Petroleum Exploration and Development

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Coal bed methane resource and its exploration direction in China

LIU Honglin; WANG Hongyan and ZHANG Jianbo

, 2001, 28(1): 71-0.

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Coal bed methane is an unconventional natural gas trapped in coal bed. Our country has rich coal and rich coal bed methane. In this paper, the author found out the difference in gas content and its controlling factor through four parameters, such as gas content per ton of coal, gas saturation, gas concentration and gas abundance. New calculation of resource shows that in China coal bed methane shallower than 2000m is about 22.5×1012m3, and the available resource of coal bed methane shallower than 1500m is about 7.29×1012m3, accounting for 32.4% of the total resources of this kind. In the Qinshui basin, Ordos basin and Liupanshui basin, there are many favorable sections for coal bed methane exploration because of high gas content, high saturation, high gas quality and high abundance. They are the most potential areas for coal bed methane exploration.

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The distribution rule of natural gas and the screening of profitable exploration areas in foreland basins of Central and West China

ZENG Xianbin; ZHANG Jinghua; JIN Hui and YUAN Suhua

, 2001, 28(1): 72-0.

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The natural gas resource is rich in Central and West China. The ratio of proved reserves is only 9.3% in the five gas rich basins there the natural gas exploratin potential is large. There are seven models of major gas fields in the foreland basins. Distribution of gas rich areas is mainly controlled by the fault-fold or rupture. After studying the type of development and distribution characteristics of large-medium-sized gas fields of each second-order structure in the foreland basins, the authors hold that the large-scale structural traps in the lower block of thrust belt, the lithological fringe in the foreland slope area and shallow secondary gas pools as well as the fault block traps in the frontal uplifts of foreland basins etc. are favourable enrichment zones of natural gas in this kind of basin. On the basis of detail geologic research for the foreland basin and the present situation for natural gas exploration, the authors draw out the useful ways to select profitable exploration areas, and select five profitable gas rich areas in the foreland basins of Central and West China. They are large-scale structural traps underneath the salt bed in the lower wall of over-thrust fault in Keyi structural zone of Kuqa foreland thrust belt in Terim basin, Lenghu―Nanbaxian structural zone in the thrust belt on the northern fringe of the Qaidum basin, Jurrasic Yanjinggou-Sumatou-Longquanshan shallow gas beds of foreland sag in northwestern Sichuan basin, lithological fringe zone in Upper Triassic Xujiahe Formation on Zitong slope of Chuanxi front slope belt and Tertiary and Cretaceous gas reservoirs of second and third structures in the southern fringe of Jungar basin.

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Oil-gas accumulation condition analysis and oil-gas prospect evaluation of Jinchang depression in Chaoshui basin

MEN Xiang-yong; ZHAO Wenzhi and WANG Zhizhi

, 2001, 28(1): 73-0.

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Through dissecting Qingtujing shallow oil reservoir and combining this with regional studies, the condition of oil-gas accumulation in Jinchang depression of Chaoshui is analyzed systematically, from this the authors suggest that the main reason that Qingtujing shallow oil reservoir could be preserved is due to anticline controlling, fault covering up and lithologic sealing, and that oil pools are small is because of severe destruction and bad reservoir physical property as well as lack of good collocation between trap condition and oil source condition. Regional study shows that the source-reservoir-sealing conditions lie the trend from bad to good from depression edge to depocenter, and trap condition is good. Finally, authors suggest that exploration in future should be done around the depocenter and early structure (e.g. Jinchuan structure) should be chosen to drill, and searching medium-small size oil-gas reservoirs should be taken as the key in basin exploration.

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Forming conditions and distribution characteristics of Tertiary oil and gas pools in Beitang sag

DENG Rongjing; CHAI Gongqian; YANG Ye; LU Fengting; WANG Jinrong and ZHU Wei

, 2001, 28(1): 74-0.

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The authors describe the geology of Beitang sag and its favorable conditions for reservoir forming from the aspects of tectonic evolution, trap condition, oil source, distribution of sand bodies and reservoirs, abnormal high pressure and coincidence of oil generation, migration, gathering and traps' forming. According to different tectonic evolution history and the assemblage of source-reservoir-seal rocks, three types of oil combination can be defined. They are Tanggu-Xincun-Paotai oil combination, Xingang oil combination and southern Xingang oil combination. Plane distribution of oil and gas is strictly confined by efficacious source rock and vertical distribution of oil beds is controlled by tectonic evolution history and the assemblage of reservoir and seal rock. The pitching ends of paleo-high are always the favorable targets to petroleum exploration because of their great thickness of sand body and good reservoir. Large-scale faults and NW trending faults also play importvant roles in distribution of oil and gas.

