Petroleum Exploration and Development

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PetroChina key exploration domains: Geological cognition, core technology, exploration effect and exploration direction

JIA Chengzao; ZHAO Zhengzhang; DU Jinhu; ZHAO Wenzhi; ZOU Caineng and HU Suyun

, 2008, 35(4): 1616-0.

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On the basis of the third evaluation on hydrocarbon resources and the distribution estimation of residual oil/gas resources, PetroChina puts forward four key exploration domains which are litho-stratigraphic reservoirs, foreland thrust belts, middle and lower combinations of the superimposed basins, and hydrocarbon-rich depressions or plays in the mature exploration area. The litho-stratigraphic reservoir has become the main body of the proved reserves growth, the foreland thrust belts are the important domains for finding significant discoveries, the middle and lower combinations in the superimposed basins have increasingly important status in increasing geological reserves, and the fine exploration in hydrocarbon-rich depressions or plays have also prodigious exploration potential. Future's residual hydrocarbon resources are mainly distributed in seven domains, which are large-scale litho-stratigraphic reservoirs, hydrocarbon-rich depressions (plays) in rift-subsidence basins, foreland thrust belts, middle-lower combinations in the superimposed basins, onshore new exploring areas and new basins, south areas of South China Sea, and unconventional resources. Among them, the former four domains have great exploration potential and are the important areas for reserves and production growth, and the latter three domains are the important fields of realizing resources strategic relay for PetroChina in the future.

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Application of multi-component seismic exploration in the exploration and production of lithologic gas reservoirs

ZHAO Bangliu

, 2008, 35(4): 1617-0.

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The multi-component seismic exploration technique has drawn great attention in the petroleum industry because it utilizes the S-wave information, reduces the ambiguity in reservoir prediction, and improves the prediction and identification possibility of reservoir fluids. To push forward the application and development of the technique, the 2D and 3D multi-component technical tests have been carried out since 2002 in the Sulige gasfield, Ordos Basin; the Guang'an gasfield, Sichuan Basin; the Xushen gasfield, Songliao Basin; and the Sanhu area, Qaidam Basin. The imaging of the converted wave is better than that of the P-wave for the gas-bearing structures in the deep igneous body of the Songliao Basin and the Sanhu area, and can define the reservoir boundaries more accurately. In the description of the tight sand gas reservoirs of the Sulige and Guang'an gasfields, the converted wave imaging improves the accuracy of reservoir prediction and fluid identification, paying the way for the arrangement of wells.

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Adsorption characteristics of low-rank coal reservoirs and coalbed methane development potential, Junggar Basin

YU Yuanjiang; WANG Yonghua; YANG Qi; LIU Dameng; HU Baolin; HUANG Wenhui and CHE Yao

, 2008, 35(4): 1618-0.

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Badaowan Formation (J1b) and Xishanyao Formation (J2x), which are the main low-rank coal reservoirs in the Junggar Basin, possess strong ability to adsorb and accumulate coalbed methane (CBM). Isothermal adsorption experiment of coal samples shows that the J2x coal reservoir has better adsorption and desorption capacity for CBM as well as considerable CBM development potential. Changji-Urumqi-Fukang region, Cainan-Balikun coalmine area and central parts of the basin attain higher adsorbability and stronger storage ability to CBM. Langmuir volume increases with and is a function of Ro. The CBM adsorbance of the reservoirs increases with pressure. Four types of CBM regions partitioned according to Langmuir volumes are CBM-rich areas, slightly CBM-rich areas, CBM-containing areas and CBM-barren areas. The Qing 1 to Qi 8 well region, the Changji-Urumqi-Fukang region, the slope belt of northwest margin and the basin belly (mainly slightly CBM-rich areas), as well as the Cainan-Balikun coalmine region in eastern Junggar Basin (CBM-rich area) should have better development potential for CBM.

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塔里木盆地满加尔凹陷下古生界烃源岩的再认识

ZHAO Mengjun; WANG Zhaoming; PAN Wenqing; LIU Shaobo; QIN Shengfei and HAN Jianfa

, 2008, 35(4): 1619-0.

