Petroleum Exploration and Development

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Temperature effects on geopressure during deposition and erosion

XIA Xinyu and SONG Yan

, 2001, 28(3): 101-0.

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Temperature effects on geopressure during deposition and erosion are explained through theoritical calculation. Calculation from fluid state equation shows that overpressure by aquathermal pressuring is two magnitudes lower than that by compaction during deposition, the ratio is mainly determined by compaction coefficient and thermal gradient, with no relation to permeability, deposition rate,viscosity and compressibility coefficient of formation water, indicating that the significance of aquathermal is negligible during most deposition environments. Effect of temperature decrease on geopressure is lower than that of porosity increase during erosion, but their ratio is not as low as that of aquathermal pressuring to compaction. Even though only thermal effect is considered, erosion would cause underpressure instead of overpressure.

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New opinions on oil and gas generation and exploration in Jiuxi basin(Ⅲ)—Oil and gas migration, pool formation and exploration target

CHEN Jianping; CHEN Jianjun; ZHANG Liping and ZHONG Ningning

, 2001, 28(3): 102-0.

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An integrated petroleum system is formed by the Cretaceous and the Tertiary in the Jiuxi basin, in which the Cretaceous developed as source, reservoir and cap rocks and the Tertiary mainly developed as reservoir and cap rocks. The contents of alkanesin oils from Liugouzhuang, Yaerxia, Laojunmiao and Shiyougou oil fields increase gradually; on the contrary, the contents of aromatic hydrocarbon, non-hydrocarbon, resin and asphalt in the oils decrease gradually. The contents of isocholestanes, Ts and C29Ts increase slightly, and the density, wax content and solidification point of the oils decrease. All of those features of the oils reflect the geological chromatogram efficient and direction of migration of the oils, suggesting that the oils migrated from west to east in an overall direction. The major source rocks (Chijinpu Formation and lower part of Xiagou Formation, Lower Cretaceous) reached a peak of petroleum generation during the late Neogene-Quaternary, that were controlled by tectonic and buried history in the Qingxi depression, and that are still in a maturity-high maturity stage now, during which oil is mainly generated and oil pools are mainly formed. The key stage for this oil system is Neogene to Quaternary, and the trap forming episode corresponds to the oil generation time. Fractures developed by the Himalayan tectogenetic movement form and improve the migrating channels and oil can be accumulated within various traps. The review about potential resources shows that the totally accumulated amount of petroleum is up to 2.5×108-4.0×108t, and still 2×108-3×108t remained resources can be found in this area, so the exploration potential is real high. The Qingxi low lift is just located between the Qingnan and Hongnan sags with high potential of oil-gas generation, that should be a target of oil and gas migration, where existed a plentiful oil-gas supply, reservoir and cap rocks well developed and various kinds of trap would be developed. Therefore, that area should be multiple oil and gas accumulation zones with bright future for exploration and would be the major directions and targets for oil and gas exploration in the Jiuxi basin.

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History of oil migration and accumulation in the Yongqing-Liuqiying buried hill (middle Ordovician) pool, Hexiwu buried hill zone, Langgu depression

ZOU Huayao and ZHANG Chunhua

, 2001, 28(3): 103-0.

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The dating-analysis of petroleum migration and accumulation for Yongqing-Liuqiying buried hill (YLBH)(middle Ordovician) pool has been carried out, based on hydrocarbon generating and expelling simulation in combination with homogenization temperature of organic inclusions. The hydrocarbon charging, through unconformity from the middle sag into the YLBH, had occurred in two separate periods, with most oil in the first and condensate mainly in the second. The oil displaced by late condensate charging could have migrated upward along faults into Eocene, resulting in condensate accumulation in the YLBH and oil in Eocene, respectively. Subject heading: Buried hill reservoir, Reservoir formation, Mode, Langgu segGenetic type of Permian reefs and its application to prediction of buried reefs in Nanpanjiang, South China. SHEN An-jiang; et al. (Hangzhou geological Institute,Research Institute of Petroleum Exploration and Development,PetroChina, Zhejiang 310023, P. R. China). Shiyou Kantan Yu Kaifa 2001, 28(3),29-32. The abundance of reef development and reef's petroleum potential in Nanpanjiang area (including Shiwandashan basin) has been identified through exploration activities in recent thirty years. Methods on prediction of buried reefs become the key of reef petroleum pool exploration. According to the relation between relative sea level change rate and reef growth rate, Permian reef in Nanpanjiang area can be divided into three genetic types: offlapping reef, aggradational reef and progradational reef. Reefs of Maokou age in Nanpanjiang area belong to progradational reef prograding from west to east, while reefs of Changxin age in Nanpanjiang area belong to aggradational reef. Based on the prograding direction of reef belts, buried reefs of Maokou age (Yabeina zone and Neomisellina zone) located in eastern part of Neoschwagerina reef belt could be predicted.

