Table of Content

28 April 2012, Volume 33 Issue 2

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Main factors controlling hydrocarbon accumulation and favorable exploration targets for the Yanchang Formation in Zhenjing area,south Ordos Basin

Yin Wei, Zheng Herong, Hu Zongquan, Liu Zhen, Shang Xiaofei

2012, 33(2):  159-165.  doi:10.11743/ogg20120201

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Through analyzing the relations between petroleum discoveries and distributions of the favorable facies zones,local structures,faults and fractures,this paper studied the main factors controlling hydrocarbon accumulation in combinition with statistical analysis of the relationship between formation test data and sand thickness,reservoir property and logging data.The results show that favorable sedimentary microfacies zones,local structural setting,and faults & fractures are the three major factors controlling hydrocarbon accumulation.Hydrocarbon mainly accumulate in the underwater distributary channel sands of the delta front.The high of NW-SE-trending broad nose structure is the favorable place for hydrocarbon accumulation.The vertical and high-angle heterotropic fractures are the main effective factures in the study area.Faults and fractures control hydrocarbon accumulation.The discovered pools with a great amount of reserves are mainly distributed near the F₂ and F₃ fault zones with large fault displacement.The sandbodies of underwater distributary channel subfacies with well-developed faults and fractures in the local nose structures in the southeastern part of the study area are the the most favorable targets for further exploration.

Hydrocarbon enrichment patterns of the 3^rd member of Funing Formation in Zhangjiaduo oilfield, Subei Basin

Jiao Lili

2012, 33(2):  166-172.  doi:10.11743/ogg20120202

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The 3^rd member of Funing Formation has a great potential for oil and gas exploration and will be one of the most important targets for reserve growth and production addition of SINOPEC Huadong Oilfield Company.However,the reservoir heterogeneity is strong and hydrocarbon enrichment patterns are poorly understood,seriously constraining future exploration and development.Based on study of the basic geologic conditions for source rocks,reservoirs,and traps,abnormal pressure is analyzed according to the rules of mudstones compaction.The abnormal pressures of Funing Formation are caused by ofundercompaction,instead of hydrocarbon generation of kerogen.The deep high-quality reservoirs are closely related with undercompaction and the high-quality reservoirs occur in areas where the abnormal pressure is high.The high abnormal pressure occurs in interval from the top 3^rd member to 4^th member of Funning Formation and forms a regional seal.Hydrocarbons mainly accumulate in low potential areas below this seal.High abnormal pressure favors hydrocarbon accumulation in the 3^rd member of Funning Formation,while low abnormal pressure may be favorable for hydrocarbon accumulation in the overlying Dainan Formation.Based on study of the regional high abnormal pressure seal and sedimentary microfa-cies,it is believed that the hydrocarbon accumulation conditions of the 3^rd member of Funning Formation are better to the south,thus the 3^rd member to the south is a favorable target for future exploration.

Characteristics of hydrocarbon accumulation in JZ20-A structure in Liaozhong Sag

Li Jianping, Guo Yonghua, Zhou Donghong

2012, 33(2):  174-182.  doi:10.11743/ogg20120203

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The lower 2^nd member and 3^rd member of the Dongying Formation, the 1^st and 3^rd member of the Shahejie Formation are four source rocks in Liaozhong Sag.The latter three are active source rocks,but the lower 2^nd member of the Dongying Formation is immature to lowly mature.The 3^rd member of the Shahejie Formation in the northern subsag of the Liaozhong Sag is the main source rocks for the JZ20-A oilfield.The source rocks in the 3^rd member of the Shahejie Formation are of high organic content and maturity,thus have great potential for hydrocarbon generation.By analyzing the inclusion of the major pay zones in the well JZ20-A,we performed the timing of the hydrocarbon generation and established the hydrocarbon accumulation model in the JZ20-A oilfield.The results indicate that the homogenization temperature of the inclusion is 120-140 ℃. The hydrocarbon charging mainly occurred at 5 Ma ago when the Minghuazhen Formtion was deposited.Hydrocarbon charging also happened at 27 Ma ago when the Dongying Formation deposited.All the reservoirs of JZ20-A oilfield are high in hydrocarbon abundance.The GOI value of the inclusion is above 5%.The characteristics of the hydrocarbon accumulation are relay-type multiple stage hydrocarbon charging,over-pressured shale sealing on both sides and oil/gas accumulation in superimposed multiple layers.

