Table of Content

25 February 2006, Volume 27 Issue 1

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Genetic classification of petroleum system and idea of exploration

Zhao Zongju

2006, 27(1):  1-10.  doi:10.11743/ogg20060101

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Based on summarizing the petroleum systems and reservoiring patterns in complex areas reworked by tectonic movements, petroleum systems can be classified into primary, regenerated and composite types through analysis of"dynamic evolution"and genetic types of reservoirs. The primary petroleum system has mainly been formed by primary hydrocarbon generation of source rocks. The oil and gas reservoirs in the primary petroleum system include primary reservoirs being sourced by primary hydrocarbon generation and secondary reservoirs having experienced remigration and reaccumulation of hydrocarbons after the primary reservoirs have been reconstructed and readjusted. The regenerated petroleum system has been formed in later stage through secondary or even multiple hydrocarbon generation of source rocks that have been reburied after the hydrocarbon generation process ceased due to uplifting. The composite petroleum system has been formed as a result of overlapping or superimposition in space and time of various petroleum systems generated from different source rocks. Different ideas should be applied while exploring different petroleum systems. Exploration of primary petroleum system should be focused on"delineation of sag (oil-generating sag) and selection of zones (favorable structural zone)". Exploration of secondary and composite reservoirs hinges on understanding the formation, evolution and reconstruction processes of reservoirs. While the key of exploration of regenerated reservoirs is to define the"secondary hydrocarbon generation center"or"regeneration center"and to stress the importance of late reservoiring.

Types of marine plays in southern China and exploration prospects

Wo Yujin, Xiao Kaihua, Zhou Yan, Yang Zhiqiang

2006, 27(1):  11-16.  doi:10.11743/ogg20060102

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Being bounded by the Silurian regional detachment, the marine stratigraphic series in southern China can be divided into lower and upper two structural layers. According to the strength and characteristics of deformation of the structural layers, as well as their combination features, the geologic configuration of marine stratigrahpic series in southern China can be classified into 7 types, i. e. single layer stable, double layer continuous, double layer fault-folded, single layer imbricated, double layer thrust-slipped, single layer thrust faulted and binary nappe types. Multiphase subsidence and upheaval since Indosinian have led to the formation of 6 kinds of burial evolution history, which can be grouped into two large types, namely"early subsidence-late upheaval"and"early upheaval-late subsidence". The initial buildup of marine sedimentary formations, later reconstruction by tectonic movements and the superimposition of the overlying non-marine formations have resulted in 4 play types, including primary type, reconstructed type, regenerated type, and epigenotype; of which the primary play type has good oil and gas preservation conditions, and thus has good exploration prospects. The plays of regenerated type and epigenotype in the Middle and Lower Yangtze areas have certain exploration prospects, too.

Hydrocarbon generating potential of bark coal in Longtan Fm and oil and gas reservoiring in southern Poyang depression

Zhou Songyuan, Xu Keding, Yang Bin, Jiang Weisan, Peng Jun, Liu Jiaduo

2006, 27(1):  17-22,69.  doi:10.11743/ogg20060103

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Coal in the Upper Permian Longtan Fm in southern Poyang depression is called bark coal, because it is rich in periblinite. The bark coal generally contains over 40% of periblinite, as well as abundant hydrogen-rich components, such as degradinite or vitrinite B and microsporinites, etc. Simulated experiment of hydrocarbon generation shows that the oil-generating rate of bark coal is as high as 413.80 kg/t, so it is one of the best source rocks for coal-derived oil. Simulated experiment of single component hydrocarbon generation verifies that the periblinite is the most favorable component fro generation of liquid hydrocarbons, and is the major contributor to oil derived from bark coal. The level of thermal evolution of the Longtan Fm in southern Poyang depression is relatively low compared with the other source rocks in southern China. The superimposition of the Cretaceous basin would have created the geological conditions for secondary hydrocarbon generation of the source rocks and late reservoiring. Oil-source correlation shows that the oil in the reservoirs in Letan 1 well is typical coal-derived oil generated from the bark coal, indicating that the prospects for exploring coal-derived oil in Longtan Fm is good in areas with favorable preservation conditions in South China.