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Genetic type of Permian reefs and its application to prediction of buried reefs in Nanpanjiang, South China

SHEN Anjiang and CHEN Zi

, 2001, 28(3): 104-0.

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The abundance of reef development and reef's petroleum potential in Nanpanjiang area (including Shiwandashan basin) has been identified through exploration activities in recent thirty years. Methods on prediction of buried reefs become the key of reef petroleum pool exploration. According to the relation between relative sea level change rate and reef growth rate, Permian reef in Nanpanjiang area can be divided into three genetic types: offlapping reef, aggradational reef and progradational reef. Reefs of Maokou age in Nanpanjiang area belong to progradational reef prograding from west to east, while reefs of Changxin age in Nanpanjiang area belong to aggradational reef. Based on the prograding direction of reef belts, buried reefs of Maokou age (Yabeina zone and Neomisellina zone) located in eastern part of Neoschwagerina reef belt could be predicted.

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The software package of trap evaluation system

GUO Qiulin; SONG Guochun; ZENG Lei; CHEN Ningsheng and JIANG Ya

, 2001, 28(3): 105-0.

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The authors advance the technical route for the evaluation of traps and introduce the functions of the software of Trap Evaluation System (TrapDEM2.0), taking the evaluation of eight traps in Erlian basin as application examples.The software package of Trap Evaluation System (TrapDEM2.0) consists of three models: trap parameter description, trap evaluation and trap database management. The first model consists of four modules: restoration of structural evolution of trap, seal assessment, fault seal prediction, and parameter distribution, in which some of the advanced techniques such as balanced section, gray method and smear coefficient analysis of fault are used. The second model consists of five modules: geology evaluation, data reliability assessment, resource/reserve calculation, economical assessment, and comprehensive selection. The techniques such as risk analysis, fuzzy theory, weighted mean, expert system, artificial neural networks are utilized in its second module, Monte Carlo and number theory are used in the third module, financial evaluation (cash flow) and minimum economical oil field analysis are adopted in the fourth module and double-factor superposition analysis in the last module. The third model is composed of three modules: basic data management, report management and graphic management.

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The fractal dimension of fractures of carbonate rocks in Hetianhe gas field and its relation to reservoir property

YANG Wei; WANG Qinghua; LIU Xiaozeng; ZHAO Rende and WANG Yuan

, 2001, 28(3): 106-0.

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Hetianhe gas field is a large Carbonate rock gas field discovered in Tarim basin. Its Ordovician reservoir is of fractured-cavernous carbonate. The authors analyzed fractures of Ordovician cores of 70m long from 4 wells of the gas field with fractal theory, and took the logarithm of number of fractures and length of the cores respectively, as a result, positive mutuality is obviously presented between the two sets of logarithmic values. Linear correlation coefficients of 4 wells are all more than 0.97. According to geologic meanings for fractal dimension of the fractures, the value of fractal dimension of the fractures from the wells located at the axis of the structure is larger than that from the wells located at side of the structure, indicating the fractures at axis of structure are more developable than that at side of the structure; the value of fractal dimension of the fractures from the wells located at the axis of the structure decreases from east to west, showing the fractures in the east of structure are more developable than that in the west of the structure; the value of fractal dimension of the fractures decreases from above to below, revealing the developable level of the fractures declines from above to below. The calculating results of the fractal dimension tallies with distribution features of the fractures in fault-sealed anticline. The fractal dimension of the fractures has a good positive mutuality on physical properties of the reservoir (correlation coefficient is 0.9049 to porosity and 0.9968 to permeability). The fractures,developing zones of fractured-cavernous reservoirs can be quantitatively predicted by calculating fractal dimension of the fractures and favorable distributing area of the reservoirs, and it can give a guide to the oil and gas exploration.

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Mechanism study of barrier water flooding

FAN Zifei; LI Yunjuan; WANG Jing and WANG Fachang

, 2001, 28(3): 107-0.

