Table of Content

28 October 2017, Volume 38 Issue 5

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Significance of oil and gas exploration in NE strike-slip fault belts in Shuntuoguole area of Tarim Basin

Jiao Fangzheng

2017, 38(5):  831-839.  doi:10.11743/ogg20170501

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For years,the carbonate weathering crust of paleo-uplifts has been a major exploration domain in Tarim Basin.A series of strike-slip fault belts were recognized with updated seismic data in the Shuntuoguole low uplift and slopes between the Tazhong and Tabei paleo-uplifts in Tarim Basin.Drilling data from the area revealed great oil or gas potential,and later significant oil and gas discoveries in the south (also called Shunnan) and north (also called Shunbei) parts as well as Shuntuo of the area verified the revelation.The left lateral strike-slip fault belts of north-east trending in the area are characterized by "layered deformation in vertical direction and segmented deformation along strike of the major slip zone in the deep".Echelon normal faults are common in the clastic rocks in the upper Ordovician and layers above it.The lower Ordovican corresponds to the major strike-slip zone developed in carbonates.Local stress field variation in echelon and side joint parts had shaped the strike-slip fault belts into three types of structural patterns:pull-apart negative flower pattern,compressive uplifting positive flower pattern and straight parallel displacement.The strike-slip fault belts with multiple stages of activities formed massive carbonate fracture-vug systems,which provided favorable conditions for the migration and accumulation of oil and gas after a later burial and dissolution process and showed obvious features of "controlling reservoir formation,hydrocarbon accumulation and enrichment".The slope zones of low-uplifts with fully developed Ordovician feature in extensive hydrocarbon accumulation along the fault belts,which is different from those in weathering crust of the exposed and denuded paleo-uplifts.The understanding of the new hydrocarbon accumulation pattern made it possible to obtain another Tahe-like discovery.Currently,about 1.2 billion tons of light oil resources have been confirmed,making the area a main "battlefield" of achieving the goal of reserve growth and productivity construction of oil and gas during the 13th-Five-Year-Plan Period by Sinopec.

Diversities and disparities of fracture systems in the Paleogene in DN gas field,Kuqa Depression,Tarim Basin

Yuan Jing, Cao Yu, Li Ji, Dong Daotao, Yang Rong, Li Chuntang, Chang Lunjie, Yang Junsheng

2017, 38(5):  840-850.  doi:10.11743/ogg20170502

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The diversities and disparities of fracture systems in low-and ultra-low-permeability sandstone reservoirs in the Paleogene in DN gas field of Kuqa Depression,Tarim Basin,were scrutinized through a combination of analytic means such as core and thin section observation,SEM,as well as analyses of clay mineral XRD,fluid inclusion,and physical properties of oil-bearing formations,with regional geological understanding.The results show that the fracture systems are dominated by tectonic fractures,followed successively by dissolution fractures,diagenetic fractures,and overpressured fractures.The tectonic fractures have 3 types (shear fractures,extension fractures,and seismic-related fractures) and 3 development stages.It was the late Himalayan stage (i.e.the end of Pliocene,2.6-1.81 Ma) when certain tectonic compression process generated the most favorable fractures for hydrocarbon accumulations.The formation of the other three kinds of fractures,i.e.the dissolution fractures,diagenetic fractures,and overpressured fractures,is suggested to be happening during the period from the late Kuqua to Xiyu (2Ma-present) and associated with dissolution by hydrocarbon charging,shrinkage by dehydration of clay minerals,and a formation overpressure by intensive tectonic compression,rapid burial processes and pressurized fluids.The disparities of the fracture systems are mainly controlled by rock types,sedimentary facies belts,the single layer thickness and the distance to major controlling faults.The underwater distributary channels in the central part of the gas field are dominated by silty and fine sandstone where the fractures are highly developed and well productivity is high.The linear density of fractures are found to be negatively related to the thickness of single layers (a s-shaped correlation),and decreases as the distance to the major controlling faults increases.The linear density of fractures in mudstone is less than 0.4 lines per meter and is observed to have no connection with single layer thickness.