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The special sedimentary facies indicated by 17α(H)-diahopanes in Tarim basin

ZHAO Menjun and ZHANG Shuichang

, 2001, 28(1): 75-0.

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It is known that, 17α(H)-diahopanes in extract and crude oil can be generated from hopanoid precursor, and their contents are obviously controlled by sedimentary environment, that is 17α(H)-diahopanes are generated easily by arranging through catalysis of acid clay in oxidation to sub-oxidation environment. So, 17α(H)-diahopanes have great indicating implication to sedimentary facies. In the article, the indicating implication to sedimentary facies for 17α(H)-diahopanes has been discussed through 3 examples of source rock and their hydrocarbons in Kuqa depression, Yecheng sag and Bachu uplift of the Tarim basin. The high content of 17α(H)-diahopanes generally indicates mudstone sedimentary of coal measure strata with shallow-lake shore to paludal facies which has the conditions easily generating 17α(H)-diahopanes.

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Dynamic numerical modelling of petroleum system(Ⅰ)—Techniques and software system

ZHANG Qingchun; SHI Guangren; MI Shiyun; GUO Qiulin and YANG Qiulin

, 2001, 28(1): 76-0.

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Petroleum system can be viewed as the basic geologic unit most suitable for modelling and evaluation of the basin. The features of the basin modelling reflect the theory of knowledge on petroleum system. The modelling and analysis for petroleum system comprises 3 aspects: ①static geologic factors; ②geologic function of petroleum system (it can be represented by modeling geologic history, geologic thermal history, hydrocarbon generation history, hydrocarbon expulsion history,migration and accumulation history of hydrocarbon); and ③ the relationship between the essential elements and processes by creating the events chart. Seeing that basin modelling has made considerable progress in the quantification of petroleum geology, it is not only a shortcut but also doable utilizing basin modelling techniques to realize the dynamic modelling for petroleum system. In this paper, a large modelling software system DYMAPS, Dynamic Modelling Analysis of Petroleum System, is presented. DYMAPS is developed on the basis of BASIMS, Basin Integrated Modeling System. The system consists of 4 parts: Pre-processing, Main modelling programs, Post-processing and Integrated evaluation. Using DYMAPS users can carry out four kinds of evaluations: (1) Background study, to study the formation background and all essential elements of a petroleum system by means of balanced cross-section modelling, sequence stratigraphic modelling, and thermal-tectonic modelling; (2) Dynamic modelling for geological processes, to rebuild the 5 histories of a petroleum system, such as geological, thermal, hydrocarbon generation, expulsion, and accumulation histories; (3) Establishment of the relationship between the essential elements and processes by creating the events chart;and (4) Doing resource assessments and prospect evaluation.

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A study on fluid inclusion of Permian-Jurassic in Turpan-Hami basin

LIU Yiqun; LIU Bin and JIAN Jun

, 2001, 28(1): 77-0.

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The research method of fluid inclusion has been adopted in the research procession of geothermal history of Turpan-Hami basin in order to understand the origin, formation period and migration of oil and gas. Research results of fluid inclusion distributed in quartzs in Jurassic and pre-Jurassic in Turpan-Hami basin represent the features of the mixed hydrocarbon-generation.The dominant hydrocarbon-generating matters come from lacustrine low forms of life and high plants and their forming environment is of brackish and reduction. Measurement of homogenization temperature indicates the formation temperatures of organic inclusions are in the range of 60-195℃. The geothermal gradients of the Jurassic mostly fall from about 2.76℃/100m in the western basin to 3.41℃/100m in the eastern basin. The geothermal gradients in the Permian in the south of the basin are in the range of 3.37-4.12℃/100m. The maturing and migrating time of oil and gas is in the times of Jurassic-Tertiary in Taibei sag located in the north of the basin and Toksum sag located in the southwest of the basin and in the times of Triassic in Tainan sag located in the south of the basin. The paleo-fluid-potential in the Triassic and Jurassic all shows the trend of being higher in the north than in the south, and indicates a regularity of oil and gas migration from north to south of the basin. The organic inclusion in these areas entered reservoirs along microfractures in tectonic movements.

