Petroleum Exploration and Development

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Evaluation criteria for Paleozoic effective hydrocarbon source rocks

ZHANG Shuichang; LIANG Digang and ZHANG Dajiang

, 2002, 29(2): 179-0.

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One of the focal points for geochemically assessing marine carbonate rocks for a long time in China is how to identify the threshold value of organic enrichment of efficient hydrocarbon source rocks. Some of the considerable views from Chinese authors spur people to believe that the carbonate rocks with TOC content low down to 0.1%(wt.) still could be as efficient source rocks. These views are as follows: (1) non-reservoir carbonate rocks typically contain less organic matter than shales but have higher hydrocarbon conversion, therefore, carbonate should have less critical source rock threshold value; (2) low organic enrichment in the present carbonate rocks in China is as a result of higher levels of thermal maturity, and so sample’s initial characteristics should be recovered; and (3) the huge thickness of a sedimentary rock can compensate for low levels of organic enrichment. However, subsequent studies including many practical exploration investigations and laboratory simulation experiments do not completely support these views above. The carbonate rocks with TOC content low to 0.1%-0.2%(wt.) could not absolutely be as potential and/or efficient source rocks. Otherwise, hydrocarbon source rocks are largely ubiquitous and should never be a major limiting factor within exploratory programs. The organic-rich rocks within marine stratigraphic intervals or marine carbonates should mainly be shale, mudstone, marl and micrite limestone instead of pure carbonate. Geochemical studies have shown that (1) the same types of organic matter have similar hydrocarbon yield and no the case that carbonate source rocks have higher conversion than that of mudstone; (2) generation and expulsion process of hydrocarbon could generally not cause the organic enrichment down obviously for those rocks containing less 1.0%(wt.) of organic carbon content deposited in epicontinental sea environment; and (3) expulsion efficiency decreases with increasing gross source rock thickness. Therefore, it is concluded that threshold value of organic enrichment for a carbonate petroleum source rock could not below that for shale (0.5%(wt.TOC)), and threshold should be independent of source rock lithology. Efficient source rocks need not too large in thickness, but must contain higher organic enrichment (>0.5%(wt.TOC)) intervals and have a certain distribution scope.

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Reconsideration on some concepts in research of hydrocarbon migration and accumulation

LI Mingcheng

, 2002, 29(2): 180-0.

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Diffusive transport and Darcy's flow of hydrocarbon may coexist and transform each other in the heterogeneous formation. Since the calculated rate of the diffusive transport and the Darcy's flow in the tight mudstone is about 18m/Ma and 15m/Ma respectively (from Welte, et al.1997), there is little difference between these two kinds of flow in the dense mudstone, and Darcy's law is suitable for descri-bing the flow in the mudstone as well. Although both the buoyant ascent and the seepage flow of oil and gas are flows through the subsurface porous media, the former, buoying on the water, moves in discontinuous phase and the latter moves together with water, in continuous phase. Hence, buoyant ascent does not need the requirements of critical migration saturation and relative permeability, and can't be described by Darcy's law, while the seepage flow requires critical migration saturation and relative permeability, and it can be described by Darcy's Law. Buoyant ascent, caused only by the difference between the densities of hydrocarbons and water, is the basic mode of the secondary migration. Episodic migration and episodic injection do take place under the ground, but the episode is one concept measured by time. The migration and accumulation of oil and gas is a continuous progress with episodic features. We can't only emphasize strong episodic activities and neglect the continuous progress. Moreover, considering the instability of oil sources and the heterogeneity of the pathways, it seems unbelievable that analysis of fluid inclusions is enough to assure that oil and gas pools formed during two or three injection stages.

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Characteristics of multi-source petroleum systems in Sichuan basin

WANG Zecheng; ZHAO Wenzhi and PENG Hongyu

, 2002, 29(2): 181-0.

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Analysis of petroleum system in the composite petroliferous basin must be integrated with analyses on the basin evolution, multi-cycle tectonic-sedimentation the basin underwent and basin type, heat mechanism of hydrocarbon forming, and geological elements of petroleum system, clearly indicating the distribution and evolution of each petroleum system in the basin. The characteristics of mutli-source petroleum system mainly include several source kitchens piled up completely or partly and shared the common migration paths and same cap rocks. Some critical moments were in the same period, some of them were not. Paleo-uplifts are favorable area for hydrocarbon early accumulation in multi-source petroleum system.