Geochemical characteristics of the Cambrian source rocks in the Tarim Basin and oil-source correlation with typical marine crude oil

Yang Fulin, Yun Lu, Wang Tieguan, Ding Yong, Li Meijun

2017, 38(5):  851-861.  doi:10.11743/ogg20170503

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27 Cambrian source rock samples collected from the Tarim Basin were analyzed for geochemical characteristics and oil-source correlation studies.Most Cambrian source rock samples show a series features such as low pristane/phytane,C₂₁ tricyclic terpane/C₂₃ tricyclic terpane values,low homohopanes content,high content of gammacerane,high relative content of C₂₈ regular steranes and C₂₇ triaromatic steroids,high content of triaromatic dinosteroids and heavier stable carbon isotopic values.The oil-source rock analysis between typical Cambrian and Ordovician oils reveals that Cambrian source rocks have a high degree of similarity with Cambrian oils and are different from those Ordovician oils.So that the Cambrian source rocks are believed not to be the major source rocks of Ordovician reservoirs.Besides,source rocks from Xiaoerbulakr,Dongergou and Sugaitebulake profiles of the Kalpin Uplift show some differences with the rest of Cambrian source rocks on source constitution,which implies partially the same organism compositions with Ordovician oils.

A new kinetic model of organic thermal evolution under the condition of hydrogen suppression:A case study from the Lucaogou Formation in the Santanghu Basin

Zhang Lei, Meng Yuanlin, Cui Cunxiao, Li Xinning, Tao Shizhen, Wu Chenliang, Hu Anwen, Xu Cheng

2017, 38(5):  862-868.  doi:10.11743/ogg20170504

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Organic matters of the source rocks in the Lucaogou Formation of the Malang Sag,Santanghu Basin are rich in hydrogen components,which suppresses the thermal evolution of organic matters.To simulate thermal evolution of organic matters,a new kinetic model of organic thermal evolution under the condition of hydrogen suppression was established integrating time,temperature,and hydrogen retardation based on Sweeny and Burham Easy %R_o time and temperature controlling kinetic model.In the new kinetic model,activity energies are adjusted by hydrogen index.The results show that hydrogen suppression contributes to 0.2% of R_o value in the Lucaogou Formation.Hydrogen suppression also resulted in delays of both initial generation of hydrocarbons and peak generation of hydrocarbons.This new established model is widely applicable to thermal histories for different kerogen types with higher accuracy.

Geological significance of light hydrocarbon index of natural gas:Taking Shenmu gas field and piedmont zone of the southwest Tarim Basin as examples

Han Wenxue, Ma Weijiao, Hou Lianhua, Tao Shizhen, Hu Guoyi, Peng Weilong

2017, 38(5):  869-877.  doi:10.11743/ogg20170505

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Light hydrocarbon has abundant geochemical information and great geological significance.Using a series of light hydrocarbon parameters,the natural gas from Shenmu gas field in the Ordos Basin and piedmont zone of the southwest Tarim Basin were analyzed.The results show that the Shenmu and Akemomu gas field are mainly coal-derived gas.However,the former is mixed by partial oil-type gas.The natural gas from Kekeya-Kedong gas field is mainly mixed gas.For the first time,the alkane index parameter is put forward.When the index is above 2,it means the gas is oil-derived gas or mixed gas.When it is below 2,it means the gas is oil-derived gas.The natural gas from Shenmu gas field originated from the same source rocks according to K₁ and K₂ parameter.However,the gas from piedmont zone of the southwest Ta-rim Basin originated from different source rocks.According to Mango parameter intersection chart,the source rocks of Shenmu and Akemomu gas field were mainly from terrestrial higher plant origins.However,the source rocks of Kekeya-Kedong gas field are mixed.Based on isoheptane and n-heptane parameter,the maturity of Shenmu,Akemomu and Kekeya-Kedong gas field is low-normal stage,mature gas and high maturity gas stage,respectively.

