustic slug by precipitation of hydroxide. Also if anhydrite or gypsum are present in the rock, calcium will react with the slug to precipitate calcium hydroxide. In addition , clays having high ion exchange capacity will exchange hydrogen for sodium , rendering the caustic such ineffective by producing water and tying up the sodium . In general, caustic reacts too slowly with silica in sandstone to cause problems. Also, most Dolomites and limestones will not react with the caustic to cause deleterious effects. As noted in table 6-1 , the amount of water in barrels required to produce a barrel of oil with caustic flooding ranges from 22 to 33 .

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3-2 Mechanisms action of Alkali Alkali reduces adsorption of the surfactant on the rock surfaces and reacts with

acids inthe oil to create natural surfactant. Alkaline chemicals can cause improved oil

recovery through the formation of emulsions. In alkaline flooding, emulsification is

instant, and emulsions are very stable. Emulsification mainly depends on the water/oil

IFT. The lower the IFT, the easier the emulsification occurs. The stability of an emulsion

mainly depends on the film of the water/oil interface. The acidic components in the

crude oil could reduce IFT to make emulsification occur easily, whereas the asphaltene

surfactantsadsorb on the interface to make the film stronger so that the stability of

emulsion isenhanced. Local formation of highly viscous emulsions is not desirable since

these would promote viscous instability. In carbonate reservoirs where anhydrite

(CaSO4) orgypsum (CaSO4·2H2O) exists, the CaCO3 or Ca(OH)2 precipitation occurs

Na2CO3or NaOH is added. Carbonate reservoirs also contain brine with a higher

concentration of divalents and could cause precipitation. To overcome this problem,

suggested NaHCO3 and Na2SO4. NaHCO3 has a much lower carbonate ion

concentration, andadditional sulfate ions can decrease calcium ion concentration in

thesolution.

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3-3 Alkaline application in the oil industry Alkali reacts with the petroleum acids during the alkaline flooding in the reservoir. To

form a surfactant hydroxide ion reacts with a pseudo-acid component which is known as

hydrolysis reaction (Equation 8). When pseudo-acid is not present in the crude oil then

little surfactant can be generated.

HAo + NaOH- ‹―› NaAo + H2O (8)

The reaction depends strongly on the aqueous solution pH and occurs at the water/oil

interface. A fraction of organic acids in oil become ionized with the addition of an alkali,

whereas others remained electronically neutral. The hydrogen-bonding interaction

between the ionized and neutral acids can lead to the formation of a complex called acid

soap. Thus, the overall reaction, equation 9, is decomposed into a distribution of the

molecular acid between the oleic and aqueous phases,

HAo ‹―› HAw (9)

and an aqueous hydrolysis where, HA denotes a single acid species, A- denotes anionic

surfactant, and subscripts o and w denote oleic and aqueous phases, respectively [29].

HAw ‹―› H+ + A-

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3-4 DISPLACEMENT MECHANISMS IN ALKALINE FLOODING

Alkaline flooding enhances the recovery of acidic oils by tow-stage processes (castor) . The first stage involves the mobilization of the residual oil by configurationalchanges like emulsification and wettability alteration . Surface-active salts are formed in situ by the acid-base reaction between the alkali and the organic acids in the residual oil . The surfactants thus generated may:

(1) adsorb at the rock surface , changing the wettability characteristics of the rock and hence the configuration of the residual ganglia of the crude oil (castor) .

2)The second stage involves the modification of the macroscopic production characteristics of the mobilized oil phase . The overall recovery efficiency may be increased in this stage by improvements in the displacement efficiency through mobility control , i.e., by reduction in the floodwater mobility .

3-5 Effect of alkali and polymer on surface tension:

Effect of alkali and polymer on surface tension of surfactant solutions The variations of surface tension with the surfactant concentration in the presence of polymer and alkali have been presented The ability to lower the surface tension between aqueous solutions and other phases is one of the most significant aspects of surfactants that raise their applicability in industries. The critical micelle concentration

25

(CMC), one of the main parameters for surfactants, is the concentration at which the surfactant solutions begin to form micelles in large amount Presence of polymer and alkali in a solution of surfactant significantly influences the surface tensions. For evaluating the effect of polymer on the surface properties, surface tension measurements of SDS surfactants have been performed in the presence and absence of polymer. it may be seen that polymer increases the surface tension of the surfactant solution due to interaction of the functional group of both polymer and ionic surfactant On theother hand, addition of alkali reduces the surface tension asalkali itself reduces the surface tension of water significantly .