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Microseismic facies analysis and reservoir prediction for Carboniferous carbonates in Meigait Slope, Tarim basin

ZHOU Lu; LI Honghui and WANG Qinghua

, 2001, 28(1): 78-0.

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Carboniferous carbonate reservoirs in Meigait Slope, Southwest depression of Tarim basin is seriously anisotropic. The microseismic facies analysis of target intervals is helpful to find out favorable carbonate reservoir zones. Based on the seismogeology marking results of downhole carbonate reservoir zones and seismic profiles across wells, the authors set up the relationship between the microseismic facies and the carbonate reservoirs, and finished the microseismic facies analysis on the reflector (Tg2′) of the bottom of the Carboniferous Xiaohaizi Limestone Member in Qunkuqiake, the west of Meigait Slope, and on the reflector (Tg2″) of the bottom of Bioclastic Limestone Member of Carboniferous Bachu Formation in the east of Meigait Slope. Some promising exploration zones of carbonate reservoirs are proposed in the paper according to the analysis of the downhole carbonate sedimentary facies and reservoir characteristics, the tectonic location (paleostructure, neotectonic) of reservoir beds, as well as the microseismic facies analysis. The result shows that the karst development zones of Carboniferous Xiaohaizi Limestone Member ocurred mainly in the southwest part of Bashituopu anticlinal belt in Qunkuqiake areas, and the favorable reservoir zones of Bioclastic Limestone Member of Carboniferous Bachu Formation are distributed predominantly over the A, B, C, D four buried hills in the south of Mazhataki structural belt.

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An approach to the calculation of hydrocarbon output of condensate gas cap reservoirs

YU Yuan-zhou; LI Baorong; YANG Guangrong and MA Xiaoming

, 2001, 28(1): 79-0.

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There are some large quantitative condensate gas cap reservoirs (gas condensate reservoirs with oil ring) in Dagang oil field. In the process of depletion recovery, gas breakthrough and oil breakthrough will exist, as a result of the unbalanced pressure fall between gas cap and oil areas. Accordingly, the hydrocarbon from producing well is likely to involve the mixture of crude oil, oil condensate and gas-cap gas as well as solution gas. The authors put forward the two calculable methods of hydrocarbon output for condensate gas cap reservoirs, through the special thermodynamic property of condensate gas, combined with the method of reservoir performance analysis. The concrete instances show that 4 kinds of hydrocarbon output can be calculated accurately with the two methods. This will play a very important role for guiding the analysis of production performance, the research of remaining oil-gas distribution, the development adjustment, determination of ultimate oil-gas recovery factors as well as recoverable reserves of the condensate gas reservoirs.

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An analysis method of stable production limits for oil fields

ZHANG Yongqing and CHENG Shuwei

, 2001, 28(1): 80-0.

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On the basis of 47 practical data from the oil field that stable production period has been finished, this paper makes some research on the stable production time and oil recovery rate (annual recovery percentage) of remaining recoverable reserves and the oil recovery rate during the stable production period, the progressively decreasing ratio of output and the regularity of changing in oil recovery rate during the stable production stage. By using statistic prediction method, the rational relations among these indexes are established. According to the research, keeping oil recovery rate of recoverable reserves at 2.5% and keeping oil recovery rate of remaining recoverable reserves at 8% are regarded as a limited empirical value for the oilfield to keep stable production for ten years. The reality of oilfield development shows that the period of stable production can be kept for a longer time if a reasonable rate of oil recovery is defined. From the theory of reservoir engineering and according to the developing characteristics in this oil field, this paper makes a research on the defined method on reasonable rate of oil recovery for keeping the stable production in the oilfield. By analyzing two examples from the oil field, this method is proved to be very practical for guiding the reasonable development of oil fields, and can become a reference to reservoir engineering technicians.

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Retrograde condensation phase change in near-critical hydrocarbon system

SHEN Pingping; ZHENG Xitan; LI Shi; LUO Kai and SUN Wenyue

, 2001, 28(1): 81-0.

