Division of Gas Accumulation System and Laws Controlling Distribution of Natural Gas in Typical Petr

Journal of China University of Geosciences, Vol. 13, No. 4, P. 306-312, December 2002ⅠSSNl002-0705Printed in ChinaDivision of Gas Accumulation System andypical Petroliferous Basins of China* S inLaws Controlling Distribution of Natural GJiang Zhenxue Pang Xiongqi Jin Zhijun Chen dongxiaBasin reservoir Research Center, University of Petroleum BeKey Laboratory of Hydrocarbon Accumulation, Ministry of Education Beijing 102249ABSTRACT Considering the existing problems of the petroleum system this paper brings forward the concept of natural gas accumulation system and presents the dividing principles. Then detailed statistics on theaccumulation factors of the 32 typical natural gas accumulation systems in China and studies on the laws controlling distribution of gas are collected. The research shows that the petroleum accumulation system is thebasic unit controlling petroleum generation, migration and accumulation. generating intensity generatingamount, accumulating efficiency and migration distance plays an important role in the distribution of naturagas. Through analysis on results of resources evaluation, discovered reserves and residurves, potentialareas in middle-scaled petroliferous basins in China are forecasted in this paper. Ordos, Sichuan Tarim andQaidam basins are found out to be the main basins developing and enriching gas accumulation systemsKEY WORDS: petroliferous basins in China gas accumulation system petroleum system, laws controllinggas, potential areaBASIC CONCEPTS AND DIVISION PRINCIPLES on structing exploration( He and Zhao, 2000; Zhang, 1999)PETROLEUM ACCUMULATION SYSTEMWe define petroleum accumulation system as the organicBasic Concept on Petroleum Accumulation Systemcombination of one or several suits of source rocks with the eThe petroleum system( Magoon and Dow, 1994; Ma- volving petroleum accumulation plays being formed during thegoon, 1992, 1990; Demaison and Huizinga, 1991)empha- formation of the basin. Although both of them adopt means ofsizes on the distribution and evolution of source rocks. a system analysis the biggest difference between them is therocks if it is mainly view of analyzing problems. Adopting theories of systemfocused on the formation distribution and evolution of the Zhou, 1988; Zang, 1985 ), and according to the formationsource rock. Most basins in China are superimposed basins, and evolution of trap petroleum accumulation system'which it is difficult to divide petroleum system. Moreover, tematically analyzes petroleum accumulation laws based oninvestigations of the laws of petroleum distribution in the sys- formation, distribution and evolution of source rockstem are insufficient currently which is a disadvantage to in-a petroleum system may contain one or more petroleumaccumulation plays i a petroleum accumulation play may beThis paper is supported financially by National Key Basic Research Project located between two petroleum depressions and belong to two(973 y Formation and Distribution of Oil and Gas in Typical Superimposed BasintroleH中国煤化工 t difficulties to the appliar"Plan Project QuantitativeModels of Petroleum Accumulation in Major Fields(960007y'CN Ging petroleum accumulation plays as the nuclear factor in the systematic analysis ofManuscript received Augustpetroleum accumulation, the difficulties canManuscript accepted September 20, 2002Meanwhile it is much more practical, for system analyconducted closely with trap which is the nucleus of explo-ration. If there is one suit of source rock in the petroleum ac- system is firstly with the help of the paleo-tectonic maps ofcumulation system petroleum accumulation system is the sub- the basin comprising oil and gas fields, the migration diredunit of the petroleum system. If a petroleum accumulation sys- tion and accumulation zones can be identified based on thetem is located between two source rocks this petroleum accu- distribution of potential source rocks according to the principlemulation system comprises some parts of the two petroleum of division groove ;secondly petroleum accumulation systemsystems( Fig. 1). Thus a close relation between petroleum in each oilfield can be divided into combination of develop-accumulation system and petroleum system is expected. The ment and evolution of tectonic unit and/or traps( jiang etformer is the development of the latter while the latter is a ba- al. 1999)sis when analyzing petroleum accumulation systemDIVISION OF PETROLEUM