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A study on validity identification of source rock by new experimental techniques for Ordovician in Ordos basin

XIE Zengye; HU Guoyi; LI Jian; JIANG Zhusheng; WU Damao and YAN Qituan

, 2002, 29(2): 182-0.

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Laser-fluorescene, environmental scanning electron microscope and rock thermal simulation techniques have been used to identify and quantify bitumen, to evaluate the genetic potential and to imitate the visible gas generation process of organic matter from Ordovician rock in Ordos basin. The conclusions have proved that the source rock had generated and expelled hydrocarbon during the process of geologic history by the existence of bitumen in rock and the visual simulation of organic matter. The source rock is effective only if the amount of gas generated in Ordovician rock is greater than that of the adsorbed by itself. Authors propose that the source rock with high abundant organic matter developed in transgressive sequence of Ordovician in Ordos.

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Deep fluid activities and their effects on generation of hydrocarbon in Dongying depression

JIN Zhijun; YANG lei; ZENG Jianhui and ZHANG Liuping

, 2002, 29(2): 183-0.

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A large number of deep fluid activities that occurred in Dongying depression can be proved in terms of abnormal of geochemistry, diagenetic mineral, heavy elements, volcanic activities, deep structure and palaeo temperature. The pathways of deep fluid activities are deep faults and magma eruption. Except accumulation of inorganic gases such as carbon dioxide, deep fluid can effect the generation of hydrocarbon after it entered the sedimentary basin by at least three means. First, the hydrogen in deep fluid will react hydrogenation with organic matters and increase the production of hydrocarbon; second, the huge thermal energy taken by deep fluid can boost maturity of source rock; the elements from deep fluid can be catalyzed for generation of hydrocarbon too. The researches about effects of deep fluid on hydrocarbon generation are magnificent both for theoretics and oil exploration.

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Analysis on the features of heavy oil and its source rocks in the west slope region of the southern Songliao basin

LIANG Chunxiu; LIU Baozhu and SUN Wanjun

, 2002, 29(2): 184-0.

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A great mount of heavy oil resource was found in Saertu oil-bearing formation in the west slope of Jilin oil field. The authors discussed the geochemistry characteristics of the heavy oil and its source rocks by analyzing the crude oil features, composition and biomarkers. The heavy oil generally was biodegraded and has great density, high viscosity, high nonhydrocarbon and wax contents. All heavy oils are mature and were mainly generated from source rocks in deep Qingshankou Formation in Changling depression and were not relative with the source rocks in Nenjiang Formation.

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Simulation of diffusion quantity of solution gas in Dawanqi oil field

CHEN Yicai; SHEN Zhongmin; LI Yanjun; HUANG Jianquan; PI Xuejun; XIE Huiwen and DI Hongli

, 2002, 29(2): 185-0.

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After analyzing the component of solution gas at different depth in Dawanqi oil field, in this paper, the authors consider that the diffusion of solution gas is remarkable in upper-oil layer in depth less than 450 meters. The diffusion not only leads to methane percent content decrease, ethane and propane etc percent content increase, but also reduces gas-oil ratio and enlarges pressure gap between formation pressure and saturation pressure of oil reservoir. According to simulation by Fick second diffusion law, the diffusion ratio of methane concentration in upper-oil layer solution gas is 54% from middle Pliocene to the end of Quaternary.

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Hydrocarbons Entrapped in the Petroleum Asphaltene

ZHU Jun; GUO Shaohui; XU Guanjun and WANG Peirong

, 2002, 29(2): 186-0.

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Non-covalent bond association networks are existed in the petroleum asphaltene, and some relatively low molecular weight components, such as hydrocarbons, are entrapped in the networks. These networks prevent the entrapped components. Due to the spatial limitation of the association networks, the indentified carbon number of the normal hydrocarbon entrapped in the asphaltence is normally not larger than C27. The entrapped components can be released from the networks by solvating and reprecipitation of the asphaltene. Differences are existed in the geochemical parameters between the entrapped hydrocarbons and crude oils and further studies are needed.

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Quantitatively evaluating hydrocarbon primary migration by mudstone compaction dynamic analysis

LUO Qun

, 2002, 29(2): 187-0.