Characteristics of the Paleogene gas reservoirs in Qikou Sag

Yu Xuemin, Jiang Wenya, He Bingzhen, Wang Shuxiang, Zou Leiluo, Wang Xiaomin

2012, 33(2):  183-189.  doi:10.11743/ogg20120204

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Two condensate gas fields,i.e,Banqiao and Qianmiqiao,have been discovered in Qikou Sag.In addition,exploration breakthrough was also made in the Chenghai buried hill and the deep Paleogene in Qikou Sag,indicating good exploration prospect.This paper systematically analyzed the Paleogene natural gas reservoirs in Qikou Sag in terms of petroleum factors including source rocks,reservoirs and cap rocks,and described the key characte-ristics of the gas reservoirs.The result indicates that the natural gas mainly accumulate in the mid-deep strata of Shahejie Formation.The shallow secondary gas reservoirs mainly occur in structural traps.In contrast,the mid-deep gas reservoirs mainly occur in structural-lithologic compound traps.The genetic type of gas is dominated by humus type.The pore space of the reservoir is dominated by pores,with fractures occurring in the mid-deep layers,indicating dual porosity reservoir.Two regional cap rocks developed during the maximum flooding are overpressured and provide favorable preservation condition for gas reservoirs.The gas reservoirs mainly occur in areas with high gas generation intensity and are characterized by late hydrocarbon charging.The hydrocarbon distribution is characteri-zed by"gas in the north and oil in the south"and"oil in the upper interval and gas in the lower interval".

Geological characteristics and hydrocarbon accumulation model of the Cenozoic Asmari-Gachsran play,Zagros Basin

Zhang Zhen, Li Haowu, Duan Hongzhen, Xu Xiangkai, Jiang Siqin

2012, 33(2):  190-199.  doi:10.11743/ogg20120205

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The Asmari-Gachsran play is an important play in Zagros Basin.We studied the paleogeography evolution,hydrocarbon source rocks,reservoir rocks,cap rocks and hydrocarbon accumulation process and model of the Asmari-Gachsran play.The Cretaceous Kazhdumi source rocks was more deeply buried due to the Noegene-Quarternary Zagoros folding and mostly reached peak hydrocarbon generation.Meanwhile,open fracture networks that penetrate the Cenozoic Asmari limestone,Pebdeh mudstone and the Cretaceous Sarvark limestone were also formed due to the tectonics,and they constitute vertical pathways for hydrocarbon migration the Kazhdumi source rocks to the above reservoirs.In most areas,the hydrocarbons in the Asmari play were directly charged from the Kazhdumi source rocks instead of the Sarvark play.The Asmari and the Sarvark reservoir share the same oil-water contact due to the connection of fractures,thus the shallow Asmari reservoirs were charged earlier than of the deeper Sarvark reservoir,and have higher filling degree.High quality source rocks,vertical open fractures connecting the source rocks and reservoirs,thick evaporate cap rock,and the good timing between peak hydrocarbon generation and trap-fracture development are the key factors controlling hydrocarbon accumulation in Asmari-Gachsran play.

Calibration of thrust faults with abnormal formation pressure data tested during drilling —an example from the Southern fold-thrust belt in Junggar Baisn