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The high-pressure mercury-free PVT apparatus is applied in this study to determine experimentally the critical point of one complex multi-component hydrocarbon system and its near-critical phase behavior described in more details. In the tests, the unusual phase phenomena are observed for the fluid in the near-critical region. That is, during the constant composition expansion process the retrograde dew-point phase change occurs twice above the critical temperature, and correspondingly dew- and bubble-point phase changes occur sequentially below the critical temperature. In both cases the volume of the first-appeared fluid at the bottom of PVT cell is relatively small, and the pressure at which the first fluid disappears is of the same value at different temperatures. The experimental findings show the behavior complexities of complicated fluids, cast more light on near-critical characteristics, and indicate the deficiency of the usual assumption of two-phase equilibrium in the PVT calculation. Thus more in-depth investigations are needed. It may be the first report that the unusual phenomena of two types occurs in the same mixture and at high temperature up to 100℃.

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Research on the diagnosis and description of wormhole

DOU Zhilin; ZENG Liufang; ZHANG Zihai; XIONG Wei; TIAN Genglin; LIU Xeuwei and HUANG Lixin

, 2001, 28(1): 82-0.

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The western Unit-7 in Gudong oil field is a shallow oil reservoir with loosened consolidation and high permeability. Its depositional cycles are mainly positive rhythm. Sand production occurs during waterflooding. Especially after the enhanced water injection and enhanced production project was carried out, sand production become serious. Very high permeable zone comes into being between wells, which is called wormhole. The mechanism and influencing factors (reservoir permeability, consolidation degree of rocks, fluid viscosity, production rate) of forming wormhole were studied by modeling and doing experiments. Diagnosis and description of the wormhole were done by using the production data because of high cost of tracer. The interrelation between different factors was calculated by using Gray theory to diagnose the existence of the wormhole; and parameters of the wormhole (direction, depth, permeability, size of throat, etc.) are worked out by use of simplified math model. All above-mentioned functions are carried out in the software. This software is applied to the explanation of information from oil/water wells (totally interpreted 290 wells/times and 42 wells/units) in western Unit-7 of Gudong oil field, and wormholes are found out in 124 wells. The result is identical with that of the tracer experiment in pilot test unit. This software is characterized by low cost, convenience and practicality.

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Mechanism analysis on the formation damage by retention of particles suspended in injection water

QIN Jishun and PENG Suping

, 2001, 28(1): 83-0.

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It looks as if a large filter that a porous system of reservoir rocks, which can capture some particles, suspended in injected-water when the water is injected into reservoir. This may cause substantial reduction in permeability of reservoir rocks. The authors collect and analyze the distribution of solid particles in injected-water and pore throat feature of reservoir rocks in the Unit 3 of Shanghe oil field and the Unit 2 of Shengtuo oil field. For the above-mentioned analysis, the authors studied matching relation between size of the particles in the water and one of the pore throats of the rock and analyzed mechanisms of formation damage by retention of particles suspended in injection water. It is found that quality of injection water is become markednessly bad from water treatment station to injection well. There is a liner relation between radius of the pore throat and permeability of the rock in log-log coordinate. And there are some differences in various styles of formation damage when injection water quality is fixed and permeability of rock is different. Finally, the authors recommend a new method for quantitatively analyzing formation damage by retention of particles suspended in injection water. By the method, which is based on the information of core, pore structure and the data of the particles we can describe quantitatively mechanism of the damage by the particles in the water and establish the criterions of the water for oilfield.

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A study on formation scaling tendency for waterflooding oilfields.

JIA Hongyu and QU Zihao

, 2001, 28(1): 84-0.

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Taking four oil fields as an example and adopting the method of computer prediction, the scaling tendency of BaSO4 and CaCO3 is studied respectively in this paper. The results show: ①BaSO4 scaling is caused by the mixing action of formation water and the incompatible injection water. The scaling tendency of BaSO4 is mainly determined by the content of scale-forming ions,the influence of temperature and pressure on the scaling tendency is very unremarkable; ②CaCO3 scaling is caused by changes of temperature and pressure or the changes and the mixing of formation water and injection water, the scaling tendency of CaCO3 is comprehensively affected by the changes and the content of scale-forming ions; ③Because of the differences of the changes and the content of scale-forming ions, the scaling tendency of oil fields is likely to be obviously different; ④In the region from injection well to production well, the CaCO3 scaling in the formation near injection well and production well is severer, while the scaling in the inner formation is milder.