Physical simulation of reservoiring process of Kela 2 gas field

Zhang Hong, He Shunli, Pang Xiongqi, Gu Daihong, Jiang Zhenxue

2006, 27(1):  23-26.  doi:10.11743/ogg20060104

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Physical simulation experiments have been performed for hydrocarbon migration and accumulation in Kela gas field in Kuqa depression, and the following 3 major understandings have been achieved:(1) In Kela 2 gas field, hydrocarbons have been generated in the deep source rocks, driven by buoyancy, migrated through thrust faults and carrier beds and accumulated in the anticlines or faulted anticlines. The thrust faults and carrier beds have played an important role in the reservoiring process of Kela 2 gas field. (2) The hydrocarbons in the Kela 2 structure have come from multiple sources rather than from a single source. (3) The gas from multiple sources have continuously accumulated in the Kela 2 structure above, resulting in the gas reservoir to be characterized by overpressure and high abundance. While the two deeper structures that are similar to Kela 2 structure and connected by faults have limited size and abundance of hydrocarbons.

Characteristics of fluid inclusions in Upper Paleozoic reservoirs in Ordos basin and their geological significance

Feng Quao, Ma Shuopeng, Fan Aiping

2006, 27(1):  27-32.  doi:10.11743/ogg20060105

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Fluid inclusions in the Upper Paleozoic reservoirs in Ordos basin can be classified into 2 types, namely inherited (non-diagenetic) and non-inherited (diagenetic) inclusions, according to their genesis. Based on fluid composition, the latter can be further divided into 3 sub-types, including brine inclusion, CO₂ inclusion and hydrocarbon inclusion. Each inclusion type or sub-type has its own specific geological significance. The reservoirs show two kinds of fluorescence colors. The liquid hydrocarbons in the fluid inclusions show blue and bluish grey fluorescence colors, while the hydrocarbons in the cements show pale yellow and yellowish green fluorescence colors. The former represents the oil feature while it was charged, while the latter represents the results of oil destruction. PVT modeling of liquid hydrocarbon inclusions shows that hydrocarbons would have been charged at relatively high temperature (120℃) and relatively high fluid pressure (38.49 MPa), which are remarkably higher than the present temperature and pressure in the reservoirs, thus the hydrocarbon properties in the reservoirs have evidently been changed.

Analysis of hydrocarbon migration stages in the 8 th member of Yanchang Fm in Xifeng oilfield

Wu Minghui, Zhang Liuping, Luo Xiaorong, Mao Minglu, Yang Yang

2006, 27(1):  33-36.  doi:10.11743/ogg20060106

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In combination with the evolutionary process simulation of burial history and geothermal history of Xifeng oilfield in Ordos basin, microfluorometric technology and microscopic thermometry technology of inclusion have been applied in the study, which indicates that hydrocarbon migration in the study area has mainly occurred in two stages. The first migration stage occurred in the Middle and Late Jurassic, while the second migration stage occurred at the end of Early Cretaceous, which was a critical period of Mesozoic hydrocarbon migration and accmulation in Xifeng area, Ordos basin. The first and second stages of hydrocarbon migration correspond to the early diagenetic stage B and the late diagenetic stage A, respectively. Since the brine inclusions in the area have mainly been formed in quartz fractures, the preservation conditions of inclusions are relatively poor, leading to a certain interpretation ambiguity of the homogenization temperatures. The screening principle of applying thermometric data of fluid inclusions met in the fractures has, therefore, been made, which can be used as reference for the application of similar inclusions.

