, Volume 36 Issue 1

    

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油气勘探
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  Comparative study on volcanic hydrocarbon accumulations in western and eastern China and its significance

  Zhao Wenzhi; Zou Caineng; Li Jianzhong; Feng Zhiqiang; Zhang Guangya; Hu Suyun; Kuang Lichun and Zhang Yan

  , 2009, 36(1): 1673-0.

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  Volcanic hydrocarbon accumulations in eastern and western China have both generality and discrepancy. The common features are as follows: their source-reservoir-caprock association is a near-source type; their reservoir properties are little affected by burial depth and possess strong heterogeneity; the main source rocks are coal measures mudstone and usually have a high geothermal evolution degree. The differences between the two areas are: volcanic rocks in the eastern area are mainly formed in Mesozoic-Cenozoic intra-continental rifts; those in the western area are in Paleozoic intra-continental rifts and island-arc. Eastern volcanic activity is characterized by central eruption controlled by deep-seated faulting movement, which produced mainly intermediate-acid volcanic rocks; western volcanic activity possesses more eruption types and periods, which produced mainly intermediate-basic volcanic rocks. Reservoir space of volcanic reservoirs is primary pores and fractures in the east, while secondary dissolved pores and fractures in the west. In terms of reservoir types and controlling factors, the eastern reservoirs are mainly lithologic and structural-lithologic, with hydrocarbon accumulations controlled by effective source kitchens, deep-seated faults and volcanic eruption structures, and the in-situ features are obvious; the western reservoirs are mainly stratigraphic unconformity reservoirs, with hydrocarbon accumulations controlled by unconformities, source-reservoir-caprock associations and large faults, and both heterotopic and in-situ features exist.
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  Classification and characteristics of karst reservoirs in China and related theories

  Zhang Baomin and Liu Jingjiang

  , 2009, 36(1): 1674-0.

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  Karst reservoirs are distributed widely in China, for which integrated geological, logging, testing and seismic identification marks can be made and their ages can be determined using unconformity surfaces, the lithologic feature and paleobiology of cavern clastic fillings and element geochemistry. The karst reservoirs can be classified as buried hill karst, reef-bank karst, internal karst, bedding deep-underflow karst, vertical deep-infiltration karst and hydrothermal fluid karst. The first three belong to base-level karsts, controlled by different-order sequence interfaces; the last three belong to non-base-level karsts, controlled by structure and fracture. The division of karst facies should takes full account of the internal relation of the base-level karsts and the non-base-level karsts, the existence of deep-turbulent flow zones and the genetic type of karsts. There are many types of corrosion fluid in carbonate rocks in petroliferous basins. It is important for the reservoir evaluation and prediction to reconstruct them and to analyze the genetic mechanics of the karst pore-cave-fracture and large-scale cave. As for the controlling factors for the karst development, the study of zonal exogenic forces should be enhanced while the study of azonal endogenic forces is emphasized.
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  Geological characteristics of low rank coalbed methane, China

  Wang Bo; Li Jingming; Zhang Yi; Wang Hongyan; Liu Honglin; Li Guizhong and Ma Jingzhang

  , 2009, 36(1): 1676-0.

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  Low rank coalbed methane is a very important and potential field of coalbed methane exploration and exploitation in China. The geological structure backgrounds of coal-bearing basins are complicated, and many coalbeds are reconstructed by multi-period and multi-property structures and combinations, as well as stress-strain. The accumulation and enrichment of coalbed methane have the following characteristics: big thickness, multiple beds, low gas content, preferable permeability, great resource and abundance. The thick and widely distributed coalbeds and huge coal resources offset the shortcoming of low gas content, probably leading to the good prospect of exploration and exploitation. Matrix shrinkage effect induced by desorption causes high permeability in exploitation of low rank coalbed methane reservoirs, which is good for coalbed methane exploitation, and prone to form industrial gas flow. Low rank coalbed methane reservoirs have a simple forming process, including one deposition and one adjustment. If the main controlling factors, such as structure, coal-forming environment and hydrologic geology, are matched well, the enriched coalbed methane zone with high production would be formed.
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  Geochemical characteristics of abiogenic gas and its percentage in Xujiaweizi Fault Depression, Songliao Basin, NE China

  Ni Yunyan; Dai Jinxing; Zhou Qinghua; Luo Xia; Hu Anping and Yang Chun

  , 2009, 36(1): 1677-0.

