Petroleum Encyclopaedia

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ENCYCLOPAEDIA OF PETROLEUM SCIENCE AND ENGINEERING (Volume 14) S.L. Sah KALPAZ PUBLICATIONS ENCYCLOPAeDIA Of' PeTROLEUM SCIENCE AND ENGINEERING Left Blank ENCYCLOPAEDIA OF PETROLEUM SCIENCE AND ENGINEERING (Volume 14) Well Logs Interpretation, and Fundamentals of Palynology S.L.Sah IB PDBucmONS KALPAZ PUBLICATIONS DELHI-11 0052 "This page is Intentionally Left Blank" Encyclopaedia of Petroleum Science and Engineering S.L. Sah ISBN: 978-81-7835-652-5 All rights reserved. No Part of this book may be reproduced in any manner without written permission. Published in 2008 in India by Kalpaz Publications C-30, Satyawati Nagar, Delhi-110052 E-mail: kalpaz@hotmail.com Phone : 9212729499 Lasser Type Setting by: Quick Media, Delhi Printed at : Singhal Print Media, Delhi "This page is Intentionally Left Blank" Dedicated to the Geophysicists, Geologists, Engineers, Scientists, Universities, Organisations, Teachers, Students, and other working in different disciplines of petroleum science and engineering Left Blank (CONTENTS ) Preface 1. Well Logs Interpretation 2. Fundamentals of Pleontology 3. Appendices Appendix-A: Evolution of Species Appendix-B: Biological Evolution Appendix-C: National Oil Company-ONGC (India) Appendix-D: Important Figures and Data India 11 15 101 241 245 265 after 60 Years (1947 to 2007) 280 Appendix-E: News in Focus India to Soon Have a Research Base in Arctic 288 Left Blank PREFACE "We usually find oil in new plau - - _. ._ ..... ...:. :L ..)_ .. 5 .. , j _ .. i-- .... :'t ----- . .. t + I R1 . ''5"" 1 .... -. to. l . ... 1->.. . ' . .. I .... " I.AS I I 1.-.-,.... .-.' I \. . ! .tt I . \ __ GA' r-f-.. f . . .- .... - . . . . I .. - - _ . . _. . t;AS- . c: .. ". ..... f"-= . ''':', : . . . :: ., --I- --'-' -- -.-.-.. -f::: -1-- -. . " --, __ L-__ . Fig. I. A compensated neutron and sonic log on the Louisiana Gulf Coast showing gas sands (Courtesy Schlumberger). a-s ;::t -J . 18 Encyclopaedia of Petroleum Science and Engineering and the acoustic is in travel time. In some of the water zones there is an apparent gas separation. Advanced Gas Diction Distinguishing between gas bearing and oil bearing reservoirs with resistivity logs is almost impossible. Although the gas bearing zones have lower water saturations than oil bearing zones the pore size variations usually marks our ability to separate the two on a pure resistivity or water saturation basis. Most gas detection today is done with the density and neutron log. Other porosity log combinations are sometimes used but are usually more difficult to analyze. The acoustic log generally is not influenced by gas when the formations are well consolidated or compacted. This includes essentially all carbonates, cements and consolidated sandstones and unconsolidated sandstones that are deeply buried and under normal net overburden stress. Normal overburden pressures are those where the pore (fluid) pressure is in the 0.433 to 0.465 psilft range. Values higher than that are considered abnormally pressured. . Gas effects on the acoustic log show up as increases in travel time (porosity calculated). The changes are apparently not related to the volume of gas (gas saturation) as the influences appear on the logs to be sharp and significant. There is little difference between 85 percent gas saturation and 60 percent gas saturation on the travel time measured. The gas effect appears to more influenced by the formation consolidation or compaction than by the gas saturation. In modestly uncompacted formations, where shale travel time is in the 100 to 125 1-1 seclft range the porosity can be corrected using the following equation: i I I I I cAL I GR , ... !)PIo II I SHALE TT 'I JA I : ,'-!-. I: I I I I , I I I 11111 ;')f 11 "1 1.11.1 TTTT I I I I 111'1..' IJI I I.lI I I I I I I I I TT I" m ITT!rf I, I II I I: I' I! II Ie TT III I , 1I'!l1 I I : I " 'I ' II I I'i I Il.l I t , :J I I I /I II : ! ' ' , '" I ! I I 11;1 ,,,,(OOLOM' : I 111111 I 1'1 j,] I I I:' ,-->: I ,;C:::;: I Tn I I '1'_1' i I I ITJI I Itt I I I I : , I I i ,1\.1 ITl, I I ' I 11: ITill19 Ii GR I CAL I I , I I 1111 NIJ i I II, ,II II', I' t ' I tTTTL ... TI 11 -:7;...,;; -! I ,IIIIII'HLII ! .... I til II: 11'1 j! !,"I T I I , I II lIT , II I I I I ! " 1131 fN I ANI-ce 27 .. if . - - '. .... - PI -1.0 l-I--. ----- H : .... : 2.8 .. : ' -. --.