Characteristics of geotemperature-geopressure system in western Qaidam basin and their relationship with oil and gas distribution

Li Heyong, Liu Zhen, Dang Yuqi, Li Weilian, Liang Quansheng, Zhang Yongshu

2006, 27(1):  37-43.  doi:10.11743/ogg20060107

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Geothermal gradients range between 2.0℃ and 4.5℃ per hundred meters in western Qaidam basin, with an average value of 3.0℃ per hundred meters. Abnormally high pressure can occur at a depth of 2 300 m and over, and the pressure coefficient can be as high as 2.0. Laterally, the temperature-pressure systems in western Qaidam basin can be divided into 9 subareas such as HPHT, according to the formation pressure coefficients and the distribution intervals of the abnormal geotemperatures. Vertically, they can be divided into the upper static pressure type and the lower overpressure type. The upper and lower temperature-pressure systems have quite different fluid energies, thus hydrocarbons are highly capable of migrating vertically and are prone to accumulate around the boundaries of temperature-pressure systems. Laterally, oil and gas pools are basically distributed in the subareas with relatively low fluid energy; there are also oil and gas pools occurring in the sub-areas with high fluid energy, but most of them are primary oil and gas reservoirs with good sealing and preservation conditions, such as lithologic and structural-lithologic reservoirs. Characteristics of present temperature-pressure systems show that the deep temperature-pressure systems of high pressure type have good sealing conditions and contain most of the oil and gas reserves, thus they would be the main targets of future petroleum exploration.

A study of reservoiring pattern of Guantao Fm in Zhuang 106 wellblock in Laohekou oilfield

Tan Maojin, Yang Bangwei, Jia Li, Zou Dejiang

2006, 27(1):  44-47.  doi:10.11743/ogg20060108

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Sandbodies of Guantao Fm in Zhuang 106 wellblock in Laohekou oilfield are mainly of channel, bank, flood plain and abandoned channel subfacies. The channel sandbodies in the upper Guantao Fm deposited in meandering river environment are the main oil-bearing formations. Migration and accumulation of the Neocene hydrocarbons in the study area, surrounded by sags with rich source rocks, were controlled by faults. The large and small faults were connected into a network. Hydrocarbons alternatively migrated along the fault planes in vertical direction and along the reservoirs in lateral direction, forming a network-blanket migration and accumulation pattern. The rich source rocks, favorable migration and accumulation conditions, as well as good reservoir-cap rock combinations have led to the formation of subtle oil and gas reservoirs dominated by lithologic and lithologic-structural reservoirs. From south to north, the number of oil-bearing layers gradually increases, their depths enlarge and the oil-bearing properties get better.

Characteristics of overthrust structures on northern edge of East Qinling-Dabie orogenic belt and hydrocarbon potentials

Xie Dongning, He Mingxi, Zhou Lifa, Xie Qifeng

2006, 27(1):  48-55.  doi:10.11743/ogg20060109

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Overthrust structure on the northern edge of East Qinling-Dabie orogenic belt consists of the southern and the northern overthrust faults, which constitutes the structural link between the East Qinling-Dabie orogenic belt and the southern North China basin. The overthrust structure is characterized by segmentation along the strike and zonation in the dip direction, i. e. it can be divided into frontal zone, overthrust sheet zone and root zone in the dip direction, and into Yuxi, southern edge of Zhoukou and Huainan-Hefei 3 overthrust segments along the strike. The tectonic evolution can be divided into 3 stages, namely Indosinian collision orogenic stage, late Yanshanian intracontinental orogenic stage and the end of Yanshanian-early Himalayan strike slip extension stage. The preservation condition of source rocks varies greatly in different zones and segments and oil and gas shows are concentrated around the frontal zone. Therefore, the frontal thrust fault zone and the foredeep zone (basin/depression) can be evaluated as the most favorable areas for exploration, while the overthrust sheet zone (basin/depression) that lies between the southern and northern thrust fault zones would be relatively favorable for exploration.