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  Gases with different origins occur in the Xujiaweizi Fault Depression. Among them, the abiogenic gases have a typical carbon isotopic reversal trend (δ13C1>δ13C2>δ13C3>δ13C4), the carbon isotope of methane is greater than －30‰, and the R/Ra greater than 0.5. According to the simulative calculation with two-source mixing (mixture of abiogenic gas and thermogenic gas), when the end composition of abiogenic gas being mixed with coal-derived gas or oil-derived gas, it will require an amount of abiogenic gas more than 80% to obtain the carbon isotopic reversal trend, which results in much heavier carbon isotope values of the mixed methane than the peak carbon isotope values of the abiogenic methane in the Xujiaweizi Fault Depression. Thus it is argued that the abiogenic gases in the Xujiaweizi Fault Depression can not simply be a result of two-source mixing. The mixing of coal-derived and oil-derived gases can not lead to the carbon isotopic reversal trend, which provides further evidence for the abiogenic origin of the deep-layer gas.
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  Depositional system and favorable reservoir distribution of Xujiahe Formation in Sichuan Basin

  Zhu Rukai; Zhao Xia; Liu Liuhong; Wang Xuesong; Zhang Nai; Guo Hongli and Song Lihong

  , 2009, 36(1): 1678-0.

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  By comprehensive analysis on the depositional system and on the main controlling factors of reservoirs in the Upper Triassic Xujiahe Formation in Sichuan Basin, the formation conditions of high-quality reservoirs under low-porosity and low-permeability background were studied. Except the transitional facies of Xu-1 member, other members of Xujiahe Formation are of terrestrial deposit, with alluvial fan, fluvial, fan-delta, fluvial-delta and lacustrine deposit systems developed. Both the facies belt distribution and paleogeographic evolution are closely related to the regional tectonic movement. The original sedimentary facies belt (sandbar microfacies of main stem of braided river) and later denudation co-control the distribution of favorable reservoirs, and the quartz overgrowth and cementation is one of the controlling factors of the tight sandstones. The favorable reservoirs are mainly developed in the high-energy channel of delta plain, with medium-coarse sandstone as the best lithology. Combining with the analysis data of effective thickness and physical property, the favorable reservoirs in the Xu-2, 4, 6 members were evaluated and predicted comprehensively. The results indicate that the center and south of Sichuan are the most favorable reservoir distribution areas.
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  Model for tight lithologic gas accumulation in Upper Palaeozoic, east of Ordos Basin

  Li Mingrui; Dou Weitan; Lin Hongbin; Zhang Qing and Jiao Jitian

  , 2009, 36(1): 1679-0.

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  The Upper Palaeozoic gas reservoirs in the east of Ordos Basin are typical tight sandstone lithologic reservoirs, which feature abundant gas source, gas contained in multiple series of strata, tight sandstone reservoirs developed and relatively good seal. According to the characteristics of the gas reservoir forming in the east of Ordos Basin, based on the forming periods, focusing on tight lithologic trap, and taking account of key factors for reservoir forming, this paper analyzed the models of gas reservoir-forming in four typical stages, including late Early Jurassic, middle-late Late Jurassic, late Early Cretaceous and late Early Cretaceous to present.It is believed that middle-late Late Jurassic and late Early Cretaceous are the key periods for the gas accumulation in the east of the basin. Due to poor physical properties of the tight lithologic gas reservoirs, the different transport layers lead to different ways of gas secondary migration. The gas reservoirs at Benxi Formation, Taiyuan Formation, Shanxi Formation and Lower Shihezi Formation have good continuity in plane, while some “small but rich” secondary gas reservoirs are usually formed at Shiqianfeng Formation and Upper Shihezi Formation in the places where transport layers develop.
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  Unsteady reservoir in Hadson Oilfield, Tarim Basin

  Sun Longde; Jiang Tongwen; Xu Hanlin; Shan Jiazeng and Lian Zhanggui

  , 2009, 36(1): 1680-0.