3-6 Effect of alkali and surfactant on the viscosityof polymer solutions :

The effects of interactions between alkali and surfactant with polymer viscosity must be considered while injecting such ASP slug for EOR. Alkali can modify the viscosity of a PHPAM solution in two ways; first, alkali provides cations into the polymer solution. These cations can reduce polymer viscosity through the charge shielding mechanism second; alkali can hydrolyze the amide groups on the polymer chain (base hydrolysis). This process can increase the polymer solution viscosity. Obviously, the net effect of alkali on the polymer solution viscosity depends on the relative extent of these two factors. Surfactant slugs are frequently used in EOR processes to mobilize residual oil by changing rock wettability or reducing IFT. To increase the efficiency of such processes, polymers can be co-injected with the surfactant slug. Under the reservoir condition, the surfactant can be mixed with polymer which leads to change of viscosity of the polymer solution. It is very important to simulate the viscosity of polymer solutions or mobility ratio for any ASP injection process. Thus, the effects of SDS on the viscosity of PHPAM solutions were examined. The effect of SDS concentration on the apparent viscosity of PHPAM polymer solution having 1,000 ppm. The apparent viscosity of polymer decreases in the presence of surfactant. These results indicate that SDS reacts physically as well as chemically with the polymer chain in deionized water. This trend is similar to that observed by and it was suggested that anionic surfactant affects the viscosity behavior of polyacrylamide through charge-shielding mechanism, which causes the shrinkage of molecular chains of polymer and the decrease of hydrodynamic radius. Comparison of alkali, surfactant, polymer, surfactant polymer

26

and alkali–surfactant–polymer flooding for EOR The additional oil recovery by alkali injection after conventional water flooding is obtained by four possible mechanisms reduction of oil–water IFT; in situ formation of surfactant by reacting with acidic components of oil; emulsification of oil into water; wettability alteration and improvement of sweep efficiency by emulsification and entrapment. NaOH is conventionally used as alkali as it is relatively cheaper and reduces the surface tension or IFT between oil and water significantly. Our earlier work reported that surface tension of NaOH in its aqueous solution decreases as its concentration increased up to 1 % and then remains almost constant. Thus, in the present study, concentrations of NaOH were varied from 0.5 to 1.0 % for flooding experiments. The additional oil recovery after conventional water flooding The additional recovery is around 14 %. Polymers are often used as mobility controller for EOR. Injection of small quantity of polymer significantly increases the viscosity of solution, which can increase the sweep efficiency of the displacing fluid in the porous media during flooding. The aqueous solution of polymer shows non- Newtonian behavior and its apparent viscosity is function of polymer concentration, shear rate, temperature, etc. For economic implementation of polymer flooding projects, concentration of different polymer is generally varied from 1,000 to 2,000 ppm and hence, the polymer concentration for this present study was kept in the aforesaid range. The additional oil recovery by injection of 0.5 PV 1,500 ppm PHPAM followed by chase water is around 16 % after conventional water flooding . Surfactants are considered as good EOR agents since 1970s because; it can significantly lower the IFTs and alter wetting properties. Displacement by surfactant solutions is one of the important tertiary recovery processes by chemical solutions. The addition of surfactant decreases the IFT between crude oil and formation water, lowers the capillary forces, facilitates oil mobilization, and enhances oil recovery. The concentrations of surfactants are generally kept above their CMC. SDS was used as surfactant for the present study and its concentration was varied from 0.1 to 0.3 %. The typical additional recovery using surfactant after water flooding the comparative picture of additional recovery of individual alkali, polymer and surfactant under economic limit is shown It has been found that the injection of same pore volume of combined surfactant and polymer gives better recovery than either of the above methods. This is because of reduced IFT using surfactant and improved mobility by polymer. The oil recovery and corresponding water cut are shown in the synergistic effects of alkali, surfactant and polymer in ASP flooding again gives higher recovery compare to others.

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3-7 Effect of alkali in ASP flooding:

ASP flooding experiments where same pore volumes of different chemical slugs were used. The effects of alkali have been studies by varying the concentrations of alkali in the ASP slug. An increase in concentration of alkali increases the additional recovery as it is well known that the injected alkali quickly reacts with the carboxylic acid groups of crude oil forming in situ surfactant. Presence of alkali in a solution significantly influences the surface and IFTs. Significantly lower values of surface tension are observed in alkali-polymer– surfactant system due to synergistic effect of surfactant and alkali compared to surfactant–polymer system without alkali. The decrease of surface tension of surfactant– polymer solution in the presence of alkali may also be due to charge-shielding mechanism and hydrolysis polymer. This reduced surface tension is one of the most important criteria for enhanced recovery of oil by increasing the capillary number of oil–water system.