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Zanazol is an oil field with edge water and gas cap whose production scheme is primarily barrier water flooding before the year of 2000. This paper studies the mechanism of barrier water flooding with 3-D 3-phase compositional simulator. The result of simulation shows that about 56 percent of barrier injection water was injected into oil ring and 44 percent into gas cap. Through comparing the results of four development schemes which are barrier water flooding, cyclic barrier water flooding (half year for injection and half year for shut-in of injectors), cyclic barrier water flooding(one year for injection and half year for shut-in of injectors) and natural depletion, it concludes that it is necessary to keep barrier water flooding in Zanazol oil field. In order to optimize the development scheme after barrier wall exists, the following three development schemes are compared: 1) Injecting water into oil ring and gradually stopping barrier water flooding in five year; 2) Injecting water into oil ring (stopping barrier water flooding); 3) Injecting water into oil ring plus barrier water flooding (the water volume injected into oil ring and barrier water injection volume is 85% and 15% of total injected water volume respectively). The simulation result shows that the accumulative recovery of the third production scheme is the highest, this development scheme can maintain reservoir pressure, isolate gas cap, prevent gas in gas cap channeling into producer and thus decrease GOR of producer. It is recommended the production scheme of Zanazol oil field changes to pattern water flooding in the oil ring and continuous barrier water flooding near GOC. To keep the stability of barrier wall developed at present, the water to be injected for barrier water flooding is about 15 percent of the overall water volume necessary to be injected for the balance of injection and production. The research result of mechanism for barrier water flooding is in structive for the accomplishment of the adjustment production plan of Zanazol oil field.

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Analytic solution for flow through horizontal well network

LIU Yuetian

, 2001, 28(3): 108-0.

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By using the elliptical cosine conformal transformation, any element of a 5-point horizontal well network can be transformed to a whole plane. The vertical wellbore in the element is transformed into an infinite circular boundary, and the horizontal well is transformed into the center of this circular region. Applying the results of the flow from a horizontal well to an infinite boundary, the analytic solution of pressure and well rate for the flow through a 5-point horizontal well network is obtained. The streamline distribution figures are presented. The longitudinal and latitudinal well spacing, and the length of horizontal section are considered. When the horizontal section length increases the producing rate goes up but the flood conformance goes down, and the breakthrough point of injected water goes closer to the end of the horizontal well.

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Using the type curves for single-phase flow to interpret two-phase flow testing data

LIU Liming and CHEN Qinlei

, 2001, 28(3): 109-0.

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While discussing the discrete form of two-phase flow governing equation with PEBI grid, the authors present the difference between simulated well testing and conventional reservoir simulation on dealing with the wellbore. A new flow rate model for well testing, which makes no hypothesis for the flow state and can be coupled with the differential equations easily, is firstly constructed. Two-phase flow well testing is analyzed using the above-mentioned model and the results of analysis indicate that under otherwise identical parameters, the span between the pressure difference curve and the pressure derivative curve of a two-phase flow remains the same as that of a single-phase flow, no matter what the initial saturation and the ratio of viscosities may be. So, when given the dimensionless quantities of the two-phase flow, all curves are coincident with the curve of a single-phase flow under otherwise identical parameters.

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The reaccumulation models and distribution prediction of remaining oil in Renqiu buried hill reservoir

XU Zhangyou and ZHANG Jichun

, 2001, 28(3): 110-0.

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The Renqiu buried hill reservoir discovered in 1975 lies in Raoyang sag of Jizhong depression; its producing horizon is of Wumishan Formation of Jixian System of Proterozoic. In general, it is a dual?-porosity massive oil pool with bottom water, which has some laminar characters as well due to existing two interior impermeable layers (Member 6 and Member 8). Over commissioning stage, high and stable production stage and production decline stage, the current recovery factor is small in waterflooded oil area. Oil saturation analysis of the cores from waterflooded zones and water driving oil test result show that the remaining oil distributes in microfracture, minute fracture and matrix of the buried hill reservoir. Based on six time lapsed deep lateral logging data from Well Renguan 6 within 15 years, remaining oil in buried hill reservoir would really be reaccumulated. With the combinational contribution of fault and buried hill top surface with two interior impermeable layers, many traps formed,which can be divided into three types of top sealing, bottom barriering and top-bottom sandwich. According to the mechanism of remaining oil reaccumulation, the distribution pattern of three remaining oil reaccumulation types is predicted. It is suggested that the potential targets should be: the remaining oils in the traps sealed by the interior fault with Member 6, interior fault with Member 8 and interior fault with top and bottom barriers.

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Simulation of component transport in surfactant flooding processes

WANG Jian; LUO Pingya and ZHANG Guoqing

, 2001, 28(3): 111-0.