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  Unsteady reservoir, characterized by oblique oil-water contact or an upside-down relation between gas-oil-water in interconnected reservoirs, refers to a kind of hydrocarbon reservoir still in the process of hydrocarbon charge or adjustment, in which a uniform oil-water contact does not come into being and there is a dynamic non-balance between gas, oil and water. This paper takes Donghe sandstone in Hadson Oilfield in Tarim Basin as an example and makes the analyses on the origin of oblique oil-water contact, showing that the Donghe sandstone is undergoing hydrocarbon adjustment with obviously unsteady hydrocarbon concentration, and neotectonic movement is the major cause of the oblique oil-water contact. We put forward the concept of unsteady reservoir based on physical modeling, which has been applied in the hydrocarbon exploration and development of Hadson Oilfield. After successive exploration and development for nearly 3 years, the Hadson Oilfield has gained increasing reserves in place and become the first large-scale marine sandstone oilfield in China, with the proved reserves exceeding a hundred million tons.
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  Lithologic and lithofacies characteristics of volcanic rock and their control over reservoirs, Changling Gasfield

  Sun Yuanhui; Song Xinmin; Ran Qiquan; Sun Yan; Gao Xingjun; Song Wenli and Zhang Dawei

  , 2009, 36(1): 1681-0.

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  Eight types of volcanic lithologies (less-pore and tight rhyolite, stomatal rhyolite, autochthonous autobreccia lava, crystal ignimbrite, crystal ignimbrite with breccia, volcanic breccia, volcanic agglomerate and sedimentary tuff) under two categories (volcanic lava and volcanic arenite) are identified using core observation, cuttings slice analysis, ECS component identification and FMI rock texture and structural interpretation. On the basis of single-well lithologic identification and lithofacies division, the facies patterns of eight sub-facies in three categories are established by using seismic attribute analysis and wave analysis. The control of such lithology and lithofacies as autochthonous autobreccia lava (top subfacies of overflow lithofacies) on the development of the reservoirs are studied, and the distribution of favorable reservoirs in Changling gasfield and the corresponding features of lithology and lithofacies are summarized, through the analysis of reservoir space type, pore structure and pore-fracture assemblage in volcanic reservoirs, which provids a basis for field development planning and production horizon optimizations.
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  Seismic sedimentology and its application in south of Central Asia

  Zhang Yi’na; Zhu Xiaomin and Liu Changli

  , 2009, 36(1): 1683-0.

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  Seismic sedimentology mainly uses 3D seismic information and modern geophysical technology to study sedimentary systems, sedimentary facies spread and its evolution history. In addition, on the basis of the high-accuracy isochronous sequence stratigraphic framework, its focus is to use the horizontal resolution of seismic data and special seismic processing technology (90° phase shift and stratal slicing), in combination with the key wells' lithologic data as well as geomorphic features of different sand types, to resume sedimentary types and evolution history．Accordingly, we carried out seismic sedimentology studies on the Lower Cretaceous Formation in the 3D seismic area south of Central Asia．We made a dynamic interpretation to the target zone by a series of stratal slices combined with the drilling core information, and obtained that the target zone mainly experienced braided delta facies－lake facies－delta facies－lake facies－braided river facies．
油气田开发
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  Horizontal well fracturing technology for reservoirs with low permeability

  Cai Wenbin; Li Zhaomin; Zhang Xialin; Zhang Bo and Zhang Qi

  , 2009, 36(1): 1684-0.

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  The horizontal well stress distribution and the rock failure criterion constitute a fracture initiation mathematical model, which was solved by the iteration method. Minimum horizontal principal stress and vertical principal stress have different influences on the fracture initiation pressure when the horizontal well orientation angle is different: the fracture is least likely to initiate when the angle is 0 and is easiest to initiate when the angle is 90°. The simulation result of 3-D hydraulic fractures propagation model matches well with the Fracpro-PT software, and it is suitable to simulate horizontal well fractures propagation. If the fracture interval is long, a multi-fracture propagation model could be built taking into account of the fractures interaction and the single fracture propagation model. Field horizontal well fracturing technology can be summarized as limited entry treatment and staged fracturing treatment, the limited entry treatment is simple with smaller reformation intensity; the staged fracturing treatment has higher reformation intensity but requires advanced facilities. The fracturing technology should be chosen according to the field situation.
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  Experimental study on dynamic imbibition mechanism of low permeability reservoirs

  Wang Jialu; Liu Yuzhang; Chen Maoqian; Liu Li and Gao Jian

  , 2009, 36(1): 1685-0.