Quantitative characterization of migration system of Yanchang Formation in Honghe oilfield,Ordos Basin

Jia Jingkun, Yin Wei, Qiu Niansheng, Xu Shilin, Chen Chunfang, Ma Liyuan

2017, 38(5):  878-886.  doi:10.11743/ogg20170506

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Previous study shows that migration system is a major factor that controlled hydrocarbon migration and accumula-tion in Honghe oilfield in Ordos Basin.To better understand migration systems in the Yanchang Formation of this oilfield,we systematically analyzed the compatibility of the fault-sandbody assemblages in the field based on geological,mud logging and well logging,as well as seismic data of the area.A quantitative approach based on two indicators (the shale gouge ratio simplified as SGR and fault tightness index represented by I_FT) was employed to study the transport capacity of faults in the study area.The results indicate that differential sealing behaviors between faults represent the differences of fault transport capacity.The effective migration-space coefficient(C_m) and sand body transport coefficient(K_s) were used to identify the main carrier beds and quantitatively analyzed their transport capacity.Study on the relationship between sandbody transport coefficients and oil and gas shows in the area revealed that sandbodies with K_s>2 have better transport capacity.A comparison between reservoir profiles of the key reservoiring period and present shows a good match between the area of oil and gas migration and accumulation and the distribution of nowadays reservoirs.The study indicates that the fault-sandbody assemblages were the main migration systems during the key reservoiring period of the low-porosity and permeability field (Honghe).It also points out that vertical migration along fractures was also possible in certain locations of the area.

Hydrocarbon charging pathway tracing with rearranged hopane parameters in Longdong area,Ordos Basin

Li Wei, Wen Zhigang, Xu Yaohui, Zhu Cuishan, Gao Yongliang

2017, 38(5):  887-895.  doi:10.11743/ogg20170507

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Oil samples from the seventh member of the Yanchang Formation in Longdong area of Ordos Basin were found to be mature-highly mature crudes of a same family that were generated by mixed lower algae and higher plants under a weak oxidation-reduction and fresh-brackish water setting and were extensive in plane distribution.Most previous studies were focused on the vertical migration and accumulation of the crude,and the horizontal migration and charging of the oil was largely neglected.Based on the thermostability analyses of rearranged hopane (diahopane)/hopane (C₃₀^*/C₃₀H) ratios,we studied the possibility of using C₃₀^*/C₃₀H ratio to trace crude migration and charging and came with supportive results.The ratios of mature-highly mature crude were observed to be a biomarker not only for thermal maturity but also for crude migration and charging,as it shows a positive correlation with two other parameters:MDR and exposure/shielding alkyl dibenzothiophenes.By applying the ratio to trace the crude charging direction in the seventh member of the Formation,we found that the crude was migrating and charging continuously southwest-and northeast-ward in the modes of wavefront to Huachi area.The result verified the idea of using the ratio as an effective parameter for tracing oil charging pathways.

Characteristics and recoverability evaluation on the potential reservoir in Sulige tight sandstone gas field

Wang Guoting, Jia Ailin, Yan Haijun, Guo Zhi, Meng Dewei, Cheng Lihua

2017, 38(5):  896-904.  doi:10.11743/ogg20170508

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Sulige tight sandstone gas field has been in the stable production stage.However,the remaining undeveloped high-quality gas reserves is not sufficient for long term stable production.It is of great significance to utilize potential reservoirs which are below current quality cut-offs,and to evaluate their recoverability to increase gas resources for long term production.Considering that the present reservoir classification criteria is not sufficient,a new comprehensive evaluation criterion of tight sands reservoir is established.Tight sandstone reservoir in Sulige gas field can be divided into 5 categories (6 types),and the Ⅲ₂ type is the most potential reservoir for future development.The potential reservoir is mainly controlled by their physical properties,which in turn related to grain size.The reservoir is fine-middle grained sandstone which belongs to middle-upper part of high-energy channel bar-braided channel,and middle-lower part of low-energy channel bar-braided channel.6 types of formation pattern and 3 kinds of development modes (indirect,combined and direct) for the potential reservoir are also summarized.Recoverability evaluation reveal the relatively good results for direct and indirect method.This potential reservoir characterization and recoverability evaluation can provide a reliable basis for future potential reservoir development.

