Oil & Gas Geology-2004, Volume 25 Issue 3

Methodology of studying coupling and decoupling of "basin" and "range"

Wu Genyao, Ma Li

2004, 25(3): 239-246. doi:10.11743/ogg20040301

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Coupling and decoupling of "basin" and "range" is to study the uniform kinematic process and geodynamic mechanism of orogeny and basin development through viewing the two as a whole.It must be guaranteed by corresponding methodology.Three topics are discussed in this paper.(1)The "basin" and "range" system should be defined correctly on the basis of determining a certain time interval;(2)Two sets of classification systems should be used concurrently.Theoretical classification system is mainly used in "normal sequence" study and regional study,while practical classification system is mainly used in "reverse sequence" study and local(mainly refer to oil and gas reservoirs)study.(3)Thoughts,methods and technical means should be integrated together based on the successful study methods of orogenic belt and basin development in recent years.Coupling and decoupling of "basin" and "range" study,including its methodology,may provide new theoretical guidance for petroleum exploration in-mainland China.

Factors affecting generation of organic-origin petroleum:development of simulating experimental study

Chen Jinyang, Zhang Hong, Xiao Wansheng, Weng Kenan, Zheng Haifei, Zeng Yishan

2004, 25(3): 247-252. doi:10.11743/ogg20040302

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Petroleum resources in the earth have been formed mainly through pyrolysis of organic matters in deeper part of the earth.In recent years, many understandings of the mechanism have been achieved through simulating experiments.Types of organic matters,temperature,pressure,catalysis and aqueous medium all have influences on the properties of hydrocarbons generated.Increase of pressure can impede or delay thermal evolution and pyrolysis of organic maters;water is the source of hydrogen and oxygen for pyrolysis reaction;and catalysis can not only change components of reaction products, but also influence the reaction mechanism.Kinetics is also an important factor influencing pyrolysis of organic matters,which provides a new way to identify various source rocks.In the future,attentions should be paid to the study of characteristics of pyrolysis of organic matters under higher pressure condition,and the development and application of field experimental apparatus.

Restudy of pool-forming pattern of Liangjialou oilfield in Dongying sag

Zhang Linye, Liu Qing, Zhang Chunrong, Kong Xiangxing, Zhu Rifang

2004, 25(3): 253-257. doi:10.11743/ogg20040303

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Liangjialou oilfield in Dongying sag,Bohai Bay basin,was previously thought to be an"indigenously generating and accumulating"oil reservoir,i.e.hydrocarbons generated in the mudstones in the middle 3^rd member of Shahejie Formation have migrated upward into the adjacent turbidite glutinite.This view,however,is not supported by the latest achievements in hydrocarbon source rock studies in Dongying sag.Oil-to-source correlation,hydrochemical characteristics of oil reservoir and reservoir pressure show that oil reservoirs in southern Liangjialou oilfield,mostly characterized by superpressure and chloride-calcium type water,have been sourced by the upper 4^th member of Shahejie Formation,i.e.hydrocarbons have firstly migrated laterally along the pathways in the rocks,and then migrated vertically upward through faults and become oil reservoirs either of "both generated and accumulated indigenously"or"generated below and accumulated above";while those in middle and northern Liangjialou oilfield,characterized by normal pressure and sodium bicarbonate water,hydrocarbons have been generated in the lower 3^rd member of Shahejie Formation, and then directly migrated vertically through faults in the source rock,so the oil reservoirs are of the type of "generated below and accumulated above". The knowledge enlightened us to reevaluate the source rocks in the middle 3^rd member of Shahejie Formation and restudy the pool-forming patterns in the similar pools around the center of the sag.

