Table of Content

25 December 2007, Volume 28 Issue 6

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Main factors controlling hydrocarbon accumulation of middle-and large-sized oil and gas fields and their distribution rules in the Tarim Basin

Cai Xiyuan

2007, 28(6):  693-702.  doi:10.11743/ogg20070601

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The formation and distribution of oil and gas pools in the Tarim Basin is complicated and controlled by many factors.The distribution of source rocks and their thermal evolution determines the plane distribution of oil and gas fields,while excellent regional seals and reservoir-cap rock combination control the vertical distribution of oil and gas.Large and stable inherited paleohighs and paleoslopes with long-term development history,and foreland thrust belts are considered to be the most favorable regions for the formation of middle and large oil and gas fields.The structural lithologic traps and low-amplitude structural traps control the Paleozoic-Mesozoic hydrocarbon accumulation.Multi-source and multi-stage dynamic accumulation-early reservoir modification and late charge adjustment dominate the hydrocarbon reservoiring in the Tarim Basin.The exploration of carbonate reservoirs shall be focused on compound traps such as the large hypergene karst and reef-bank facies with dissolution pores,as for clastic rock formations,the exploration shall aim at large Silurian stratigraphic overlap traps and structural lithologic traps.The Tabei uplift is the hope for improving reserves and production and all-round exploration of composite hydrocarbon reservoirs should be strengthened.Tazhong paleohigh,Hetianhe palaeouplift,Bachu uplift,Guchengqu paleohigh,and Manan faulted fold belt,shall be the potential areas for further discovery of oil and gas fields,and the superdeep layers and the Cambrian pre-sah dolomites are worthy of further prospecting and investigation.

Marine hydrocarbon enrichment rules and palaeouplift-controlling hydrocarbon theory for the Paleozoic Tarim craton basin

Zhao Jingzhou, Wang Qinghua, Shi Baohong, Qin Shengfei, Liu Hongjun, Yang Binyi, Cao Qing

2007, 28(6):  703-712.  doi:10.11743/ogg20070602

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The distribution of marine hydrocarbon reservoirs in the Paleozoic Tarim craton basin is very complex. The formation and distribution of large oil and gas fields are controlled by several factors including paleouplifts, effective source rock distribution and later tectonization.Among these factors,the palaeouplifts and their slopes are the most important because they have the most favorable combination of hydrocarbon accumulation conditions in the craton basin.The palaeouplifts in the Tarim craton basin can be divided into four types:inherited,residual,superimposed,and failed.The first two types,which are larger in scale and have long history of development, as well as their slopes,are the best for oil and gas enrichment.That oil and gas accumulation is controlled by palaeouplifs,hydrocarbon is enriched in the slopes,reservoiris in the high of uplifts are easy to be adjusted and destroyed and the slope areas are favorable to hydrocarbon enrichment and preservation,are the rules of the hydrocarbon accumulation and distribution in the Tarim craton basin.The muhiphase of accumulation and muhistage tectonic adjustment are the important characteristics of the marine hydrocarbon accumulation in the Tarim craton basin.The Late Caledonian and the Early Hercynian were the main periods for the formation of primary oil reservoirs in craton areas.The Late Hercynian was both the main period for the formation of primary gas reservoirs and the important period for the adjustment of earlier-formed reservoirs to secondary hydrocarbon pools.The Yanshan and the Himalayan periods were the main periods of adjustment,finalization and destruction of earlyformed hydrocarbon reservoirs.It was therefore concluded that the theory of late stage hydrocarbon accumulation was not applicable to the multicyclic marine Tarim craton basin.Consequently,the inherited and residual palaeouplifts and their slopes were considered to be the most favorable regions for the discovery of giant oil and gas fields in the Paleozoic craton basin.Base on these understandings,a palaeouplifts-controlling hydrocarbon theory was put forward and discussed.

