Oil and gas resource potential of the lower members of Eh3 in the lower Tertiary of the Biyang Depre

18Pet.Sci(2012)9:18-2410.1007/s12182-012-0177-x0il and gas resource potential of the lowermembers of En3 in the lower Tertiary of theBiyang Depression, ChinaGang Wenzhel*, Wang Qingyu2 and Luo Jiaqun3' College of Geosciences, China University of Petroleum, Bejing 102249, China2 Exploration & Development Research Institute, Daqing Oilfeld Company, PetroChina, Heilongjiang 163712, China3 Rescarch Institute of Petroleum Exploration and Development, Henan Oifield Company, SINOPEC, Henan 473132, China。China University of Petroleum (Beiing) and Springer- Verlag Berlin Heidelberg 2012Abstract: The lower Tertiary En is divided into two sections: the upper members of En and the lowermembers of En3 in the Biyang Depression. The first section is generally regarded as a key target of oiland gas exploration, but the resource potential of the lower members of En3 has been neglected. Wehave obtained new knowledge about Ens from comprehensive geological research. The lower membersof En3 are high-quality and main source rocks, which have good oil and gas resource potential. This is anew direction for oil and gas exploration. The geochemistry characteristics of source rocks of the lowermembers of En3 in the lower Tertiary of the Biyang Depression were analyzed in detail. A basin modelingmethod was applied to hydrocarbon generation of the lower and upper members of En3 source rocks, theoil and gas resource potential was comparatively analyzed, and then favorable tectonic zones were pointedout. In the lower members of En3, a set of semi-deep lake to deep lake high-quality source rocks occursrich in algae organisms, mainly of type I, with a high abundance of organic matter. Most of the sourcerocks are just in the peak stage of hydrocarbon generation, which is a favorable foundation for formingabundant oil and gas resources in the Biyang Depression. The comparative analysis of the hydrocarbon-generation quantities between lower and upper members of the En3 source rocks shows that the lowermembers of En3 have good oil and gas resource potential, and the hydrocarbon-generation quantityaccounts for 51% of the total in En3. Specifcally, the oil-generating quantity accounts for 50% of the tota!and the gas- generating quantity accounts for two thirds of the total. Therefore, source rocks in the lowermembers of En3 of the Biyang Depression have good oil and gas resource potential, which is a key factorfor future deep oil and gas exploration.Key words: Geochemistry, source rocks, hydrocarbon generation potential, Biyang DepressionThe Biyang Depression is a relatively independent Biyang Depression, the density of driling is not adequate, andsecondary structural unit in the Nanxiang Basin located the exploration degree is relatively low. Many reservoirs arebetween Tanghe and Biyang counties of Henan province, subtle reservoirs (Yu et al, 2007). Besides, information such asChina. It is a down-faulted basin formed in the Mesozoic- time and space distribution of the lower members of En3 sourceCenozoic Eras. It covers only 1,000 km2 but its oil and gas rocks, organic types, organic matter abundance, maturity andreserves are abundant. The main oil and gas reserves are hydrocarbon generation history is not clear. Neglecting thefound in the Eogene Hetaoyuan Formation and the main existence of high quality hydrocarbon source rocks of the lowerexploration layer is En3(Qiu et al, 2005b; Yu et al, 2007; Sun members of En leads to an underestimate of the deep-seatedet al, 2008; Luo, 2003; Luo et al, 2008).hydrocarbon resource potential.Achievements have been gained due to the high explorationTherefore, based on the geochemical characteristics ofdegree and detailed research on the upper members of Ena the En3 source rocks, we compare the potential of oil and(Wen et al, 2006; Qin et al, 2005; Zeng et al, 2005). However, gas resource of the upper members of En3 with that of therelatively lttle study has been done on the lower members lower membe中国煤化工tribution to provideof En and more attention is needed. For deep hydrocarbon guidance fortargets formed by the lower members of En3 source rocks in theMYHCNMHG1 Geological background*Corresponding author. email: gwz@cup.edu.cnAccording to stratigraphic sequence, tectonicReceived July 21, 2011characteristics and development history, the Biyang20Pet.Sei(2012)9:18-24group in the lower members of En3 is thicker than 100 m, pelitic source rocks have the same characteristics as the En3.8and the distribution areas of pelitic source rocks from En3.8 source rocks. In the En3.6 sedimentary period, the subsidenceto upper En3.s show a variation from small to large, which rate of the Biyang Depression became higher again, and theagrees with the change of sedimentary facies of the Biyang lake area became larger. Widespread thick pelitic source rocksDepression.developed, and the depocenter extended to the Bidian-ZhaoaoThe Biyang Depression started to subside in the En3.8 area. In the En3.s sedimentary period, abundant and thicksedimentary period, and developed a deep lake in the pelitic source rocks developed due to the larger and deepernorthwest of the Anpeng-Andian area due to humid climate lake, and this was also the biggest lake erosion period in theand increased rainfall. The source rocks which are thicker than lower En3 sedimentary history. In summary, the pelitic source100 m relatively occurred in a small area. In En3. sedimentary rocks were affected by the subsidence rate of the depressionperiod, the sedimentary center was still in Anpeng-Andian and the change of sedimentary facies, which also determinedwith a lower subsidence rate. The lake area reduced and the the size and quality of source rocks.En3-6 source rocks' thickness mapne deep■Bidtard