Table of Content

28 June 2012, Volume 33 Issue 3

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Hydrocarbon generation-expulsion mechanisms and efficiencies of lacustrine source rocks:a case study from the Dongying sag, Bohai Bay Basin

Cai Xiyuan

2012, 33(3):  329-334,345.  doi:10.11743/ogg20120301

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Source rocks formed in lacustrine fault basins are strongly heterogenous.The Dongying sag is one typical representative of the continental fault basins with the major source rocks including the Upper Es⁴,Lower Es³ and Middle Es³ members of the Paleogene Shahejie Formation deposited in saline water and fresh water environments.Based on the analysis of sedimentary facies and organic features,a comparative study of the residual hydrocarbon yields and hydrocarbon generation potential indices between the ordinary source rocks (TOC<2%) and high quality source rocks (TOC>2%) for the three members of Shahejie Formation was performed to understand their differences in hydrocarbon expulsion mechanisms and efficiencies.As they are different in depositional environments and buried depths,their hydrocarbon generation-expulsion potentials and efficiencies are significantly differe-nt.In comparison with the ordinary source rocks,the high quality source rocks are the main contributor to hydrocarbon accumulation.They not only can generate abundant hydrocarbons,but also can expulse hydrocarbons efficiently thanks to their microstratifications.In addition,hydrocarbon expulsion models were built for source rocks deposited in different environments.The source rocks that were deposited in saline water environment generate hydrocarbons in two stages,i.e.immature and mature stages and expulse hydrocarbons in longer period and higher efficiencies.In contrast,the source rocks that were deposited in fresh water environment only generate hydrocarbons in mature stage and feature in shorter hydrocarbon expulsion period and lower expulsion efficiencies.The Upper Es⁴ Member has the greatest contribution to hydrocarbon pooling,followed by the lower and middle Es³ members.

Shale gas accumulation conditions of the Upper Ordovician-Lower Silurian in Sichuan Basin and its periphery

Nie Haikuan, Zhang Jinchuan, Bao Shujing, Bian Ruikang, Song Xiaojiao, Liu Jianbin

2012, 33(3):  335-345.  doi:10.11743/ogg20120302

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The sedimentary facies,thickness,distribution,organic matter types and content,maturity,porosity,and gas content,of the Upper Ordovician-Lower Silurian dark shale in the Sichuan Basin and its periphery are investigated by field observation and sampling on 25 outcrops and laboratory test of adsorbed gas content,geochemical and physical parameters.In comparison with the major producing gas shales in U.S.,the shale in the study area features in favorable sedimentary facies,large thickness,high TOC,high maturity,high porosity,and high gas content,all being favorable geological conditions for shale gas reservoir development.Parameter models were built for predicting shale gas play fairways.The results show that the shale gas play fairways in the study area occur in the Southern Sichuan-Northern Guizhou,Western Hubei-Eastern Chongqing and Northeastern Sichuan(Chongqing)-Northwestern Hubei,among which the Southern Sichuan-Northern Guizhou play fairway is relatively high in gas content,thus is most prospective in shale gas exploration at present.With the measured gas content,the volumetric method gave a resource volume in the range of 2.2-8.5 TCM and a median value of 5.3 TCM.

Characteristics of organic-rich mudstone reservoirs in the Silurian Longmaxi Formation in Upper Yangtze region

