OIL&GAS GEOLOGY-2009, Volume 30 Issue 6

Concept,research status and trend of "hydrocarbon pooling patterns"

Wu Chonglong, Lin Zhongmin, Mao Xiaoping, Wang Lianjin

2009, 30(6): 673-683. doi:10.11743/ogg20090601

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Based on analyses of the case studies of typical hydrocarbon pooling patterns,five types of hydrocarbon pooling patterns are identified,and a new definition for the hydrocarbon pooling pattern is put forward in this paper.According to the study,the elements of hydrocarbon pooling include basic geologic conditions,drive force and medium,mechanism,and process of reservoir evolution,et al.Comprehensive analysis of hydrocarbon pooling patterns should be based on all these elements.Moreover,the method for establishment of each pooling pattern and its range of application should be in accordance with the levels of exploration and research.In practice,one or more of these four elements can be selected as the primary elements,with the others as secondary ones,to establish the hydrocarbon pooling patterns at basin,depression,sag and trap levels respectively.

Relationship between tectonic uplifting & erosion and formation of abnormal pressure

Bao Youshu,

2009, 30(6): 684-688,691. doi:10.11743/ogg20090602

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Based on the principles of physical chemistry,a formula is established for quantitatively calculating formation fluid pressure after tectonic uplifting and erosion in a closed system.The calculation results with the formula show that formation pressure after tectonic uplifting and erosion in a closed system depends on such factors as initial formation pressure before tectonic uplifting,compressibility coefficient and expansion coefficient of formation fluid,compressibility coefficient of pore volume,temperature variation before and after uplifting,and erosion thickness.An analysis of compressibility coefficient and expansion coefficient of formation fluid as well as compressibility coefficient of pore volume reveals that an abnormal low pressure is likely to be formed in water-bearing sandstone formations,while an abnormal high pressure is more possible in gas-bearing formations after the uplifting.

Evaluation of energy of restricted and closed aquifer in over-pressured gas reservoirs

Hu Junkun, Li Xiaoping, Li Yan, Ye Liang, Ren Ke

2009, 30(6): 689-691. doi:10.11743/ogg20090603

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A new method for evaluating the energy of restricted and closed aquifer in over-pressured gas reservoirs is proposed in this paper.Based on the generalized material balance principle and in combination with performance of over-pressured gas reservoirs,this new method can be used to calculate multiple of aquifer—the ratio of aquifer volume to pore volume of gas-bearing zones—for a restricted and closed aquifer in over-pressured gas reservoirs.Then the aquifer energy can be evaluated by using the multiple of aquifer.By applying the method to the well X-3 in Xin Chang gas field,we evaluated the aquifer energy for the reservoirs based on a calculated aquifer multiple of 0.080 5 for the restricted and closed aquifer.The case study shows that this new method is reliable and effective.

Facies-constrained reservoir prediction of P₁h₃ channel sandstone in Daniudi gasfield,the Ordos Basin

Xu Jie, He Zhiliang, Dong Ning, Zhou Xiaoying, Li Jun, Zhu Shengwang

2009, 30(6): 692-696,705. doi:10.11743/ogg20090604

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The reservoirs of the 3^rd member of the Permian Lower Shihezi Formation(P₁h₃) in the Daniudi gas field in the Ordos Basin are typical fluvial deposits.As reservoir prediction with seismic attributes is constrained by seismic resolution,uncertainty occurs in the prediction of channel sandstone reservoirs.High-resolution sequence stratigraphy is applied in this paper to figure out the distribution pattern of sedimentary facies of the targets in P₁h₃.It has been made clear that the seismic reflector on the top of P₁h₃(T₉^f) has the geologic significance of an approximate isochronous surface in the whole study area.The relationship between the thickness of the upper sandstone interval in P₁h₃ and the average amplitude of T₉^f conforms to the principle of tuning amplitude.Thus,the amplitude attributes that are sensitive to the sandstone in the P₁h₃ are optimized.According to integrated analyses of seismic facies,logging facies and sedimentary microfacies,it is thought that the plan view of sensitive amplitude attribute of P₁h₃ is consistent with the distribution pattern of sedimentary facies.Favorable zones for sandstone development could be predicted through relevant analysis.Application in area near the D66 well shows that 90% of the prediction matches the real drilling results.Therefore,under the constraints of sedimentary microfacies and sedimentary characteristics,seismic attributions can be used to accurately predict and characterize complex reservoirs.