Deposition and genetic analysis of Carboniferous Kalashayi Formation in Tahe oilfield

He Faqi, Zhai Xiaoxian, Yu Renlian, Pu Renhai

2004, 25(3): 258-262. doi:10.11743/ogg20040304

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Sedimentary characteristics and genesis of the Carboniferous Kalashayi Formation sand-shale sequence in Tahe oilfield are analyzed through integrating palaeontological,log,core,seismic and geochemical data.Overall,the sandstones in Kalashayi Formation are of progradational sedimentary sequence that get coarser and thicker upwards.The upper Ⅰ-Ⅲ oil reservoir groups are mainly of fluvial facies,while the lower Ⅳ-Ⅴ oil reservoir groups are of tide-effected fan delta front facies and plain facies.The evidences of tidal influences include:(1)rich in charophyta fossils with individual brackish Ostracoda and Acritarch microfossils;(2)local wavy,lenticular,bioturbate and scour-and-fill beddings;(3)a strontium/barium ratio ranging between 0.021 and 0.716,suggesting an environment from brackish to fresh water;(4)the Ⅳ-Ⅴ oil reservoir groups,as a whole,are the transition facies from tidal flat "double peak limestone" in the Bachu Formation to fluvial deposition of Ⅰ-Ⅲ reservoir groups.

Two types of Cambrian source rocks and related petroleum systems in Tarim basin

Yang Wei, Wei Guoqi, Wang Qinghua, Xiao Zhongyao

2004, 25(3): 263-267. doi:10.11743/ogg20040305

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Cambrian source rocks,including mud shales and carbonates,are among the main source rocks in Tarim basin.The mud shales,developed in an under-compensation environment,are mainly distributed in the eastern part of the basin and have an average TOC of 1.87% and an effective thickness ranging from 120m to 415m;while the carbonates,developed in an intra-platform evaporative lagoonal environment,are mainly distributed in the western part of the basin and have an average TOC of 0.42% and an effective thickness between 288m and 324m.The two types of source rocks gave rise to different petroleum systems.The hydrocarbon generating center of the petroleum system with basin facies mud shales to be the source rocks,was located in Manjiaer sag,and the reservoirs are mainly Cambrian-Ordovician carbonates and Silurian,Carboniferous,Triassic and Jurassic sandstones;while that of the petroleum system with the platform facies carbonates to be the source rocks might be located in Bachu high and the surrounding area,and the reservoirs are mainly Lower Ordovician and Carboniferous.

Thermal evolution history and hydrocarbon generation in superimposed basin:taking the southern structural zone in Turpan-Hami basin, Xinjiang, as an example

Feng Qiao, Liu Yiqun, Zhang Xiaoli, Zhou Lifa, Hao Jianrong

2004, 25(3): 268-273,293. doi:10.11743/ogg20040306

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Several sets of source rocks have developed and experienced multistage thermal evolution in Turpan-Hami basin, a superimposed basin, as a result of long-term basin evolution and multiphase tectonic activity, thus hydrocarbon-generating history is very complicated. Study of the basin's southern structural belt indicates that this area has experienced multiphase tectonic movements and modifications since Late Paleozoic. Structural thermal system and thermal evolution can be divided into five stages, including an extensional rift stage with rapid burial and super-high temperature gradient from Carboniferous to Early Permian; a post-rift depression stage with relatively rapid burial and high temperature gradient during Middle Permian; an intracratonic depression stage with steady subsidence and relatively high temperature gradient from Late Permian to Triassic; a broad sedimentation stage with steady subsidence and relatively low temperature gradient from Jurassic to Cretaceous; and a compressional orogenic stage with relatively quick subsidence and low temperature gradient during Cenozoic. Source rocks in various horizons and regions have different organic maturation and evolutional history. Both source rocks in Permian Lucaogou Formation in Tainan depression and Middle-Upper Triassic Xiaoquangou Formation in Tuokexun depression have experienced two hydrocarbon-generating processes. The reservoir types and hydrocarbon properties in Tainan depression are obviously different from those in Tuokexun depression, due to differences in burial history and hydrocarbon-generating history.

Characteristics of gas accumulation in northeastern Sichuan basin

Xu Yangang, He Ziai, Zeng Fangang

2004, 25(3): 274-278. doi:10.11743/ogg20040307

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Gas reservoirs in northeastern Sichuan basin are distributed in three overpressured systems,i.e.Lower Cambrian-Silurian(∈₁-S),Lower Permian-Lower Triassic(P₁-T₁)and Upper Triassic-Middle Jurassic(T₃-J₂),and are characterized by multilayer superimposition.The scale of gas accumulations depends on degasification of water-soluble gas under overpressured condition.A burial depth of 4500m can be taken as boundary,under which water is produced,while above which gas is produced,and gas output increases along with the increase of uplifting.Formation and preservation of gas accumulations in northeastern Sichuan basin are determined by burial depth in Yanshan period,elevation in Himalayan period and preservation of abnormal pressure system.Pressure sealing is the key factor to gas accumulation.Therefore,gas exploration in this area should be based on prospecting the superimposed multilayers,and aiming at the overall abnormal pressure system.