Research on the characteristics of marine hydrocarbon evolution and accumulation in China

Zhang Kang

2007, 28(6):  713-720.  doi:10.11743/ogg20070603

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Marine hydrocarbon accumulation and evolution in China is characterized by old age and frequent modification,especially by tectonic movements in the later period.Strong heterogeneity is one of the features of marine reservoirs in China.The reservoir spaces of carbonates are dominated by pores,fractures and vugs formed or enhanced by karstification.The existence of favorable primary pores and vugs is one of the conditions for karstifieation.According to the degree of karst development,the karst reservoirs can be divided into four types, including Naxi,Tahe,Renqiu,and Puguang.Hydrocarbon generation and accumulation occurs in multistage and is influenced especially by the neotectonic movement.Several source rocks of different types and of different horizons may have contributed to the reservoirs.Consequently,source control theory,to a certain degree,is not applicable to these reservoirs.It is recommended to divide these reservoirs into primary,quasi-primary,and secondary reservoirs according to the relationship between hydrocarbon reservoirs and source rocks.The preservation conditions are critical to commercial hydrocarbon accumulations.Marine hydrocarbon exploration shall stress the importance of basic studies on petroleum geology and focus on areas with favorable preservation conditions,so as to provide information for exploiting deeper strata under ductile beds.Oil and gas exploration and development shall be carried out simultaneously and more attention shall be given to gas.

Comparison and evaluation of main factors controlling hydrocarbon accumulation in the Shaya,the Katake and the Bachu Uplift,the Tarim Basin

Li Tiejun, Yan Xiangbin

2007, 28(6):  721-730.  doi:10.11743/ogg20070604

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As the major exploration targets in the Tarim Basin,three uplifts,namely,the Shaya,the Katake and the Bachu Uplift,contained an accumulative proven geologic reserves which account for 66.78 % of the basin's total by the end of 2006.However,they varied greatly in the scale of their proven geologic reserves-a phenomenon caused by differences in effective source rocks,development and distribution of high-quality reservoirs,and tectonic evolution history(especially late tectonic activities).Comparative analysis on main factors controlling hydrocarbon accumulation in these uplifts revealed that the Shaya Uplift had the best condition for hydrocarbon accumulation,the Katake Uplift had a less favorable accumulation environment,and the Bachu Uplift had the worst.

Lithofacies paleogeographical characteristics and reef-shoal distribution during the Ordovician in the Tarim Basin

Zhang Lijuan, Li Yong, Zhou Chenggang, Li Meng, Han Jie, Zhang Bo

2007, 28(6):  731-737.  doi:10.11743/ogg20070605

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The Ordovician is the key period of tectonic movement and depositional evolution in the Tarim basin and its peripheral area.From the Early to Middle Ordovician,the sea level begun to rise slowly and the Tarim basin basically inherited the Late Cambrian sedimentary settings.In the early Late Ordovician,the regional tectonic movement converted from extension to compression,the peripheral area of the basin(mainly to its south) kept uplifting,and the differentiation of topography was enhanced in the platform.In Ordovician,Tarim basin developed two types of platform marginal facies and the paleoclimatic conditions were favorable for reef development.The marginal facies on the steep slop of platform was relatively narrow,the reef-bank complex was large in thickness and good in continuity in direction parallel with the platform margin and the high energy facies belt was located on the outer margin,with Tazhong I slope break zone as a typical example.In contrast,the marginal facies on the gentle slope of platform was relatively wide,the reef complex is relatively small in thickness,composed of small reefs and distributed in Lunnan,the edge of Bachu uplift and Hetian area.Platform marginal reefbanks,intraplateform banks and karst unconformities are main targets of exploration.

Distribution of marginal facies and main controlling factors of reservoirs in the Ordovician,the Tarim Basin

Zhao Zongju, Zhou Xinyuan, Wang Zhaoming, Shen Anjiang

2007, 28(6):  738-744.  doi:10.11743/ogg20070606

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Through research on the Ordovician sequence stratigraphy,sedimentary facies and carbonate reservoirs in Tarim basin,this paper discusses the distribution of platform marginal facies and main controlling factors of reservoirs in the Ordovician.Four stages of platform marginal high-energy facies belts are identified,including the Penglaiba Formation of the lower Lower Ordovician,the Yinshan Formation of the upper Lower Ordovician to the lower Middle Ordovician,the Yijianfang Formation of the middle to upper part of the Middle Ordovician,and the Lianglitage Formation of the middle Upper Ordovician.The main factors controlling the effective formation of carbonate reservoirs in these marginal facies are that the high-energy bank facies grainstone serves as the main material basis for the effective formation of reservoirs,followed by the barrier reefs and micrite mounds;the fresh water dissolution,mixed-water dolomitization and mixed-water dissolution,caused by contemporaneous exposure of marginal carbonate due to Milankovitch or the third-rank sea level dropping,are the chief constructive diagenesis for the formation of effective reservoirs;secondary vugs and cavities were generated by the karstification of the Ordovician marginal carbonate during the Silurian and the Devonian;and the organic acid dissolution and magma hydrothermal fluid dissolution during deep burial of the Permian and the open fault-fracture system parallel or small-angle obique to the major compressional stress are constructive for forming effective reservoirs in the Ordovician marginal carbonate.