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Considering its vertical distribution characteristics, this article argues that the Lower Palaeozoic source rock in the Manjiaer Sag is composed of three sets of source rocks of Middle-Lower Cambrian, Middle-Lower Ordovician and Upper Ordovician. The source rock of the Middle-Lower Ordovician Heituwa Formation has similar sedimentary facies and developmental features to the Middle-Lower Cambrian source rock, and has abundant organic material. The Upper Ordovician source rock is poor and limited in distribution. The source rocks have different thermal evolution histories. In central and western Manjiaer Sag, Middle-Lower Cambrian source rock entered oil generation peak in Late Caledonian and Early Hercynian, Middle-Lower Ordovician source rock in Late Hercynian, and Upper Ordovician source rock in Late Yanshan and Himalayan. The threefold division of the source rock is the foundation of detailed study on the derived source and the accumulation process of marine oil in Tarim platform area.

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Control of strike-slip faulting on reservoir formation of oil and gas in Nanpu sag

DONG Yuexia; WANG Zecheng; ZHENG Hongju and XU An-na

, 2008, 35(4): 1620-0.

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According to the data of seism, gravity, drilling, etc, this paper reexamines the Baigezhuang fracture and the Xi'nanzhuang fracture and analyzes the control of structural deformation on the hydrocarbon accumulation in the Nanpu sag. The Baigezhuang and Xi'nanzhuang fractures merged into a base strike-slip fracture which had distinct left strike-slip at the Yanshan stage lasting until the Es stage and controlled on the Es deposition. The Paleogene basin-forming in the Nanpu sag was controlled by the left strike-slip Baigezhuang-Xi'nanzhuang base fracture and the Nanpu sag was a strike-slip stretching sag. The NE and NW strike-slip fault belts with conjugate shearing were formed by the Neogene fault strike slipping and controlled the distribution of secondary structural belts. The substantial hydrocarbon accumulation in the Nanpu sag has matched in time with the Neogene fault movement, which is favorable to oil and gas migration and trap formation, so the oil and gas are distributed vertically along fault belts as multiple layers

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Forecasting of fracture reservoirs in thin carbonate rocks of precipitous structure belt, East Sichuan

LIU Hong; CAI Zhengqi; TAN Xiucheng; HE Xiuqiong; Lü Bin; DU Weifeng; MU Chun and CHEN Dongliang

, 2008, 35(4): 1621-0.

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Taking the T1j21 fracture reservoir of the Dachiganjing structure belt as a case, this article adopts the trend surface fitting method and the difference method to calculate facial curvature, uses the three point cyclographic method and the curve fitting method to calculate linear curvature, then normalizes the four obtained curvature values and gets the four corresponding relative curvature values. The maximal relative curvature value (i.e. comprehensive curvature) is used to forecast fracture type reservoirs. This is called the comprehensive curvature method and it can overcome the deficiency of the single curvature calculating method. The analyses of the oil and gas shows in drilling and the daily gas production data of gas wells show that the new method has better effects than the single curvature calculating method in fracture forecasting. The correlation coefficient between the comprehensive curvature value and the daily gas production data is the biggest, indicating that the new method improves the forecasting accuracy.

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Reservoir-forming conditions of platform margin belt in southern slope of Tazhong, Tarim Basin

GAO Zhiqian; FAN Tailiang; LIU Dianbo; LI Yao and YU Meili

, 2008, 35(4): 1622-0.

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Based on the new seismic and logging data, this paper identifies the location and shape of the platform margin belt in Tazhong, Tarim Basin and studies its structural characteristics and reservoir-forming conditions using isochronous sequence framework, structural analysis, sedimentary evolution and other methods. The platform margin belt is a large composite slope break belt formed from the end of the early Ordovician to the early of Late Ordovician. Its east section is a complicated faulted slope break resulted from erosion before Late Ordovician, and its west is a carbonate sedimentary slope break in which the platform margin reef flat complex was developed in the Lianglitage Formation of the Upper Ordovician. The belt can be divided into six parts with different structural and sedimentary characteristics. The first and second parts are the superimposed segment of the on-lap trigonal zone and the erosional trigonal zone, in which karst and lithologic reservoirs were well-developed. Platform margin reef flats were well-developed in the fifth part. These three zones are the main exploration targets.