Faulted structure and hydrocarbon accumulation in western Qaidam basin

Fang Xiang, Jiang Bo, Zhang Yongshu

2006, 27(1):  56-61.  doi:10.11743/ogg20060110

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Oil and gas reservoirs in western Qaidam basin are often associated with faulted structures. In the southern part of western Qaidam basin, several hydrocarbon accumulation zones are distributed along the faulted zones, such as Shaxi-Gas-Youshashan, Yuejin No. 2-Yuedong and Wunan-Lucaotan hydrocarbon accumulation zones. Structural-stratigraphic-lithologic composite oil and gas reservoirs controlled by faulted nose-like structures are distributed along Chaixi and other faults. in the foothill belt of the Altun Mountain in the west. Structural-fractured reservoirs, including Youquanzi, Kaitemilite, Nanyishan and Jiandingshan, are distributed along Yingbei, Nanyishan and Jiandingshan faults in the north. The formation of faults in western Qaidam basin has been related to the Meso-Cenozoic intense compressional and strike slip movements in Altun and Kunlun mountains. The faults are mainly of reverse and strike slip faults, with a few synsedimentary normal, decolle-ment and reversed faults. The fault trends include mainly NE, NW and nearly N-S. Horizontally, the faults appear as parallel, en echelon, oblique-crossing, orthogonal, reverse"S", lenticular and divergent fault complexes. Vertically, they are combined in the form of imbricated, thrusted and flower-like fault complexes. The structural reservoirs formed by the thrust type and orthogonal and oblique-crossing fault complexes are best developed. Faults have not only controlled the distribution of hydrocarbon-generating sags and the formation of structural traps, but have also controlled, to a certain extent, the distribution of favorable reservoir facies belts, such as river delta and fan delta facies. Large amount of fractures formed by faulting improve the poroperm characteristics of reservoirs. Laterally connected oil pools, in which hydrocarbons were generated in the source rocks above and migrated through faults and accumulated in the reservoirs below, are common in the southern part of western Oaidam basin.

Cretaceous-Cenozoic regional tectonic evolution in Jiuquan basin and petroleum exploration

Pan Liangyun, Xie Jielai, Li Mingjie, Zheng Menglin

2006, 27(1):  62-69.  doi:10.11743/ogg20060111

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Jiuquan basin, located on the western part of the northern edge of Qilian orogenic belt, is a petroliferous basin on the western end of the Corridor basin group. According to the changes of tectonic setting, formation and evolution of Qilian orogenic belt, stratigraphic distribution in the basin and characteristics of tectonic deformation, the Cretaceous-Cenozoic regional tectonic evolution in Jiuquan basin can be divided into 3 stages, i.e. the Early Cretaceous extensional rift-faulting stage, Late Cretaceous-Paleocene compressional uplifting stage, and Eocene-Oligocene downwarping and Neogene compressing stage. The Early Cretaceous extensional rift-faulting stage controlled the distribution of Lower Cretaceous source rocks and reservoir facies belts, and the salient areas would be favorable for the formation of buried-hill reservoirs. The Late Cretaceous-Paleocene com presso-uplifting led to the formation of reversed structural traps in the basin. The Eocene-Oligocene downwarping and Neogene compressing stage accelerated the maturation and evolution of the source rocks and led to the formation of many structural traps, it was also the major period for accumulation of hydrocarbons in the basin. The structural reservoirs in the piedmont thrust belt on the southern edge of the Cenozoic foreland basin and the structural-stratigraphic and lithologic reservoirs in the Early Cretaceous rifted basin would be the targets of further exploration in Jiuquan basin.

Tectonic evolution and extensional pattern of rifted basin:a case study of Dongpu depression

Su Hui, Qu Liping, Zhang Jinchuan, Wang Pingxia, He Feng, Wang Min, Wang Qi, Hu Yujie

2006, 27(1):  70-77.  doi:10.11743/ogg20060112

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Dongpu depression is a typical rifted basin in eastern China. The tectonic evolution of the basin includes an Early Paleozoic-Triassic cratonic basin cycle and a Cenozoic rift basin cycle. The latter can be subdivided into 4 stages, including initial rifting, intense rifting, late rifting and Late Tertiary integral downwar-ping. The basement extension in Dongpu depression increases, as a whole, from north to south. The extensional tectonic deformation is of simple shear extensional pattern in the upper earth crust, and of pure shear extensional pattern in the lower earth crust. The mutation zone of detachment surface might be the main factor causing the lateral tectonic transformation belt from Sangcunji to Qiaokou to Baimiao, and the difference of tectonic activity and the enrichment of oil and gas in the northern and southern parts of Dongpu depression.