A discussion on main factors controlling deep carbonate reservoirs in the Tarim Basin

Zhang Tao, Yan Xiangbin

2007, 28(6):  745-754.  doi:10.11743/ogg20070607

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The carbonate reservoirs in the Tarim basin are characterized by old age,deep burial,various types and complex genesis.Through analyzing the characteristics and genetic mechanisms of karst reservoirs,reef-bank reservoirs,dolomite reservoirs and fractured reservoirs,this paper discusses the main factors controlling reservoir heterogeneities.It concludes that favorable sedimentary facies was the material base for forming excellent reservoirs,sequence boundaries controlled the early formation of pores,paleouplifts and tectonic movements determined the development and preservation of the karst and reef-bank reservoirs,and later modification by burial and denudation was critical to the formation of quality reservoirs.On the basis of controlling factor analysis,the paper further suggests that the karst reservoirs were mainly controlled by tectonic uplifting,palaeo-geomorphology and palaeo-drainage system,the reef-bank reservoirs were controlled by the edge high energy facies on platform edge,the dolomite reservoirs mainly developed under the unconformity,and the fracture reservoirs were the products of multiphase tectonic movements.Combining with macro geological background,the fractured karst reservoirs,reef-bank reservoirs,and inner dolomite reservoirs are recognized as favorable exploration targets in Tarim basin.

Segmentation characteristics and dynamic mechanism of the Che'erchen Fault in the Southeast Tarim Basin

Wang Buqing, Wang Qinghua, Han Lijun, Han Jie, Wang Ligang

2007, 28(6):  755-761.  doi:10.11743/ogg20070608

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The deep and large-scale Che'erchen Fault has been active since the end of the Early Paleozoic. However,it wasn't until the end of the Mesozoic that the Altun Fault,the West Kunlun Fault,and the Che'erchen Fault,were combined as one whole system.According to the geometric and dynamic characteristics of the fault,the Che'erchen can be divided into two segments from west to east:the western segment and the eastern segment.The former with its well-developed branches has experienced several intense tectonic activities since the end of the Early Paleozoic,while the latter was active before the Mesozoic but less active after the Mesozoic.The long-distance stress resulted from collision between the Indian Plate and the Eurasian Plate had controlled the structural deformation of the Che'erchen Fault since the Mesozoic.During the Mesozoic and the Cenozoic,faulting in the western segment of the Che'erchen Fault was rather strong due to the structural stresses of both the Altun Fault and the West Kunlun Fault;while faulting in the eastern segment of the fault was less intensive because the compressive stress from the Ahun Fault was offset by the rising of the Altun Mountain and the piedmont tectonization of the Ahun Mountain.

Characteristics of the Ordovician buried hill reservoirs in Tahe-Lunnan oil area

Pang Wen, Jiang Tongwen, Zheng Junmao, Shi Hongxiang

2007, 28(6):  762-767.  doi:10.11743/ogg20070609

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The Ordovician in Tahe-Lunnan oil area contains buried hill type reservoirs developed during the Paleozoie and finalized in the Mesozoic.Multi-stage tectonic uplift and denudation resulted in well-developed buried hill and karst,forming fracture-vug systems that constitute the Ordovician reservoirs.Weathering crust karstification mainly happened in the west and central areas of Tahe-Lunnan oil area,while deep karstification mainly occurred in the east in the whole Ordovician.Oil occurs in buried hill but only enriches locally to form oil pool, and the distribution of oil and gas is controlled by the development of reservoirs.Multiple stages of oil generation,migration,accumulation,and tectonic adjustment in this oil area caused the Ordovician reservoir characteristics varying with different structural zones:the west part of the area contains heavy oil reservoirs,the west of the central slop hold oil of normal density,Sang-ta-mu fault horst,the south slop of Sang-ta-mu,and the east of Lunnan fault horst,harbor condensate gas reservoirs with oil rim,and the east slope has condensate gas reservoirs.Hanging hydrocarbon reservoir with an inclined oil-water contact was also formed due to the skylight effect at the buried hill top.