Yang Geng, Li Wei, Bai Zhenhua, Wang Xiaobo, Li Benliang

2012, 33(2):  200-207,224.  doi:10.11743/ogg20120206

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The complex surface geology and intensive tectonic activities causes the poor seismic imaging in the southern fold-thrust belt,Junggar Basin,challenging structural interpretation.During the seismic interpretation of the Manas structure,we first projected the outcropped strata and faults onto the seismic lines with topographic data,then defined seismic horizons with the vertical seismic profile(VSP)and acoustic logging data of well Mana-1 and Mana-002,and finally fixed possible deep faults according to the seismic reflectance signatures.Some faults encountered during drilling can be identified by using dipmeter data.However,as chaotic seismic reflections exist in the middle-shallow layers on seismic reflection and thrust faults slipped along the shale and mudstone in the Paleogene Anjihai Formation,it is hard to identify the thrust faults in this structurally thickened formation by using dipmeter data.Correlation of seismic reflectance anomaly with fault depth in well Mana-1 and Mana-002 indicates that there is certain relationship between the thrust faults and the abnormal formation pressures tested during drilling.A series of the thrust fault points of the wells are identified by monitoring abnormal formation pressure and the pressure gradient during drilling,and they are verified by both the pressure data of wells and the fault points identified in the adjacent wells.The well formation pressure data tested with the Modular Dynamic Test(MDT)shows that two pressure systems exist in the Ziniquanzi Formation and are separate by a thrust fault.The final seismic structural interpretation demonstrates that the Horgos-Manas-Tugulu thrust belt is composed of a series of imbricate fans.

Effects of tectonic compression on hydrodynamic force in Kuqa Depression

Zhang Fengqi, Wang Zhenliang, Fan Changyu, Zhao Xuejiao

2012, 33(2):  208-216,235.  doi:10.11743/ogg20120207

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Late Himalayan tectonic compression was strong in Kuqa Depression,Tarim Basin,resulting in complex hydrodynamic force distribution.In order to understand the effects of tectonic compression on hydrodynamic force in Kuqa Depression,we simulated the distribution of the maximum principal compressive stress of Kuqa Depression in the Late Himalayan period.The tectonic compression model was used to evaluate the amplitude of tectonic overpressure in the main tectonic zones of Kuqa Depression in the Late Himalayan period.The evolution history of fluid pressure in the major target formations of Kuqa Depression was defined and that of gas pressure potential was restored by integrating the depositional overpressure with the tectonic compressive overpressure. Based on restoration of tectonic stress field and paleohydrodynamic force,we analyzed the effects of tectonic compression on hydrodynamic force and the characteristics of gas migration and accumulation in Kuqa Depression.Tectonic compression can change the hydrodynamic force in Kuqa Depression during strong tectonic activity.The enhancement of hydrodynamic force can increase gas migration force, being favorable for gas migration.The lowe-ring of hydrodynamic force can reduce gas migration force,being favorable for gas accumulation.Tectonic compression also can change the direction of hydrodynamic force,turning the local traps into relatively low potential areas,to which gas migrate.Areas with weak hydrodynamic force in the direction of stronger hydrodynamic force are favorable for hydrocarbon accumulation.

Sedimentary features of fluvial-dominated delta in the Kepingtage Fm in Keping outcrop area and their significance for petroleum exploration

Bai ZhenRui, Xing Fengcun, Li Huixian

2012, 33(2):  217-224.  doi:10.11743/ogg20120208

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The Silurian marine clastic reservoir in Tarim Basin is an important exploration play,in which some exploration breakthrough has been made in Central Tarim and North Tarim.However,no consensus has been reached about its sedimentary environment and characteristics,influencing future exploration.Based on the outcrop research and microscopic analysis of thin sections,this paper reveals that the Kepingtage Formation(Fm)in the Keping outcrop area can be divided into three third-order sequences.Large-scale fluvial-dominated delta deposits(mainly delta front and pro-delta deposits)are recognized in the Kepingtage Fm.Further more,several microfacies such as underwater distributary channel,inter-branch channel bay,mouth bar,distal bar and pro-delta mudstone are identified.The existence of large incised channel on the lower boundary of sequence indicates that large-scale deep water turbidite sandbody may develop in deep water.This delta deposits combination in the study area is of great significance for petroleum exploration in the Silurian marine clastic reservoirs in Tarim Basin.Favorable source rock conditions,large sandbody and multiple reservoir-source rock combinations are favorable for hydrocarbon accumulation.The turbidite sandbodies possibly developed in the deep water area are also the potential exploration targets.