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Simulation experiment on distribution of fault smear layer

LU Yanfang; ZHANG Faqiang; WU Cgunxia and WANG Yaming

, 2001, 28(1): 538-0.

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According to Coulomb-Mohr theory about plastic deformation and breakage of viscous or nonviscous friction material, the simulating experiment set to simulate fault smear is designed and installed, after sandstone and mudstone layers of varied thickness and diagenetic stage are sculptured with slay, sand and cement, a lot of experiment is done by the set. The quantitative relationship of smear layer length and thickness vs. the lithology, thickness and diagenetic stage of strata faulted, and fault displacement are found by observing and analyzing the experiment results. The experiment has brought to light the distribution laws of smear layer in underground, and provided scientific basis for quantitatively studying fault seal to oil and gas.

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Studying method of diffusion coefficient of natural gas

LI Haiyan; PENG Shibi and FU Guang

, 2001, 28(1): 539-0.

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Two sets of measuring instrument of controllable temperature type are fitted, which can be used for measuring the diffusion coefficient under high temperature and high pressure. They are much better in simulating the natural gas diffusion of strata condition than the traditional types, which can only measure the common temperature and pressure. Applying the instruments established, the diffusion coefficiens of natural gas of ten rock samples of dry condition and water-saturated condition are measured respectively. Therefore,6.09, the conversion coefficient of saturation medium of measured diffusion coefficient is determined using Fick regulation and van der Waals equation. Moreover, the temperature correction of measured diffusion coefficient is obtained applying the Stocks-Einstein equation. The diffusion coefficients after the correction are all less than the measured ones, and the differential values become less with the increase of depth, which indicates that the molecules of natural gas get more active with temperature increases. This conclusion can well illustrate that the correction result fits the strata condition.

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Speciation analysis of hydrocarbon microseeping components and their indicatives of oil and gas resources

WEN Baihong; LIN Pei and LIU Xianyang

, 2001, 28(1): 542-0.

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According to the nature of speciating medium and its form of interaction with the medium, speciation forms of hydrocarbon micro-seeping components in soil and rocks include:(1) volatile, (2) solution, (3) adsorption, (4) absorption,(5) inclusion,and (6) combination. Extraction of different speciation forms of hydrocarbon micro seeping components has established more than ten geochemical methods for oil and gas exploration. An indicative index of oil-gas resources (SI) is proposed to evaluate effectiveness of the geochemical methods. From estimating SI for 5 utilized methods (hydrocarbon acidolysis, mercury thermolysis, alteration carbonate, trace element electrochemically extracting and total metal analysis) for oil and gas detection in Ordos basin, their effectiveness is evaluated in the following order: trace element electrochemically extracting > hydrocarbon acidolysis > mercury thermolysis > total metal analysis = alteration carbonate. The results show that trace element electrochemically extracting method by utilizing absorption form of hydrocarbon micro-seeping trace elements has good indicativity of oil-gas resources and resolution for reservoir boundary, and that the spectral diagram of extracted trace elements can be used as a new tool to evaluate the attributes of the hydrocarbon microseepage anomalies.

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The characteristics of surface geochemical exploration of hydrocarbon in Biru basin, northern Tibet

CHENG Dingsheng; HAN HUI; LI Yongtie; LEI Zhenyu and GUO Zujun

, 2001, 28(1): 543-0.

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The Qinghai-Tibet Plateau is the only blank space of petroleum exploration in a large scale. Biru basin is much less explored. In this paper, according to the actually tested data and experiment results, the authors probed the efficiency for applying the surface geochemical exploration in Qinghai-Tibet Plateau, especially under the conditions of hydrocarbon source rocks being widely exposed. The research results indicate that, in the samples being strongly weathered or from the exposed limestone area, methane and heavy hydrocarbon content indices are of most valid, and then the fluorescence spectrum and ultraviolet spectrum indices, but altered carbonate index is not valid. In Biru basin, the hydrocarbons being detected n soil are mainly sourced from underground hydrocarbons by micro-leakage, and they are less affected by biological activity, which shows that geochemical results can really reflect the hydrocarbon information underground. The organic matter are high mature or overmature and at the gas-generating stage. In Biru basin, there occurs high surface geochemical abnormality, especially in the center of the basin. Kemenxialamen area is the hydrocarbon prospect area.