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Structural pattern and its control on hydrocarbon accumulations in Wushi Sag, Kuche Depression, Tarim Basin

ZHENG Min; PENG Gengxin; LEI Ganglin; GUO Huaqing; HUANG Shaoying; WU Chao and LI Yuejun

, 2008, 35(4): 1623-0.

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Affected by the South Tianshan orogenesis, the faulted structure patterns in the Wushi Sag are very complex. Aimed to find out the basic characteristics of the structures, this article studies many seismic profile sections, the regional geology, the structural patterns and the formative stage of the structures. The Wushi Sag has three main fault patterns (face to face thrust, back to back thrust, sphenoid thrust), and many local fault structural patterns (fault-bend fold, fault-propagation fold, duplex structure, outburst structure, growth structure, etc). There mainly develops four groups of reverse faults (NE, NEE, NW, EW) and one group of NNW trending strike-slip faults. According to the structural background, seismic profiles and balanced cross sections, the main fault in the studied area experienced at least five evolving stages which are pre-Mesozoic, late Permian-early Tertiary, Jurassic, late Jurassic-early Cretaceous, and late Neogene. The structural styles have close relationship with source rocks, hydrocarbon reservoirs, and the character and distribution of petroleum systems.

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Numerical calculation for the distance to target center in directional and horizontal wells

LU Gang; LI Xiaoguang and SHAN Junfeng

, 2008, 35(4): 1624-0.

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The calculation of the distance to target center is important in the trajectory quality inspection, and its core is to solve the coordinate of the entry point to targets. The entry point is a cross point of trajectory and a spatial plane: in directional wells, this plane is the horizontal plane; in horizontal wells, it is the vertical plane of the target axis. A scanning algorithm for target-entry interval is given according to the concept of directed distance from point to plane. This method can fast determine the target-entry interval. This paper studies the numerical iterative method - bisection and its convergence performance, which is used to solve the key-parameter equation of target-entry point, and gives detailed formulas for three interval curve types of spatial arc, cylindrical helical and natural curve. Theoretical and practical cases show that bisection method is very effective in solving the numerical solution of target-entering point.

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An unsteady seepage flow model considering kickoff pressure gradient for low-permeability gas reservoirs

FENG Guoqing; LIU Qiguo; SHI Guangzhi and LIN Zuohua

, 2008, 35(4): 1625-0.

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Kickoff pressure gradient occurs when gas flows in a low permeability reservoir. In order to describe the unsteady seepage flow in this kind of reservoir, an unsteady-state seepage flow mathematical model which takes kickoff pressure gradient into consideration is built up based on predecessors' research and the characteristic of start-up pressure gradient existing in low velocity non-Darcy percolation flow (the fluid flow boundary expands outwards constantly). Combining the Laplace space analytic solution by using Green function method with the numerical approximation, the non-linear mathematical model can be resolved. An equation for calculating single-well control radius is established, and a single-well control radius chart board is drawn up which can be used to calculate single-well control radius. Case study indicates that the unsteady seepage flow model taking kickoff pressure gradient into account can correctly present the percolation mechanism and real production performance of a low-permeability gas reservoir.

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Development techniques for deep complex fault block reservoirs with low permeability in Zhongyuan Oilfield

DAI Shengqun; ZHANG Changmin; YIN Taiju; GONG Fuhua and ZOU Shilei

, 2008, 35(4): 1626-0.