Diagenesis and reservoir characteristics of the Lower-Middle Carboniferous carbonates in Kenkyak area,Pre-Caspian Basin

Wang Rui, Zhu Xiaomin, Chen Yefei, Li Kongchou

2012, 33(2):  225-235.  doi:10.11743/ogg20120209

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By using core,thin section,SEM,porosity,permeability and geochemical data,this paper studied rock types,reservoir spaces and diagenesis of the Lower-Middle Carboniferous carbonate rocks in the coring interval of well A in Kenkyak area,Pre-Caspian Basin.The Lower-Middle Carboniferous carbonate reservoirs are grainstones and micrites of open platform facies with strong vertical heterogeneity and can be divided into two types,ClassⅠand ClassⅡ.The Class I is high quality reservoir with intergranular dissolved pores and intragranular dissolved pore as the main pore types.In contrast,the ClassⅡis moderate to poor reservoirs with pores dominated by intercrystalline pores and intercrystalline dissolved pores.Cementation and dissolution are the main diagenesis processes controlling the two types of reservoirs.The cementation mainly includes bladed-fibrous calcite cementation in normal seawater diagenetic environment and mosaic-granular-subhedral calcite cementation in burial diagenetic environment.The dissolution includes meteoric dissolution and burial dissolution,with the latter being critical for the formation of classⅠreservoir.The cementation is well developed in the classⅡ reservoir.

Poroperm characteristics of deep volcanic reservoirs in Songliao Basin

Wu Yanxiong, Wang Pujun, Bian Weihua, Yu Miao, Wang Peng, Wang Bo

2012, 33(2):  236-247,264.  doi:10.11743/ogg20120210

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Different types of volcanic rocks are developed in Songliao Basin.Exploration activities revealed that oil/gas shows occur in all the volcanic rocks.In order to further understand the characteristics of favorable volcanic reservoirs,a comparative study for reservoir space,pore structure and physical property is conducted by using core,thin section and test data.The distribution of primary voids are extremely uneven in different types of volcanic reservoirs,that of secondary pores and fractures is better,and that of primary micropores and fractures is relatively even.Five throat types are identified,including coarse throat,medium-coarse throat,fine throat on the high side,fine throat and very fine throat.There are 6 types of porosity distribution,including high porosity with single peak,high porosity with double peak,medium porosity,medium-low porosity,lower porosity and low porosi-ty.Permeability distribution can be grouped into five types,namely high permeability,medium-high permeability,medium permeability,medium-low permeability and low permeability.Based on the four parameters mentioned above,it is believed that vesicular rhyolite,rhyotaxitic rhyolite,spherulitive rhyolite,ignimbrite,brecciated lava and breccia reservoir have good poroperm characteristics,while tuff,massive basalt,tuffaceous breccia and sedimentary tuff are poor in reservoir quality.

Sequence stratigraphy of the Paleogene Dongying Formation and its significance for stratigraphic-lithologic reservoirs exploration in the central-south Liaoxi salient

Guo Tao, Wang Jun, Shi Wenlong, Zheng Jinggui, Wang Baoquan, Xu Chunqiang

2012, 33(2):  248-255,264.  doi:10.11743/ogg20120211

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The control of palaeotopography on the distribution of sandbodies has been well studied in continental rifted basin,while the control of palaeotopography dynamic changes caused by syndepositional structure movement on the sand distribution is less studied.Through the systematic study of tectonic-sequence stratigraphy and sedimentary facies of the Paleogene Dongying Formation in the central-south Liaoxi salient,the LST,TST and HST are recognized in the 2^nd member of the Dongying Formation according to system tract boundaries and the seismic reflection features of deltas.A high resolution sequence stratigraphy framework is established.On the basis of the fine division and correlation of sequence stratigraphy unit,the paper studied the palaeotopography and the development and evolution of depositional system.The study reveals that braided river delta,meandering river delta,sublacustrine fan and lake are well developed in the study area.There are three transform belts along the boundary fault in the salient from north to south.The areal and spatial variation of activity of the transform belts is the key factor controlling the migration of delta lobes.Four types of stratigraphic-lithologic traps,including fault-lithologic trap,sandstone updip pinchout trap,lithologic trap and stratigraphic overlap trap,are recognized in the 2^nd member of the Dongying Formation based on the sandbody characterization of each system tract.