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Base on analysis of the main factors influencing hydrocarbon primary migration, the paper points out the flaws in using mudstone compaction static analysis to study hydrocarbon primary migration, and provides the new viewpoint of mudstone compaction dynamic analysis and quantitative evaluating hydrocarbon primary migrating, sets up its geological model, mathematics model and modeling flow process. At last, with Qingshankou main hydrocarbon resource rock in Qianchang sag of Songliao basin as a typical example. The author of this paper uses the new viewpoint and method to dynamically analyze the hydrocarbon resource rock and estimate its hydrocarbon primary migrating amount. This result is very close to the results obtained by other methods as well as that of predecessors.

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Evaluating oil density and viscosity with geochemical pyrolysis data

HOU Lianhua; LIN Chengyan; WANG Jinghong; LIU Zonglin and SUN Xinghai

, 2002, 29(2): 188-0.

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Different influence factors have different extra appearance and mechanism in different components of geochemical pyrolysis degradation. In this paper, updating models of light，middle and heavy constituent constrained by oil density were built up on the bases of pretreatment to sample weight, porosity and volume. Correlatively quantitative polyparameter evaluation models of oil density and viscosity were built up after correcting geochemical pyrolysis degradation data, getting residual hydrocarbon content and better parameters correlativity to oil density and viscosity. A set of perfect evaluation methods of correcting data, getting oil density and viscosity were formed. Using these methods, a higher precision of oil density and viscosity in 48 layers of 37 wells in different reservoirs has been obtained.

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Comparison of integrated decision results between fuzzymathematics and grey theory

SHI Xiaofei; SHI Guangren and ZHANG Qingchun

, 2002, 29(2): 189-0.

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When the geological integrated evaluation was conducted on the 42 traps in the north region of Kuqa Foreland basin, we employed the multi-hierarchical fuzzy integrated decision method and the single-hierarchical gray integrated decision method. By using the same original basic data and the same definition method of weight coefficients, the secondary hierarchical evaluation is at first performed on source rock, trap, reservoir bed, preservation and configuration histories, and then the integrated decision was conducted. Although there exist some differences of the relative order of trap quality from integrated decision evaluation between the two methods, their total trends are the same, and the decision results on better-quality traps are consistent with real exploration, proving they are effective quantitative geological evaluation methods. In the practical exploration evaluation, the two methods together with other integrated evaluation methods should be comprehensively applied to get the reasonable integrated decision values of exploration prospects.

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An experimental study on starting pressure gradient of fluids flow in low permeability sandstone porous media

LU Chengyuan; WANG Jian and SUN Zhigang

, 2002, 29(2): 190-0.

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This paper presents the laboratory methods to obtain the complete non-Darcy flow curves of different low permeability sandstone porous media. The study develops a new “capillary pressure equilibrium method” to measure the starting pressure gradient, combining well with the conventional “differential pressure-flow rate method”. Meantime, the relationships between starting pressure gradient and fluid viscosity, displacement pressure or the air permeability of the sample cores, especially the characteristics of permeability change when flow rate is low, are described and discussed. According to the experiment results, this paper get some useful experience formulae as well as applied plots.

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Determing water driving effectiveness of oil reservoir with fuzzy comprehensive evaluation method

TANG Hai; HUANG Bingguang; LI Daoxuan and ZENG Fanhua

, 2002, 29(2): 191-0.

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The oil recovery under water drive is an important factor for the evaluation of water displacement efficiency of a reservoir. Based on the analysis of advantage and shortage in the oil recovery determination using empire formulas, water displacement curves and decline curves, this paper presents a new “Fuzzy Comprehensive Evaluation Method” which contains 7 types (i.e. rock grain texture, rock pore texture, flow properties of reservoir, reservoir sensitivity, distribution of oil and gas sand bodies, reservoir energy and crude oil properties) of 24 geology factors. The application results showed that the “Fuzzy Comprehensive Evaluation Method” could accurately evaluate the oil recovery for different reservoirs in different production period, and it's a simple, applicable and scientific method that can be used broadly.

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A study on the remaining oil distribution in Block Wen95 of Wennan oil field

LIU Qiujie

, 2002, 29(2): 192-0.