Stratigraphic division of the Upper Carboniferous-Lower Permian in Daniudi gasfield,the Ordos Basin

Guo Shuyuan, Zhang Guangquan, Chen Shuwei, Li Hao

2009, 30(6): 697-705. doi:10.11743/ogg20090605

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A research into the lithologic assemblage,sedimentary cycle,marker beds,and sedimentary evolution of the Benxi and Taiyuan formations as well as the regional geology reveals that the Benxi Formation was formed during the Late Carboniferous Benxi age.Its lower member consists of bauxitite and is equivalent to the ferrallite interval regionally and its upper member composes of sandstone and mudstone interbeded with thin coal and 1-3 local limestone layers and regionally corresponds to the Bangou member.The Taiyuan Formation can be divi-ded into three members.Its lower member is sandstone and mudstone with thin coal interbeds,regionally corresponds to the Jinci member,and its age is the Late Carboniferous.The middle member consists of coalbed,limestone and equivalent mudstone and regionally corresponds to the Maoergou member.The upper member consists of interlayering sandstone and dark mudstones with coal and 0-2 limestone interbeds and regionally corresponds to the Dayao member.The age of the upper and middle members is the early Permian.

Physical simulation of hydrocarbon accumulation in low-permeability lithologic reservoirs:an example from the Yanchang Formation in the Upper Triassic of the Ordos Basin

Li Yuanhao, Liu Jianping, Liang Yan, Du Yuguo, Huang Jinxiu, Zeng Jianhui

2009, 30(6): 706-712. doi:10.11743/ogg20090606

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In the late Triassic Yanchang period,the Ordos Basin was a continental depression basin.The deposits of lake-delta facies are prevalent,and hydrocarbon reservoirs are mainly low-and ultra-low-permeability litholo-gic type.A research into the area reveals that the abnormally high pressure resulted from hydrocarbon generation in the Chang-7 Formation serves as the major dynamic force for the episodic migration of oil toward low-permeability reservoirs.Physical simulation was performed to analyze the process and features of hydrocarbon accumulation in low-permeability reservoirs under different pressures and to compare the characteristics of episodic hydrocarbon accumulation and steady hydrocarbon accumulation under different charging pressures and at different charging direction.The results show that,regardless the direction of hydrocarbon expulsion from source rocks,the higher the pressure in the low-permeability lithology reservoirs is,the higher the hydrocarbon accumulation efficiency and the oil saturation are.

Characteristics and major controlling factors of reservoirs in the Xujiahe Formation of the central and western Sichuan Basin

Feng Mingshi, Liu Jiaduo, Meng Wanbin, Wang Jun, Zhang Xiang, Feng Yanhong

2009, 30(6): 713-719. doi:10.11743/ogg20090607

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In this paper,reservoir characteristics,sedimentation and diagenesis of the Xujiahe Formation in the central and western parts of the Sichuan Basin are studied through microscopy observation of cast thin sections,analysis of physical properties,scanning electron microscope and X-diffraction.The results show that pores in the Xujiahe Formation of the study area are mainly residual primary intergranular pores and intragranular dissolution pores.With an average porosity of 5.83% and average permeability of 0.283×10^-3μm²,the reservoirs are classified as low-porosity and low-permeability reservoirs.Sedimentation and diagenesis are the main factors controlling the development of reservoirs.Favorable facies belts for the development of reservoirs are river mouth bar and underwater distributary channel microfacies in the delta front.Compaction is the main influencing factor which led to the loss of porosity in the reservoirs.Early rim cementation of chlorites helped to protect the residual primary intergranular pores,and dissolution contributed the most to the development of reservoirs.

Current terrestrial stress direction of the Shaximiao Formation in the Yanjinggou Structure of the West Sichuan Depression

Deng Hucheng, Zhou Wen, Jiang Haogang, Jiang Wenli

2009, 30(6): 720-725,731. doi:10.11743/ogg20090608

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Reservoir of the Shaximiao Formation in the West Sichuan Depression is of low porosity and permeability.To know the current terrestrial stress direction is the basis for effective fracturing in this area.Through tracking down the P-wave direction of natural earthquakes in the West Sichuan Depression over the years and referring to researches on current terrestrial stress direction in adjacent structures,the current terrestrial stress direction of the study area is analyzed and predicted.By the paleomagnetic directional experiments and velocity anisotropy experiment with single-well core,the maximum principal stress direction is measured and calculated.The results show that the calculated current terrestrial stress direction is consistent with that of the adjacent structures.Eventually,according to various data and experimental results,the current terrestrial stress direction of the Shaximiao Formation in the study area is determined to be a NW direction.