Diagenetic facies types and logging identification methods for low-permeability tight sandstone reservoirs:a case study on the 8^th member of Xiashihezi Formation in Sulige gasfield,Ordos Basin

Zhang Haitao, Shi Zhuo, Shi Yujiang, Wang Liangliang, He Lujun

2012, 33(2):  256-264.  doi:10.11743/ogg20120212

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Sulige gasfield in Ordos Basin is a typical tight gas reservoir.According to clastic constituents,diagenetic mineral assemblage,interstitial matter,and diagenesis types,et al,we identified 6 diagenetic faceis types in the 8th member of Xiashihezi Formation(He8)reservoir of Sulige gas field,including intergranular pore+strong solutional phase of volcanic material,intercrystal pore+solutional phase of volcanic material,intercrystal pore+solutional phase of debirs,intercrystal pore+cementation phase of quartz,hydromica cementation+weak solutional phase of debris and compaction+cementation tight phase.In addition,we analyzed the impacts of different digenesis on log responses.On the basis of these studies,a method for continuously and quantitatively identifying diagenetic facies was established by using gamma ray,interval transit time,density and deep lateral resistivity log data.Logging data of Well Z65 were processed with this method,and a comparison with the thin section data and mercury injection data show that the results are accurate.Based on single well diagenetic facies identification,we defined the diagenetic face distribution in He8 reservoirs of Sulige gasfield.The central part of the gas field is dominated by intergranular pore+strong solutional phase of volcanic material and intercrystal pore+solutional phase of volcanic material,which are the favorable diagenetic faces belts.

Sedimentary characteristics and evolution of the 1^st member of Dainan Formation and the 1^st member of Sanduo Formation in Qutang and Haibei Sub-sags,Hai’an Sag

Wei Xiangfeng, Zhang Tingshan, Liang Xing, Yao Qiuchang, Tang Xingyou

2012, 33(2):  265-276,301.  doi:10.11743/ogg20120213

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Through fine core observation and description,eleven different lithofacies were recognized in the 1^st member of Dainan Formation and the 1^st member of Sanduo Formation.According to the characteristics of logging data and lithofacies associations, and in combination with the regional depositional environment,this paper documents that the 1^st member of Dainan Formation is of braided delta sedimentary system and the 1^st member of Sanduo Formation is of fluvial sedimentary system with braided-river in the lower part and meandering-river in the upper part.During the deposition of the 1^st member of Dainan Formation,braided-river delta front were well developed in the northern fault terrace zone and the south-eastern slope zone of Qutang Sub-sag and the south-western slope zone of Haibei Sub-sag,and sandbodies of underwater distributary channels constitute the framework of the braided-river delta fronts at this time.During the deposition of the lower part of the 1^st member of Sanduo Formation,the study area was dominated by the braided-river channel and flood plain deposits,and channel bars were well developed.During the deposition of the upper part of the 1^st member of Sanduo Formation,the sedimentary subfacies changed to meandering river channel,bank and floodplain,with point bar deposits developed in the convex bank of channel.The sandbodies of underwater distributary channels,channel bar in braided river and point bar in meadering river have relatively good poroperm characteristics,and thus are favorable facies for hydrocarbon accumulation.

Sedimentary facies and their evolution of the 4^th-middle 3^rd members of Shahejie Formation in Minfeng area, Dongying Sag

Yuan Guanghui, Cao Yingchang, Wang Yanzhong

2012, 33(2):  277-286.  doi:10.11743/ogg20120214

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No consensus has been reached on the types of sandy conglomerate fans in the 4^th-middle 3^rd members of Shahejie Formation in Minfeng area.Based on observation and description of cores from 26 wells and in combination with seismic data,logging data,and grain size characteristics,this paper systematically studied the sedimentary characteristics of sandy conglomerate fans,including nearshore subaqueous fans,fan deltas and deep water turbidite fans in the 4^th-middle 3^rd members of Shahejie Formation in Minfeng area.Fan deltas dominate the bottom of the lower 4^th member and middle 3^rd member of Shahejie Formation,while the nearshore subaqueous fans are predominant in the middle to upper part of the lower 4^th member,the upper 4^th member and the lower 3^rd member of Shahejie Formation.Deep water turbidite fans exist in each interval,but their scales are small.On the basis of identifying the types of sandy conglomerate fans in different intervals,we analyzed the synsedimentary tectonic activity,the geometry of boundary fault,paleoclimate,water depth and the close and open of lake basin,and determined the evolution and distribution characteristics of the main sedimentary facies in different periods. Based on these studies,this paper puts forward a sedimentary evolution model for the sandy conglomerate fans in the steep-slope zone of rifted lacustrine basin under the successive controls of the'high angle plate fault-high angle listric fault’,offering an appliccable instruction for oil and gas exploration in similar area.