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With the increasingly mature of development of Zhongyuan oil field， the development difficulty has become more and more remarkable. The main production layers have entered into the high water-cut development stage, while the main problems that the well patterns are not complete, the water-flooding control degree is low, the contradiction among layers is outstanding, the water-flooding result isn't tangible, and so on are more exposed. The main factors influencing water-flooding development are small-sized sand body, bad reservoir permeability and porosity, striking differential among layers, complex pore configuration, etc. In order to meet the needs of producing remaining oil, knowing and mastering the remaining oil's macroscopic and microscopic distribution, and then defining the remaining oil reserves and the recoverable reserves is the important ground for tapping reservoir potential. Using the fine reservoir geological model,the current development situation of the Block Wen95 was analyzed and evaluated, and then through taking full use of water and oil wells production and injection profiles, C/O logging data, adjustment well water-breakthrough analyses, and numerical reservoir simulation, the remaining oil distribution has been quantified and visualized. Through the quantified and qualified studies of the remaining oil distribution, and combined with the research on geological and development factors influencing remaining oil distribution, the article clarified the characteristics of the remaining oil distribution in Block Wen95 reservoir in three respects: first, the oil remained in the produced or less produced oil-bearing sand bodies; second, the oil remained in the retention area of the contracted layers; and third, the oil remained in the heterogeneous payzones of the reservoirs. This study explored a way to develop the remaining oil at the high water-cut stage, which can guide the development of the same type of reservoir.

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Application of domain decomposition method in thermal recovery simulation

WU Shuhong; LIU Xiange and GUO Shangping

, 2002, 29(2): 193-0.

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Many reservoir engineers have known the importance of domain decomposition method in numerical reservoir simulation, but its application in thermal simulation is seldom. In this paper the probe study was made on the application of the method in thermal simulation. Based on the multi-phase, multi-component of thermal simulation, the domain decomposition method suitable to fully implicit solution method was derived. Finally, the comparison between the thermal simulation with and without domain decomposition method was carried out. The result shows that the application of domain decomposition method in thermal simulation is successful and its calculation result is believable; application of domain decomposition method can increase calculation speed and decrease the CPU time.

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A study of the disposal arithmetic between layers of the multi-layers pseudo-3D model

DAI Tao; YUE Guanglai; YANG Yaozhong and ZHOU Weisi

, 2002, 29(2): 194-0.

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The Multi-Layer 2D-2Phase Numerical Reservoir Simulation Model cannot solve the problem of cross-flow between layers. Considering the fluid as three-dimensional, the Multi-Layer Pseudo-3D Model, which is an improved method of the Multi-Layer 2D-2Phase, regards the cross-flow between layers as pseudo source remit item and adds it into the 2D-2Phase equation, to implement an approximate consideration of 3D reservoir. The method makes the simulation results close to the real reservoir which are connective between layers, and the software which is developed is faster than 3D-3Phase black oil model, and it enlarges the scope of the simulation software and improves the simulation precision. Contrasted with the black oil model, it has the same result and it is applied in the numerical reservoir simulation of Daluhu oil field, which is located in Dongying, Shandong, and improved 32.4% of the whole run efficiency than the black oil model.

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Petroleum exploration of Tanggu oil field in Beitang sag of Huanghua depression, Tianjin, China

DENG Rongjing; YANG Hua; LU Fengting; QIAN Maolu; YANG Yanjun; LI Jianying and GUO Fuwei

, 2002, 29(2): 195-0.

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Beitang sag with difficult petroleum exploration is located in the north region of Huanghua depression, from which, since 1964 no big breakthrough has been taken place in petroleum exploration. In the past 10 years, a lot of hard work has been done in terms of basin analysis, regionally integral dissection and choosing the Tanggu structure as the breakthrough point of exploration, as a good result, a midium-sized oil field with OOIP of 50 million tons was finally discovered. Reviewing the petroleum exploration history of Tanggu oil field, and summarizing its exploration achievements within the latest 30 years, the paper points out that the great success of this oil field's exploration is mainly a result of more concerning on acquisition and processing of seismic data, deepening geology study, wide implementation of newly developed technology and improvement of processing technology.

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Controlling of Dongying sag structure on the Tertiary sedimentary sands bodies

MA Lijuan; XIE Xinong and REN Jianye

, 2002, 29(2): 426-0.