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A mathematical model of component transport in surfactant flooding has been built up, in which the needed physical-chemistry parameters were modeled as chemical concentration dependent functions. The parameter of “effective displacement zone size” was defined to quantify and analyze the mechanisms that many factors such as adsorption, diffusion-dispersion, slug size, and displacement velocity influencing on component transport processes and results. The validity and durability of surfactant ORS-41 transport in porous media during ASP combination flooding in Daqing oil field are analyzed. The research achievements will not only be a guideline for engineering & technology project design and dynamic monitoring of combination, but also can replace partial flow displacement in laboratory and assisted mechanism investigation. The distinct feature of the developed simulator is the very skillful process of boundary conditions in the calculation of mathematical model in chemical slug injection, and providing more reliable and accurate results by using finite differences solution of prediction and correction format. The reliability can be examined by corresponding physical simulation (displacement) experiments

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The application of four-dimensional seismic technology to heavy oil production

HUO Jin; ZHANG Xinguo; WU Ping; FENG Liwei and HE Xin

, 2001, 28(3): 112-0.

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The response of seismic information to the steam-heated zone is observed mainly through the variation of amplitude, interval velocity and time delay of the reflected wave. The zones with obvious variation belongs to the advancing scope of steam front, and those with no or less variation have not been influenced by the steam heat, i.e., remaining oil distributed zones. The remaining oil distributed zones of Well 95159 exist in three areas as between Well 95159 and Well 95178, south to Well 95140 and north to Well 95197. Based on the study of remaining oil distribution and some other dynamic production data, we improved the steam flooding process through sorted adjustment, planar infill drilling and profile control by plugging and packing, and the result is satisfactory. In 1999, the oil production decline was reduced from 1995's 5.5% to -6.7%, and the oil to steam ratio from 1995's 0.12 to 0.27%.

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A study on the relative permeability curves of the west area of Block 7 in Gudong oil field

HUANG Wenfen; WANG Jianyong and FAN Zheyuan

, 2001, 28(3): 113-0.

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The relative permeability curve reflects the flowing law of oil and water under different water-saturation, which is the basic data of productivity predicting in the development designing. On the other hand, the changes of eigenvalue of the relative permeability curves could reflect the changes of pore structure, which is useful for taking effective measures to tap the remaining oil. According to the results of analysis of the characteristics of the different water-drive stages relative permeability curves of the west area of Block 7 in Gudong oil field,the porestructure and fluid flowing features of the reservoir have changed through long-term flooding. These changes, such as irreducible water saturation and residual oil saturation decreasing, the water saturation of equal-permeability point and water relative permeability under residual oil saturation increasing, reflect that the reservoir porosity enlarged, clay mineral and specific surface area of pore reduced, and the surface of pore is more hydrophilous. Analysis of relative permeability parameters indicates that influences of porosity to permeability and permeability to residual oil saturation and the oil displacement efficiency have been enhanced relatively. Study results provide theoretic dependency for tertiary recovery measures that are established in improving pore structure and oil displacement profile and reducing contradiction between pores.

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In-situ stress analysis and evaluation by using of electric logging

OUYANG Jian and WANG Guiwen

, 2001, 28(3): 114-0.

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At present, the major methods for measuring present-day in-situ stress are earthquake mechanism analysis, hydraulic fracturing, borehole cave-in and so on. These methods all measure the local point only and hard to get a vast amount of in-situ stress data due to the limitation of engineering and economic conditions. In recent years, by studying the data of mudstones of foothill structural belt in the west of China and that of the electric logging of limestone in complex structures in the south of China, the authors find that the resistivity of mudstone and limestone deposited stably is highly sensitive to in-situ stress, the resistivity of mudstone and limestone located in compressive stress area is one order of magnitude higher than that in normal stress area. The authors hold that by using electric log to analyze and evaluate quantitatively the present-day in-situ stress can obtain not only a high resolution, but also the information of generally continuous vertical in-situ stress. The authors briefly present initial results achieved by using the two methods—counting up the electrical well logging data and analyzing in-situ stress quantitatively by sample experiments, set forth the relations among wide-ranging abnormal high pressure in foothill structural belt, complex structures near the region of the borehole and the in-situ stress near the region of the borehole and put forward the research direction in in-situ stress analysis and evaluation by electric logging in the coming years.

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Applying surface survey markers to stratigraphic correlation in Qaidam basin by jointing them to seismic events

CAO Yinghui and SHI Guangren

, 2001, 28(3): 506-0.