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Mechanism study of condensate influencing on productivity

LIU Yuhu; YUAN Shiyi; SONG Wenjie; LI Baozhu and Wang Jinxun

, 2001, 28(1): 546-0.

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Complicated mechanisms and many influencing factors are involved in developing a condensate gas reservoir. This paper studies the influence of retrograde condensate liquid on productivity based on a single-well radial model. Combined with the productivity equation of reservoir engineering, the conclusions are drawn. It is shown that condensate has a dominant effect on productivity, and the decline of production capacity resulting from condensation could amount to 20% in the case of condensate gas reservoir with medium-high content of condensate, largely because the condensate lessens formation permeability and gas relative permeability. In this case, the productivity equation should be corrected. Two corrective methods are presented in this paper. It is also shown that control of gas condensate forming is one of key factors for developing a condensate gas reservoir.

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The elliptic transient flow of vertically fractured well in anisotropic reservoir

Song Fuquan; Liu Ciqun and Wu Baizhi

, 2001, 28(1): 547-0.

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The authors analyze the steady flow and transient flow of vertically fractured wells with infinite-conductivity or finite-conductivity in anisotropic reservoirs. The flow in formation can be regarded as elliptic flow, and the flow in vertical fracture is linear for finite conductivity wells. First, the formulae of approximate steady production and pressure distribution are derived at elliptic coordinate, an example shows the influence of anisotropic coefficient (Kx/Ky) to production, that is to say that the bigger anisotropic coefficient is, the smaller production is, at condition of same average permeability. Then the approximate formulae of well testing are deduced by using average mass conversation, and some typical curves are drawn and analyzed. It shows that: the smaller anisotropic coefficient is, the more the well-bore pressure is, and well testing curves go up. In log-log coordinate system, the slopes of well testing curves of vertically fractured wells with infinite-conductivity and finite-conductivity respectively are 0.5 and 0.25 at initial time, at later period the derivatives of well testing curves are 0.5.

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Thermal stability of polyacrylamide solution prepared by oilfield produced water

KONG Bailing

, 2001, 28(1): 550-0.

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The experimental results show that long-term thermal stability of partially hydrolyzed polyacrylamide (HPAM) solution, prepared by oilfield-produced water depends mainly on the dissolved oxygen (O2) content. The lower the concentration of O2 in HPAM solution, the better the thermal stability of HPAM solution. When the concentration of O2 is 1.5 mg/L, it is needed 40 mg/L thiourea to stablize HPAM solution; at saturated O2 (8.0mg/L) condition, over 300mg/L thiourea is needed. Ageing 210 days at 75℃, the viscosity of 1000 mg/L HPAM solution containing 50 mg/L polyhydroxy compound and 40 mg/L thiourea and 0.5 mg/L?O2 is increased from 23.2 mPa·s to 62.8 mPa·s. The polyhydroxy compound, by crosslinking, can enhance obviously the viscosity of HPAM solution. The mechanism of HPAM degradatin is a radical reaction. As the concentration of O2 is high, the presence of low amount thiourea would catalyste the radical reaction, and accelerate the HPAM thermal degradation.

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The principles of selecting and testifying facies models in stochastic modelling

ZHOU Liqing; XIONG Qihua and WU Shenghe

, 2001, 28(1): 551-0.

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The two-stage simulation is widely accepted in the stochastic modelling. How to input a suitable facies model to parameter modelling, selecting and testifying facies models are critical to stochastic modelling, in addition to selecting facies modelling method. The paper proposed the principles of selecting and testifying facies models, i.e. the principle of fitting to the geological phenomena, the principle of the realization by wide spacing wells closing to the dense spacing well original facies model, the principle of reasonablely facies controlled parameter modelling, and the principle of fitting to petroleum production data. The S4 bed in Sha2 Member of Shahejie Formation, ST oil field is selected as an example of selecting a facies model from many facies modelling realizations and testifying the selected facie

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The development trend of reservoir protection technology

FAN Shizhong and DOU Hongmei

, 2001, 28(1): 556-0.