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Tertiary system in Dongying sag is of typical faulted lake-basin deposits, and its structural activity is tightly relative to sedimentation. Dongying sag is divided into three facies belt such as actic region, sag region and ramp region. Through the study, the authors find that the north of the slope break region of the slope structure in the basin developed mainly the variable genesis glutenite fan bodies, the subsalt relief and fault activity controlled the genetic type and through-going of the fan bodies. Because the fault activities in the single-fault slope break are different from that in step-steep slope break, the sedimentary system of glutenite fan bodies controlled by the fault is also different. Basin deep sag lies in downthrow of fault with developing sidely delta front fluxoturbidite. There are totally three propels from east to west. Three propels correspond to structure action of S3, S2 and S1 respectively. South ramp region results in differential settlement of deposit slope on the same slope due to a series of development of reverse adjusting fault, controlling a set of braided river delta or shallow lake shore system. Tertiary palaeostructral activity in Dongying sag and its control on settlement system and skeletal sand are studied to find the arrangement relation between reservoir a

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Fractured reservoir features of Huangqiao CO2 gas field

ZHU Lihua and GUO Nianfa

, 2002, 29(2): 427-0.

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Huangqiao CO2 gas field in Jiangsu is the largest CO2 gas field in China. Owing to long terms of stratum impaction and epidiagenesis, original porosity and permeability in marine strata had been changed greatly, and oil and gas reservoir conditions relatively changed bad. For the most marine strata, basically original reservoir ability was lost, for example, 58.4% carbonatite original porosity is less than 1%; 95.5% carbonatite permeability is less than 1×10－3μm2; 20% original porosity of clastic rocks is less than 1%; 95% permeability of clastic rocks is less than 1×10－3μm2. Therefore, it is impossible for marine rocks by their original pores to cumulate big gas field. Under this condition, structural fracture was developed universally in marine strata, which greatly reduced insufficiency of the original pores. Huangqiao CO2 gas field, basically relying on fracture reservoir volume, may percolate through the same strata, therefore, fracture reservoir layer, in the fact, is a volume, not a layer. Owing to the fractures developed in the marine strata, Huangqiao CO2 gas field became a large CO2 gas field in China, whose gas in place reaches 64×108m3.

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Applying prestack depth migration to complex gedogic structure Imaging gained by using velocity model with gradient

WU Xiaozhou; CHEN Likang; ZOU Caineng; HU Ying and LIANG Hong

, 2002, 29(2): 430-0.

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Since 1990's, 3D depth migration has become a key seismic imaging technique in those areas that have severe lateral velocity variation in subsurface medium. However, in East China, there are some complex fault-block oil fields which have subtle velocity variation both laterally and vertically in the upper formation; their oil source rock is in the deeper formation; and their migration pathway is some dominated by faults. Hence, to find the dominant faults is the most important task in these kinds of oil fields. 3D prestack and poststack time migration have been used to image these faults, but the result is not as accurate as geologists expect because of the complex faulting system. 3D prestack depth migration was tested using velocity model with gradient, and reasonable result was achieved. Baidong structure is presented as a case study to demonstrate that 3D prestack depth migration is an effective technique to image those complex faults.

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The applications of under balance directional well in the Well Feng 501

WU Qingzhong; XIA Yuanming; YANG Yufei and WANG Liuxin

, 2002, 29(2): 431-0.

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In order to develop the anticlinal belt oil reservoir of Fengcheng Formation in the lower plate of Wu-Xia fault block, which is located at the northwestern of Junggar basin in Karamay oil field, and considering its thin pay zone, the experts designed a under balanced directional Well Feng-501. During the drilling, the directional under-balanced and directional well engineers made some analyses of the difficult problems in drilling the under balanced hold angle section, and taken several measures:(1)Choosing the right kick off point (KOP); (2)Using bottom hole assembly (BHA) as simply as possible under the condition that meeting the directional technology; (3)Using self-floating single-spot measurement instrument to circulating mud during the surveying and (4)Proper operation in the under-balanced drilling. Using these measures, we successfully drilled the Well Feng-501. During the drilling, oil and gas shows were found. After putting into production, commercial flow was gained. The success of the Well Feng-501 widen the ways to explore the lower pressure fault belt oil reservoirs.

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Fully implicit simulation model for low-velocity non-Darcy flow

ZHOU Yongyi; PENG Shimi; LI Yun and LI Yang

, 2002, 29(2): 434-0.