Liu Wei, Yu Qian, Yan Jianfei, Men Yupeng, Zhang Haiquan, Wu Jian

2012, 33(3):  346-352.  doi:10.11743/ogg20120303

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Mineral composition and brittle mineral contents of organic-rich mudstone are critical to fracturing,so they are important parts of shale gas reservoir description and evaluation.X-ray diffraction and microscopic observation were performed on outcrop samples from organic-rich mudstones in the Silurian Longmaxi Formation in the Upper Yangtze region.The results show that the contents of brittle minerals average about 50-70%.The clastic minerals of organic-rich mudstones mainly consist of quartz,few feldspars and very few detritus in the lower Longmaxi Formation of the Silurian on Wangcang,Leibo and Xishui outcrops.The clastic mi-nerals have clear angular shape and scattered distribution and no clear orientation.Authigenic brittle minerals are mainly calcites and dolomites.Calcites and dolomites show semi-euhedral to euhedral crystalline,relatively rich in local strata forming slight fringes.Pyrites are common but its content is low.Biogenic minerals are rare and mainly of siliceous radiolarians with the characteristic of dissolution.Regionally,brittle mineral combinations can be divided into two types:quartzs-feldspars and quartzs-feldspars-calcites-dolomites.High calcite and dolomite contents occur in main sedimentary centers,i.e.Luzhou-Yibin area in Sichuan,Wulong-Shizhu area in Chongqing and the northern margin of Central-Guizhou-Xuefeng uplift.Hannan ancient land and Central Sichuan uplift are different from Central Guizhou-Xuefeng uplift in the capability of providing detrital sediments,resulting in different mineral composition in the marginal shallow water deposits.In summary,the key to find brittle-mineral rich areas is the reconstruction of palaeogeography,especially the analysis of sedimentary microfacies.

Shale gas accumulation conditions and play evaluation of the Devonian in Guizhong Depression

Wang Pengwan, Chen Ziliao, He Xunyun, Dong Li, Xu Zhengyu, Ma Liqiao, Dong Yong, Huang Ling

2012, 33(3):  353-363.  doi:10.11743/ogg20120304

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A set of dark shales of intraplatform depression-deep shelf facies was deposited in Guizhong depression during the Devonian when the Guizhong depression experienced intracontinental rifting.Outcrop observation and integrated analysis of drilling and geochemical data indicate that the Middle-Lower Devonian shale in Guizhong depression feature in large thickness(the maximum cumulative thickness up to 1 000 m),high abundance of organic matter(TOC of 0.53%~9.46%),moderate thermal maturity(R_o of 1.33%~3.62%),well-developed micro-pores,nono-pores and micro-fractures,favorable clay mineral composition,moderate burial depth,and relatively good sealing conditions.All these characteristics reveal its high potential for shale gas exploration.Based on the shale gas exploration experiences of North American,in combination with the practice of marine shale gas exploration in south China, we put forward evaluation criteria for shale gas play.Paly evaluation results with these criteria show that the area to the west of Nandan-Xincheng-Mashan is a potential play for shale gas exploration in the Devonian in Guizhong depression.

Reservoir characteristics and their influence factors of the Lower Cambrian dark shale in northern Guizhou

Li Juan, Yu Bingsong, Zhang Jinchuan, Li Yuxi, Wu Jingshu

2012, 33(3):  364-374.  doi:10.11743/ogg20120305

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In order to assess the gas potential of the dark shale of the Lower Cambrian Niutitang Formation in the northern part of Guizhou,samples were collected from 20 outcrop cross sections of the Lower Cambrian Niutitang Formation in the northern part of Guizhou and many experiment tests such as physical property,SEM,mercury porosimetry,specific surface and pore size were conducted.Preliminary study results show that the average content of quartz and clay minerals are 56.3% and 30.5% and the effective porosity and permeability are 8.24% and 0.127×10^-3 μm² respectively.Pore sizes cluster around 4.0 nm.The pores are dominated by mesopores.The analysis of the relation between pore volume and quartz content,clay mineral contents and TOC shows that the content of quartz is negatively correlated with the volumes of micropore and mesopore,but slightly positively correlated with macropore;clay mineral contents are just the opposite to quartz content;TOC is positively correlated with mesopore and macropore to some extent;and vitrinite reflectance has a weak positive correlation with macropore.