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Because the distribution of outcrops is universal in the intermountain basin, it is important to fully use surface markers to calibrate seismic events at the place where wells are rare. Four procedures are discussed in this paper to calibrate seismic events with surface survey marker. Firstly, drawing the relative position map of seismic lines and surface survey markers according to their coordinate systems. Secondly, calculating the apparent dip in the direction of seismic line. Thirdly, calculating the slant interval transit time. Additionally, if the elevation of seismic line and surface markers are not equal, the elevation correction is needed. Finally, tracing the seismic event that the interval transit time equates to Δt in the seismic section. This method is not only simple but also effective for the stratigraphic correlation in the intermountain basin. A good result has been achieved in the stratigraphic correlation at Lenghu-7 structure, Qaidam basin by using this method.

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High-speed and high-efficiency development technology for Shengli very shallow sea oil field

SONG Wanchao

, 2001, 28(3): 507-0.

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Chengdao oil field is a large very-shallow sea oil field in China's Bohai Bay. Because of its complicated state of the sea and geological condition, many kinds of new techniques and methods are explored, introduced, developed and applied in the process of research and design of reservoir geology, reservoir engineering, production technology and maritime work. Chengdao oil field now has had a overall production capacity of 2.48×106t per year since it was put into production in 1993, and attained high-speed and high-efficiency development, during which a complete set of production technology has been developed for Shengli very shallow sea oil field.

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A formula for evaluating practicability of producing remaining oil at the top of positive rhythm reservoir by horizontal sidetracking

YU Qitai; XIE Xuquan; LUO Hong and CHEN Suzhen

, 2001, 28(3): 510-0.

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By using numerical reservoir simulation of 1/4 unit of a five-spot pattern in a positive rhythm reservoir, which is first produced by the vertical well to water cut 98%, then by the horizontal sidetracking to water cut 98%, a multiple regression formula of relative increase of recovery factor of the horizontal sidetracks in contrast with the vertical well was obtained by using reservoir engineering and mathematical statistics. Then using the Cipachev water displacement curve the maximum recoverable reserve was calculated, using the decline curve of the Arps decline index n=0.5 the production profile was simulated and by applying the orthogonal design to different parameter programs the economic evaluation of the horizontal sidetracks was carried out as well. In terms of the results of evaluation, a formula for evaluating practicability of producing remaining oil at the top of positive rhythm reservoir by horizontal sidetracking has been proposed, which is based on the principle of balance between investment and output. The formula considers 3 main kinds of factor affecting the effects of the horizontal sidetracking: reservoir parameters, well parameters and economic parameters. It is shown that horizontal sidetracking is a very important technology for producing remaining oil of mature oilfields, which has a very large potential.

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Well test analysis in multi-layer reservoir

ZHANG Wangming; HAN Dakuang; LIAN Qixiang and CHENG Yuanzhong

, 2001, 28(3): 511-0.

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A multi-layer reservoir may have a pressure behavior different from that of a single-layer reservoir, and objective of well test analysis is to obtain individual-layer permeability and skin factors. This paper discusses some characteristics of pressure draw-down and build-up behavior in bounded commingled reservoir, and studies especially mechanism of differential depletion during well production and inter-layer cross-flow after shut-in well. The results demonstrate that differential depletion is due to difference of reservoir parameters and pore volume among layers. Inter-layer cross-flow will be happen when differential depletion occurs.As a result, there are “step shapes” on pressure buildup curves. Based on only well-bottom pressure data, a constrained nonlinear regression algorithm for well test analysis is presented, and dynamic and static multi-layer reservoir information provided by production logging is considered as the constrains. Applications of oil field examples indicate the method can explain each layer parameters in the absence of single-layer transient test or MLT.

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Procedures for improving producing utility of low efficient wells and their application results

XIAO Li-ping; WU Xuguao; MENG Jianhua and ZHAO Puguang

, 2001, 28(3): 514-0.

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In 1988, 243 of the 527 oil producing wells of Wengmingzai, Weichang and Mazhai oil fields had an input-output ratio of only 1∶0.82 due to high water-cut pay zones, difficult zonal production, bad well condition, formation damage and plugging, low permeability and frequent grind leading to suspension of wells. Since 1999, a serious technical measures have been adopted, including analysis of the reasons causing low efficiency of wells,well produing performance analysis at well-site, integration of subsurface, wellbore and surface methods, which results in the realization of increasing oil production by controlling the well suspension and improving producing efficiency of wells while reducing their production cost. The practicable methods adopted integrally for this field, including converting the low efficient wells into water injectors, increasing the affection directions, workover, recompletion, fracturing and water shut-off for not fully perforated well patterns; increasing the liquid production for non-response wells; controlling the electric power consumsion and suspension of those wells with an input-output ratio larger than 1∶0.85; and shutting-in or intermittent opening oil wells,collecting timely the oil produced for the low potential or low production capacity wells,are very useful in reducing the production cost by 31.9% and increasing the input-output ratio to 1∶1.25.