Relation between features of strike-slip faults and hydrocarbon accumulation in Subei basin

Liu Yurui, Liu Qidong, Yang Xiaolan

2004, 25(3): 279-283,293. doi:10.11743/ogg20040308

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The Shigang, Chajian and Wubao fault systems in Subei basin represent, laterally, combined characteristics of a major fault with main linear shift zone, horsetail splays and en echelon lambda-type structures, and, vertically, structural features of cone-like fracture, forced monocline and fractured main shift zone. Shear and compressive fracture planes can be observed in rocks beside the faults. Based on the above characteristics, it is believed that the Shigang, Chajian and Wubao fault systems are of discrete-type right lateral strike-slip faults. Stress analysis indicates that Subei basin has experienced both agents of extension and right lateral strike-slip, while right lateral wrench movement is the main cause of strike-slip faults, which has been controlled by Tanlu fracture zone. It is the features of discrete-type right lateral strike-slip of the Shigang, Chajian and Wubao fault systems that control the formation and distribution of oil and gas traps, as well as the migration and accumulation of oil and gas in Subei basin.

Oil/gas shows in lithologic reservoirs in Niuzhuang sag and their main controlling factors

Gao Yongjin, Qiu Guiqiang, Chen Dongxia, Zhang Jun

2004, 25(3): 284-287,299. doi:10.11743/ogg20040309

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Sandbodies in Niuzhuang sag are mainly distributed in deep sag, area between deep sag and gentle slope zone,as well as central low upwarped area. They can be divided into 3 types, i.e. subaqueous alluvial fan, deep water turbidity fan, and frontal slump turbidity fan, of which the subaqueous alluvial fan sandbodies are thick and have good poroperm characteristics and oil/gas shows, while the oil/gas shows in deep water turbidity fan sandbodies are poorer, and that in slump turbidity fan sandbodies are the poorest. The main factors that control oil/gas shows in sandbodies are burial depth, sedimentary facies and types of sandbodies, as well as structural setting, poroperm characteristics and pressure of sandbodies. Reserves and oil saturation in sandbodies would significantly be heightened along with the increasing burial depth. The better the sandbodies'poroperm characteristics are, the better the oil/gas shows would be. They would also be significantly improved with increasing pressures. They are good in the deep sag, and become poorer towards the gentle slope zone, and become the poorest in the central low upwarped zone.

Analysis of thermal evolution and hydrocarbon-generating history of source rocks in Qingnan sub-sag in Jiuxi depression

Gao Bo, Cheng Keming, Zhang Dajiang, Tu Jianqi, Hu Yong, Yang Zhiming

2004, 25(3): 288-293. doi:10.11743/ogg20040310

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Thermal evolution of Lower Cretaceous source rocks in Qingnan sub-sag in Jiuxi depression is studied by using several methods including evolution of soluble organic matter, rock pyrolysis, biomarker parameters and vitrinite reflectance. It is revealed that the depth of oil threshold ranges from 4000 to 4100m in the sub-sag. Most of Zhonggou Formation is in immature stage, the bottom of Zhonggou Formation and the upper Xiagou Formation are in low-mature stage, the lower Xiagou Formation and the upper Chijinpu Formation are in mature stage, and the lower Chijinpu Formation is in wet gas-condensate generating stage. Study of geothermal history in Qingnan sub-sag with the Easy-Ro(%) numerical modeling software shows that the Cretaceous and Tertiary palaeo-geothermal gradients are 30℃/km and 29℃/km,respectively.Hydrocarbon generating history of the source rocks has the following characteristics:(1)the Lower Cretaceous source rocks in Qingnan sub-sag have not experienced secondary hydrocarbon generation and the main oil-generating period is from Neogene to Quaternary;(2)the source rocks in lower Xiagou Formation and the upper Chijinpu Formation are in mature stage with large amount of hydrocarbon generation,i.e.they are the main source rocks;(3)source rocks in the upper Xiagou Formation and Zhonggou Formation make little contribution to hydrocarbon generation, due to the low thermal evolution of organic matter;(4)although rocks at the bottom of Chijinpu Formation have experienced relatively high thermal evolution, they have limited hydrocarbon generating capacity, as they are mainly composed of coarse clastic rocks with low abundance of organic matter.