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Many researches show that the fluid flow in low permeability media doesn't obey the Darcy's law, and needs a start-up pressure gradient. It is very difficult for the conventional numerical reservoir simulation theories to describe the characteristic of fluid flow in low permeability media, because they are all based on the Darcy's law. On the basis of the predecessors' research findings, a non-Darcy flow fully implicit numerical simulation model is presented in this paper to characterize properly the special flow phenomenon in low permeability media. Besides, the finite difference expression of this model and the responding fully implicit process for the model is given in this paper, and the function modifications of the existing simulator has been done. Finally, an example is given in the paper. The results indicate that under the same other conditions and during the same time, the greater the start-up pressure gradient, the lower the oil recovery and the smaller the cumulative water injection quantity; on the contrary, the less the start-up pressure gradient, the higher the oil recovery and the more the cumulative water injection quantity. The analyses demonstrate that the results of the example are reasonable and the model developed in this paper could represent the characteristic of low velocity non-Darcy fluid flow in low permeability media.

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Comprehensive adjustment of development mode of common swage recycling in Weigang high pour point oil field

YANG Kun; FAN Zhonghai; ZHU Nansong; XIE Zhongwen and LIN Zhong-wei

, 2002, 29(2): 435-0.

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The oil displacement efficiency of Weigang oil field can be improved for it's typical high pour point reservoir, and this is to the advantage of the oilfield to improve development effect. But for the middle-small sized oil fields, it is harmful of effective development because of its high cost of production. By means of normal temperature water displacement numerical simulation at earlier stage of development, it is found that the high pour point crude reservoirs like Weigang which have characteristics such as high formation temperature, high formation wax precipitation temperature, high geothermal gradient, fast formation temperature variation compensation have been still keeping the original temperature in the well bottom after ten years development. The influence of cold water flooding to development effect is mainly at bottom zone of water flooding well, and it has little influence on production well and even whole reservoir. Utilizing sewage recycling development to oil field is not only raises water injection temperature, but also improves development effect, as well as protects ecology environment, and therefore oilfield can enjoy a long-term sustained development.

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An analysis on intrinsic factors influencing the properties of pre-crosslinking gelled particles

BAI Baojun; LIU wei; LI Liangxiong; LIU Gehui and TANG Xiaofen

, 2002, 29(2): 438-0.

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A new kind of in-depth deverting agent, called pre-gelled particle, has been developed to control conformance of mature reservoirs. The particles are formed from gels on the ground using gelation system, and then experience several processes such as particle forming, baking, pulverizing, and sieving. The gel particles disperse in water, but they do not dissolve in it. This paper mainly analyzes the influence of acrylamide, crosslinker, initiator, additive and heat stabilizer on elastic modulus and swelling ability of gel particles. The best formula ratio is given for this kind of gel particle.

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The application studies of bio-surfactant as sacrificial adsorbate in ASP flooding

LI Daoshan; LIAO Guangzhi and YANG Lin

, 2002, 29(2): 439-0.

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A study was made to see the feasibility of using bio-surfactant (rhamnolipid fermentation liquor) as a sacrificial agent in the ASP flooding pilot test. The interfacial tensions between solutions containing only bio-surfactant and/or surfactant (ORS) and crude oil were stu-died at a constant NaOH concentration. The interfacial tension between bio-surfactant-ORS system and oil is lower than that of ORS alone. The interfacial activity of the compound (mixture) of bio-surfactant and ORS is obviously synergetic. Adsorption isotherms of the bio-surfactant and ORS system were established to assess the sacrificial effect of bio-surfactant. Static adsorption experiments indicate that adsorption loss of surfactant (ORS) can be reduced by 25-30% by bio-surfactant and ORS mixture or pre-adsorption with bio-surfactant on oil sand. The ASP flooding was tested with bio-surfactant and ORS. The concentration of ORS is decreased by 50% to that of the original ASP flooding in which 0.15% bio-surfactant was added. In the test area, the oil recovery factor is averagely increased by 16.64%(OOIP). The relative concentration of ORS in the produced well effluent for bio-surfactant ASP flooding test is the same as ASP flooding of only ORS.

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Experimental and mechanism research about permeability damage with the change of stress

FAN Xueping and XU Xiangrong

, 2002, 29(2): 444-0.

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In practical production situation, many petroleum reservoirs are sensitive to the stress. The fluid pressure and effective stress will change in the course of production, and then it will induce the productivity decreasing. In this paper, the experimental principle of core analysis was described briefly. Based on the experimental data, the experimental results indicate that permeability will be damaged with the change of effective stress. At the experimental condition, the constructive relation about the effective stress and permeability was regressed as a quadratic equation, which was demonstrated by the thick canister elastic deformation mechanics and porous concept. Speedy and deep pressure decline should be avoided in case of the reservoir damage.