Progress and significance of research on relation between specific surface area and organic matter in argillaceous source rocks

Zhu Xiaojun, Cai Jingong

2012, 33(3):  375-384.  doi:10.11743/ogg20120306

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The enrichment of organic matter in source rocks is a topic of concern and studying the relation between organic matter and specific surface is important to recognizing the enrichment mechanism of organic matter.Specific surface area of argillaceous source rocks is complex in components and is controlled by various factors such as pore size,components,mineral constituents,inner surface and external surface of clay minerals.Each measuring method for specific surface area has its own limitations.For example,mercury porosimetry is suitable for measuring mesopores and macropores,nitrogen adsorption method is the best in measuring micropores and external surface,and EGME method is fit for measuring micropores and inner surface.Therefore,it is crucial to choose the right method to detect the specific surface area of argillaceous source rocks.The occurrence modes are different for different organic matters,especially the soluble organic matter,which is absorbed on the external surface of minerals by physical adsorption,or enters into the inner surface of minerals via chemical adsorption.All of these result in the variations and differences of the correlation between organic matter and specific surface.Consequently,in addition to the features of minerals and organic matter's occurrence,it should be paid attention to find the suitable method to determine the specific surface area in argillaceous source rocks.

Possibility of tight sand gas reservoirs in Jixi Basin

Wang Weiming, Lu Shuangfang, Wang Shihui, Liu Shi’en, Wang Guilei, Mu Guodong, Jiang Siqin, Xu Jianjun

2012, 33(3):  385-391,398.  doi:10.11743/ogg20120307

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Jixi Basin is still immature in petroleum exploration,especially for tight sand gas.Based on summarizing accumulation conditions of tight sand gas reservoirs at home and abroad,we discussed the tight sand gas accumulation conditions in Jixi Basin in respects of structure,source rock and reservoir.According to the geoche-mical data of the dark mudstone samples of Ji D8 well,the tight sand gas resources was estimated by the method of chemical kinetics.The results show that Jixi Basin is a small rifted basin featuring in multiple-cyclic tectonic evolution and rapid deposition.Its tight gas geological conditions are quite different from the large tight sand gas reservoirs in North America.However,large-scale coalbeds in the Chengzihe Formation in Jixi Basin provide abundant gas source for the tight sand gas reservoirs.Superimposition and closely contact of source rocks and re-servoir are also in favor of the migration and accumulation of gas.Sweet spots of tight sand gas may exist in the tectonically stable region of the central depression in Jixi Basin.

Re-evaluation of source rocks and petroleum resources of Nanyang depression in Nanxiang Basin

Lü Mingjiu

2012, 33(3):  392-398.  doi:10.11743/ogg20120308

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Kerogens of source rocks in the Nanyang depression of Nanxiang Basin are dominated by type Ⅱ₁ and type Ⅱ₂,and the organic types of the middle and lower Member Ⅱ of Hetaoyuan Formation (HF) are better than that of the Member Ⅲ of HF.The organic matters of the Member Ⅱ of HF are mainly sourced from bacteria and lower plants,while that of the Member Ⅲ of HF from plants.The organic matter abundance of the source rocks of HF are different for different sub-members.The richest one is the lower Member Ⅱ,followed by the upper Member Ⅲ.The organic matter abundance of the middle Member Ⅲ is moderate just like the middle Member Ⅲ.The upper Member Ⅱ is the lowest.The distribution area of active source rocks gradually becomes smaller upwards,and the source rocks concentrated in deep depression to the south.The resources in place by this reassessment are 104 million tons,much larger than 62 million tons by the last assessment.The resources of the middle Member Ⅲ are the largest,accounting for 37.5% of the total resources, followed by the upper Member Ⅲ,the lower and middle Member Ⅱ.The resources of the Member Ⅲ account for 59.6% of the total resources,indicating that the Member Ⅲ is the main source rocks of the Nanyang depression.However, the resource exploration maturity for the depression is quite low,indicating that the exploration potential for the depression may be large.

Geochemical characteristics and hydrocarbon generation potential for the Jurassic source rocks of Bohu depression in Yanqi Basin