Sedimentary environment of Permian source rocks in Yili basin

Miao Jianyu, Zhou Lifa, Deng Kun, Li Jianfeng, Han Zhongyuan

2004, 25(3): 294-299. doi:10.11743/ogg20040311

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Based on TOC distribution, gas chromatograms of saturated hydrocarbons and types of organic matter in various source rocks, this paper studies sedimentary environments of source rocks and their effects on abundance and types of organic matter. Source rocks in Yili basin are mainly distributed in the Permian Tamuqisayi and Basiergan Formations deposited in a weakly reducing to reducing environment in temperate climate,where the water body is characterized by relatively high palaeo-salinity with faintly alkaline to alkaline aqueous medium. Sedimentation zones with strong reduction and relatively deep water body are favorable places for deposition and preservation of original organic matters, thus the source rocks have abundant organic matters of favorable types.

Oil and gas reserves and their distribution in Tarim basin

Xu Xianghua, Zhou Qingfan, Zhang Ling

2004, 25(3): 300-303,313. doi:10.11743/ogg20040312

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Oil/gas reserves is one of the important achievements got in petroleum exploration. Growth, change and distribution pattern of reserves comprehensively reflect the exploration history and future exploration potential of a basin. Exploration in Tarim basin has entered into a new development stage since the middle of 1980's,and oil and gas reserves have been increasing continuously.By the end of 2001,cumulative proved oil and gas reserves in place had reached 538 million tons and 613.195 billion m⁸,respectively,in Tarim basin.Exploration degree of both oil and gas are low (4.65% and 5.39%,respectively),indicating that there are still large petroleum exploration potentials.The discoveries in Tarim basin are mainly of medium oilfields and large gas fields,and the abundance of oilfields ranges from low to medium,while that of the gasfields ranges from medium to high.Distribution of reserves that have already been discovered is significantly uneven in various structural units and horizons.The proved oil reserves in place are mainly distributed in the Ordovician,Carboniferous,Triassic and Tertiary in Shaya and Katake uplifts,while the proved gas reserves in place are mainly distributed in the Cretaceous and Tertiary in Kuqa depression.

Oil and gas exploration in low oil-abundance area to the south of Yellow River in Dongpu sag

Peng Jun, He Xianli, Sun Qing, Duan Hongmei, Jiang Yunjing

2004, 25(3): 304-308,318. doi:10.11743/ogg20040313

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In low oil-abundance area to the south of Yellow river in Dongpu sag,oil and gas distributions are characterized by hydrocarbons to be accumulated in near-source limbs of structures, fault blocks controlling oil accumulation, oil/gas pools being small and scattered, and low level of trap fullness, due to poor quality of source rocks, complexity of structures and poor combination of reservoirs and seals. It is quite different from the high oil-abundance area in the north. Progressive exploration and development should be carried out in the low abundance area in the future, on the basis of careful interpretation of exploration targets, and taking fault block groups as appraisal objects and directional drilling as a measure.

Prospects for exploration and development of coalbed methane in Yizikong basin in Liupanshui area

Wang Xu, Wu Yunlong, Qin Xiaoqing, Su Fuyi

2004, 25(3): 309-313. doi:10.11743/ogg20040314

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The Permian coal measures in Yizikong basin in Liupanshui area have workable seams of 20- 40 m thick with gas content of 10- 20 m²/t. Coals are mainly of rich coal, coking coal and lean coal, which are favorable for development of cleat. Coals are in massive or lumpy texture. Permeability of coalbed is relatively high. The basin has coalbed methane resources of 358.78 billion m³ with an average abundance of 429 million m³/km². Therefore, prospects for exploration and development of coalbed methane in the basin are bright. Evaluation through drilling several wells in the basin shows that Jinzhuping block is a favorable area with further exploration and development potential, while Liangshan block is a poor area without any development value.