Numerical simulation of palaeotectonic stress field of Yingcheng Fm in Gulong-Xujiaweizi area:prediction and comparative study of tectoclase development area

Wei Chunguang, Lei Maosheng, Wan Tianfeng, Jie Weiqiang

2006, 27(1):  78-84,105.  doi:10.11743/ogg20060113

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Fractured reservoir is one of the main oil and gas reservoirs in Gulong-Xujiaweizi area of Daqing oilfield, and Yingcheng Fm is the main deep gas target in this area. The tectonic event that has influenced the tec-tonization of Yingcheng Fm in this area is believed to have occurred after the deposition of the 1 st member of Qingshankou Fm during early Late Cretaceous. The tectonic differential stress value at this stage has been measured by using the quartz dislocation density method, and the tectonic stress field at this stage in the study area has been numerically simulated by using the elastic-plastic incremental method. The simulation shows that the maximum principal stress in the area was in NNE-SSW direction in early Late Cretaceous, and the tectonic stress values was characterized, as a whole, by nearly meridional and zonal distribution. The tectoclase development zones of Yingcheng Fm in Gulong-Xujiaweizi area are predicted to be located in the western part of Gulong area and the western and northern parts of Xujiaweizi area, and they would be the favorable oil and gas accumulation areas.

Ordovician-Silurian sedimentation and diagenesis in northeastern Tarim basin

Zheng Bing, Cheng Qiuquan, Gao Renxiang

2006, 27(1):  85-92.  doi:10.11743/ogg20060114

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The Ordovician is composed of silty mudstone and limestone, and the Silurian is a typical flysch formation composed of four depositional cycles of glutinite in the northeastern Tarim basin. The reservoirs occur at the bottom of each cycle. All of the 4 cycles have been inverted. Diagenesis is obvious at a depth of 1 500 m where sparry calcite (Ⅰ) has been precipitated from water rich in atmospheric CO₂ with δ¹³C in the range of -4‰ and -6‰, and 818O in the range of -5‰ and -6‰. At a burial depth of 2 400-2 600 m, δ¹³C and δ¹⁸O in the carbonate (Ⅱ) formed in the sulfate reduction zone are in the range -7‰ to -10‰ and -8‰ to -10‰, respectively, where the dissolution of feldspar constitutes the 1st secondary pore zone. Dolomites (Ⅲ) with wavy extinction have been formed at a burial depth of 3 800-4 000 m, along with the decarboxylation in the methane generating zone, the δ¹³C is in the range of -11‰ and -16‰, while in the carbonate directly formed from CO₂, the δ¹³C is ±20‰, and the δ¹⁸O both in dolomite and carbonate range from -12‰ to -13‰, temperatures measured from secondary SiO₂ inclusions are in the range of 110℃ and 120℃. This interval constitutes the 2nd secondary pore zone. The depth interval of 4 500-4 700 m is a wet gas generating zone, the δ¹³C and δ¹⁸O in carbonate (Ⅳ) formed in this interval are in the range of -27‰ to -31‰ and -13‰ to -14‰, respectively, and the temperature measured from inclusion thermometry is 130 -140℃; and the massive dissolution of ferroan calcite has resulted in the formation of the 3rd secondary pore zone. Large amount of dry gas (Ⅴ) were generated at a burial depth of over 5 000 m, where the 8 C ranges from -18‰ to -20‰ and δ¹⁸O ranges from -13‰% to -14‰, being accordant with the inclusion's homogenization temperature of 150-155℃. This interval constitutes the 4 th secondary pore zone with porosity in the range of 15% to 20%. The folded strata might have been inverted during Hercynian movement, uplifted and eroded about 5 000 m and associated with'retrodiagenesis'.

Depositional characteristics of fluxoturbidite and exploration technologies of subtle reservoirs in the Dongying sag