Diagenesis and porosity evolution of tight sand reservoirs in the 2^nd member of Xujiahe Formation,western Sichuan Depression:an example from Dayi region

Luo Wenjun, Peng Jun, Du Jing’an, Du Lei, Han Haichen, Liu Huan, Li Jianbo, Tang Yong

2012, 33(2):  287-295,301.  doi:10.11743/ogg20120215

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The percentage of gas production from low-permeability gas reservoirs is increasing in China.However,the low-permeability gas reservoirs are geologically complex and can not be predicted easily,impeding their exploration and development.The second member of the Upper Triassic Xujiahe Formation in western Sichuan depression of Sichuan basin has poor poroperm characteristics as a whole and belongs to low porosity and permea-bility reservoirs.Based on the study of reservoir characteristics and diagenesis,this paper determines the filling sequence and relative content of cements of each stage through microscopic observation of thin sections.Characteri-stic inclusions are identified in cements of each stage and used to measure temperature.The results in combination with burial history and thermal history are used to determine the forming time of cements of each stage,hydrocarbon charging time and their sequences.In addition,the paper describes the rate and causes of porosity change in different periods,reconstructs the reservoir forming history and determines the time of reservoir tightening.Finally,this paper presents further exploration targets according to the analysis of hydrocarbon charging history.

Overview of separate injection technique for polymer flooding in Daqing oilfield

Li Haicheng

2012, 33(2):  296-301.  doi:10.11743/ogg20120216

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Three separate injection technologies for different stages of development are developed in Daqing oilfield,including concentric separate-injection,eccentric separate injection,and separate-layer molecular injection.The concentric separate-injection technology controls injection rate of each layer by using concentric injection allocator which regulates injection pressure.The eccentric separate injection technology controls injection rate of each layer by using eccentric injection allocator to generate enough differential choke pressure to regulate injection pressure.The separate-layer molecular injection weight technology controls injection rate of each layer by using molecular weight regulator or pressure regulator chosen according to reservoir property.This paper described in-detail their process principles,technical parameters,application scale and their effects et al.According to the actual stages of polymer injection in the oil field,this paper presents the rational timing and principles of separate injection as well as the corresponding test cycles.In addition,the principles for selection of separate injection technologies are also proposed according to the types of pay zones.Short clamping distance of the polymer injection technology and efficient measurement technology of separate injection wells in the polymer flood oilfield are the key research direction in Daqing oilfield.

Experimentals study on percolation characteristics of ordinary heavy oil reservoirs:a case study from the Qigu Formation reservoir in Nine-4 Block of Xinjiang oilfield

Wang Ziqiang, Zhang Daiyan, Yang Jun, Kou Gen, Yang Fei

2012, 33(2):  302-306.  doi:10.11743/ogg20120217

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Heavy oil reservoirs feature in high viscosity,non-Darcy flow,and the existence of start-up pressure.According to the percolation characteristics of heavy oil reservoir,a reasonable method for measuring the start-up pressure was designed.The start-up pressure gradient of oil phase and the relationships between velocity and pressure gradient under irreducible water saturation was studied through various percolation experiments at different viscosity,permeability and temperatures conditions with the natural cores from Xinjiang oilfield.The experimental formulas of start-up pressure gradient,velocity-differential pressure curve parameters,mud logging-derived permeability,and fluid viscosity were established through experimental data regression.These experiments indicate that the start-up pressure of heavy oil reservoir can be determined rapidly and accurately with the expe-rimental method.The influences of oil viscosity on start-up pressure gradient are greater than that of reservoir physical properties.The start-up pressure gradient and velocity-pressure curve parameters are well correlated with the ratio of mud logging-derived permeability to fluid viscosity.