Factors influencing oil recovery efficiency and comprehensive classification of oil reservoirs

You Xiuling, Zhang Ling, Luo Yunxiu

2004, 25(3): 314-318. doi:10.11743/ogg20040315

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Factors influencing oil recovery efficiency can generally be classified into two large categories: geological features of reservoirs and development and production technologies. As for reservoirs whose reserves have just been proved in exploration stage or in the initial stage of development, geological features of reservoirs are the main factors that influence oil recovery efficiency. Rational and comprehensive classification of oil reservoirs is based on application of analogue method and empirical data. There are various classification methods based on a single factor, such as trap types, physical properties of crude oil,rock types,poroperm characteristics, original reservoir drive mechanism, etc.. None of them, however, is suitable for estimating oil recovery efficiency. Principles of comprehensive reservoir classification are developed on the basis of statistics of geological features and recovery efficiency of each reservoir type by using the available data of more than 400 reservoirs. A new method of comprehensive reservoir classification is presented for estimating recovery efficiency.

Diagenesis and pore evolution of Ordovician carbonate reservoirs in Qianmiqiao buried hill

Yang Chiyin, Wu Zhanguo

2004, 25(3): 319-323. doi:10.11743/ogg20040316

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Ordovician carbonate reservoirs in Qianmiqiao buried hill have experienced two periods of bare karst and post-Paleogene deep buried diagenesis. The bare karst during Indosinian-early Yanshan epoch, an important period for the formation of reservoir spaces, belongs to karst development mode of haystack hill-hollow type. Detailed study of 6 cementation events shows that deep-buried karst in Himalayan period, a critical period for the development of current reservoir pore system, is related to corrosive thermal fluids. The zones characterized by both local thermal fluid karst and surface karst under the outcropped anticlinal axes control the distribution of pores in Ordovician reservoirs in Qianmiqiao buried hill. Reservoirs are best developed in the anticlinal axes formed by compressional thrusting during the Indosinian epoch, especially in the areas where the shapes of anticlines within the buried hill harmonize with that of top of buried hill.

Analysis of water production characteristics of carbonate gas reservoirs: taking Su 4 gas reservoir in Huabei oilfield as an example

Liu Linyu, Liu Yiqun, Li Wenhou, Chen Gang

2004, 25(3): 324-327,332. doi:10.11743/ogg20040317

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Water production is one of the key problems encountered in development of gas reservoirs. Water produced from carbonate gas reservoirs can be divided into condensate water and formation water, and the latter can severely influence normal recovery of gas. There are three modes of water production including water production from gas producing intervals, vertical water breakthrough and rising gas-water contact. Although the carbonate gas reservoir has a unitized pressure system, pores are generally characterized by their heterogeneity with three secondary porosity zones, due to the modification made by tectonic movement and diagenesis. As a result, gas-water contact varies greatly between wellblocks, and there will even be a wide unsteady gas-water transition zone, thus formation water production can easily occur during dynamic development.

Application of system reconstructability analysis in evaluation of hydrocarbon prospective area

Liang Haiyun, Ding Jianke, Li Haiyan, Zhu Runmin

2004, 25(3): 328-332. doi:10.11743/ogg20040318

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System reconstructability analysis is a widely developing field of general system theory. It provides a foundation for solving the problems of complex and heterogeneous systems with continuously and rapidly changing qualitative and mass relationship, as well as structural relationship, which are difficult to describe in the form of mathematic analysis. System reconstructability analysis consists mainly of factor analysis, program evaluation and expert opinions. Evaluation of hydrocarbon prospective areas is complicated with many uncertainties, due to the combined impacts of natural factors, such as geologic conditions, geographic environment and resource potential, as well as policy, law and regulation, investment climate and market environment. Evaluation made with a single index would have large eventuality and instability. A system model for evaluation of hydrocarbon prospective areas has been developed by applying system reconstructability analysis. It preliminarily solves the problem met in evaluation, such as the lack of data set and strong non-linearity.