Shi Zhengyong, Yan Yongxin, Jin Yunyun, Zhang Hui

2012, 33(3):  399-406.  doi:10.11743/ogg20120309

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This paper evaluated the coal measure source rocks of the Middle and Lower Jurassic Xishanyao Formation,Sangonghe Formation and Badaowan Formationin of Bohu depression in Yanqi Basin by using many organic geochemical methods.The results showed that the source rocks are higher in abundance of organic matter.The Lower Jurassic Badaowan Formation is good source rock,while the Xishanyao and Sangonghe formations are moderate source rock.The types of organic matter are dominated by kerogen Ⅲ with few kerogen Ⅱ₂. Most of the organic matters are within oil window.The organic matters in the Xishanyao Formation are low mature;that in the Sangonghe Formation are partly mature,and that in the Badaowan Formation are mature and in peak oil-generation stage.By comparison of the hydrocarbon generation capacity of the three subsags and the three Formations,the Badaowan Formation is identified as the main source rocks in Yanqi basin.In addition,similar with the source rocks in the Badaowan Formation,the source rocks in the Sangonghe Formation of Qilipu subsag also have high TOC,good organic matter type,suitable thermal maturity,thus have great potential for hydrocarbon generation.According to exploration experiences in recent years,the area along both sides of the structural highs and slope zones of Qilipu subsag is favorable exploration play.

Migration system types and their control on hydrocarbon accumulation in central fault depressions of Hailar-Tamtsag Basin

Li Mingyi, Yue Xiang’an, Jiang Qingchun, Wang Hongwei, Wu Yulin

2012, 33(3):  407-416,423.  doi:10.11743/ogg20120310

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The types of source-reservoir-cap rock assemblages,migration systems and their control on hydrocarbon accumulation in the main central fault depressions in Hailar-Tamtsag Basin(Haita Basin)were investigated by analyzing spatial combinations of hydrocarbon accumulation elements and processes.Three types of source-reservoir-cap rock assemblages were recognized,including self-source and self-reservoir,up-source and down-reservoir,and down-source and up-reservoir.Different source-reservoir-cap assemblages have different hydrocarbon migration and accomulation systems.For the self-source and self-reservoir type,hydrocarbon migration pathways are pore-fracture and comb-like systems.Subsags connected by the pore-fracture system and tilting uplifts and uplifts within sag connected by the comb-like system are favorable for development of lithologic reservoirs.For the up-source and down-reservoirs type,the migration system is flower-like.The reverse structures connected by the flower-like system are favorable for hydrocarbon accumulation.For the down-source and up-reservoir type,the migration systems are step-like or inverted U-shaped.The palaeouplifts connected by unconformities are favorable for hydrocarbon accumulation.

Hydrocarbon accumulation phases of Majiang paleo-oil reservoir in Guizhou

Gao Bo, Wo Yujin, Zhou Yan, Peng Yongmin, Liu Quanyou, Li Shuangjian

2012, 33(3):  417-423.  doi:10.11743/ogg20120311

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Majiang paleo-oil reservoir is one of the largest marine paleo-oil reservoirs in South China.There is debate about its forming time.This paper investigates the hydrocarbon accumulation period by analyzing the geochemical characteristics and genesis of reservoir-bitumen.The study shows that the distribution of n-alkanes of saturated hydrocarbon chromatogram from the reservoir-bitumen is complete,but the base line is up convex,and 25-norhopane exists.It indicates that crude oil charging occurred at least in two stages in this paleo-oil reservoir.The reservoir-bitumen in Ordovician and Devonian originated from the same source rocks,indicating that the massive crude oil charging occurred after deposition of the Devonian.Reservoir-fluid inclusion thermometry and K-Ar dating of autogenous illite,in combination with thermal history of source rocks,were used to investigate the hydrocarbon accumulation phases.The results shows that Majiang paleo-oil reservoir experienced small-scale hydrocarbon accumulation and damage during the Late Caledonian time,large-scale hydrocarbon accumulation during the Hercynian time,oil-gas conversion in the IndoChinese time,and large scale damage during the Yanshan time, and the Hercynian time is suggested as the main accumulation stage of Majiang paleo-oil reservoir.