Hydrocarbon accumulation conditions and enrichment rules in Tahe oilfield

Yun Lu, Jiang Huashan

2007, 28(6):  768-775.  doi:10.11743/ogg20070610

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The Tahe oilfiled is located at the Arkekula salient of the Shaya uplift in the northern Tarim Basin.Its main body is the large scale unconformity-fractured-vuggy reservoir in the Ordovician carbonate.It is superposed by the Carboniferous and Triassic low amplitude anticlinal,lithologic and composite traps,which form secondary reservoirs through connection by faults and unconformities,and show vertically the characteristics of composite play.The Tahe oilfield occurs at the slope of paleo-craton basin and on the edge of large hydrocarbon kitchen. The rich resource rock is the material bases for the formation of large oilfield;the large nose shaped salient with long-term development controls hydrocarbon migration and accumulation;the multi-stage unconformities are effective pathways for lateral hydrocarbon migration;the faulting,fracturing and karstification form the network reservoir consisting of pore,fracture,rug;the favorable reservoir-seal assemblages are important conditions for forming large oilfield.The present complicated hydrocarbon accumulations are caused by long term hydrocarbon generation,multi-stage tectonic movements and multi-phase hydrocarbon charging.

Characteristics and main controlling factors of the Ordovician carbonate rock reservoirs in Lugudong area,the Tarim Basin

Hu Jianfeng, Cai Zhenzhong, Ma Qing, Li Jianjun, Huang Longcang, Li Baohua

2007, 28(6):  776-783.  doi:10.11743/ogg20070611

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The Ordovician carbonate reef-bank complex reservoirs in the Lungudong area of the Tarim Basin are the important exploration targets in the recent development scheme of Tarim Oilfield Company.The reservoir rocks mainly include sparry grainstone,fine-granular grainstone,mieritic grainstone,and micrite,among which the sparry grainstone has much better poroperm characteristics.Matrix porosity of these reservoirs are low with dissolution vugs and fractures as the main pore space.The reservoirs can be divided into the following four types :cavity,vug,fracture,and fracture-vugg,whose development was dominated by sedimentary facies,solution, and fracturing.The Ordovieian carbonate reef-bank reservoirs in the Lungudong area are characterized by extensive,superimposed and continuous distribution.

Characteristics and patterns of complex hydrocarbon accumulation in the Lower Paleozoic carbonate rocks of the Tazhong Palaeouplift

Yang Haijun, Han Jianfa, Chen Lixin, Wu Guanghui, Ji Yungang

2007, 28(6):  784-790.  doi:10.11743/ogg20070612

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Based on the analysis of the typical oil and gas pools in the Lower Paleozoic carbonate rocks of the Tazhong Palaeouplift and by using geochemical analytical methods,that the Cambrian was the major source rock contributing to the marine carbonate reservoirs in Tazhong area and the natural gas in the Lower Paleozoic reservoirs was mainly cracked gases from fossil oil reservoirs were clarified.The marine carbonate reservoirs in the Tazhong palaeouplift was characterized by complex hydrocarbon accumulation features as generated in lower zones and preserved in upper zones,multiple reservoir-cap rock assemblages and multi-stage hydrocarbon accumulation.The complex hydrocarbon accumulation pattern was also established for the marine carbonate reservoirs in the Tazhong Palaeouplift,and three potential exploration targets,namely reef-bank complex,karst unconformity and inner dolomite,were nailed down in the Lower Paleozoic of the Tazhong palaeouplift.

Hydrocarbon migration and exploration potential in the unconformities at the top of the Middle-Lower Ordovician in the central uplift belt,the Tarim Basin

Zhou Bo, Wang Yi, Luo Xiaorong, Yun Jinbiao, Zheng Menglin

2007, 28(6):  791-796.  doi:10.11743/ogg20070613

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Taking the top of the Middle-Lower Ordovician unconformity as the target,the source rocks in the Middle-Lower Cambrian and the Middle-Lower Ordovician were selected for their oil and gas contributions to establish hydrocarbon migration patterns.As the Middle-Lower Cambrian source rock is far from the top of the Middle-Lower Ordovician unconformity vertically,most of the hydrocarbons migrated vertically and distributed along the faults.While for the Middle-Lower Ordovician source rock,the invasion-percolation theoretical model was applied to characterize its contribution to the top of the Middle-Lower Ordovician unconformity and revealed that the hydrocarbon migration there is mainly lateral.Based on a comprehensive analysis of contributions of these two sets of source rocks,the Tazhong area is considered to be a favorable area for the hydrocarbon exploration.