ACCUMULATION SYSfrar nures tosk area ITEM AND STATISTICAL CHARACTERISTICS OFACCUMULATION FACTORS OF TYPICAL GASupBEARING BASINS IN CHINAsource rockleaWe divide the petroleum accumulation systems of themain petroliferous basins in China based on principles forego-eration amounts, the efficiency of migration and accumulationand migration distance for every petroleum accumulation system are calculated the detailed data are given in Table 1etroleum system-HestmmulatiorsystemCONTROLLING OF ACCUMULATION FACTORS ONFigure 1. Comparison of petroleum accumulation sysGAS ACCUMULATION SYSTEM IN PETROLIFERtem and petroleum systemOUS BASINS OF CHINAGas accumulation system is the basic unit constrainingPrinciples and Methodologies of Dividing Petroleum Acration, migration and accumulation and plays an im-cumulation Systemportant controlling role on the gas distributionBecause of the complication of geological process it isdifficult to establish the division criteria of the petroleum acGas Accumulation System with Higher Gas Generationcumulation system. Whether the criteria are over detailedIntensity Bearing More Gas Fieldsover simple or not it may bring inconveniences to the opera-Intensity of gas generation is plotted against the maxi-tor, Jin( 1997)summed up common principles as the followmum gas field reserves of gas accumulation systems in midings( CNPC, 1997 .Nine Five year plan projecf Quaniti- large gas fields Fig 2 ). It is observed that there is an in-tative Models of petroleu Accumulation in Major Fieldscreasing trend of the maximum gas field reserves increasing(960007y'medium-term report): 1 )Both source rocks and with the accretion of gas generation intensity. It is also foundmain petroleum accumulation zones should be considered on that there is a minimum limit of the gas generation intensity todivision i (2)A reservoir with uniform interface of oil, gas form a large gas reservoir, and it is impossible to form a gasand water can only be attributed to one petroleum accumula- reservoir if the gas generation intensity is smaller than thetion system (3 For superimposed basin with several source minimum level. The reason is that natural gas will be depletrocks and accumulating periods accumulation cycle( the ed by dissolution, diffusion and adsorption in the process ofcombination of the source reservoir and cap )should be first- migration and accumulation. Gas reservoirs can be formed only divided according to structural layers and abnormal pressure ly if thestrata, then petroleum accumulation system; (4 )For each中国煤化工accumulation cycle commonly take accumulation unit as theCNMHGnucleus and the migration channels as main clue and the location of source rocks as boundary to divide the petroleum acImulation systemThe concrete division method of petroleum accumulationTable 1 Division of petroleum accumulation system and statistical characters ofaccumulation factors of typical gas-bearing basin in Chinaaveragees/ system/ tensity/ amount(10t)k(10m2(10°m3)km-2) km492.26446.62900970.054738.9422.96446.62900970.0547Sanhu425,36446,62900970.0547Taijinaier50246.6646.630290970.54780east area of Wubaidi104.5539.51887911515103200.06980-1006Dachiganjing208.51887970-8015103200.06945.115103200.0693379.5187234978400.045710 Sichuanwest area of Wolonghethe East Si- Tieshan18.1102,2187234978400.0457wangjiaba1872314978400.0457chuan12Fucheng39.3101.41872314978400.0457Weiyuan781400.0525northwest Zhongba392022.5882000.2l1central slope middle gas field 4 830 2896.16 48 55221848400.13Kela 218564593.70.50515-20727.5309.7529090.425Yangtake18.34440641.6456818Tabei upliftJilake52.5127.65200251300000.09880-100Bachu uplift Hetianhe173.2620204495112250.121100-150Kekeya27.5365,2590890.1625 TuhaTaibei0.064Yizhong28127232621305070.09727 BohaiwanHuanghua Banqiao17049841495400.11322.7152.362303426960,04448.2123.23500210000.05830 Qiongdongnan west brim Ya 13-110773300010Dongfang 1-1287.7996.851600480002.076Ledong 22-1165.84311080324001.33of gas generated is larger than the amount depleted which re- fieldeserves wIgas generation intensityflects that the accumulation of gas is more difficult than that of and there is a critical minimum limit of gas generation intensihich shows that in the area with thegas generationintensity the risk of oil exploration is lower than the gaGas Accumulation System with Larger GenerationFigure 4 is the correlation map between the total gasAmount Bearing Reservoirs of Bigger Scale中国煤化工 ion amount of the midire 3 is tationn gas generation largeIt shows that there is anCNMHGintensity and gas field