Characterization of fluid inclusions and timing of gas accumulation in Upper Paleozoic reservoirs of Hangjinqi area,Ordos Basin

Zhao Guiping

2017, 38(5):  905-912.  doi:10.11743/ogg20170509

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Hangjinqi area is one of the major gas exploration targets in Ordos Basin.Analyses of occurrence characteristics,composition and homogenization temperature of fluid inclusions from Hangjinqi area were carried out to identify the main gas reservoiring stages and timing.The results show that fluid inclusions from the Upper Paleozoic Hangjinqi area are mostly distributed in quartz overgrowth or healed fractures of pebbly sandstone,medium-grained and fine sandstones.Two stages can be identified with gas/liquid hydrocarbon inclusions and gas/liquid brine inclusions dominated.They can be oval,sub-prismatic,long strip,semicircular,and irregular in shape with carbon dioxide and methane as the dominant gas components.The homogenization temperature distribution of brine inclusions,associated with hydrocarbon inclusions,has a wide range and multiple peaks.Samples from three plays,namely the Shilijiahan,Xinzhao,and Shiguhao,in the area,show a remarkable disparity in their homogenization temperature distributions.By projecting the homogenization temperatures of the inclusions from the plays on the paleo-geothermal field evolution history of the area and analyzing the thermal evolution history of source rocks,we suggest that the primary reservoiring stage of Shilijiahan play is from the Eocene to the present.The Xinzhao play also has its primary reservoiring period from the Eocene to the present,but there is the possibility of a secondary reservoiring stage ranging from late Early Jurassic to middle Late Jurassic.The reservoiring stage in the Shiguhao play is still from the Eocene to the present based on inclusion temperature data and gas migration characters.

Analyses of features and source of natural gas in the Upper Triassic Xujiahe Formation,Woxinshuang area,eastern Sichuan Basin

Lin Shiguo, Wang Changyong, Yi Shiwei, Gao Yang, Li Mingpeng, Li Shining, Li Shuang

2017, 38(5):  913-921.  doi:10.11743/ogg20170510

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Source analysis of natural gas is one of the geological challenges involving exploration decision-making.Exploration and development of the Xuejiahe Formation in eastern Sichuan Basin is relatively lagged behind and the source of natural gas there is still a mystery due to the fact of lacking basic geological study.Gas composition and isotope analyses show that the natural gas from the Xuejiahe Formation of Woxinshuang area features in low content of methane,high content of heavy hydrocarbon,and lower aridity coefficient.The carbon isotope values were measured to be δ¹³C₁<-40‰ and δ¹³C₃ > δ¹³C₂ > δ¹³C₁.The gas from the Xuejiahe Formation is continental oil-type gas or mixed gas from primary cracking of kerogen and is now at the mature and highly mature wet gas stage.The Formation in the area has well deve-loped dark mudstone.Organic geochemical analyses indicate a kerogen Ⅰ and Ⅱ dominated mudstone with high content of organic carbon and chloroform bitumen "A",indicating relatively high hydrocarbon generation potential.The organic matter of the mudstone was measured to be at the mature to highly mature wet gas stage.Gas from the Formation in the area has a maturity as same as that of source rocks.Combining this understanding with the gas composition and isotope analyses results,we suggest that the gas in the Xuejiahe Formation is mostly autogeneous gas and differs utterly from that in the underlying Carboniferous,the Maokou,the Longtan,the Changxing,the Feixianguan,the Jialinjiang and the Leikoupo Formations.

Characteristics and influencing factors of shale reservoirs in the Niutitang Formation of northwestern Hunan Province,and east margin of Sichuan Basin

Qin Mingyang, Guo Jianhua, Huang Yanran, Jiao Peng, Zheng Zhenhua, Qing Yanbin, Wu Shiqing