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A study on the optimum injection time of water shutoff agents

LI Kehua; WANG Renfang and ZHAO Fulin

, 2001, 28(3): 515-0.

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Water plugging treatment in oil fields is a key measurement to control water in production well and improve waterflooding performance by reducing fluid channeling through high-permeability thief zones.It plays an important role in waterflooding oil fields. The effect of such treatment often depends on placing the water shutoff agents in thief interval. Based on the difference of pressure drop rate in higher and lower permeability zones and the core experiments, the effect of well shut-in time on the distribution of water shutoff agents was studied in this paper. It was proved that the water shutoff agents have an optimum injection time to play their plugging effect theoretically and experimentally. Based on the characteristics of pressure drop curve, the mathematical equation was obtained from curve fitting. The optimum injection time of water shutoff agents may be determined by using the method of calculating extreme value mathematically. It was turned out that selecting an appropriate time to inject water shutoff agents is very important to fully play their plugging effect.

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Building reservoir model at the design phase of oilfield development plan

WANG Hui and ZHAO Jianhui

, 2001, 28(3): 518-0.

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Reservoir model is the final result of reservoir description, which is the basis of numerical reservoir simulation. The more precise conceptual model can be built in designation phase of field development plan. There are only few wells in this phase, so it is very difficult to build very accurate reservoir model just by log data. This paper presents a novel method used to build reservoir model, which can integrate seismic data, log data and geology data using geostatistics software GRIDSTAT. First, seismic data volume were directly inverted to porosity. Second,“hard data” (log data),“soft data” (seismic data) and the geologist's view to reservoir distribution (reservoir sedimentary faces) are integrated to build reservoir model by geostatistics method. Integrating all kinds of geological information of reservoir distribution to build reservoir model is the apparently merit of this method, which provides more precise reservoir model to reservoir engineering, quantifies the geological conception, and is useful for making field development plan. The reservoir model of Nanpu35-2 oil field was built by this method, which accurately described the reservoir distribution and met the need of reservoir simulation and designation of field development plan.

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Mathematical modeling of dynamic chromatography fingerprint monitoring in the oilfield development

JIN Xiaohui; ZHU Dan and LIN Renzi

, 2001, 28(3): 519-0.

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The contribution of individual layers to liquid production is different from each other in the production due to heterogeneities of reservoir rocks and the fluid distribution. Dynamically geochemical monitoring in oilfield development is to estimate the variation of bulk liquid production according to the composition of chromatography fingerprint in the reservoir using chromatography fingerprint correlation analysis developed in 1990's. The aim is to monitor the behavior of fluid in the reservoir, to carry out reservoir management, and make measure to raise oil recovery factor. Physical and mathematical models based on the QR calculation have been made according to the process of commingled production of different pay zones. Chromatography fingerprint parameter database can be established using allocation experimental technology to carry out the research of chemical and mathematical modeling and to determine the characteristic methods of those and the four constrained conditions of model parameters. Modeling results show that the constrained conditions of chromatography fingerprint parameters in calculation are:(1) the parameter reflecting the heterogeneity of each single pay zone remains constant with the variation of contribution; (2) for one fingerprint compound, the content of this compound in the commingled samples are under the control of the relative contribution of single pay zone respectively ; (3)a certain discrete degree must be exist between the array of the parameters of each zone. Therefore mathematical modeling on dynamic monitoring of three-pay zone commingled production has been resolved by choosing new parameter. The comprehensive research has been developed on the theory model of dynamically geochemical monitoring technology and dynamic analysis of oilfield exploitation. This is significant in theory and practice.

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Petroleum geologic characteristics and exploration prospect of Fula sub-basin in Muglad basin

LU Yancang; HE Bizhu; WANG Xiulin and WANG Wangquan

, 2001, 28(3): 524-0.