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This article builds up the computational models of the minimum oil-bearing area, development investment, development profit, economic feasibility, decline rules and economic reserve scale of deep low-permeability reservoirs. Study shows that the minimum oil-bearing area of the marginal reservoir is 0.02 km2; the economic threshold production is affected by reservoir burial depth, price of the crude oil, and operation cost of per ton of oil, of which burial depth and crude oil price are the sensitive factors affecting the economic production capacity; minimum reserve scale is affected by burial depth, recovery and consumption price of the crude oil and the operation cost of per ton of oil, of which burial depth and the consumption price of the crude oil are the sensitive factors affecting the economic reserve scale. Because of the increasing crude oil price, the original low-efficiency or invalid reserves could be reestimated as the economic ones. The Es36-7 reservoir of the block Wei 360 is on the edge of the economic development.

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Effect of practical techniques in producing remaining oil in Gudong Oilfield

WANG Xuezhong and ZENG Liu-fang

, 2008, 35(4): 1627-0.

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In recent years, the Gudong Oilfield has made a great progress in the description and production of remaining oil. By drilling new wells in old districts, carbon-oxygen log, fine reservoir description, etc., the remaining-oil distributed zones were predicted, and by drilling horizontal wells in old districts, surfactant-polymer-combination flooding pilot etc., the remaining oil was produced. By Dec. 2007, it had drilled 43 horizontal wells, and the cumulative oil increment amounted to 42×104 t. According to the statistics of the drilled effective thickness of new wells, the evaluation of the obtainable productivity, the comparison between the actual drilled effective thickness and the estimated, and the production comparison between new wells and the old wells, the method of drilling new wells in old districts improved the resources utilization degree, oil productivity and recovery. The first-ever S-P composite flooding pilot was carried out in Sep. 2003 in the Gudong Oilfield. By Dec. 2007, the cumulative oil increment was 13.1×104 t. The evaluation results of the Weng-model and the graduation-decline method indicated that the S-P pilot increased the oil recovery factor by 7.6%. Predicting recoverable reserves after deducting ineffective liquid production, evaluating production index after eliminating production time difference, dividing the oilfield development phase using the production rate of recoverable reserves and other evaluation methods are helpful to the understanding of the oilfield development rule.

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Pressure gradient computation and application of wireline formation tester

WANG Changxue; CAO Wenli and WANG Xiangrong

, 2008, 35(4): 1628-0.

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One function of the wireline formation tester is to calculate pressure-depth gradient line (pressure gradient） from testing data. Its application is limited resulting from the uncertainties in the computational method which often results in a big deviation. The effect of the reservoir thickness, the effective measuring point number and the measurement error distribution of pressure-measuring points on the computational precision of pressure gradient was studied by numerical simulation. The result is: the thicker the measured reservoir and the more the measuring-point number and the closer the measurement errors of all measuring points are, the higher the computation precision is. The selection of measuring points should take into account fluid character, formation pressure coefficient, reservoir connectivity, etc. Pressure gradient can be applied in the analysis of the fluid character, the oil-water interface, the vertical connectivity of reservoirs, the pressure systems, the vertical change of formation fluid in single wells, and in the assistant evaluation of reservoirs in multi-wells.

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Low-cost drilling and completion techniques for coalbed methane in southern Qinshui Basin, Central China

QIAO Lei; SHEN Ruichen; HUANG Hongchun; WANG Kailong and XIAN Baoan

, 2008, 35(4): 1629-0.

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The southern Qinshui basin is rich in coalbed methane (CBM), it is the first area that obtained good results in the commercial development of CBM in China. No.3 layer, the main producing zone, is buried shallow and the formation pressure is stable. So the low-cost drilling techniques, such as the small rig, second-spudding well structure and air or clean water drilling can satisfy the production demand. Based on the special requirements in the CBM development, such as drilling geology, draining water during gas production and low cost technology, this article establishes the optimum trajectory model of cluster wells for producing CBM, and makes a in-depth study on the optimum design of well trajectory and the composition of drilling tool. It also evaluates the economic benefits of low-cost vertical wells and four-well-composition cluster wells. The result indicates that CBM can be produced with high profits using the low-cost drilling and completion techniques. The four-well-composition cluster well technique is cheaper than the vertical well and may save 4.518% of the total drilling cost.