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The option method for evaluating the value of petroleum reserves

WU Qiu-nan

, 2002, 29(2): 445-0.

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Petroleum reserves can be seen as call options from which the holder of options has the right but not obligation to acquire the reserves in a specified time. The author of this paper describes the option characteristics of oil reserves, classifies the oil reserve options into three sequential options (i.e. exploration option, development option and production option), and discusses the determinants of the option prices. After the stochastic diffusion process of underlying assets was assumed, the partial differential equation which determines the value of the developed petroleum reserves is created with the no-arbitrary equilibrium circumstance. The finite-difference approach is used for the nonanalytical solutions of the model.

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The study on terminology, technological process and kernel content for petroleum system

ZHAO Wenzhi; HE Dengfa and FAN Tuzhi

, 2002, 29(2): 461-0.

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Petroleum system, as a very important tool, has been applied to evaluation of hydrocarbon resource potential and finding oil and gas pools. However, there are a lot of confusion on understanding, terminology and, application of petroleum system to petroleum exploration because of differences in understanding of petroleum system among the researchers. The importance of unifying technical terms of petroleum system is discussed, and its position, basic contents, technological process and applications to petroleum exploration are discoursed in this study. A set of unified terms of petroleum system in Chinese and their relative terms in applications of petroleum system are presented also. The authors hold that reconstruction of petroleum system process using thought of tracing the root of the matter by following clues can be carried out according to the four main geological elements, four geological processes and their relationship of association in evaluation of petroleum system. Mapping key contents in critical movement can be applied to describing process and limit of petroleum system formation. The serial techniques for evaluation of petroleum system are introduced in this paper.

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The research of coal-formed gas accelerating the increase of natural gas reserves in China

XIA Xinyu; QIN Shengfe; WEI Yanzhao and TAO Shizhen

, 2002, 29(2): 468-0.

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The prompt increase of the natural gas reserves in China in the recent years is mainly contributed by the successful exploration of coal-formed gas. From the Natural Gas Science and Technology Research Project in the beginning of 1980s, over 69% of new-proved gas reserve is coal-formed gas. By the end of 2000, 78.9% of the proved reserves of the large and medium gas fields (with proved gas-in-place over 100×108m3 in each) is coal-formed gas, all the four largest gas fields in China are coal-formed gas fields. The research on coal-formed gas geological theory, achievements in the State Science and Technology Research Project during the past 20 years, widened the exploration target area, brought about the prompt increase of coal-formed gas reserves.

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An approach to the hydrocarbon resource potential of Bohai Bay basin

WANG Yuman; NIU Jiayu; QIAO Hansheng and CUI Wenqing

, 2002, 29(2): 469-0.

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By using SL3DBS (a system of numerical basin simulation) and the method of accumulating plays and stressing evaluation of deep-seated beds and plays, the hydrocarbon resource of 21 Tertiary sags of Bohai Bay basin was reevaluated. Combining the result of Tertiary and that of Palaeozoic, it is obtained that the total hydrocarbon resource of the basin, 35 percent of which is situated in the deep-seated beds, amounts to about 235×108t oil equivalent and the residual hydrocarbon resource amounts to about 150×108t oil equivalent. In the basin, residual hydrocarbon resource is chiefly situated in those domains such as the deep-seated beds of the Tertiary of rich hydrocarbon sags, the shallow sea and the Palaeozoic, which are less explored. Thus, the rich hydrocarbon sags of the land, where residual hydrocarbon resource potential exceeds 4×108t oil equivalent, are main areas of progressive exploration for the future; the shallow sea is a favourable exploration area where large-medium sized fields will probably be found. Of the basin, 18 sags have been picked out as favourable exploration areas of the land and the shallow sea; in the future exploration, complex and subtle types of reservoirs will be principal domains.

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Feature of mixed gas in central gas field of Ordos basin

CHEN An-ding

, 2002, 29(2): 480-0.