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Fula sub-basin is a Mesozoic and Cenozoic continental rifted basin, which is controlled by the Center Africa Strike-slip fault. There has been three sedimentary cycles developed from Cretaceous to Quaternary. AG Formation lacustrine facies shale and claystone deposited during early Cretaceous is of organic-rich, which is rated as good-to-excellent source rock. After that, there have been two assemblages of reservoir and seal in Cretaceous formation. Fula sub-basin has plain and clear structural framework. There are three positive and two negative structural units in this sub-basin.Structural types are mainly roller-over anticlines, faulted noses and so on. These traps distributed in belts. 4 reservoir-forming zones are identified. This sub-basin is of great hydrocarbon resource and prospects, has a good exploration potential.

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Experiences and lessons in oil and gas geochemical exploration

LIU Chongxi; ZHAO Kebin and CHENG Jun

, 2001, 28(3): 525-0.

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After analyzing the experiences and lessons in petroleum geochemical exploration of previous decades with the examples of exploration in Tarim, Junggar and some other basins, the authors hold that the reasons why the development of petroleum geochemical exploration is sometimes easy, sometimes difficult; sometimes rises and sometimes falls, is that the tendency of injuring credit of the results of geochemical exploration is present in previous work, which is mainly characterized by:(1)Violating“The Technical Regulation for Oil and Gas Geochemical Prospecting”: Ignoring procedures of oil and gas geochemical exploration, confusing stages of exploration, evaluating trap with survey achievement in little scale and few precision, or reflecting oil and gas fields by lower stage area abnormities.(2)Ignoring research on interference factors in geochemical exploration. Interference factors widely exist. Constraining interference factors is an important topic for researchers with more experiences. Having constrained physical geography landscape, rock qualities, modern biological geochemical actions and human pollution into full limit, the abnormities can be defined that reflect the information of oil and gas. (3)Ignoring the construction of the work team working for geochemical exploration. The work team should be a group in which professionals from various fields work in a good synergy. However for a long time past, the development of this technique has been restricted and also the credit of this technique injured, due to the fact that some non-professional groups have low technical competence and poor comprehensive research abilities.(4)Ignoring geological survey. Fieldwork is poor in quality. People were impatient for seeking partial and mineral-caused abnormities in works for the first time. Besides, methods for data processing and defining abnormities are very single, etc.,these are the important reasons of reducing the confidence level of achievements. Geochemical exploration is techniques and methods with scientific basis and developing potentiality. Some problems that influence its development above-mentioned are mostly produced under the circumstances of non-serial competition and out of control; it should not to attribute all problems to the technique itself. Petroleum geochemical exploration technique is a method that has scientific basis and great potentialities, it will certainly develop healthily and rapidly if the unhealthy tendencies above-mentioned are checked up.

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Features and genesis of regional geochemical fields of the main hydrocarbon-bearing basins in China

TANG Yu-ping; DING Xiangyu; WU Xianghua; WEI Wei and LI Shanggang

, 2001, 28(3): 548-0.

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The key geochemical prospecting indicators of 14 main hydrocarbon-bearing basins and their various characteristics have been analyzed statistically, and the genesis and variation of the indicators have been discussed. Based on this, a criterion has been proposed to classify the regional geochemical field of the main hydrocarbon-bearing basins in China. A variation trend has been pointed out in this paper that the geochemical background field descends gradually (i.e. high background field exists in the basins of the West, medium background field in the basins of the Central, the East and the offshore basins and low background field in the basins of the Northeast); while the indicator variability increases constantly from west to east (e.g. the variation coefficient of acidolyzed hydrocarbon ranging from 0.21 to 0.40 in the north of Tarim basin, 0.37 to 1.2 in the central and eastern basins and 1.11 to 3.50 in the south of Songliao basin) with the lower humidity coefficient of hydrocarbons in the west and the higher humidity coefficient in the east. Geochemical field of the main hydrocarbon-bearing basins in China obviously relates to geothermal gradient, which reveals the relatives between them genetically.

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Applying the comprehensive geophysical technology to the prediction of oil-bearing potenlial in saline lake deposit

PENG Luping; LI Zaiguang and CAO Zhenglin

, 2001, 28(3): 549-0.

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The processing of the seismic, logging and geological information is made according to seismic-geological conditions of salt lake basin through multi-dimensional predictive technique, which extracts seismic efficacious multi-attribute information. By using many kinds of geologico-physicsal model and with the help of multidimensional analysis geological prognostic objectives are defined, and prognostic evaluation of oil-bearing features for salt lake basin. The application to salt lake basin indicated that multidimensional predictive technique could effectively reduce the ambiguous solutions of prognostic object, and obviously cut back wraps, which shows this is an applicable technique.

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Geochemical characteristics and natural gas sources of Bozhong depression, Bohai Bay basin

HUANG Zhengji and LI Xiufen

, 2001, 28(3): 560-0.