Characteristics and main controlling factors of the Upper Ordovician reef-bank reservoir development in the Tazhong I slope-break zone

Wang Zhaoming, Zhao Kuanzhi, Wu Guanghui, Zhang Lijuan, Wang Zhenyu, Luo Chunshu, Li Xinsheng

2007, 28(6):  797-801.  doi:10.11743/ogg20070614

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The huge reef-bank complexes developed in the Upper Ordovician along the Tazhong Ⅰ slope-break zone feature in large areas of shoals and small size of reefs,and vertical multistage accretion and overriding of multicycle reef-bank and lateral connection as a whole.Static and dynamic data indicate low matrix porosity of the complex,suggesting a reservoir with super low permeability.The reef-bank complex also developed cavityfracture reservoirs,cavern reservoirs and cavity reservoirs.The secondary dissolution cavities and structural fractures are the most effective reservoir and flow space.The researches show that the favorable sedimentary facies belt is the foundation for the formation of reef-bank reservoirs,high-quality reservoirs mainly distribute along the reef-bank facies belt on the edge of platform,karstification and tectonism are essential for improving the poroperm characteristics of the ancient carbonate reservoirs,and the large fracture-rug systems formed by these factors contribute most to the high and stable production of oil and gas.

Geochemical behaviors of the Ordovician formation water in the Tazhong area and its origin and evolution

Li Pengchun, Liu Chunxiao, Zhang Yuan, Long Liping, Zhang Lihong

2007, 28(6):  802-808.  doi:10.11743/ogg20070615

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Chemical compositions of the Ordovician formation water in Tazhong area are dominated by cations as K⁺ + Na⁺ and anions like Cl^-.The water is mostly of CaCl₂ type with salinity ranging from 4.8 to 220.2 g/L and r_Na+/r_CI- ratio varing between 0.26 and 0.85,suggesting a small change of water property and a possible origin from mixing of fresh water with sea water after evaporation and inspissation.Influenced by fracturing effect, the plane distribution of formation water salinity is characterized by obvious regionalization ;while affected by regional unconformities,the vertical distribution of ion concentration and salinity is featured in zonation.The relationship between cation concentration of Cl^- and HCO₃^- and anion concentration of Na⁺ + K⁺ and Ca²⁺ indicated that the likely diagenesis process in the study area was mainly dissolutions of NaC1 and carbonate,and that the dolomitization(ferrodolomite)and albitization of calcite resulted in excess of Ca²⁺ and deficit of Mg²⁺, forming CaCl₂-type fluid.Formation water in the area can be classified into two groups:normal-pressure high-salinity water and abnormal high-pressure low-salinity water.The former may be related the leaching of atmospheric water and to the water-rock interaction during burial,while the latter may be connected with the closed system formed by the type of water itself.The area between TZ-Ⅰ slope break and TZ-Ⅱ structural zone is considered to have favorable conditions for accumulation and preserving of hydrocarbons.

Analysis on paleohydrodynamic force and gas accumulation characteristics in the Kuqa Depression,the Tarim Basin

Wang Zhenliang

2007, 28(6):  809-815.  doi:10.11743/ogg20070616

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Analysis of the causes of overpressure in the Kuqa depression reveals that there are two types of overpressure:the depositional overpressure and the tectonic compressive overpressure.Constrained by such direct evidences as measured pressure,forming pressure of fluid inclusions,and palaeo-pressure during the epoch with the maximal burial depth,the depositional overpressure in different geologic periods are reconstructed in accordance with the mathematical model of fluid pressure evolution.On the basis of mechanism of structural compaction,the amplitude of tectonic overpressure in the Himalaya period is evaluated.The evolution history of fluid pressure in target strata is obtained and the development of gas pressure potential is restored by combining these two kinds of overpressures.The impact of hydrodynamic force upon gas migration and pooling is also studied.The results show that the target was under depositional overpressure before the deposition of Kuche Formation,and since then went through the decline of depositional overpressure and rising of tectonic overpressure.Three modes of gas migration including continuous charging,early charging with later standstill and early charging with early standstill are recognized based on analyses of the pressure relationship between the Jurassic source rock and the lower Cretaceous reservoir rock.Gas pressure potential gradients in different geologic periods show that the lateral migration and accumulation was most active after the deposition of Kuche Formation.The major cause of the late accumulation of gas was the intensifications of gas migration and accumulation by tectonic movement since the Quaternery period.