--/------/------ 2.9 ',:-;-' 'i"r .... -, -N ... o o o SHALE CORRECTED POROSITY (%) Fig. 31. To find porosity from the acoustic log (After Hi\Chie, 1982). matrix travel tim\!. Continue this changing oflinear combinations until we obtain a porosity match. Porosity and lithology determination from MID ploto, we use to density, neutron and acoustic logs to obtain both apparent matrix density (Pma a) and apparent matrix travel time (tma a) from earlier figures and from Figs. 32, 33 and 34. Having determined the apparent matrix density and travel time we can enter earlier Fig. 30 and obtain some idea of the matrix materials. In this case the formation must be gas free and clean for the determination to be reasonable. The triangles constructed 56 Encyclopaedia of Petroleum Science and Engineering DUERMtWA liON OF (.t ".,)", FROM SONIC ANr; CN.l t tOGS Fig. 32. To detennine (tm.) a from sonic and CNL logs (Courtesy Schlumberger). Well Logs Interpretation OETERMINATIC)N Of' (P ..... lr. FROM FOC' AND tOGS Fig, 33, To determine (Pm) a from FDC and SNP logs for fresh mud (Courtesy Schlumberger). 57 58 Encyclopaedia of Petroleum Science and Engineering Fig. 34. To detennine (1m) a from sonic and SNP logs (Courtesy Schlumberger). Well Logs Interpretation 59 Fig. 35. MID solutions for various rock combinations (After Hilchie, 1982). 60 Encyclopaedia of Petroleum Science and Engineering % dol- --VIs + Vdoa + Vsd = 100% Fig. 36. Matrix density for tri-matrix : sandstone, limestone, and dolomite. %anh-v + v + v = 100% dol anh sd Fig. 37. Matrix density for tri-matrix : sandstone, dolomite, and anhydrite. Well Logs Interpretation 61 Pm. Fig. 38. Matrix density for tri-matrix : limestone, dolomitl, and anhydrite. using clean matrix points indicate the possible solutions. Using three porosity logs we are only allowed to try and solve for three rock types. That is a point represented by : Pma a = 2.72 gmlcc and tma a = 50 microsec!ft falls in two triangles. It could be a combination of dolomite, limestone and quartz or it could be limestone, anhydrite and quartz. Both of these triangles, or mathematical solutions can be solved with no problems. Of course only one is probably correct for the given formation. Or if the rock actually contains four matrix components none of the solution may be correct. Fig. 35 shows a break down of the triangles for limestone, dolomite and anhydrite. We can go into one triangle with the apparent matrix density and travel time and obtain the proportions of limestone and dolomite. Anhydrite is obtained by subtracting the percent of limestone and dolomite from 100 percent. These mineral fractions should only be considered, at best, approximate. Using these mineral fraction we can then enter Fig. 36 and obtain an apparent matrix density for the combination of the three minerals. The apparent matrix density can then be used with the conventional density porosity chart to obtain a porosity. Figs. 37 and 38 are matrix density charts for mineral combinations of sandstone, limestone and dolomite and dolomite, 62 Encyclopaedia of Petroleum Science and Engineering sandstone and anhydrite, respectively. Fig. 39 is a conventional density porosity chart. In complex lithologies even with the best data we can only approximate porosity. Secondly, using two porosity logs in complex lithologies can result in porosities that are significantly different than the true porosities. :..,. III , +: j:. itt '.: f . '" "i :..L:' . -, i , il , 't .. .. .G U ffl . t ... " E " .. LL :::;:;::;:::;: 1 II J ' . , I I I t' .. , tl . .. E' '" - 1'"1,.:: I ::; .. : I : .... : r .... _ ..... I J . ....... .. l -- I 30 t -i t ive . . .:. 20 40 60 80 100 120 I w 100 120 LW Fig. 41. Pulsed neutron log applicability (After HiIchie, 1982). 68 Encyclopaedia of Petroleum Science and Engineering determined from the usual water catalogs, Rwa and SP analyses. The cross section of methane (or gas) is a function of both temperature and pressure as these control the hydrogen content of the gas. The pressure of the reservoiHs-OOtained by dividing depth by 2 in psi. Usually oil is assumed to have a cross section of 22 cu. The PNC logs are not too sensitive to the type of the rock. An analysis of Fig. 45 shows that the interval 6592-6620 (all NLL depths) is hydrocarbons and actually produce oil. There is an oil-water contact at 6596 (NLL). The sand at 6553-6568 (IES) was the original completion and shows water saturations on the NLL of 55 to 80 percent. Th