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Among the natural gases discovered in Bozhong depression, hydrocarbon gas is dominant and non-hydrocarbon gas is small. Of the gases found below the Dongying cap rocks, most are wet gas and a few are dry gas. This dry gas was formed by pyrolysis. But among the gases found beneath the Minghuazhen cap rocks, most are dry gas and a few are wet gas. This dry gas was formed by biodgradiation. The gases from Shahejie and Dongying source rocks are mostly oil-type gas. The gas of QHD30-1 is mixed gas and mainly from the coal-derived gas from pre-Tertiary source rocks. The formation of natural gas in the Bozhong depression is characterized by multiple sources, multi-periods and continuous generation and expulsion. So its exploration potential is good in Bozhong depression. The regions where the Dongying cap rocks well developed are the major exploration targets of natural gas.

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The characteristics of abnormal pressure in deep formations in Qikou sag, Huanghua depression, Bohai Bay basin

LIU Guangdi and WANG Deqiang

, 2001, 28(3): 561-0.

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Three pressure zones were identified by pressure data derived from sonic log in Qikou sag, Huanghua depression. These three pressure zones were the hydrostatic zone, the upper overpressured zone and lower overpressured zone. The bottom depth of the hydrostatic zone is approximately 2,000m. The upper overpressured zone mainly occurred in the central part of the sag, while the lower overpressured zone developed all over the sag. The thickness of the upper overpressured zone is only several hundred meters and the pressure coefficient is 1.3-1.4. The top depth of lower overpressured zone is 2,000-2,500m in marginal area and 3,000m in the central part. With the value of 1.5-1.6, the pressure coefficient is higher in the lower overpressured zone than in the upper one. The pressure coefficient is vertically higher in the first member of Shahejie Formation, as compared with that in the second and the third members of Shahejie Formation, and is horizontally higher in the central part of the sag, as compared with that in the marginal area. The distribution of abnormal pressure is mainly controlled by the burial depth and strata, and is also closely related to diagenesis.

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Characteristic analyses of proven OOIP in Jiyang depression

GUO Yuanling; ZHAO Yueqiang; SHI Hongxia and GAO Lei

, 2001, 28(3): 584-0.

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The characteristics of OOIP in Jiyang depression, a non-marine fault basin, are very representative. From the analysis of buried horizon, pool type, crude-oil nature, production performance, reserves increase history and quality change, we know that pool distribution and enrichment have been controlled by the structure and sediment in Jiyang depression, and that the production performance of sandstone-structural oil reservoirs is much better in all kinds of oil reservoirs. After the exploration of about 40 years, Jiyang depression has experienced peak reserves increase and stepped into such a present stage as mainly looking for medium and small sized subtle complex lithologic pools and structural pools, oil reserves increasing steadily and proven oil reserve quality having a tendency to decrease totally.

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On the match of various exploration engineering technologies

YUE Jin; LIU Wenlin; HU Suyun; HE Haiqing; DONG Jie; LIN Jian and WANG Yongli

, 2001, 28(3): 585-0.

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China is looking for new oil and gas resources in new area with harsh surface conditions, extremely complex subsurface structures, as well as new reserves in maturing fields by progressive exploration. The selection of the exploration targets is important, at the same time, the fully development and comprehensive utilization of advanced and applicable exploration technologies are even more important. In the coming five to ten years, oil and gas exploration of PetroChina will focus on the five key types of target (lithological reservoirs with large area but low petroleum abundance, composite subtle reservoirs, composite structural reservoirs on steep slopes in foreland basins, fractured and cavernous carbonate reservoirs in stabilized area of platform basin, buried hill reservoirs in down-faulted area of platform basin, and complex faulted block reservoirs in the mature oil regions). Based on different geological characteristics of these targets, the analysis of the demands for exploration engineering technologies (seismic acquisition technology, seismic processing technology, comprehensive seismic interpretation technology, well logging technology, drilling and completion technology and fracturing and acidizing technology) is conducted. The common features of oil and gas exploration targets include: concealment, complexity, delineation difficulty and poor data quality, so whence matching the exploration engineering technologies stress must be laid on their accordance, applicable effectiveness, reasonable match as well as creativeness. 6 successful examples of comprehensive utilization of exploration technologies are introduced. The progress of oil and gas exploration depends on the advancement of exploration engineering technologies. The authors hold that in the future the advancement of every single exploration engineering technology and the progress of comprehensive exploration technologies should be given more attention to.

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, Volume 28 Issue 3