, Volume 35 Issue 5
    

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    油气勘探
  • Significances of studies on natural gas geology and geochemistry for natural gas industry in China
    DAI Jinxing; NI Yunyan; ZHOU Qinghua; YANG Chun and HU Anping
    , 2008, 35(5): 1634-0.
    Abstract ( ) Download PDF ( ) Knowledge map Save
    In the recent decade, great development has been made in natural gas industry. By the end of 2007, the total proved geological reserves of natural gas is 6×1012 m3. At the same time, the increase rate of annual production gets greater and greater. From the 100×108 m3/year in 1976 to 500×108 m3/year in 2005, the required time for an increase of 100×108 m3 is 20 years, 5 years, 3 years and 1 year, respectively. The significances of studies on natural gas geology and geochemistry are: in the 1970s, it was proposed that coal measure be good gas source rocks and that the coal measure hydrocarbon generation be dominated by gas generation with some oil generation, which opens new opportunity for coal gas exploration and makes coal gas increase from 9% to 70% in the total natural gas in China; according to studies on the semi-quantitative and quantitative controlling factors on large gas fields formation and natural gas accumulation zones, 7 out of 11 large gas fields of more than 1 000×108 m3was predicted in advance by 4-11 years; the gas sources of Feixianguan Formation accumulations are various, and we expect that there is a coal gas generation center from Longtan Formation in Bazhong, north Sichuan, which is favourable for large coal gas fields.
  • Hydrocarbon accumulation significance of Chang91 high-quality lacustrine source rocks of Yanchang Formation, Ordos Basin
    ZHANG Wenzheng; YANG Hua and Shanpeng
    , 2008, 35(5): 1635-0.
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    The comprehensive identification by logging and organic geochemistry reveals that the Chang91 high-quality source rock of black lacustrine mud shale mainly develops in the south of Zhidan region. The source rock has both strong hydrocarbon-generating capability and strong hydrocarbon-expulsion power. According to the characteristics of high C30-rearranged Hopane and extremely low C30 Hopane of the Chang91 source rock, in combination with other geochemical parameters in oil-source correlation, Chang8-Chang9 reservoir oil has a close relationship with Chang91 source rock in the south of Zhidan region and there is a poor correlation between Chang91 reservoir oil and Chang91 source rock in other areas. Chang91 source bed is important zonal oil source rock and it plays an important role in the formation of the Chang8-Chang9 reservoir in the Yanchang Formation, south of Zhidan region.
  • Genesis, classification and evaluation method of diagenetic facies
    ZOU Caineng; TAO Shizhen; ZHOU Hui; ZHANG Xiangxiang; HE Dongbo; ZHOU Chuanmin; WANG Lan; WANG Xuesong; LI Fuheng; ZHU Rukai; LUO Ping; YUAN Xuanjun; XU Chunchun and YANG Hua
    , 2008, 35(5): 1636-0.
    Abstract ( ) Download PDF ( ) Knowledge map Save
    Based on the controlling of diagenesis and diagenetic facies on reservoir development, this paper discusses the formation, classification and evaluation of diagenetic facies and its application and significance in petroleum exploration. For constructive diagenetic facies such as clastic rock, carbonate rock, and igneous rock, eight kinds of genetic mechanisms are developed, including dissolution of organic acid, dolomitization and so on. Nine constructive diagenetic facies and seven destructive diagenetic facies are classified. A naming scheme for diagenetic facies is proposed reflecting lithology, diagenesis, porosity and permeability, that is, "porosity and permeability level + rock type + diagenesis type". Diagenetic facies are evaluated synthetically and quantitatively on the basis of sedimentary facies, log facies, seismic facies, rock cores, and thin sections. And "four steps" and "superposition of three charts" are put forward as the methods of evaluation and mapping. Favored reservoirs, "sweet spots" and lithostratigraphic traps could be predicted according to the distribution of different types of diagenetic facies. The development of the study on diagenetic facies is also discussed in the paper.