Tectonic evolution and hydrocarbon accumulation of Laizhouwan depression in southern Bohai Sea

Niu Chengmin

2012, 33(3):  424-431.  doi:10.11743/ogg20120312

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Laizhouwan depression in the southern Bohai Bay is complicated in hydrocarbon accumulation and is low in exploration maturity.An oil discovery with reserves around hundred millions of tons was obtained recently.Laizhouwan depression is characterized by fault depression and strike-slip inversion.According to the feature and strength of fault activity,the faults were divided into three types which have different control on depression pattern,sedimentary system and hydrocarbon migration system.Furthermore,the tectonic evolution of Laizhouwan depression was divided into three stages:the early rifting stage during deposition of the Kongdian Formation to the Member Ⅲ of Shahejie Formation,the strike-slip stage during deposition of the Member Ⅱ of Shahejie Formation to Dongying Formation and the late activation stage since the Neogene.The tectonic evolution controls trap formation,sediment filling,subsidence center migration,and source rock formation and evolution.The late strong tectonic and volcanic activities are helpful for late hydrocarbon accumulation in Laizhouwan depression.

Characteristics of Silurian Paleo-oil reservoirs and their significance for petroleum exploration on the southeast margin of Sichuan Basin

Ma Wenxin, Liu Shugen, Huang Wenming, Zhang Changjun, Xu Guosheng, Yuan Haifeng

2012, 33(3):  432-441.  doi:10.11743/ogg20120313

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In order to understand the hydrocarbon accumulation characteristics of the Silurian carbonates on the southeast margin of Sichuan Basin,this paper studied reef-shoal facies sedimentary features and paleo-oil reservoirs in the Lower Silurian Shiniulan Formation based on the comprehensive field and laboratory research of petrography and geochemical analysis.The Lower Silurian Shiniulan Formation is composed of upward-shallowing three cyclic deposits,of which the third cyclic deposits are bioherm-shoal facies on platform margin occurring along Lintanchang-Liangcun-Dingshan structures.The reservoirs of reef-shoal facies are rich in bitumen,indicating that they are lithologic paleo-oil reservoirs of shoal-reef type.These paleo-oil reservoirs are small in resource scale and scatter in regional distribution.Their resources are estimated to be about 6.62?10³ t.The oil of the paleo-oil reservoir is mainly sourced from the Sinian paleo-oil reservoir,partly from the Silurian source rocks.The formation and destruction of the Shiniulan paleo-oil reservoir includes the following process:the Sinian oil reservoirs were destroyed and the escaping oil accumulated in the Shiniulan Formation to form the oil reservoir(Late Triassic to Early Jurassic).The oil of the oil reservoir was cracked to gas due to the long term deep burial,to lead to the gas reservoir(Middle Jurassic to Middle Cretaceous).Finally,the gas reservoir was destroyed by folding and quick uplifting(since 80 Ma).The exploration prospect in the Silurian in southeast Sichuan Basin is not as good as in the eastern Sichuan-eastern Chongqing.

Characteristics and genesis of hydrothermal dolomites of Qixia and Maokou Formations in northern Sichuan Basin

Shu Xiaohui, Zhang Juntao, Li Guorong, Long Shengxiang, Wu Shixiang, Li Hongtao

2012, 33(3):  442-448,458.  doi:10.11743/ogg20120314

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Taking outcrop dolomites in Guangyuan Xiagou coal mine in northern Sichuan Basin as an example,this paper studies the characteristics and genesis of hydrothermal dolomite reservoir.From the bottom to the top of the outcrop cross section,the dolomitization gradually enhances;the color of rocks changes from dark to light;the lithologies change from bioclastic limestones to patchy dolostones,then to medium-and coarse-grained dolomites,and end up with the Maokou Formation marlstones.The medium-to coarse-grained dolomites occur at the top of the Qixia Formation and the bottom of the Maokou Formation,and are composed of medium-to coarse-grained subhedral or euhedral dolomites and some saddle-like dolomites.Dissolved caverns and pores are well-developed and filled with asphaltares.The δ¹³C value (PDB) and δ¹⁸O value (PDB) of micritic limestones are 3.23‰ and -5.03‰,respectively.The δ¹³C value (PDB) and δ¹⁸O value (PDB) of the dolomites are 3.29~4.14‰ and -6.07~-6.75‰ respectively.Fluids may be sourced from magmatic hydrothermal fluid,or meteoric water experiencing deep circulation.The deep hydrothermal fluids migrated up along open faults and slowed down or even stopped when arriving at the Qixia and Maokou Formations due to the sealing of marl and politic dolostones in the Wu Jiaping Formation.The stagnant thermal fluids caused dolomitization dissolution of the surrounding rocks.Therefore, it is possible that hydrothermal dolomite reservoirs occur at the top of Qixia Formation and the bottom of Maokou Formation.