Yin Taiju, Zhang Changmin, Li Zhongchao

2006, 27(1):  93-98.  doi:10.11743/ogg20060115

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Fluxoturbidite is the product of redeposition of frontal sheet sand or river mouth bar sandbodies, which avalanche and slide when the external shearing force triggered by gravity and earthquake overcome the internal cohesive force. It is characterized by siltstone and fine sandstone with good sorting and relatively high tex-tural and compositional maturities. According to the areal development characteristics of turbidite, it can be basically divided into two types, namely non-channelized and channelized turbidites. The conventional sedimentary cycle correlation and high resolution sequence stratigraphic correlation technologies are not applicable in fluxoturbidite areas, due to their unique genesis. Well data and seismic data should be integrated to recognize large stratigraphic boundaries and marker beds and realize strata correlation step by step. Fluxoturbidite reservoirs are dominated by micropores and are of moderate to low porosity and low permeability reservoirs; the average porosity of single layer is generally below 23%, and the average permeability is less than 50×10^-3μm². Evaluation of fluxoturbidite reservoirs should be focused on the areal continuity, connectivity, thickness and oil-bearing properties of sandbodies. Fluxoturbidite reservoirs have been deposited in deep lake near the rich source rocks. Hydrocarbons would migrate vertically, laterally or along faults in short distance and accumulate in lithologic and lithologic-fault screened traps. Sedimentary microfacies analysis and seismic inversion are commonly used for reservoir prediction during exploration of fluxoturbidite reservoirs. Based on the results of reservoir prediction, 11 targets are presented for exploration of fluxoturbidite subtle reservoirs.

Preliminary study of the boundary of Kaijiang-Liangping trough in northern Sichuan basin and its characteristics

Wei Guoqi, Chen Gengsheng, Yang Wei, Yang Yu, Jia Dong, Zhang Lin, Xiao Ancheng, Chen Hanlin, Wu Shixiang, Jin Hui, Shen Juehong

2006, 27(1):  99-105.  doi:10.11743/ogg20060116

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Kaijiang-Liangping trough controls the distribution of platform edge oolitic shoal in the Feixianguan Fm in northern Sichuan basin. It is found from the seismic section that the eastern boundary to be a breakpoint, while the western boundary appears as an onlap point. In respect of sedimentary petrography, basin and slope facies are developed between the two boundaries mentioned above, which are represented by thin bedded marl and debris flow sediment, respectively. The earliest platform edge oolitic shoal deposit is located along Jiangyou-Zitong-Nanchong-Linshui-Dianjiang. The Feixianguan Fm is of basin facies on the western side of the trough with sediments of over 600 m thick and on the eastern side of the trough with sediments of over 500 m thick. Based on various evidences, the western boundary of the trough is basically determined to be approximately along Qinglin 1 well-Bailong 1 well-Si 1 well-Longhui 1 well, while its eastern boundary is a-long Tiandong 10 well-Chuanyue 83 well-Chuanfu 82 well. The trough is bounded by faults in the east, so the boundary location has only a little change in the course of the closing of the trough, while the western boundary is composed of slopes and the boundary location has gradually changed along with the closing of the trough. It is predicted that the area of platform edge oolitic shoal can be up to 3?10⁴km² in the northern Sichuan basin. On the west side of the trough, the platform edge oolitic shoal is mainly distributed in the area encircled by Jiangyou, Guangyuan, Liangping and Linshui; while on the east side of the trough, it is mainly distributed in Yunyang, Wanxian and Lianghekou (of Tongjiang).

Heterogeneity of non-marine reservoirs and its influences on recovery factor; take Gaoshangpu and Yonganzhen oil reservoirs in Jidong and shengli oilfields as examples

Yin Zhijun, Lu Guoyong, Zou Xiang, Yang Zhipeng

2006, 27(1):  106-110,117.  doi:10.11743/ogg20060117

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Reservoir heterogeneities mainly include interformational, intraformational and areal heterogeneities. The following understandings are achieved from study of the Gaoshangpu deep reservoir and other reservoirs in Jidong and Shengli oilfields. The interformational heterogeneity may result in monolayer breakthrough in the main sublayer, early watered out the main layer, low recovery percent in the non-major reservoirs and low oil displacement efficiency during waterflood development. The intraformational heterogeneity controls and affects the swept volume of the injectant in single sand layer, directly determines the waterflood efficiency, and is the key factor influencing the distribution of the remaining oil. The areal heterogeneity directly influences the swept area and sweep efficiency of the injected water, and thus controls the areal distribution of the remaining oil. Based on these understandings, several geological and developmental measures, including subdivision of layer series for development, separate zone water injection and detailed study of flow unit, are presented to effectively lower the influences of various heterogeneities on the ultimate recovery factor of oil reservoirs.