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  Based on the theoretical and physical models of the fluid flow between fracture and matrix in low permeability reservoirs, this paper establishes the experimental methods of dynamic imbibition between fracture and matrix, and studies the effect of parameters, such as displacement velocity in fracture, viscosity ratio of oil and water, wettability of matrix, initial water saturation, on dynamic imbibition. In a low permeability fracture reservoir, the water flows along fractures under pressure gradient and is imbibited into the matrix due to the capillary force during water flooding. Then, the oil in the matrix is displaced into the fracture with the imbibited water, and the oil in the fracture is displaced to the outlet with the injected water. There exists an optimal displacement velocity of 3.0 mL/h and the highest imbibition efficiency is 35.5% under the experimental condition. In a certain extent of displacement velocity, the imbibition result is best under the action of both capillary and viscosity forces. The imbibition efficiency of water wetting core is the highest. The smaller the viscosity ratio of oil to water, the higher the imbibition efficiency. The higher the initial water saturation, the lower the imbibition efficiency, because the capillary pressure becomes smaller.
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  Geo-modeling for thin carbonate reservoirs developed with horizontal wells: A case from DL Oilfield, Oman

  Zhao Guoliang; Shen Pingping; Mu Longxin; Gao Wenkai and Li Yanming

  , 2009, 36(1): 1687-0.

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  Developing thin bed reservoirs with horizontal wells is an important technique, which has been widely adopted all over the world. It is a big challenge how to integrate seismic, geology, logging and testing data, and employ optimum modeling strategies to build a high resolution geological model for meeting thin reservoir development in horizontal wells. Taking DL Oilfield, Oman for example, in response to carbonate reservoirs mainly controlled by deposition, the geo-modeling strategies of “three-step geological modeling methodology” (that is depositional model, facies model and petrophysical model) and integrated deterministic modeling and stochastic modeling were employed based on multi-disciplinary knowledge and geological concepts as well as incorporating various data. Especially, data from multi-lateral horizontal wells have been fully taken advantage of in the process of modeling to enhance the accuracy of the geological model. Statistical model comparisons and reservoir simulation tests indicate that the built geological model is reliable and accurate.
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  Productivity of horizontal wells with segmental perforation

  Luo Wanjing; Wang Xiaodong and Li Fanhua

  , 2009, 36(1): 1688-0.

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  Segmental perforation is widely used for horizontal wells. Due to multiple perforated segments, the production forecast in every perforated segment of the horizontal well becomes complex. Using the Fourier Transform, principle of potential superposition, trigonometric function transform, and asymptotic analyses to solve the pseudo steady-state flow model in 3D circular-boxed media, and the uniform flow rate & production rate model of horizontal well is obtained. After comparing with the productivity of vertical wells, an equivalent borehole-diameter model can be obtained. Based on the model, a procedure to evaluate the productivity of segmental perforation horizontal well is presented by means of the principle of superposition. The output of both ends of a horizontal well is greater than the other parts at the same perforation length; it is more important to obtain high productivity by enlarging the perforation length than increasing the perforation spacing. Horizontal wells should be perforated by different segmental perforation lengths (the middle perforation length is greater than the ends of horizontal wells) to achieve a balanced production or injection. The method can determine the yield of each perforated interval.
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  Complex fracture shapes in hydraulic fracturing with orientated perforations

  Zhang Guangqing and Chen Mian

  , 2009, 36(1): 1689-0.