Factors controlling sandbody development and models of stratigraphic-lithologic traps of Zhujiang Formation in Huizhou area,Pearl River Mouth Basin

Chen Weitao, Du Jiayuan, Long Gengsheng, Chen Shuhui, Li Xiaoping, Zhang Shangfeng, Zhang Changmin

2012, 33(3):  449-458.  doi:10.11743/ogg20120315

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Huizhou is an area with the highest exploration maturity in Pearl River Mouth Basin,wherein the Zhujiang Formation is the primary oil-producing layer and has the potential of finding stratigraphic-lithologic traps.Through analyses on the factors controlling sandbody distribution of the Zhujiang Formation in Huizhou area,this paper concludes that various factors including palaeogeomorphology,sequence stratigraphy,delta-dominated sedimentary facies distribution and hydrodynamics in transitional zone during basin transformation and subsequent tectonic movements all have important influences on the formation and distribution of sandstones.Sedimentary facies determines the macroscopic distribution of sandbodies,and sequence structure influences the lateral and vertical sandbody development and sandbody stacking patterns in different system tracts.Sedimentary facies and sequence structure are the two main controlling factors.Based on the study of the controlling factors and the discovered lithologic hydrocarbon reservoirs,this paper establishes development models of stratigraphic-lithologic traps of Zhujiang Formation in Huizhou area,and analyzes the favorable area and types of stratigraphic-lithologic traps.We believe that the lithologic pinchout traps around sedimentary slope-break and/or within transgressive system tracts are the best ones for hydrocarbon accumulation.

Characteristics and prediction of fracture-vug carbonate reservoirs -an example of P_z layer in A oilfield

Wang Zhaofeng, Chen Xin, Wang Peng, Yu Wenwen, Li Qiang

2012, 33(3):  459-466.  doi:10.11743/ogg20120316

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This paper studied the reservoir of P_z layer in A oilfield.Fine cross-well calibration by using the technique of log-seismic integration can improve the lateral continuity and reliability of stratigraphic correlation.Mo-dern karst patterns were introduced to guide basement top structure interpretation,and to delineate pinch-out line and structural trap.The newly found buried hill structure is 52.7 km²,which increase the exploration area.We divided the palaeogeomorphology into peak-cluster depression,peak forest valley and paleo-erosive gulley with 3D visualization technique.Based on integration of geologic data,logging data and seismic response,we divided the reservoirs into three types including cavern-pore fracture-pore and fracture types.We delineated the distribution of the reservoirs through seismic inversion and ant tracking modeling.Type Ⅰ reservoirs(i.e.cavern-pore type)mainly occur on paleo-structure highs and their thickness enlarge along with their increasing height.Type Ⅱ reservoirs(i.e.fracture-pore type)distribute at the slope of the structure.Type Ⅲ reservoirs (i.e.fracture type)occur near faults,thus are significantly affected by the faults.

Reservoir characteristics of low porosity and permeability sandstone of Member Ⅰ of Xiashihezi Formation in Daniudi gas field,Ordos Basin

Hou Ruiyun

2012, 33(3):  467-478.  doi:10.11743/ogg20120317

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Daniudi gas field is located in the northeastern part of Yishan slope in Ordos Basin.One of the major reservoirs is the braided channel sandstone in Member Ⅰ of the Lower Permian Xiashihezi Formation.The sandstones consists mainly of lithic sandstones and lithic quartz sandstones with medium compositional and structural maturity.The sandstone reservoir is of strong heterogeneity.The porosity and permeability of the reservoirs are 4-14% and (0.05-2)×10^-3 μm² respectively, which repsent the typical characteristics of low porosity and permeability reservoirs or even tight reservoirs.The reservoir is at A₂-B substage of the late diagenetic stage.Mechanical compaction,quartz overgrowth and calcite cementation are the main diagenesis for decreasing porosity of sandstone.Intergranular dissolution pore is the major pore type.Sedimentary microfacies,lithology and diagenesis are the main factors influencing reservoir properties.Using grey relational analysis(GRA)method,this paper divides the reservoirs in Member I of Xiashihezi Formation into three types based on multiple parameters such as sedimentary microfacies,reservoir macro-and micro-charac teristics.Type Ⅰ reservoirs have relatively high porosity and permeability,while type Ⅱ has relatively moderate porosity and permeability.The distributions of three different types of reservoirs are predicted and the evaluation criteria of the reservoirs in Member I of Xiashihezi Formation are also established.