Hydrocarbon accumulation pattern in the Mesozoic of Mahuangshan area in the western margin of the Ordos Basin

Ding Xiaoqi, Zhang Shaonan, Xie Shiwen, Feng Yibo

2009, 30(6): 726-731. doi:10.11743/ogg20090609

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An analysis is performed on the fault characteristics,typical reservoirs,and residual pressure distribution in the Mesozoic of the Mahuangshan area in the western margin of Ordos Basin.The results show that the hydrocarbon distribution and plays there vary greatly in different structural belts and structural control on reservoirs is significant.In the thrust belt in the western margin,proximal plays and distal plays are predominant.The re-servoir types here are mainly fault-block and faulted anticlinal(nose) reservoirs,featuring in small area but high oil column and small reserve but high production.While in the central depression,the indigenous plays are predominant.The reservoirs here are tight low-permeability type featuring in large area,low oil column,and low production.In the eastern uplift belt,proximal,distal and indigenous plays all occur.The reservoirs are dominated by anticline-lithologic reservoirs.

Gas and water distribution in gas reservoirs of the Xujiahe Formation,Guang'an area,the central Sichuan Basin

Fan Ru, Shao Hui, Jia Ailin, He Dongbo, Zhang Xuelei, Deng Shenghui, Wei Yunsheng, Ji Lidan, Cheng Taotao

2009, 30(6): 732-739. doi:10.11743/ogg20090610

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The gas reservoirs in the Xujiahe Formation,Guang'an area,central Sichuan Basin,are porous-litho-logic tight gas reservoirs.Production test data of 78 wells in the area were analyzed and the following conclusions were obtained.Pore throats in these reservoirs form the main carrier system during the pooling process,and the migration,accumulation and distribution of gas and water is controlled by the physical properties and heteroge-neity of these reservoirs.Gas accumulation is affected by the structures during the later reformation of these reservoirs,and the relatively low amplitude of the structures causes the poor gas-water differentiation,thus water production is common in the gas wells there.The gas reservoirs can be divided into three zones(primary gas zone,secondary gas zone,and gas-water zone) according to the gas and water distribution.Three patterns of gas and water distribution are correspondingly proposed,namely highly permeable zone pattern,single sandbody pattern and micro-fracture-controlling pattern.

Sedimentary model of the Permian sandy conglomerate in the footwall of the Kebai Fault,the Junggar Basin

Zhang Shuncun, Chen Lihua, Zhou Xinyan, Jiang Huan, Shi Ji'an, Jia Fanjian, Wu Zhixiong

2009, 30(6): 740-746,753. doi:10.11743/ogg20090611

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This paper aims at developing a sedimentary model of the Permian sandy conglomerate in the footwall of the Kebai Fault in the Junggar Basin,which can provide a reference for predicting good reservoirs.Sedimentary features of the sandy conglomerate in the study area are examined through core observation,thin section analysis and scanning electron microscope analysis.Tectonic settings and depositional conditions are taken into consideration and logging data are also consulted.The depositional environments of the sandy conglomerate in the study area can be divided into two types,namely above-water and underwater environments.Overall,the main feeder channels are large in water volume,and stable and continuous in water flow.Physical properties of the sandy conglomerate reservoirs differ greatly in different depositional environments,and the best occurs in underwater distributary channel on fan delta front.The control of shoreline on reservoir physical property is highlighted,while the distinction between alluvial fan margin and fan delta plain is obscured.A sedimentary model with alluvial fan-fan delta-lacustrine facies integrated is proposed and 3 sedimentary facies and 8 sedimentary subfacies are identified in the study area.

Sequence stratigraphy of the upper third member of the Shahejie Formation in Liuxi area of the Raoyang Sag,the Jizhong Depression and exploration of subtle reservoirs

Liu Yongqiang, Liu Xiaolong

2009, 30(6): 747-753. doi:10.11743/ogg20090612

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Exploration of subtle reservoirs is a hot topic and one of the future directions in oil exploration.In this paper,research on sequence stratigraphy of the upper third member of the Shahejie Formation(Es³) in the Liuxi area of the Raoyang Sag,the Jizhong Depression is made based on basic principles of sequence stratigraphy and by using seismic,logging and lithofacies and other data.Sequence stratigraphic framework of the Liuxi area is established.According to the research,the upper Es³ is a complete third-order sequence which can be divided into lowstand,lake transgression and highstand system tract.Based on these results,the plane distribution features of sedimentary facies in each system tract are analyzed under the sequence stratigraphic framework.The upper Es³ is dominated by braided river delta facies,of which the delta front subfacies is the most extensive.The sandstone in the lowstand system tract and the source rock in the lake transgression system tract form an excellent source-reservoir-seal combination,which is favorable for the development of subtle reservoirs.Considering the regional structure features,it is suggested that the favorable exploration targets for subtle reservoirs should be the sand body in the braided river delta front of the lowstand system tract in the upper Es³ in the central and southern parts of the study area.