Reservoir sensitivity evaluation of the Triassic Baikouquan Formation in Wuerhe oilfield,Junggar Basin

Gong Qingshun, Shou Jianfeng, Jiang Zhongpeng, Huang Geping, Wang Yanqing, Ni Guohui

2012, 33(2):  307-313.  doi:10.11743/ogg20120218

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Triassic Baikouquan Formation reservoirs in Wuerhe oilfield in Junggar Basin are of alluvial fan facies with low-porosity and low-permeability.No industrial oil flow can be tested without stimulation due to the low initial energy.Previous stimulation with water-based fracturing fluid failed,but stimulation with oil-based fracturing fluid in W36 well was successful.By using reservoir evaluation technique and experimental analysis techno-logy and referring to the standards of clastic reservoir evaluation,this paper thoroughly studied the sensitivity of sandy conglomerate reservoirs sensitivity within alluvial fan of Baikouquan Formation based on analysis of large amount of core flow test data.It is pointed out that understanding reservoir sensitivity and improving fracturing technique are quite important for prevention of formation damage and oil recovery.The study indicates that high content of clay minerals such as mixed illite/smectite and kaolinite is the main cause of strong sensitivity of the reservoir.Water sensitivity,salt sensitivity and volume flow rate sensitivity of the reservoir in Baikouquan Formation are moderate to strong(above average).Velocity sensitivity is a relatively weak.According to the results and production experiments,following measures,such as using dewatered oil-based fracturing fluid,controlling salinity of fracturing fluid(above 6 000 mg/L)and controlling flow velocity/volume flow rate,are proposed for preventing reservoir damage from sensitivity and increasing oil-gas production.

Geochemical monitoring technology of single layer production in commingled producing wells

Shui Leilei, Peng Ping’an, Huang Heting, Liu Yuming

2012, 33(2):  314-320,328.  doi:10.11743/ogg20120219

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A geochemical monitoring technique is developed through integrating single component separation,quantitative GC analysis of absolute concentration with multi-internal standards,biomarkers GC-MS analysis and carbon isotope analysis.It can rapidly and effectively identify the differences of crude oil produced from different layers.Multiple geochemical production monitoring indexes were selected through clustering statistical analysis and crude oil blend proportion experiment,and their applicability was evaluated.Qualitative GC-MS analysis of the fingerprint compounds verified that they are non-mixed compounds.The fingerprint technology was used to perform separate-layer production monitoring in four commingled producing wells in W1 and W2 oilfields.The error is only about 10% to 15%,indicating that this technology can accurately identify the major pay zone.It is quick and economic and can be combined with production logging.

Water sensitivity experiment and damage mechanism of sandstone reservoirs with ultra-low permeability:a case study of the eighth oil layer in the Yanchang Formation of Xifeng oilfield,Ordos Basin

Liao Jijia, Tang Hongming, Zhu Xiaomin, Ren Mingyue, Sun Zhen, Lin Dan

2012, 33(2):  321-328.  doi:10.11743/ogg20120220

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Taking the eighth oil layer of Yanchang Formation in Xifeng oilfield in Ordos Basin as an example,this paper investigates reservoir characteristics through cast thin section observation,SEM,image analysis and whole rock analysis,and studies water sensitivity through core flow displacement experiment.In addition,the changes of microscopic features within cores before and after water sensitivity experiment such as clay mineral occurrence and pore structure are qualitatively and quantitatively determined by using SEM and capillary flow porometer respectively,so as to investigate the mechanism of water sensitivity.The eighth oil layer of Yanchang Formation in Xifeng oilfield is a sandstone reservoir with ultra-low permeability.Its clay minerals are dominated by kaolinite,chlorite and illite,with no montmorillonite but some mixed-layer illite/smectite(only 11.4%).The degree of water sensitivity damage is moderate to strong.The damage from expanding clays is limited.The mecha-nisms of water sensitivity damage in cores include reduction of effective throat radius caused by secondary amorphous;damage or scattering of the paragenetic structures of clay minerals;dispersion of non-expanding clay mineral assemblage and cracking of their single crystal;collapsing of structure of matrix in pores and throat-plugging caused by migration of fine particles.