  • Role of basement faults in gas accumulation of Xujiahe Formation, Sichuan Basin
    WANG Zecheng; ZHAO Wenzhi; LI Zongyin; JIANG Xingfu and LI Jun
    , 2008, 35(5): 1637-0.
    Abstract ( ) Download PDF ( ) Knowledge map Save
    The Xujiahe Formation is characterized by large gas-bearing area, low reserve abundance, low yield, and dominantly lithologic gas pools because sandstone reservoirs are tight and low permeable, structures have gentle relief, and faults and fractures are undeveloped. Searching sweet-spots is the key step in gas exploration. The basement heterogeneity in the Sichuan basin has led to the activity of basement faults in NE and NW directions since Meso-Cenozoic, which influences the evolution of sub-structure zones and causes the occurrence of fractures and minor faults in Xujiahe Formation reservoirs. These fractures and minor faults improved the reservoir quality, provided path for gas migration, and contributed to the formation of local gas-rich trends. Meanwhile, later activity of basement faults caused abnormally high geothermal field, accelerating the thermal evolution of source rock. The area of basement faults has the most favorable conditions for gas accumulation and is the main target for gas exploration.
  • Three hydrocarbon generation and accumulation processes of marine carbonate rocks in northeastern Sichuan Basin, China
    QIN Jianzhong; MENG Qingqiang and FU Xiaodong
    , 2008, 35(5): 1638-0.
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    The solid asphalt characteristics, inclusions homogenization, and diagenesis are studied in northeastern Sichuan Basin. During Indosinian movement, the source rocks in O3w (Upper Ordovician Wufeng Formation) and S1l (Lower Silurian Longmaxi Formation) generated low-mature heavy oil, meanwhile, the organic reef facies of Upper Permian Changxing Formation formed reservoir space for the heavy oil. The Permian and O3w-S1l source rocks generated peak oil during early Yanshan movement. The homogenization temperature of hydrocarbon fluid inclusions formed during the aforementioned two stages ranged from 100 to 150 ℃.During late Yanshan and Himalayan movements, the early formed oil and source rocks and soluble “organic matter” all had reached high and post mature stages. The present natural gas reservoirs were formed by cracking. Therefore, there are three hydrocarbon generation and accumulation processes in northeast Sichuan Basin, which occurred during Indosinian movement, early Yanshan movement and late Yanshan movement, respectively.
  • Relationship between deformation structure and petroleum accumulation and preservation, Qiangtang Basin, Tibet
    GUO Zujun; LI Yongtie; NAN Zhengbing and YE Hefei
    , 2008, 35(5): 1639-0.
    Abstract ( ) Download PDF ( ) Knowledge map Save
    There are about 235 outcropped anticlines in Qiangtang Basin, Tibet, which are dominantly of Jurassic age. Based on geophysical exploration, surface geologic survey, and regional tectonic stress, these anticlines can be classified into four types, viz., simple structure, united structure, complex structure and twisted structure. These four-type structures are distributed in different places in the basin and are mainly formed in the two deformation phases of late Yanshan movement and Himalayan movement. The two phases match with the two periods of hydrocarbon generation, so the structures provide good conditions for hydrocarbon accumulation. The new tectonic movement of Qinghai-Tibet plateau is generally thought as the important factor causing reservoir damage. However, the analysis of fault nature, effective seal rock distribution and plateau uplifting indicates that the faults in the basin are mainly compressive, the internal structure is stable, and the intervals of interest are well preserved and have a good exploratory potential.
  • Sand body types and reservoir properties in Cretaceous Jiufotang Formation in Luxi Sag
    SUN Chao; ZHU Xiaomin; ZAN Guojun and LEI Angui
    , 2008, 35(5): 1640-0.