reserves in mid-large gas field accumuIncreasuei reserves with the accretion of thelation system. Obviously there is an increasing trend of gas gas generation inten120the laws of gas distribution in gas accumulation system. Threeconclusions could be acquired according to Figs. 6 and 7e10⊕7O More than 95 of mid-large gas fields are d7ered within 100 km from the source area There is a decreas-d of the number of gas fields of mid-large scale withincreasing of the migration distance( Fig. 6).Moreover, more26than 95 percent gas reserves of mid-large gas fields are dis-23ributed in areas within 50 km from the source area(2 More than 95 of the numbers and reserves of midlarge gas fields concentrate in an area within 50 km fromas field reserves/10'msource area, and decrease with the increasing of migrationdistance. This shows that source rocks control the distributionFigure 2. Correlation map between the intention of gasof natural gas( Fig. 7). Therefore, to trace efficient sourcegeneration and maximum gas field reserves of therocks is the premise for exploring large gas fieldslarge gas field accumulation system. 1. Sebei 1 :2bei 2:3. Tainan 4. Taijinai er:5. Wubaiti:6Dachiganjing ;7. Longmen;8. Gaofengchang ;910011. Shuangjiaba,1Fuchengzhai : 13. Weiyuan ;14. Zhongba:15. MoxiRengo16. middle gas field:17·Kea2;18.Yaha;19.§602Yingmai 7:20. Yangtake 21. Yakela 22. Jilake23. Hetianhe 24. Kekeya :25. Qiudong ' 26. Suqiao27. Banqiao 28. Wenliu ; 29. Wangjiatun 30. Y13-1 :31. Dongfang 1-1 32. Ledong 22-1100l00010000100000gas field reserves/I0'mcanthe total gas generation amount must reach or exceed a critical Figure 3. Correlation map between the gas generationamount. For example, to form a gas reservoir with 100 x 10 intensity and gas field reserves of mid-large gas fieldmgas the total gas generation amount must reach or exceed accumulation system. Large gas fields(O): 1. Ya 1320 000 x 108m, and to form a gas reservoir with 1 000 x 10 1 2. Sebei 1 3. Sebei 2: 4. Wubaiti 5. Wolonghemgas, the total gas generation amount must reach or exceed6. Weiyuan :7. Tainanmiddle gas field :9. Y50000×108m3a : 10. Kela 2 :11. Yakeya:12. Yingmai 7. mid gasfields(A): 1. Dachiganjing 2. Gaofengchang :3Gas Accumulation System with Higher Migration EffiShuangjiabei 4. Fuchengzhai ; 5. Zhongba 6. Wenciency Bearing Mid-Large Gas Fields with Larger Re- u,7. Suqiao ,8.Banqiao; 9. Xinglongtai: 10Jinzhou 20-2,11. Wangjiatun 12. Qiudong 13Figure 5 shows relationship between migration and accuTaijinar ermulation efficiency and gas field reserves in gas accumulationsystems of mid-large gas fields. It demonstrates that gas re-3 Most mid-large gas fields are discovered within 1590 km from the source area it demonstrates thatserves are larger in the gas accumulation system with highermore easily than oil. The number and reserves of large gasaccumulation efficiency. Migration efficiency reflects geologiccumulation condition of a gas accumulation system. Fa- fields中国煤化工 istance firstly, then de-creaseole geological conditions tend to form larger gas reservoirHCNMH Stance within 20-60 kmfrom source area is favorable. 'This is probably not the realcase as the reserves for deep basin gas accumulations whichre very likely to occur in the central part of the source rockControlling of migration Distance on Gas Distributionarea, not taken into considerationMigration distance is also an important factor controllingusing the distributive law of mid-large gaspredict the favorable potential distribution areas which in1000clude large-scale paleo-upheaval area the structure belt within large subsidence center, large-scale structure belt of anticline, large-scale fault zone, large-scale slope belt, large19scale lithologic pinchout zone large-scale unconformity zonelarge-scale ancient buried hill the reservoir bed and the saltX32roof rock with large thickness. Moreover, the favorable poten0100tial areas are predicated by fully applying petroleum geologicalgas filed reserves/I0"mltheories of China with advanced petroleum geological theoriesFigure 4. Correlation map between the total gas gener- abroad such as theory on terrestrial originated oil theory ofation amount and the accumulation amount of the mid- source controlling theory of superimposed accumulation playlarge gas field accumulation system( 1-31 refer to theory of coal-related hydrocarbon, and theory of deep basinFig 2gas. Also exploration for mid-large oil and gas fields undercomplex geological conditions can be conducted by fully apPREDICTION OF POTENTIAL DISTRIBUTION AREA plying