2017, 38(5):  922-932.  doi:10.11743/ogg20170511

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The Niutitang Formation in northwestern Hunan Province,eastern margin of Sichuan Basin is regarded as having great potential and one of the major shale gas exploration targets with its wide distribution,large thickness,favorable burial depth,high content of organic matter,high maturity and etc,in south China.An parameter well,the Huaye-1,in the Formation of the area,was chosen to be studied with systematic means including observation of thin sections,XRD mineral analyses,physical property tests,SEM imaging and low-temperature N₂ adsorption/desorption experiments with core and drilling cutting samples,to probe into the characteristics and influencing factors of the reservoirs.The deep shelf facies of the Niutitang Formation developed dark carbonaceous shale and siliceous shale rich in carbonaceous and siliceous material,as well as pyrite,but lean in clay minerals (mainly illites).The shale reservoirs are of ultra-low porosity and permeability.The SEM images and low-temperature N₂ adsorption/desorption experiments show that the reservoirs contain mostly cylindrical pores (organic pores),narrow parallel-plate pores (clay mineral interlayer pores),tapered tube pores with openings around (intergranular pores among clay minerals) and tapered plate pores (micro-crack).The mesopores (sized between 2 to 50 nm) contribute an average of 60.3% of BJH volume.The development of the micropores is found to be affected by multiple factors:the deep-water muddy continental shelf provided the material basis for the pores,the high content of TOC facilitated the growth of organic pores (especially organic macropores),the composition and content of minerals dominated the types and amounts of the pores,and the thermal evolution of organic matter promoted the development of organic pores and micro-cracks.

Redox conditions and organic enrichment mechanisms of black shale:A case from the Wufeng-lower Longmaxi Formations in Well A in Zhaotong shale gas demonstration area

Wang Pengwan, Zhang Lei, Li Chang, Li Xianjing, Zou Chen, Zhang Zhao, Li Junjun, Li Qingfei

2017, 38(5):  933-943.  doi:10.11743/ogg20170512

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The Wufeng-lower Longmaxi Formations are the main exploration targets of the Zhaotong shale gas demonstration area.Based on systematic tests of organic carbon,trace elements and REE (rare earth elements) upon samples from Well A in the area,as well as petrological and logging data,we analyzed the variations of geochemical parameters of relevant elements in black shale samples from Well A and tried to reveal the redox conditions of black shale and discuss the possible mechanisms of organic matter enrichment in the area.The results show that the sub-member I of the Wufeng-lower Longmaxi Formations in the area have the highest content of TOC,which is averaged at 3.13% and displays an upward decreasing trend.The enrichment of relevant elements is also observed to be connected with TOC content.Redox parameters such as trace elements and REE indicate that the Wufeng-lower Longmaxi Formations had once experienced anaerobic redox water body turning to a suboxidizing water body with the sub-member I in an anoxic-anaerobic environment,the sub-member Ⅱ in an anoxic environment and the sub-member Ⅲ in an anoxic -oxygen enriched environment.Among them the water body reducibility of layers I-1,I-3,and I-4,is stronger than that of layers I-2 and I-5.And there were still disparities in the forming mechanisms of redox environment for organic matter enrichment in black shale of the Wufeng and Longmaxi Formations against a high paleo-productivity in the area.For the Wufeng Formation,it was a stagnant water body that preserved the organic matter in an anaerobic-anoxic environment,and for the lower Longmaxi Formation,it was sea level rising that kept a rich organic matter in an anaerobic environment.The sub-member I at the Wufeng-lower Longmaxi Formations has the richest TOC and thus is regarded as the best target for shale gas development.

Hydrocarbon accumulation patterns and their controlling factors of Putaohua reservoirs in Chaochang area,Songliao Basin

Chang Yan, Liu Dameng

2017, 38(5):  944-951.  doi:10.11743/ogg20170513

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To answer the questions concerning the hydrocarbon accumulation patterns and main controlling factors of Putaohua reservoirs in Chaochang area,Songliao Basin,we studied the hydrocarbon sources,accumulation features,main controlling factors as well as accumulation patterns of the reservoirs through source rock assessment,crude-source correlation,analyses of conduit systems,oil-water contact,and controlling factors of accumulation,and reservoir type identification.The results show that crude in the reservoirs are mostly from the first member of the Qingshankou Formation in Sanzhao sag in the west and Chaoyanggou terrace in the east.The underlying Fuyang oil-bearing layer also made some contribution.Faults in the area can be classified into three types:source rock-rooted faults,carrier faults and sealing faults,among which,the carrier faults dominate the area.Sandbodies are largely inner front channel sands in the northwest part,and outer front sheet sands in the southeast part,with the former having better storage capacity and physical properties than the latter.A comprehensive analysis comes to a conclusion that hydrocarbon accumulation in the area was gene-rally controlled by source rocks,source rock-rooted faults and sandbodies.There are mainly two types of accumulation pattern:near-source accumulation and updip accumulation. The study is meaningful in term of guiding the identification of future exploration targets and reserve estimation in Chaochang area.