    Abstract ( ) Download PDF ( ) Knowledge map Save
    Comprehensive analysis of seismic, log, core and granularity data shows that there are four genetic types of sand bodies in Cretaceous Jiufotang Formation in Luxi Sag, including sand bodies of subaqueous distributary channels in the front of meandering river delta, braided river delta and fan-delta, and sand body of fluxoturbidite fan. They have middle to high porosity and low to very low permeability. The sand bodies of subaqueous distributary channels converge towards the Wushijiazimiao subsag from the southwest, southeast, northeast and northwest of the Luxi Sag. The fluxoturbidite fans are developed in front of those sand bodies and scattered in half-deep to deep lake facies of the Wushijiazimiao subsag. The subaqueous distritutary channels sand bodies are reservoirs of the structural petroleum pools near the main fault in Luxi Sag, and the fluxoturbidite fans of the upper segment of Jiufotang Formation developed in Wushijiazimiao subsag may form lenticular sand lithological pools and are the preferred exploration targets in the future.
  • Sedimentary characteristics and hydrocarbon accumulation rules in northwestern Junggar Basin: A case from Jiamuhe Formation of No.5 and 8 area
    ZHU Yanhe; WANG Yingmin; YUAN Shukun and XING Xiangrong
    , 2008, 35(5): 1641-0.
    Abstract ( ) Download PDF ( ) Knowledge map Save
    The foreland thrust belt of the northwestern margin of the Junggar Basin is a key area for studying coupling between the basin and mountains, basin origin and orogenic belt evolution, and development of sedimentary systems. The Permian Jiamuhe Formation in No.5 and 8 area is composed of volcanic, volcaniclastic and clastic rocks. The low subunit of the formation consists of 2 third-order sequences PSQ1 and PSQ2, and the middle and upper subunits are PSQ3 and PSQ4. The low subunit is filled mainly by volcanics and volcaniclastic rocks, and the other two subunits are filled by coarse fragments of dominant fan delta. The facies developed in the studied area includes fan delta, crater, proximal crater and distal crater facies, and most known hydrocarbon accumulations are found in the former three facies. The volcanics and sands of fan delta are the main reservoirs. The pool-formation is dependant on the spatial configuration of structure, diagenesis, source, trap, etc.
  • Quantitative study on reservoir diagenesis in Northern Dagang Structural Belt, Huanghua Depression
    JIN Zhenkui and LIU Chunhui
    , 2008, 35(5): 1642-0.
    Abstract ( ) Download PDF ( ) Knowledge map Save
    Sandstone reservoir experienced diagenesis of compaction, cementation, dissolution and replacement in Northern Dagang Structural Belt. The compaction intensity is quantitatively classified into 6 grades according to the relative content of grains with different types of grain-contact. Compaction of the sandstone reservoir in the study area is from moderate (grade Ⅲ) to moderate-intensive (grade Ⅳ). Cementation includes quartz overgrowth, calcite cementing and clay mineral cementing. The quartz overgrowth occurs from 2 200 – 3 300 m. Calcite cement is calcsparite. The precipitation depth of calcite cement is determined to be 2 300 to 3 100 meters using cathodoluminescence, inclusion thermometry, etc. The authigenic clay mineral fills in the pores. Its distribution is related to burial depth. Dissolution includes corrosion of detrital feldspar and calcite cement. Compaction is related to burial depth, sandstone composition and cementation, cement precipitation is related to transformation of clay minerals, and dissolution results from thermal evolution of organic matter.
  • Superiorities of support vector machine in fracture prediction and gassiness evaluation
    SHI Guangren
    , 2008, 35(5): 1643-0.
    Abstract ( ) Download PDF ( ) Knowledge map Save
    To contrast the application results of multiple regression analysis (MRA), artificial neural network (ANN) and support vector machine (SVM), they were applied to two case studies. Case 1 is the fracture prediction based on 34 samples of Wells An1 and An2 in the Anpeng Oilfield of the Biyang Sag, Nanxiang Basin. Case 2 is the gassiness evaluation of 40 samples in tight sandstones in the Tabamiao area, Ordos Basin. (1) The nonlinear methods, SVM and ANN, are far superior to the linear method, MRA; (2) SVM presents absolute superiority due to zero error and fast speed, indicating that it is the best machine-learning method so far; (3) ANN is almost as superior as SVM in Case 1, but ANN is less precise than SVM in Case 2; (4) MRA is fast and can establish the order of dependence between the study target and its related multi-geological-factors which cannot be estimated using SVM and ANN. Therefore, SVM is recommended when describing any complex relationship between a target and its related geological factors and MRA can be used as an auxiliary tool.