advanced explorative technology such as seismic techOF MID-LARGE GAS FIELDS IN PETROLIFEROUS nologies for mountainous areas elaborate seismic technologyBASINS OF CHIINAfor low-height trap with deep buried depth further study andAfter a comprehensive study on gas accumulation system technologies of reservoir modification on carbonate reservoir ofin which mid-large gas fields have been discovered and those buried hill and beach and offshore seismic explorationin which mid-large gas fields are hopeful to be discoveredthe evaluation and ranking are carried out based on their re. Forecast on Potential Distribution Area Favorable foraining resource potential. The research and exploration ad- Mid-Large Gas Fieldsvances made by formelists and scholars are referredexploration will focus on four basiand when determining gas accumulation system in which mid- Sichuan, Ordos Tarim and Qaidam in China. According tofields are hopeful to be discoveredthe investigation of diverse geological conditions twenty-threeaccumulation systems favorable for mid-large gas fields are se-lected for evaluation and ranking. The detailed results areshown in Table 2. It indicates that the accumulation system ofmiddle gas field in Ordos basin is the most favorable for theformation of mid-large gas fields whose predicted resource is10 920x 10 m and the residual resource is 8 x 108 m4★24The next is gas accumulation system of western area of Chuan食23dong with residual resource of 68 052 x 10 m, gas accumulation system of eastern area of Chuandong with residual resource of 6 143 x 10 m, and gas accumulation system of10000gas filed reserves/10"m'Hetian River with residual resource of 4 492 x 108 nFigure 5. Correlation map between the migration efficiency and gas field reserves of accumulation system inmid-large gas fields(1-31 refer to Fig. 2 ).中国煤化工Methodology and Principle to Predict Potential DistribuCNMHGFirstly predicting the potential distribution of mid-largeas fields by using the results of resources evaluation discovered reserves and remaining resources potential. SeccTable 2 Prediction and evaluation on gas accumulation system of potential mid-large gas fields in petroliferous basins of Chinaaccumulation systemsourcebjective stratapredictiobasinhydrocarboncodedIneage29009729001581510320ⅢlDDZTT04978407490805.290.852SichuanIv southwest Weiyuan778140Z,P88200TⅥ middle moxi149940T253.8Ordos009202896.16802473.481ⅧKela2T,J1856l81949.497IX YahaT,91645K,E,N52357.0918O,T,J72725E,K,O309.741857.4920XI yangtaker,J44406K,E249.19543.922Ⅻ YakelaO,∈TJ170450JKO∈Z1704XⅢ Jilake0,T130000T,CXⅣ Hetian5l1225C,O5112Xv KekeyaE227249N,E2272365.25190783.936XⅥ Qiudong190781l78193.39Yizhong XⅦ130507C-P,O1305117890.2615BohaiWamnghua XⅧ149540132077.6412E21000021001231977XX Yal107757334.7217Qiongdongnan X XI Dongfangl-1 E, N48000E,N2400l40458.511hai XLll Dongfang 22-132400E1620l18973.3914Note:* residual resource( 10mr);**.residual/total400035002000150000-10-2030405060708090100102030405060708090100>100migration distance/kmmigration distance/kmFigure 6. Migration distance and distribution of gas Figure 7. gas distribution within the migration area infields in petroliferous basins of China. No. mid-large petroliferous basins of China. accumulationgas field numberamountCONCLUSIONS(3 )Based on analysis of diverse geological conditions(1) Applying the principle and methodology of the twenty-three accumulation systems favorable for mid-large gaspetroleum accumulation system the authors divide 32 gas ac- fields are selected for evaluation and ranking. The gas accucumulation systems in the main petroliferous basins of China. mulationTV凵中国煤化工 Is the most(2 )The research indicates that the petroleum accumula- formationCNMHG gas accumulation systemtion system is the basic unit to control hydrocarbon genera- of western area of Chuandong and eastern area of Chuanxi andtion migration and accumulation The intensity and amount Hetian River rank the second the third and the fourth reof gas generation and the efficiency and distance of gas mi- spectivelygration etc. play important role in the distribution ofREFERENCES CITEDods. USGS Bulletin 1912, 1989b: 2-9Demaison G, Huizinga B J, 1991, Genetic Classification of Petroleum Magoon L B, 1992. The Petroleum Systenmr-Status of Research andSystem. AAPG Bulletin, 75 10): 1626-1643Methods. USGS Bulletin 2007 1992a: 98He d, Zhao W, 2000. Characteristics of Composite Petroleum System of Manoon L B, Dow W G, 1994. The Petroleum System. AAPG Memoired Basins in China. 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