Petrologic and geochemical records of interaction between reducing fluids and mudstone caprocks:A case from the mudstone in the Qingshankou Formation of Wangfu Depression in southern Songliao Basin

Ming Xiaoran, Liu Li, Song Tushun, Liu Na, Yang Huidong, Yu Lei, Bai Hanggai

2017, 38(5):  952-962.  doi:10.11743/ogg20170514

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Reducing fluids percolated from natural gas reservoirs or fields may cause composition variation (especially the macro and trace elements) of mudstone caprocks.The variation records the interaction between the reducing fluids and mudstone caprocks and may be used as an indicator of the locations of oil and gas reservoirs.By resorting to natural analogy,we studied the mudstone samples from the the Qingshankou Formation of Wangfu Depression in southern Songliao Basin to analyze the variation of mudstone composition caused by reducing fluids and the migration of the fluids in cap rocks of gas fields (reservoirs).The results show that the reducing components in the fluids are mainly methane,followed by hydrogen sulfide.During the fluid-rock interaction process,the red Fe³⁺ in the mudstone was reduced to colorless Fe²⁺,causing a phenomenon called bleach.The Fe²⁺ then migrated in the form of colloids with the fluids and reprecipitaed as iron concretions elsewhere.During the bleach process,the increasing U content,and decreasing Ga and Sc contents,as well as the veritical changes of the U,Mo,V and Ni contents,are suggested to be connected with the reductivity of the fluids.In mudstone caprocks,the reducing fluids were driven by buoyancy to migrate vertically and the uplifting of strata might cause dropping of fluid surface.The regular variation of trace elements in the mudstone caprocks may be used as indicators to the flow pathways and directions of the reductive fluids.

Provenance of sediments and its effects on reservoir physical properties in Lishui Sag,East China Sea Shelf Basin

Chen Chunfeng, Zhong Kai, Zhu Weilin, Xu Donghao, Wang Jun, Zhang Bocheng

2017, 38(5):  963-972.  doi:10.11743/ogg20170515

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In order to determine the provenance of sediments and play fairways in Lishui Sag,East China Sea Shelf Basin,we analyzed and characterized the provenances of the sediments in the sub-sags in eastern and western Lishui Sag through detrital zircon U-Pb dating and discussed the influences of different provenances on the physical properties of sandstone reservoirs in the Sag.The results show that sediments in the west sub-sag were mostly sourced from Minzhe Uplift Zone in the western part of the Sag where volcanic rocks are predominant with some intrusive and metamorphic rocks.The sandstone formed by sediments sourced from this provenance has high plastic content and low resistance to compaction,thus porosity loss is relatively largeduring compaction processes.The sediments in the east sub-sag were mostly sourced from Yushan Uplift Zone in the eastern part of the Sag where sedimentary rocks and intrusive rocks are predominant.The sandstone formed by sediments sourced from this provenance has low plastic content and strong resistance to compaction,thus porosity loss is relatively small during compaction.It is suggested that the provenance differences indeed have certain impact upon the physical properties of the reservoirs in the Sag.

Structural evolution mechanism and sealing of faults on the crest of anticline E in Niger Delta