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  Based on rock mechanical tests and practical data interpretation, a three dimensional finite element model is established to study factors influencing fracture shape in orientated hydraulic fracturing. The stress interference around neighboring perforations causes fracture initiation, and the main factors influencing fracture shapes are horizontal principal stress difference and the angle between the perforation orientation and the maximum horizontal stress. The computations also reveal that hydraulic fractures will not always initiate along perforation orientation, and usually the initial hydraulic fracture is in a zigzag shape. When the horizontal stress difference and the perforation angle are great, dual fractures will happen along perforation and the maximum stress directions. So improving the accuracy of stress measurement and orientated perforation can avoid the generation of complex-shape hydraulic fractures.
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  Laboratory study of water shutoff in the fracture-cavity carbonate reservoir

  Long Qiulian; Zhu Huaijiang; Xie Hongxing; Liu Qiang; Bai Fengluan and Chen Qiufen

  , 2009, 36(1): 1690-0.

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  To restrain the too-fast rising of water cut in oil wells in Ordovician fracture-cavity carbonate reservoirs in Tahe Oilfield, two effective water shutoff agents (modified tannin gel water shutoff agent and flexible water shutoff agent) are studied in laboratory. The results indicate that the modified tannin gel water shutoff agent represents good stability at high temperature and resistance against the corrosion by high-salinity brine, and the flexible water shutoff agent may be long stable under high temperature and high-salinity circumstance and easily broken down, which is optional for shutting off the water exit fractures or caves in Ordovician carbonate reservoirs in Tahe Oilfield. The laboratory study of fracture-cavity carbonate cores plugged with the two agents shows that the increase of the agent injection leads to an increase of depth of plugging section and higher breakthrough pressure gradient in the initial stage; the accumulation of the shutoff agent makes the flow path narrower when a certain depth of plugging section is reached, raising the residual resistant factor.
石油工程
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  Damage evaluation for water-based underbalanced drilling in low-permeability and tight sandstone gas reservoirs

  Zhao Feng; Tang Hongming; Meng Yingfeng; Li Gao and Xing Xijin

  , 2009, 36(1): 1691-0.

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  With the characteristics such as small pore throats, strong water wetting and well-developed fractures, the low-permeability and tight sandstone gas reservoir is liable to be damaged during operation, even in the underbalanced condition. At water-based underbalanced drilling, water blocking and stress sensitivity are the main damages for low-permeability and tight sandstone gas reservoirs. Such damages are evaluated by using Fractures Visualization Test System and Capillary Flow Porometer. The results indicate that low-permeability and tight gas reservoirs still have very strong water blocking damage in the process of underbalanced drilling, and the lower the initial permeability, the bigger the water blocking damage. Given certain effective stress, the lower underbalanced pressure is accompanied with more serious water blocking damage, and over-low underbalanced pressure can not protect formations. Given certain underbalanced pressure, the higher effective stress brings about more serious water blocking damage. Now, the water blocking damage evaluation in underbalanced condition is just under study. Next work should focus on the simulation of real in-situ operations in reservoir and applying the laboratory evaluation results into onsite engineering design.
国际交流与合作
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  Formation and distribution of litho-stratigraphic reservoirs inside sequence stratigraphic framework, north of South Sumatra Basin

  Mao Zhiguo; Fan Tailiang; Wang Hongyu; Sun Yuanhui; Liu Yaming; Gao Zhiqian and Bai Bin

  , 2009, 36(1): 1692-0.

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  South Sumatra Basin is a Cenozoic back-arc rifted depositional basin developed at the joining point of Eurasian-Asian, Indian-Australian and Pacific plates. It experienced an integral cycle of transgression-regression, resulting in multiple depositional systems including alluvial apron, river, delta and shallow-sea carbonate. The sequence stratigraphic theories and research methods were used to define the sequence stratigraphic framework of Cenozoic formations in the north of South Sumatra Basin and to analyze the relationship between sequence stratigraphic framework and reservoir forming elements. The regularity and cyclicity of sequence stratigraphy controlled the development location and array model of source rock, migration system, reservoir and cap rock. The distribution of litho-stratigraphic reservoirs in sequences is related to such geologic conditions as hydrocarbon evolution of source rocks, extension of reservoirs, type of source-reservoir-caprock assemblage and migration system, and it is regular and predictable. Three categories and eighe sub-categories ligho-stratigraphic reservoirs are developed in the north of South Sumatra Basin, and are the major exploration area for replacement of petroleum reserves.