Study diagenetic reservoir facies of low permeability reservoir with genetic neural network; take Shahejie Fm in block 3 of Bonan oilfield as an example

Li Haiyan, Peng Shimi

2006, 27(1):  111-117.  doi:10.11743/ogg20060118

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Taking Shahejie Fm in block 3 of Bonan oilfield as an example, the pattern recognition method based on genetic artificial neural network is used to study the diagenetic reservoir facies of low permeability reservoirs. Based on study of the sedimentary facies and diagenesis of reservoirs, 7 parameters including flow zone index, porosity, permeability, median grain diameter, shale content, mean radius of pore throat and variation coefficient etc. are selected and neural network pattern recognition method is used to identify the diagenetic reservoir facies of Shahejie Fm in block 3 of Bonan oilfield through building learning and predicting models of genetic neural network. Four diagenetic reservoir facies are recognized, namely secondary pore diagenetic reservoir facies resulted from strong dissolution of unstable components (type Ⅰ), secondary pore diagenetic reservoir facies resulted from dissolution of carbonate cements (type Ⅱ), relic intergranular pore diagenetic reservoir facies after strong compaction and cementation (type Ⅲ), and tight diagenetic reservoir facies after extremely strong compaction and strong cementation (type Ⅳ). The reservoir properties of the type I reservoir facies are the best, while that of type Ⅳ are the worst and they are nonreservoirs or poor reservoirs.

Preliminary approach to the integrated exploration method of subtle reservoirs in non-marine basin and its application

Wu Dongsheng, Yang Shengu, Liu Shaohua

2006, 27(1):  118-123.  doi:10.11743/ogg20060119

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Integrated exploration of subtle reservoirs is a multidisciplinary research work under the framework of sequence stratigraphy with the information integration system as the platform, which can be performed in three stages, including basic data compilation, regional comprehensive evaluation and target prediction. In the basic data compilation stage, an information platform should be built to realize integrated management of multiple source data and achievements. The regional comprehensive evaluation should be carried out in the following steps, including the building of a regional isochronal sequence stratigraphic framework, study of the characteristics of sedimentary system and subtle traps, study of the reservoiring pattern of subtle reservoirs, and prediction and evaluation of the spatial distribution of subtle reservoirs, so as to illustrate the types, features, forming conditions and spatial distribution of the subtle reservoirs. Target prediction should be performed in steps including selection of the working area, high accuracy correlation of sequential framework, recognition and characterization of subtle traps and evaluation of oil/gas-bearing properties of subtle traps, so as to recognize and evaluate subtle reservoirs and finally determine the targets for exploration drilling. The information integration system can be developed on the basis of the COM GIS system and should have the functions of integrated management of petroleum exploration information and multidisciplinary data, comprehensive presentation and application of research achievements, as well as tapping mass data. Application of the integrated exploration methodology in the research of subtle reservoirs in Dainan Fm of Jinhu sag, Subei basin, shows that it is practical and effective.

Well test analytical model and pressure characteristics of multizone, non-isopachous and lateral heterogeneous composite gas reservoirs

Fu Weishu, He Shunli, Ran Yingzhi, Zhang Guangying

2006, 27(1):  124-130.  doi:10.11743/ogg20060110

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In view of the characteristics of uneven development of lithology and strong heterogeneity in Sulige low permeability gas reservoir of Changqing oilfield, a well test analytical model for multizone, non-isopachous and lateral heterogeneous composite gas reservoirs is established, which comprehensively takes into consideration the skin effect, wellbore storage effect, formation characteristics of gas reservoirs and variation of formation thickness. Laplace transformation is used to achieve the numerical solutions of reservoir pseudopressure under two typical outer boundary conditions, infinity and closed boundary, to plot the typical curve of bottom-hole pressure drawdown, and to analyze the pressure behavior characteristics. This model has been used to interpret the real well test data of Sulige gas reservoir, and the interpretation results are in good accordance with the actual production performance, indicating that it is practical for studying the characteristics of low permeability gas reservoirs.