Structural features and natural gas exploration in the Kelasu structural belt,Kuqa Depression

Lei Ganglin, Xie Huiwen, Zhang Jingzhou, Wang Yueran, Huang Shaoying, Ye Maolin, Zhang Guowei

2007, 28(6):  816-820,835.  doi:10.11743/ogg20070617

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The Kelasu structural belt of the Kuqa Depression has favorable geologic conditions for hydrocarbon accumulation.Its structural development and evolution are controlled by regional thrust faults.It is characterized by apparent zonation from south to north,segmentation from east to west and vertical layering.Four structural zones from south to north and five segments from west to east were identified according to different regional faults and structural styles.Faults controlled structure development and their differences,while three factors,namely palaeotectonic setting,detachment layer,and intensity of compressive stress,exerted influence upon the characteristics of the faults,forming different pooling and preserving conditions.The belt is an ideal prospective area for gas exploration because of its well-developed reservoirs,relatively thick salt beds,and location far away from multi-stage activating faults.Dabei and Keshen areas are more practical targets for gas exploration.

Controlling effects of palaeouplifts and dual overpressure systems on gas accumulation in the Kuqa foreland basin

Sun Dongsheng, Jin Zhijun, LÜ Xiuxiang, Yang Minghui

2007, 28(6):  821-827,855.  doi:10.11743/ogg20070618

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Six palaeouplifts of the Yanshan period and one anticline of low amplitude at the end of the Paleogene were identified in the Kuqa foreland basin according to strata contact relations,sedimentary characteristics,and seismic reflectance signatures.This paper concludes that the palaeouplifts at the end of the Yanshan period controlled oil accumulation,the anticline of low amplitude at the end of the Paleogene controlled gas accumulation, and the thrust anticline trap at the end of the Neogene was rich of gas.The conclusion suggests that palaeouplifts of foreland basin had a similar controlling effect on hydrocarbon distribution as that of palaeouplifts in craton basin.Two vertical overpressure systems were identified in the Kuqa foreland basin.The deep overpressure system was caused by the generation of a large amount of hydrocarbons under conditions of fast burial,while the shallow overpressure system was the result of a late lateral tectonic compression.A large amount of earlier-generated gas were accumulated in the palaeouplifts,leading to the formation of the deep overpressure systems.The palaeouplifts determined the location of the Neogene thrust anticline and thus the distribution of present gas reservoirs.

Seismic response characteristics and prediction of carbonate rock fractured-vuggy systems in the Tarim Basin

Yan Xiangbin, Guan Luping, Wang Shixing

2007, 28(6):  828-835.  doi:10.11743/ogg20070619

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The fractured-vuggy system of the Ordovician carbonate in Tarim Basin is defined as network-like reservoirs composed of effective fractures and vugs formed by multistage and multicycle of dissolutions,diagenesis, and fracturing.Generally,the scale and extension of fractured-vuggy system is critical to hydrocarbon accumulation in the Ordovician and stable and high production from Ordovician reservoirs.The present seismic technologies are still insufficient in detecting and distinguishing single small fractures or rugs.However,larger fracturedvuggy system consisted of many fractures and vuggies can be effectively detected and predicted,especially with the help of seismic wave dynamic parameters,which are much reliable than kinematics parameters.The detection of fractured-vuggy system can be achieved through integration of the following techniques:coherence analysis, amplitude attributes,multi-scale fracture detection,frequency difference analysis(FDA),and wave impendence inversion.However,fractured-vuggy systems of different origins and sizes in different areas require different combinations of these techniques and methods.

Forward modelling and seismic wave field characteristics of fractured-vuggy reservoirs in the southern part of Tahe oilfield

Huang Xubao, Gu Hanming

2007, 28(6):  836-840.  doi:10.11743/ogg20070620

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The characteristics of seismic response from the heterogeneous Ordovician fractured-vuggy carbonate reservoirs in Tahe oilfield are complicated.However,the forward modelling technique can be used to simulate the characteristics of seismic wave propagating through this kind of reservoirs and provide a theoretical principle for fractured-vuggy reservoir prediction.With drilling data from the southern part of Tahe oilfield,different random cavity-medium models were established through threshold truncation and continuous random perturbation modes. Seismic well-tie sections were also used in the construction of the seismic-geologic model that works better in simulating the real karst fractured-vuggy carbonate reservoirs.Pseudo zero offset section and stacked migration section were obtained through forward modelling of seismic wave field in heterogeneous medium.On these bases, the seismic response characteristics of fractured-vuggy carbonate reservoirs were summarized.