An analysis of oil source in the Kebai fault zone,the Junggar Basin

Jiang Xiangqiang, Liu Guangdi, Gao Gang, Yang Haifeng

2009, 30(6): 754-761,767. doi:10.11743/ogg20090613

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The Kebai fault zone is one of most prolific areas in Junggar Basin.But its oil source is still poorly understood.Crude samples from the area feature in relatively low solidifying point and low content of saturation hydrocarbon and wax.The samples can be classified into type A and type B according to their biomarker characteristics.The distribution of different types of samples presents a clear zonation.According to the oil migration direction indicated by the geochemical index of crude samples,it is believed that the oil is mainly sourced from the source rocks in the overthrust Fengcheng Formation—a conclusion verified by the spatial distribution of strata in the zone.The pooling pattern in the area is also summarized and future exploration targets are predicted in the paper.

An exploratory research on geological conditions of hydrocarbon pooling and distribution patterns of reservoirs in the Bongor Basin

Song Hongri, Dou Lirong, Xiao Kunye, Hu Yong, Ren Lizhong

2009, 30(6): 762-767. doi:10.11743/ogg20090614

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The Bangor Basin,a Meso-Cenozoic rift basin developed under the influence of the West and Central Africa Rift Systems,is located in the joint of the West Africa Rift System and the Central Africa Rift System.The basic geological conditions in the Bongor Basin are favorable for hydrocarbon pooling,including multiple sets of quality source rocks in the Lower Cretaceous,multiple sets of sandbodies with good reservoir properties,effective traps,3 quality regional seals and excellent source-reservoir-seal combinations.The structural traps and the structural-lithologic traps are predominant.The distribution of hydrocarbons is under the control of the distribution of hydrocarbon kitchen and mature source rocks,regional seals,reservoir sandbodies and secondary structu-ral zones.For further exploration,the focus will be the middle section of the northern slope zone,pre-Mesozoic basement,east and west sides of the northern slope zone and the southern steep slope zone.

Major controlling factors for oil accumulation and destruction in paleo-reservoirs,Sazhi area,Chuxiong Basin

Peng Jinning, Liu Guangxiang, L? Junxiang

2009, 30(6): 768-772. doi:10.11743/ogg20090615

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Oil and gas seepages and asphalt shows are not rate from the Lower Cambrian to the Cretaceous in the Chuxiong Basin.An analysis of Sazhi plaeo-reservoirs in the basin reveals that they were destroyed mainly because of surface exposure caused by later structural uplifting and large-scale erosion.Extensional fractures induced by later compression and thrusting connected the reservoirs with the surface and therefore also contributed a lot to the destruction of the reservoirs.There are two types of reservoir space.One is original pores which dominate the lower part of the reservoir(the Upper Triassic),and the other is fractures which are predominant in the lower part of the reservoir(the Jurassic).Bitumen occurring in the pores of the lower reservoir interval is believed to be the remnant of early-formed lithologic-stratigraphic reservoirs,indicating that the slope and uplift zones are the favorable places for the formation of paleo-lithologic-stratigraphic reservoirs as they are regarded as the final destination of oil and gas migration.

Application of the material balance method to the energy evaluation of fractured-vuggy carbonate reservoirs

Li Jianglong, Zhang Hongfang

2009, 30(6): 773-778,785. doi:10.11743/ogg20090616

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The driving mechanisms of the fractured-vuggy units are classified into four types:closed elastic drive,elastic drive with water invasion,elastic drive with closed aquifer,and elastic drive with both closed aquifer and water invasion.A material balance equation is established for each type of driven mechanism.These equations take the characteristics of fractured-vuggy carbonate reservoirs into full consideration,and thus are different from the former equations.This paper puts forward several indexes for evaluating the energy of fractured-vuggry units,including the elastic production rate,the volume of water invasion and multiple of closed aquifer,and proposes a method for evaluation of fractured-vuggy carbonate reservoirs.This method can determine the energy characteristics of fractured-vuggy units and drive mechanisms and can be used to quantitatively calculate the energy and invasion water volume.The calculated results show that the established method can be used to evaluate the energy characteristics of fractured-vuggy units.