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The damage mechanism of reservoirs, the temperature sensitivity of deep wells and deep-water wells and the development trend of completion fluid technology, aciding technology and underbalanced drilling technology are summarized in the paper. On the basis of investigation, the authors hold that formation damage of the horizontal drilling and extended reach drilling is mainly due to fines migration, solids plugging; the damage of fractured carbonate reservoirs mainly composed of limestone is due to solid invasion and solid plugging; the permeability of tight gas reservoirs is seriously reduced because of the aqueous phase trapping (water and oil), and the damage extent is closely related to permeability of the reservoir, interface tension, surface wettability and initial water saturation. The temperature sensitivity of deep wells and deep-water wells will change the minerals into the water sensitive, cause mineral dissolution and precipitation, wettability reversal and emulsion plugging. A new treatment technology with well completion fluids suitable for filter-cake removal and wellbore cleanup—combining the prevention with the treatment is presented. After treatment, the permeability of reservoirs is 40% higher than the initial one. Acidizing is one of most important methods for removing damaged reservoirs duo to its low cost and good results. The prescription suitable for treating various sandstones and carbonate rock is presented. And finally the authors state that the kernel of underbalanced drilling is the selection of appropriate drilling and completion fluids and negative well bore pressure. The experiences that 100 under-balanced wells of Canada increase production at the later stage of oilfield development are given.

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A laboratory simulation on asphslt damaging super heavy oil reservoir during thermal recovery

ZHANG Renxiong; XIANG Yang and LI Xiaomei

, 2001, 28(1): 557-0.

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Du-84 block of Shuguang oil field in Liaohe is an unconsolidated super heavy oil reservoir, with oil viscosity of 22×104mPa·s, and asphalt and gelatinoid content up to 45.7%. The cleaned and unconsolidated core samples are packed to make the porosity and permeability of core samples equal to the average value of the block. A specific heavy oil phase behavior simulation equipment is used, and the thermal recovery experiment of 12 core samples has been carried out. Experiment temperature is divided into three levels (100, 200, 300℃), and pressure four levels (3.5,7.5,11.5,14.5MPa). The principle conclusion of thermal recovery experiment is as follows: asphalt deposition is closely related to temperature and pressure. The asphalt-aggregated states are of island, film sheet, star point, net and cloud which fill up the pores or form bridge-plug at the pore-throat. This will result in the wettability conversion and permeability decrease, capillary pressure increase, and throat size decrease.

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The minimum operation fee determination for economical oilfield production

LIU Bin; GUO Fujun; YANG Li; XIAO Xun and SONG Yulin

, 2001, 28(1): 564-0.

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Most of the oilfields in China have entered into the mid-late production period. Production decline is inevitable. The increasing production cost has direct influence on the economical benefit. The economical production is the production when balance is achieved for revenue and cost, i.e., profit is zero. The minimum operation fee method is to calculate the economical production by determining the minimum operation fee of a single well from the production strategic point of view. When the after-tax revenue of well production equals the minimum well daily cost, the well daily production is the economical production; however, when the after-tax revenue of a single well can not compensate the minimum operating fee for normal work, the daily production is non economical. This method considers the geological parameters and also the economical parameters.

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Potential, distribution and exploration strategy of petroleum resources remained onshore China

ZHAO Wenzhi and DOU Lirong

, 2001, 28(1): 592-0.

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Petroleum resources onshore China are abundant, through half century of exploration a great achievement has been made in China. However, its exploration degree onshore is not high, the proved ratios of oil and gas are 26.9% and 5.4%, respectively. The undiscovered resources are still very large. About 42.4% of remaining oil resources is in the rift basins of East China and 46% in the superimposed basins of West China. About 37% of remaining gas resources is in the Sichuan and Ordos basins of Central China and 28.1% in the Tarim basin. Although the remaining resources are abundant, their quality is relatively poor, the exploration difficulty is big, and the exploration cost will increase greatly. As a result, the petroleum exploration will face a great challenge in the next decade. In order to keep the sustainable growth of petroleum industry and open new exploration frontiers to find more commercial oil and gas reserves, basic theory research should be carried out, risky exploration mechanism and economic evaluation and decision making system should be established and strengthened, and advanced and practical techniques should be developed.

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Preliminary thinking on leading edge technology development of Daqing oil field in the 21st century

CHAO Huaqing

, 2001, 28(1): 593-0.