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There are two different opinions on origin of gases in Ordovician reservoir of the central gas field of Ordos basin: (1) Gases are mainly sourced from Ordovician carbonate source-rock, it is a mixed gas in which sapropelic gas dominates; (2) Gases are mainly sourced from Carboniferous coal-bearing source-rock, it is a mixed gas in which humid gas dominates. Recently it is proposed that sapropelic gas in mixed gas is still sourced from Carboniferous. The opinion on origin of gases is associated with estimating of “low abundant" carbonate source-rocks. In this paper the nature of two source-rock and two types of gas distinguished mainly by ethane carbon-isotope have been introduced. Based on argon isotope and the relation of iso-heptane value with δ13C2, the sapropelic gas in mixed gas of the central gas field can but come from Ordovician，not Carboniferous. The methods to divide oil-gas into C1-5, C6-12 and C12+ fraction, the phenomenon of “characteristic transfer" and principle of relation of concentration and feature-contribution should be used for discovering and research mixed gas. It is pointed that gas reservoir in the central gas field was formed by mixing both dry gas from Carboniferous and more dry gas from Ordovician, 80% of gross is sourced from Ordovician carbonates. It is explained why carbon isotopes of C6-12 light hydrocarbon cannot be used to prove gas origin.

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Geological and geochemical evidences of the Tertiary biogenic gas in Qaidam basin

ZHANG Xiaobao; HU Yong; DUAN Yi; XU Zi-Yuan; ZHOU ShiXing and WANG Jinpeng

, 2002, 29(2): 481-0.

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Quaternary biogenic gas is very enriched in Qaidam basin where exist the biggest biogenic gas field, Sebei gas field, but if the widely distributed Tertiary in the basin can generate biogenic gas and form industrial gas fields is still unknown. On June 20, 2001, industrial gas pools producing several tens of 105m3 of natural gas daily was found firstly at the depths from 1273m to 1322.5m in the Well Yishen-1 in the basin. In the natural gas from the well CH4 is predominant, being 98.01%; heavy hydrocarbon is low, only 0.17%; C1/C1-5 is up to 0.998; δ13C1 is very light, being －67.3‰; indicating it is typical biogenic gas. The40Ar/36Ar of the gas is 318, which means the gas source rocks are young, possibly Quaternary or Tertiary rocks. Deduced from the geological conditions of the natural gas it should be self-generated and self-reservoired biogenic gas. This conclusion is of important significance to probing the forming mechanism and pool-forming regularities of the biogenic gas, increasing the natural gas reserves and developing the new area of natural gas exploration in the basin.

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The effect of abnormal overpressure on deep reservoir forming in Dongpu depression

SU Yushan; WANG Shenglang; ZHANG Lianmeng and WANG Deren

, 2002, 29(2): 504-0.

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Overpressure is very prominent in Dongpu depression, and in some area the geopressure is extra high. The authors of this paper hold that the mechanism of abnormal pressure is related with disequilibrium compaction, aquathermal expansion, hydrocarbon generation and better sealing strata. The abnormal overpressure has good sealing effect on reservoir, and it can promote the generation of abnormal high pores and their preservation, so it controls the accumulation of oil and gas in deep formation. It also causes episodic hydrocarbon expulsion and later reservoir forming. The restrain on hydrocarbon generation results in increase of deep resources. Based on these studies, this paper presents the reservoir-forming pattern of deep formation which controlled by overpressure-sealed box.

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The unconformity surface in the Permian of Junggar basin and the characters of oil-gas migration and accumulation

WU Kongyou; ZHA Ming and LIU Guangdi

, 2002, 29(2): 505-0.

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There are many unconformity surfaces in Permian system of Junggar basin, which are very important for oil and gas to migrate with long-distance and in great-scale and to accumulate. Seismic section comprehensively interpreted to discover that patterns of unconformity sections in the Permian include fold unconformity, fault-fold unconformity, truncation unconformity, onlap unconformity and parallel unconformity. Each of them has the different distributing regularities in basin, and the type of unconformity surface controls oil and gas migration along it. On the basis of analyzing log responses and cores, the unconformity surfaces in vertices are divided into three parts: under-conglomerate, weathering claystone and paleokarst zone, this structure forms the double paths of the oil and gas migration. It connects reservoirs and faults which formed in different times to construct the regional migrating network. The unconformity surfaces in the Permian of Junggar basin not only are the important paths for the oil and gas migration, but also are the good places for the oil and gas accumulation. Undersurfaces can form reservoirs which are covered by the unconformity surfaces, and upsides can form lithologic reservoirs characterized by stratum onlapping.

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, Volume 29 Issue 2