Geologic implications of seismic spectrum imaging and its application to researches on sedimentary features

Zhang Lei, Lu Shuangfang, Zhang Xuejuan, Yang Zhiru, He Xin

2009, 30(6): 779-785. doi:10.11743/ogg20090617

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The accurate understanding and rational application of the geologic implications of seismic spectrum imaging are helpful to precise description of reservoir distribution patterns and sedimentary features.On the basis of summarizing geological implications of seismic spectrum imaging,we validated the geological imformation reflected by the frequency division slice of amplitude tuning cube of the Chao-86 wellblock in the Chaoyanggou oilfield with well data,estimated thickness of sandstone and seismic attributes.The Fu-I oil layer in the study area has different sedimentary features in the east and west sides.In the east side,although the single channel sandbody is thick,the total thickness of sandstones is small due to the small number of superimposed channel sands.The sediments are sourced from the provenance in the northeast.In contrast,in the west side,although the single channel sandbody is thin,the total thickness of sandstones is relatively large,thanks to the large number of superimposed channel sands.The sediments came from the provenance in the southwest.Frequency division slices not only can accurately reflect the areal distribution and vertical thickness of the channel sandbodies,but also can indicate the provenance,vertical variation and areal distribution of thin reservoirs.

PSO-SVM-based fracture identification method

Qu Ziyi, Zhou Wen, Luo Xin, Dai Jianwen

2009, 30(6): 786-792. doi:10.11743/ogg20090618

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Fracture identification is one of the key issues and difficulties in exploration and development of fractured reservoirs.Based on response characteristics of conventional logging data to fractures,we proposed an identification method called PSO-SVM that integrates the Particle Swarm Optimization(PSO) with the Support Vector Machine(SVM).By taking the reservoirs in the Yan'an and Yanchang formations in the western Mahuang-shan block for examples,we identified conventional logging parameters that can respond well to fractures through a crossplot analysis,and performed an overall optimal selection of model parameters by using the PSO.Based on these works,we built a model for identification of fractures in the study area.The model was applied to single well in the study area for identification of fractures and a synthetic column map was produced by comparing the model outputs with core photos and logging curves.The application of the method shows that the modeling result matches well with the geological reality and can truthfully reflect the growth of fractures.

Identification of producible pay intervals in shallow to medium gas pools in western Sichuan Basin

Yang Jinlin

2009, 30(6): 793-796. doi:10.11743/ogg20090619

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An evaluation method for aggregate index G_i of drilling and logging is proposed based on a calculation of weight coefficients for all parameters gathered during drilling and logging.The drilling and logging parameters as well as capacity building of gas wells in the gas pools in western Sichuan Basin are analyzed.For the gas well targeted at the reservoirs in the Penglaizheng and Shaximiao formations in XC gas field,industrial gas flow is highly possible to be achieved after fracture treatment when the Gi are larger than 6.0 and 12.5 respectively.The method is also proved effective in guiding layer selection during workover and stimulation of old wells,with a success rate of more than 70%.

An experimental study of displacement efficiency of polymer flooding under high temperature reservoir conditions:an example from Shuanghe oilfield in the Biyang Sag

Han Jie, Zhang Liqing, Zhou Yongqiang, Tang Dazhen

2009, 30(6): 797-800. doi:10.11743/ogg20090620

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According to the characteristics of high temperature(84.3℃) and low permeability of reservoirs in the Shuanghe-V block of the Biyang Sag,polymers 1630s and ZL-I with different degrees of hydrolysis are selec-ted for an experiment on oil displacement efficiency.Thanks to its high viscoelasticity,displacement efficiency of high concentration polymers is obviously higher than that of low concentration polymers.However,considering the cost,polymers of 1 600-2 000 mg/L is proposed for use.An additional experiment on displacement efficiency of different slug sizes is conducted too.The results show that the displacement efficiency of bigger polymer slug is higher than that of smaller polymer slug.However,the incremental displacement efficiency is insignificant when the slug size exceeds 0.5 PV.Therefore,the suggested size of slug should be between 0.4 PV and 0.5 PV.Comparing the experiment results before and after the maturing of the polymers,we find that polymer 1630s with low degree of hydrolysis is more favorable for this high-temperature reservoir.

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