Xie Zhaohan, Sun Yonghe, Yan Yumin, Hu Guangyi, Fan Tingen, Liu Zongbao

2017, 38(5):  973-982.  doi:10.11743/ogg20170516

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Numerous faults were developed on the crest of anticline E in deep water of Niger Delta.They were observed to dip mostly in the same direction and arrange in a domino style.Uncertainties remain in such domains as what their me-chanism is,how many stages they had experienced,and what role they played in dividing oil from water.Based on structural analysis,we studed the axial plane migration of E anticline through structural balanced sections and back-stripping of pa-leotectonic maps.Guided by the theory of fracture nucleation,we identified the active stages and mechanisms of the faults and then categorized the faulting systems to further perform assessment of sealing capacity of the faults.Gravitational sli-ding was identified as the evolution mechanism of the normal faults at the crest of the anticline.A correspondence of multiple stages between the domino-style normal faults and the anticline axial plane migration was also established.We proposed that the E structure had experienced four evolution stages and developed 7 types of faulting systems,among which,3 were gravitational sliding step-faults -quite unique in the area-and were controlled and deformed by gravity against a paleo-anticline setting.Thrust faults and faults with multi-stage movement are the best sealing faults,gravitational sliding step-faults have sealing potential,and later extensional faults have no sealing capacity.About 16 faults were selected as potential sealing faults.The results show a critical SGR value of 8% for weak sealing,and 20% for fully sealing.There were 8 fully-sealed faults that could form different oil/water units in its hanging and foot walls,respectively.There were 4 weakly-sealed faults that could not separate oil from water but only influence responses to water flooding.The study can be used to guide drilling and injection-production planning of oil fields in the area.

Petroleum resources assessment methodology in play exploration stages

Sheng Xiujie, Jin Zhijun, Xiao Ye

2017, 38(5):  983-992.  doi:10.11743/ogg20170517

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The assessment results of prevailing statistical methods used in the petroleum industry are,to some extent,ina-dequate in helping the formulation of effective exploration strategies.There are still plenty of rooms of improvement in terms of assessment methods.Aiming at enhancing the economy of commercial discoveries and dealing with challenges faced during exploration deployment planning,we proposed that:(1) Differentiating the applicable scope and conditions of marginal,conditional and spatial probability mathematical assessment models and providing information concerning geological-constraint risk so as to improve success rate of exploratory drilling in less-explored areas;(2) Providing more objective data samples for solving general reservoir scale distribution models by delineating highly-explored areas with the guidance of petroleum accumulation theories and sorting and merging reserve assessment units into oil and gas reservoirs (samples) that went through the same geologic processes according to the time order of first discovery well;(3) Taking into consideration the effect of different exploratory investments upon oil and gas discoveries and eliciting expectation maximization algorithm to work out the Pareto distribution parameters based on exploration efficiency plates,so as to predict more objectively the resource potential of oil and gas and the structure of reservoir scales;(4) Using scenario trees representing respectively geological and market uncertainties and geology-or strategy-related Bayesian networks to combine effectively and organically investment portfolios and exploration strategies.

Research on and development of prediction method of water cut in water flooding oilfield

Gao Wenjun, Xu Bingtao, Huang Yu, Li Junzhi, Ou Cuirong

2017, 38(5):  993-999.  doi:10.11743/ogg20170518

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On the basis of a new oil phase relative permeability curves,combined with the material balance equation and Welge equation,a new model for predicting water cut is derived.Under certain conditions,it can be converted to the Logistic model.In the new model,the relationship between undetermined coefficients,development dynamic and geological static parameters is clear,so many water control measures have become more theoretically supported.Meanwhile,combined with water-oil relative permeability curves and Welge equation,either the Logistic model,the Goempertz model or Usher model cannot be deduced.Furthermore,some limiting conditions remain in our solution,such the new model requires that the number of wells still not be changed.However,coupling and direct methods have been proposed to build prediction model of water cut.By means of expanding the two methods,with rich,diverse prediction models of water cut,it has been fully possible to describe the complex and diverse water content and process of time change.After field applications of the model,positive results are acquired,and thus may be applied to other oil fields.

An experimental study on enhanced heavy oil recovery by steam flooding and chemical assisted steam flooding

Zhang Shuxia, Liu Fan, Mu Baoquan

2017, 38(5):  1000-1004.  doi:10.11743/ogg20170519

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Steam flooding and chemical assisted steam flooding are important EOR methods for heavy oil reservoirs.In order to compare the two methods,we performed simulated steam flooding experiments on samples from Tahe heavy oil reservoirs in Xinjiang,China,to assess their EOR effects under different steam injection parameters.The results show that,during steam flooding,the oil recovery is positively correlated to injection temperature but insensitive to injection pressure,and that adding some additives,such as n-pentane,n-hexane,and n-heptane,can greatly improve the recovery.It is also noteworthy that the recovery factor of heavy oil tends to lower along with increasing injection pressure during steam flooding,while it increases to some extent along with increasing injection pressure during chemical assisted steam flooding.