Well test interpretation methods and application in deep condensate gas reservoir with low permeability

Huang Xuefeng, Yang Shigang

2004, 25(3): 333-337,343. doi:10.11743/ogg20040319

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Considering the phase change and percolation characteristics of deep condensate gas reservoirs with low permeability,such as Pu 67,Baimiao and Qiaokou condensate reservoirs in Zhongyuan oilfield,conventional and modern well test interpretation methods,applicable to these reservoirs,have been developed by integrating phase equilibrium computation process of condensate oil-gas system that take into consideration of physical and chemical interfacial effects,such as pore medium adsorption and capillary condensation,and condensate oil-gas two-phase percolation equations,as well as well test interpretation methods of homogeneous condensate gas reservoirs that are achieved through introducing linearization of condensate oil-gas two phase pseudopressure function and percolation flow equation.A case study of the influences of pore medium adsorption and capillary condensation on well test interpretation results has also been made.

Application of neural network in well test analysis in low permeability oilfield

Wang Anhui, Yu Shuying, Zhang Yingkui, Wang Longyuan, Miao Deshun, Sheng Guojun, Liu Jiajun, Wang Linfang

2004, 25(3): 338-343. doi:10.11743/ogg20040320

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"A" oilfield is a typical low permeability sandstone oil reservoir that has relatively successfully been developed in Jilin oilfield area.The well test interpretation is relatively complicated.The times of radial flow occurring on wells'pressure build-up curves account for only 20%～30% of the total times occurring in all tested wells.This paper introduces an integrated interpretation technology by integrating pattern recognition,neural network BP algorithm and well test interpretation software.It can specifically divided into the following steps:(1)analyze and interprete the bilogarithmic and semilogarithmic diagrams of wells with radial flows,and find out the pseudoslopes(m₁,m₂,m₃ and m)in the continuous flow section,at the flex point,in the transitional section and on the straight line section of radial flow;(2)applying the neural network BP algorithm to construct the mathematical relation among m₁,m₂,m₃ and m;(3)input the basic testing data of the wells without radial flow into the well test interpretation software,derive the m₁,m₂ and m₃,and then derive m with BP algorithm;(4)substitute the parameters mentioned above and fitting them through to the three curves in the bilogarithmic and semilogarithmic diagrams,and in historic fitting diagram to be fitting to one another.

Roles of geochemical prospecting technique in exploration of subtle oil & gas reservoirs

Zhu Huaiping, Li Wu, Wu Chuanzhi, Sun Lichun, Liu Fuchun

2004, 25(3): 344-348. doi:10.11743/ogg20040321

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Geochemical prospecting techniques, with the advantages of high reliability,adaptability,flexibility,economy and continuity,can play an important auxiliary role in exploration of subtle oil/gas reservoirs.Examples,such as Shuanghe,Renqiu and Ansai oilfields,show that near-surface geochemical responses are strong in subtle oil and gas reservoirs and have explicit geological significances.Geochemical prospecting techniques can be used to discover subtle oil/gas reservoirs,guide seismic prospecting, delineate limits of oil/gas reservoirs,evaluate oil/gas shows in the trap and discriminate fluid attributes.

Application of hydrocarbon fingerprint analysis to geochemical description of gas pools

Gou Jie

2004, 25(3): 349-353. doi:10.11743/ogg20040322

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Hydrocarbon fingerprint characteristics of natural gas can be effectively used to analyze connectivity between gas layers in J_3p1 gas pool in Xinchang gas field.In wellblocks or intervals favorable for gas accumulation,certain hydrocarbon fingerprint parameters that are related to gas accumulation and preservation conditions show evident regularity,such as C_3-4/C_5-6,alkane C_5-6/C_7-8 and hexane/cyclehoxane show obvious increasing trend,while normal alkane/isoalkane,cyclopentane/cyclohexane and isomeric mono-substitution/isomeric poly-substitution show relatively decreasing trend.All the hydrocarbon fingerprint parameters of gas layers in J_3p1 gas pool in Xinchang gas field show prominent lateral variation and connectivity between gas layers is poor,indicating the characteristics of structural-lithologic gas pool.The clear regularity of hydrocarbon fingerprint parameters from shallow to deep layers reflects the chromatographic effect and the component separating process during gas migration and accumulation,i.e.gas pools have mainly been formed through vertical migration of hydrocarbons generated from the deep source rocks.All these indicate that conditions of hydrocarbon accumulation and preservation would become better and better to the deep layers,and there will be the possibility of discovering gas pools at depth.

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