  • Quantitative evaluation on the heterogeneity of clastic rock by wireline logs
    LI Chaoliu and ZHOU Cancan
    , 2008, 35(5): 1644-0.
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    Full-hole micro-resistivity imaging logging provides 2-D high resolution graphics, from which detailed electric property variation can be seen. A new model computing the dispersion degree of array data is presented to estimate the anisotropy coefficient C in sand reservoirs, and thus making it possible to study the heterogeneity quantificationally with sequential log data. Referring to the standard about heterogeneous degree of permeability in clastic reservoirs of land facies, this paper divides the reservoirs into 3 types: homogeneous (C＜0.15), relatively homogeneous (0.15≤C＜0.5), and very anisotropic (C≥0.5). Taking the distributary channels in braided river and the mouth bar in delta front as two examples, it correlates the core permeability with these computed anisotropy coefficient curves, and illustrates that this model is very useful for investigating the inner anisotropism and its quantitative analysis.
  • Origin of low resistivity pays and forecasting of favorable prospecting areas
    YANG Chunmei; ZHOU Cancan and CHENG Xiangzhi
    , 2008, 35(5): 1645-0.
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    The relationship between petrophysical and geological genesis of low resistivity pays is established through the study of 54 low resistivity pays in 8 basins. Combining with the comprehensive analysis of sedimentary environment, diagenesis, tectonic evolution etc, this paper presents five types of typical low resistivity exploration targets, including low-relief lithologic-structural traps in the gentle-slope depositional system, natural water-flooding areas with fluid heterogeneity characteristics in relatively active tectonic movement zone, shallow layers with high content of montmorillonite among clay mineral and slowly depositional fine sandstone layers, weakly hydrodynamic thin multilateral sand and shale with resistivity anisotropy, and conductive mineral developed areas such as pyrite. Mud invasion in drilling is an engineering reason for some low electrical resistivity.
    • 油气田开发
  • Non-linear seepage flow models of ultra-low permeability reservoirs
    LI Songquan; CHENG Linsong; LI Xiusheng and HAO Fei
    , 2008, 35(5): 1646-0.
    Abstract ( ) Download PDF ( ) Knowledge map Save
    Non-linear seepage flow is caused chiefly by medium deformation and threshold pressure gradient (TPG) in low and ultra-low permeability reservoirs. According to laboratory experiment on medium deformation and TPG, a new stress sensitive coefficient is defined, and the variation rules of the coefficient and TPG (including single phase and oil-water two phases) are analyzed. The non-linear seepage models of single phase and oil-water two phases are set up with consideration of medium deformation and TPG. The single phase model is solved on the condition of constant flow rate, changing production rate, and constant bottom-hole pressure respectively. For oil-water non-piston displacement flow, the fractional flow equation, oil/water front equation, pressure equation and production equation are put forward with solultions. The reservoir engineering application shows that the production rate decline in low permeability formations is more serious than that in medium-high permeability formations, and non-linear factors exert serious influence on oil-water two phases flow when the velocity is low. Moreover, reasonable injector producer distance can be determined by the models.
  • Reusable potential prediction of long-time shut-in oil wells
    WANG Lijun; LI Xiaofeng; CHANG Rong; SU Shidong and YU Hong
    , 2008, 35(5): 1647-0.
    Abstract ( ) Download PDF ( ) Knowledge map Save
    Comprehensive reusable potential prediction models and relevant principles are established in order to reuse the potential of long time shut-in oil wells, which have been shut in during the high water-cut stage of an oil field, considering economic efficiency and development conditions. The comprehensive reusable potential prediction models include the following: the prediction model of economic potential, based on the economics profit and loss balance principle, can determine the closing economic limitations of different stages of oil wells and predict whether a long time closed oil well has reusable economic potential or not; the prediction model of redevelopment potential based on Fuzzy Mathematics theory provides quantitative evaluation by calculating the redeveloping potential index. Comprehensive reusable potential predictions of 287 long time shut-in wells of P oil field have been done with the model and principles, and 10 wells were selected to put into reproduction in 2006 and achieved good results with an average daily production of 2.15 t per well and the ratio of annual input to output was 1 to 5.