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Application of herringbone multilateral horizontal well in heavy oil reservoirs

YI Faxin; YU Chen; LI Songbin and ZHU Tai-hui

, 2008, 35(4): 1630-0.

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Herringbone multilateral wells and borehole allocation designed according to reservoir conditions can effectively increase the bare area of reservoirs, the deliverability, the swept volume, and the oil recovery. The Well Du 84-Xing H238Z, which is the first herringbone multilateral well allocated and implemented in the Liaohe Oilfield, has four branches and is 837 meters long in horizontal section. The well makes substantial breakthroughs in well construction, optimized drilling technology, formational protection and completion technology. Sidetracking technology is the key technology for herringbone multilateral wells, and can improve discrimination accuracy and trajectory control accuracy through logging while drilling (LWD). After the Well Du 84-Xing H238Z was put into production, its maximum daily rate of cyclic steam stimulation achieved 152.6 ton, the average daily rate was 1.41-1.85 times that of other wells in the same block.

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3D geological modeling of dual porosity carbonate reservoirs: A case from Kenkiyak pre-salt oilfield， Kazakhstan

CHEN Yefei; CAI Dongmei; FAN Zifei; LI Kongchou and NI Jun

, 2008, 35(4): 1631-0.

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The 3D geological model of dual porosity reservoirs in the Kenkiyak pre-salt oilfield is built step by step based on the detailed core observation and employing core data, log data, geological data and seismic data. Firstly, the sedimentary facies model is built on the basis of analyzing seismic facies and electro-facies, and the models of reservoir matrix properties controlled by the sedimentary facies are then built based on structure analysis and methods optimization. Secondly, the fracture distribution model is established applying the results of the seismic property analysis and the core fracture description. Thirdly, the three-dimensional integrated geological model of the dual porosity reservoirs is set up by combining the matrix property models with the fracture distribution model and applying the filtration theory between matrix and fractures. The set of methods finally provides a fracture distribution model, a fracture equivalent permeability model and a dual porosity equivalent permeability model, which can be directly provided to reservoir engineers for numerical simulation.

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Sedimentary facies and types of carbonate rock reservoir in Caspian Seashore Basin: A case from Carboniferous

FANG Jiazhong; WU Lingang; GAO Gang and ZHAO Baoshun

, 2008, 35(4): 1632-0.

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By the observation under microscope on the cored sessions of the Well 2092 and the Well 2399A, four types of sedimentary microfacies including bank, howe between banks, lagoon and tide channel are identified. Based on the relation of sedimentary microfacies and logging curves, the characteristics of the corresponding logging are established. There are four types of reservoirs which are fractured reservoir, combination pore and crack reservoir, microcrack-pore reservoir and pore reservoir. The fractured reservoir is distributed between banks and in lagoons. The combination pore and crack reservoir is developed in the bank formed in high energy and in the shoal environment. The microcrack-pore reservoir is mainly distributed in the bank with high energy, and also developed in the tide channel. The pore reservoir is mainly developed in the shoal microfacies with relatively low energy and in tide channel microfacies.

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Improving development profit by using reservoir based completion

Lü Xiaoguang; ZHANG Xuewen; LIU Yongxi; Bradford W Sincock and Budi Tyas Utomo

, 2008, 35(4): 1633-0.

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Implementation of well completions enabling multiple hydrocarbon reservoirs to be produced by a single well can save production cost and enhance recovery. Aiming at the characteristics of the three kinds of oil and gas reservoirs in the Jabung block in Indonesia, that is, gas cap oil-rim reservoir, multiple hydrocarbon reservoirs and heterogeneous multiple-sand reservoir, this paper puts forward optimized completion methods by using conventional technology and down-hole equipment. The new methods are able to develop multi-reservoir sands at the same time or successively without additional completion jobs. In addition, the novel completion enables water injection wells to selectively control injection and can improve the recovery of hydrocarbons from producing wells. The above strategies have been applied to different types of reservoirs, providing an effective means for maximizing reserves recovery, controlling operating expenditures, and improving the overall benefit of development wells.

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, Volume 35 Issue 4