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In the 21st century, Daqing oil field has to face new challenges mainly reflected in: (1)Unbalance in reserve-production ratio is tending to be serious after recovering cumulative productidon 70.32% of petroleum recoverable reserve; (2) Development difficulty increasing dramatically, with overall economic benefit getting poor;and (3) More strict requiements must be put forward in recognization and restructuring, due to the fact that market competition becomes more intense. From now on, the key work during development of Daqing oil field will be coverted from petroleum production rates to economic benefit, and overall targets will be coverted from continuous stable production to sustainable development, leading edge technology development in two levels will be accelerated. One level is about recent leading edge technology, focusing on increasing the employment percentage of and the total oil produced over the proved OOIP, which includes 3 sets of core techniques: (1)A complete set of techniques for improving waterflooding recovery factor at late high water cut stage; (2)Polymer flooding combined with ASP technique;and (3) Completion set of techniques for effective development of peripherial low permeability, low reserve richness and low single well productivity reservoirs. Another level is mainly about oil field long-term development requirements in the 21st century, focusing on new exploration and investigation in three directions:(1)Foam flooding, microbial flooding and other replacing new techniques after EOR; (2)Related techniques for effective development of newly incremental proved reserves in deep tight natural gas reservoir and complex fault-block oil and gas reservoirs;and (3)Related techniques required by market development for oil fields both at home and abroad. In the future, focus will be put on improving overall economic benefit of developing Daqing oil field through energetically developing and applying advanced hydrocarbon recovery techniques, continually deepening reorgnization, restructuring and mordern enterprise management and endeavoring to realize oil field sustainable development in the 21st century.

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A comparison study on the exploration potential between Bohai Bay basin and Subei basin.

QIAN Ji and HAN Zheng

, 2001, 28(1): 618-0.

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Although big differences exist in basin formation and hydrocarbon formation, there are still similar discovery rule and process between Bohai Bay basin and Subei basin. The cognizance achieved through the comparison studies on reserve increase, accumulate reserve to resource ratio, reserve proveness velocity, the distribution of oilfield size and the exploration stage between the two basins indicates that for the Bohai Bay basin, the distribution of oilfield size accords with lognormal distribution, large and medium oilfields account for 64% of total oilfields number, reserve increase has passed the peak of sine curve and still in later high peak period, the new peak is predicted after the year 2000, the potential will be in deep prospects, various new type of reservoir onshore and wide exploration domain offshore. For the Subei basin, the distribution of oilfield size does not accord with a complete lognormal distribution. Most oilfields are small in size, the reserve increases rapidly and waves gently, its petroleum exploration is in early high peak period and will get into the later high peak period by the end of the tenth “Five-Year Plan". The potential will be in slope, deep prospects, gas prospects in the eastern basin and wide exploration domain offshore. As long as the research, technology, investment could be ensured, the speed of the exploration and development in the tenth “Five-Year Plan" period of the two basins will keep the same as that in the ninth “Five-Year Plan" period.

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New opinions on oil and gas generation and exploration in Jiuxi basin (Ⅰ)—Basic petroleum and geological condition and oil-generating potential.

CHEN Jianping; CHEN Jianjun; ZHANG Liping; ZHONG Ningning and WANG Zhizhi

, 2001, 28(1): 619-0.

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Jiuxi basin has been explored for more than half a century. Six oil fields have been discovered and 1×108t OOIP has been proven in the basin. However, the petroleum exploration in the basin keeps low level up to now. Based on the new seismic data obviously different from the past,the Qingxi depression of Jiuxi basin may be divided into three tectonic units: two sags (Qingnan sag and Hongnan sag) and one uplift (Qingxi low uplift) which is sandwiched between the two sags. The Lower Cretaceous source rock in the depression mainly formed in semi-deep to deep lacustrine environment with a small area and large thickness (more than 2500m thick in both Qingnan and Hongnan sags). The main source rock is distributed in Chijinpu，Xiagou and Zhonggou Formations with organic carbon content from 1% to 2%, hydrocarbon generating potential (S1+S2) from 6mg/g to 8mg/g and chloroform bitumen “A” and total hydrocarbon content being 1.5‰ and 0.9‰, respectively. Organic matter is mainly composed of type II and type I kerogene containing rich perhydrous macerals and with high hydrocarbon potential. Being near the Hongnan sag, Qingxi low uplift is tectonically favorable for petroleum migration and accumulation,and should be the main exploration target in Jiuxi basin.

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, Volume 28 Issue 1