  • Methodology for horizontal well pattern design in anisotropic oil reservoirs
    LIU Yuetian
    , 2008, 35(5): 1648-0.
    Abstract ( ) Download PDF ( ) Knowledge map Save
    Anisotropic permeability has prominent affects on horizontal well networks. Well lines, horizontal sections of the wells, and the principal direction of anisotropic permeability should be parallel or perpendicular to each other, in which the horizontal well sections should be perpendicular to the direction of the maximum principal permeability. The geometric parameters of the well pattern are calculated with the degree of anisotropy. Numerical reservoir simulation results are consistent with the theoretical analyses. The reservoir development results of the optimized well pattern considering the affects of anisotropy are remarkably better than that of non-optimized well pattern. With the selection of area of well pattern unit, lateral well spacing and horizontal well length as the independent parameters, 84 kinds of model cases are provided as references for practical reservoir engineering designing.
  • A productivity prediction model for the complex well with formation damage
    AN Yongsheng; WU Xiaodong; HAN Guoqing and LI Fanhua
    , 2008, 35(5): 1649-0.
    Abstract ( ) Download PDF ( ) Knowledge map Save
    According to the characteristics of formation damage in anisotropic reservoirs, a semi-analytical production prediction model for complex wells considering formation damage is established. In this model, the reservoir anisotropy is fully considered based on the theory of coordination conversion through which the parameter of reservoir and well is calculated in the isotropic space, and the formation damage caused by the invasion of drilling fluid and completion fluid is represented by skin factor which can be introduced into the semi-analytical model. The new production-prediction model for complex wells can fully reflect the characteristics of formation damage caused by the invasion of drilling fluid and completion fluid in anisotropic reservoirs and the impact of formation damage on productivity. The new model presented in this paper is more accurate and can better meet practical requirements than the existing one.
    • 石油工程
  • Application of multilateral wells with limited sand production to heavy oil reservoirs
    ZHOU Shouwei; SUN Fujie; ZENG Xianglin and FANG Maojun
    , 2008, 35(5): 1650-0.
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    Multilateral wells with limited sand production are proposed to produce offshore heavy oil reservoirs. This technique was studied through lab experiments and numerical simulation. Permeability increases with sand production, and formation fines of less than 39 μm diameters are the main fines that jam pore throats and influence permeability the most. For a given total length of branches, productivity decreased slightly with increasing branches, suggesting that the number of branches should not be too many, two or three are better; and productivity increased with the increase of branch angles, but the increase of productivity decreases. Field test was carried out in NB35-2 oil field and the individual layer deliverability of a multilateral well with limited sand production is three times the multilayer production of the common deviated well.
  • Technique of multi-pulse gas load fracturing
    PU Chunsheng; SUN Zhiyu; WANG Xiangzeng and LUO Mingliang
    , 2008, 35(5): 1651-0.
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    In de-stressing and fracturing formation with multi-pulse gas loading, the pressure gradient of deflagration gas along cracks affects crack initiation and extension. The overlay principle is used to resolve complicated loads of borehole wall into simple ones; based on elastic mechanics and linear elastic fracture mechanics, a function describing gas pressure distribution along the crack is proposed to derive the corresponding stress strength of crack top; and then the conditions of crack initiation in borehole rocks are concluded. The conditions reflect the influence of gas pressure gradient varying with time on fracture geometry. The example analysis and field contrast test reveal that, compared with the common High Energy Gas Fracturing, the multi-pulse gas loading fracturing gives rise to higher crack initiation pressure, lower crack arrest pressure, greater extension of fracturing time, and forms 2-3 times fracture length in the formation. Combined with hydraulic fracturing, it can lower formation breakdown pressure and further improves formation permeability.
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