Comprehensive fracture prediction technologies and their application to carbonate rocks in Tazhong area

Gong Honglin, Pan Jianguo, Wang Hongbin, Wang Zhenqing, Li Chuang, Li Luming

2007, 28(6):  841-846.  doi:10.11743/ogg20070621

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Fractures of carbonate reservoirs are complex in Tazhong area and are critical to the poroperm characteristics of the reservoirs,hydrocarbon migration and accumulation,and productivity of wells.Taking into consideration the characteristics of fractures in the Ordovician carbonates in the Tazhong area,this paper presents three fracture prediction technologies,including coherence processing,strain analysis,and numerical simulation. High coherence facies indicates dense formation and low coherence facies may mean the existence of karst cavities or fractures,while extreme low coherence facies reflects faults of different grades.Strain analysis predicts the density of fractures caused by multi-phase tectonic movements,through drilling calibration and taking into consideration the parameters such as strata thickness,lithology,and fracture orientation.Constrained by strain magnitude,curvature,and other seismic attributes,the numerical simulation determines plane distribution and development of fractures through probabilistic simulation.According to the cutting relationship,filling components and filling orders of fractures observed in core samples,this paper predicted the fractured zones in the Ordovician carbonate reservoirs in Tazhong 16 -Tazhong 30 wellbloek by combining logging data,fracture prediction results of the foregoing three technologies,and analysis of regional tectonic stress field.The prediction results are consistent with the statistics of fracture parameters of the cores taken from the Ordovician carbonate reservoirs in the field,showing that these technologies are practical and effective in predicting fractured zones in carbonates.

Research on the fracture-vug unit division of fractured-vuggy carbonate rock oil pools—an example from the Ordovician oil pools in the principle producing area of Tahe oilfield

Chen Zhihai, Ma Xujie, Huang Guangtao

2007, 28(6):  847-855.  doi:10.11743/ogg20070622

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Fractured-vuggy reservoirs originated from the development of paleo-karst fractured-vuggy system are the basic geological units for hydrocarbon accumulations of fractured-vuggy type.Importance should be attached to the connectivity within a fractured-vuggy reservoir and that among different fractured-vuggy reservoirs during the development of this kind of reservoirs,i.e.fractured-vuggy units are the basic development units of fracturedvuggy pools.However,both domestic and overseas literatures failed to offer a clear definition for fractured-vuggy reservoir and fractured-vuggy unit and the research on fractured-vuggy unit division still needs to be carried on. Taking the Ordovician fractured-vuggy pool in Tahe oilfield as an example,this paper presents basic concept and distribution mode for fractured-vuggy units and proposes principles and methods for their division.After the study on fractured-vuggy reservoir distribution,fluid properties and well productivity and inter-well connectivity in Tahe oilfield,the paper defines fifteen fracture-vug units in the principle producing area of the field,providing useful references for further development adjustment and management of the field.

A discussion on development strategies for the Ordovician fractured-vuggy carbonate rock reservoirs in Tahe oilfield

Li Zongyu

2007, 28(6):  856-862.  doi:10.11743/ogg20070623

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The Ordovician reservoir in Tahe oilfield is a typical fractured-vuggy carbonate reservoir.Both production performance and correlation studies show that conduit flow and seepage flow coexist in the reservoir.Caverns and associated fracture zones serve as flow and storage space for these reservoirs.The flow regime is characterized by typical conduit flow in the caverns and by seepage flow in minute fissure-pores.Based on flow regime and production characteristics,this paper,supported by fractured-vuggy reservoir model,studies the dynamic characteristics,production performances,water breakthrough,production decline and waterflooding under conduit flow and seepage flow conditions.It also discusses optimal production rate,productivity,and well pattern,and presents technical solutions of coning prevention,water plugging,and waterflooding for developing fractured-vuggy reservoirs.They can serve as guidance in the development and comprehensive management of the Ordovician reservoirs in Tahe oilfield.