Gooraphia●B41 Well nameV loline(m)Boundary linesloperegion心Secondary structural line“Fig. 2 Contour map showin the thickness of the Eo source rocks in the Biyang Depression3.3 Organic matter types and abundance of the lower2.00members of En3 source rocks1.80The En3 source rocks are mainly dominated by algae,Type I organic matter. According to the H/C and O/C atomic1.60 .comparison chart (Fig. 3), the source rocks are mainly40|-dominated by Type II and secondarily by the Types I and II2kerogen.1.20In addition, the kerogen maceral results show that theIBorganic matter in the lower members of En3 source rocks was呈1.00上mainly amorphous sapropelinite and amorphous huminiteof sapropelinite. Vitrinite accounts for less than 10%, and0.80+1inertinite accounts for less than 5%. So both the organic0.60matter maceral analysis and the organic matter type indexagree with the above conclusion (Table 1). Furthermore, HI0.40indexes of the lower En3 source rocks in well BQ31, YQ3,B145, B224 and B227 are all more than 470 mg/g.TOC and0.20lower than 670 mg/g.TOC, and all of the evidence indicates中国煤化工that the source rocks belong to the Type I and Type II.0.00.MYHCNMHG 025 0.3Fig. 4 is a total organic carbon contour map of the lowermembers of En36 source rocks. We can find that the high0/Corganic abundance areas mainly occur in the semi-deep toFig. 3 Map showing the kerogen H/C-O/C of the Lower Tertiarydeep lake area and the edge of the lake basin. The highestHetaoyuan Formation source rocks in the Biyang DepressionPetSci(2012)9:18-24_2Table 1 Kerogen macerals and types of organic matter in the lower members of En in the Biyang DepressionSaptopelinitewellitLuyerAmorphousAmorpborsAlinite TotulCutinite Subern Resinite SporopllceinypeBQ31310.4 E3540s4BQ31 448 E,81075YQ3 8425 Eno095YQ3 782.5 Exs 317203265 104(IIBI45 936.4 Bu, S30596(B224 1563 Eso4:B22 1427 Exo39142B270 3647 Br90B270 4010 E)292 6B270 4185 Bas93935B270 4288 PEss)393 411organie abundance areas concentrate around the edge of shelf by contrasting each group of the lower En,, becausethe lake basin, and the abundance reduces from the edge this shelf was exposed to strong uplift and denudation into the center and falls to 1.0% in deep lake area due to the the Liaozhuang group period, and the biggest denudationhigh maturity of source rocks in the deep lake. There are thickness was about 1,000 m. The sourcerocks in this areamany explanations for this observatin. The lake (acustrine became mature because of the thermal evolution beforefacies) in the Biyang Depression was mainly dominated bydenudation, so the maturity remained the same as the periodalgae, and itis true that the delta front and prodeta had a before denudation, which can be tstifidi by the thermalgreat amount of algae, but the deep lake area was lacking evolution history of the source rocks. According to the R。in algae. The delta front and prodelta were close to thecontour map, the En3 source rocks are all mature. The sourceestuary so the lake brought abundant nutrient and luxuriantrocks which are at the oil peak stage (R。=1.0%) and theorganisms, resulting in a high sedimentary rate so thatgas condensate -wet gas stage (Ro>1.2%) enlarged with thethe organic matter can be well preserved. The deep lakeincreasing depth, but always in the Anpeng-Andian area.reducing environment is favorable for the preservation oforganic matter, whereas the deep lake source rocks occur 4 Potential of the E, source rockswidely, algae of the deep lake is good for bydrocarbongeneration. The Wangji-Zhangchang-Qiandulou-Shuanghe 4.1 Hydrocarbon-generation quantity contrastareas have high organic abundance with an average around between the upper members and the lower members2.0%, and these areas were all in the delta front. The of En3 source rocksabundance of organic matter in the Biyang Depression ismostly above 0.5%, but this index is low in the easternBased on the first order chemical reaction kinetics andXinzhuang-Houzhuang area, which reveals that the wholethe Arrhenius law, we select geothermal gradient parametersdepression has a high level of organic abundance which is(Qiu et al, 2005a), denuded thickness of each layer, chemicalkinetics parameters and hydrocarbon accumulation coefficientgood for hydrocarbon generation.in the Biyang Depression, according to the chemical3.4 Maturity of the lower members of En source dynamics hydrocarbon-generating history model (Shi, 2004;rocksPepper and Corvi, 1995a; 1995b; Pepper and Dodd, 1995;Pang et al, 2010), the oil-generating quantity of the En3 sourceThe lower members of Exas source rocks are all mature duc rocks is 2.33 bllinin tonne, and the gas-gnerating "to the high geothermal gradient (4.1°C/100m) and deep burialis 199.48 billion m' and the total hydrocarbon- generationdepth (Fig. 5), with Ro over 1.2% in the Anpeng-Andianquantity is 2.53 billion tonne. For the lower members of E3area that is located in the middle deep depession, indicating source rocks, the oil generating quantity is 1.17 bllini tone,that this area reached the mature stage and is entering gasthe gas-generat中国煤化工n m' and the totalcondensate and natural gas phase, which is consistent with lhydrocarbon-g: bllion tonne. Forexploration results. Ro is about 0.5% in Gucheng Xinzhuang the upper metYHCN M H Gthe olgneratingwhich is located in the north shelf, showing that most ofquantity is 1.16 billion tonne, the gas-generating quantitythe lower members of En: source rocks are mature. Itis is 62.88 bllion m, and the total hydrocarbon-generationdiscovered that R。is between 0.5% and 1.0% in the northquantity is 1.22 billion tonne..24Pet.Sci.(2012)9:18-24Pepper A S and Dodd T A. Simple kinetic models of petroleum Wen z x, Wang H M, Chen C Q, et al. Formation and distribution offormation. Part I: oil-gas cracking. 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