Effect of polymer solution on pore structure characteristics

Li Zhaoxia, Xia Huifen

2012, 33(3):  479-483.  doi:10.11743/ogg20120318

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Resistance coefficient & residual resistance factor of polymer solutions with different molecular weight and mass concentration were studied based on water flooding,polymer flooding and subsequent waterflooding tests.This paper also researched the pore structure characteristics of the cores after the polymer flooding by conventional mercury porosimetry,and analyzed the influences of polymer flooding with polymer solution of different molecular weight and mass concentration on pore structure of cores.The results show that the resistance coefficient and the residual resistance factor increase and the amplitude of permeability decline enlarges along with the increasing molecular weight and mass concentration of polymer solution.Capillary pressure curves were successively arranged from bottom left to top right,pore volume reduces at big pore throat but enlarge at smaller pore throat.The average pore radius & mean values,skewness,structure coefficient and uniformity coefficient show a decreasing trend.The above results have great significances for the research of post-polymer flooding EOR methods.

Interwell-connectivity analysis for fracture-vug reservoirs in the block-4 of Tahe oilfield,Tarim Basin

Yang Jian, Cheng Qian, Li Jianglong, Liu Zhongchun

2012, 33(3):  484-489,496.  doi:10.11743/ogg20120319

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The types of reservoir spaces of the Ordovician carbonate reservoir of theblock-4 of Tahe oilfield in Tarim Basin are dominated by cavern solution pore and vug,and fracture systems formed by karstification and tectonic movement.The caverns are discrete and the main reservoir spaces,while the fractures are the major migration pathways.The typical characteristics of the carbonate reservoir in the study area are of large burial depth,strong heterogeneity and large difficulty in petroleum production and so on.This paper analyzes the interference features of production performance of 7 wells in S48 unit of block-4 in Tahe oilfield.Four types of reservoir spaces are recognized based on analysis of static datum,including cavern-,fracture-,fracture-vug- and tight-types.Based on the analysis,four types of inter-well communication model are proposed,including inter-well ca-vern communication,inter-well fracture communication inter-well fracture and vug communication and inter-well non-communication.Finally,the interference well test theory and tracer diffusion theory are used to analyze the flow coefficient and quantify inter-well connectivity.It is pointed out that inter-well communication models and connectivity should be integrated into the prediction and production of residual oil in fractured-vuggy carbonate reservoir.

Application of development seismology to reservoir prediction of Lamadian oilfield in Daqing placanticline

Wang Qi, Li Hongmei

2012, 33(3):  490-496.  doi:10.11743/ogg20120320

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Taking Saertu oil layer of Lamadian oilfield as an example,this paper discusses the application of seismic attribution technique and curve reconstruction and inversion technique.Seismic attribution technique is sui-table for describing characteristics of reservoirs such as Sa I layer with sandstone interbedding in mudstone,especially the main channel sandbody in area with sparse well control.While,curve reconstruction and inversion technique is suitable for highly accurate prediction of inter-well sandbody,thus is critical for tapping remaining oil in oilfield with high water cut. Based on sedimentary facies correction through log/seismic integration,5 models were built,including channel side accretion,channel continuity,channel size,channel combination and channel timing.Log differences and elevation changes are integrated with inversion slice to characterize the vertical evolution of channel sands and finally to determine the boundary of a single channel sandbody.The complex superimposition relationship between early channel sandbody and late channel sandbody determine the complicated spatial distribution of remaining oil.These understandingsprovide a solid basis for extracting the remaining oil and improving flood pattern.