3-8 Alkaline conservation equation

The alkaline is assumed to exist only in the water phase a concentration in a water injector. The distribution of the injected alkaline is modeled by solving a conservation equation which is given in Equation 23 where ρw,ρr is the water and rock density, Ca is the alkaline concentration, Caa is the adsorbed alkaline concentration, μseff is the effective viscosity of the salt, Dz is the cell center depth, Bw Br is the water

28

and rock formation volume respectively, T is the transmissibility, krw is the water relative permeability, Sw is the water saturation, V is the block pore volume, Pw is the water pressure and g is the gravity acceleration.

3.9 Alkaline effect on water-oil surface tension

The effect of alkaline on the water-oil surface tension is modeled by a

Combination Effectwith surfactant. The modification is done by the water-oil surface

tension which is

Givenin Equation 24.

wowo surf stalkC A C

Where wo surf C is the surface tension at surfactant concentration as well as zero

Alkalineconcentration and stalk A C is the surface tension multiplier at alkaline

concentration.

3.10 Alkaline effect on surfactant/polymer adsorption

The alkaline can reduce the adsorption of both surfactant and polymer on the rock

surface. This is modeled by modifying the mass of adsorbed surfactant or polymer

whichis given in Equation 25 where V is the pore volume of the cell, Φ is the porosity,

ρr is the mass density of the rock , Cas , p is the surfactant/polymer adsorbed

29

concentration and AadCalk is the adsorption multiplier at alkaline concentration

Chapter 4 : Figures and tables :

30

31

32

33

34

4

35

Conclusion In the present study, experiments have been performed to examine the interactions of alkali, surfactant injection for enhance oil recovery. The effects of alkali and surfactant on polymer viscosity leads to the optimum concentration of polymer required for mobility control in the presence of other chemicals. The results on the effects of alkali and polymer on surface tension of polymer solution leads to optimum concentration of surfactant required for reduction of interfacial tension between oil and water. The effectiveness of ASP system on EOR was tested with a series of flooding experiments performed in the sand-pack systems.

Recovery efficiencies vary 23–33 % of original oil in place over the conventional water flooding. Several mechanism viz., reduction IFT, emulsification of oil and water, solubilization of interfacial films, wettability reversal, viscosity improvement, etc. are responsible for the EOR. Based on the experiments data and relative cost of different chemicals, concentration range of alkali (0.7–1.0 wt%,), polymer (1,500–2,500 ppm) and surfactant (0.2 wt%) have been recommended for successful ASP flooding. It has shown success in some field attempts and has a potential for giving greater incremental oil recovery .

Problem in using are mainly : 1.Scaling and plugging in the producing wells. 2.High caustic consumption.

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References :

1- Erle C. Donaldson , Gorge V. Cgilingharian and Teh Fu Yen , enhanced oil recovery ll process and operations , 1989 , Tokyo .

2- Sume Sarkar,Evaluation of Alkaline, Surfactant and Polymer Flooding for Enhanced Oil Recovery in the Norne E-segment Based on Applied Reservoir Simulation. 2012. Norway

3- Zoltán E. HEINEMANN . PETROLEUM RECOVERY , April 2003, Leoben.

4- Larry W. Lake, Fundamentals of Enhanced Oil Recovery , jun 2000. Texas . USA

5- Don W. Green and G. Paul Willhite , Enhanced Oil Recovery , 1998 Richardson, Texas, USA.

6- Erle C. Donaldson , Gorge V. Cgilingharian and Teh Fu Yen, enhanced oil recovery l ,1989 , Tokyo .

7-Schlumberger, 1998, Oilfield glossary: Schlumberger Web site, available at http://www.glossary.oilfield.slb.com/en/Terms/d/.

8- http://www.glossary.oilfield.slb.com/Terms/a/alkaline_flooding.aspx

9- http://www.slideshare.net/AmitNitharwal/advancement-in-enhanced-oil-recovery?qid=46223491-0ab6-4486-8a80-ec0eb7e84b72&v=&b=&from_search=15

10- https://www.onepetro.org/journal-paper/SPE-8848-PA

11- http://www.investopedia.com/terms/e/enhanced-oil-recovery.asp

12- https://en.wikipedia.org/wiki/Enhanced_oil_recovery

13- http://www.diva-portal.org/smash/get/diva2:589681/FULLTEXT01.pdf

14- https://www.onepetro.org/journal-paper/SPE-8848-PA37

15- http://www.glossary.oilfield.slb.com/Terms/a/alkaline-surfactant-polymer_flooding.aspx

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