Petroleum Exploration and Development

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Salt structures and exploration of oil and gas

JIA Chengzao; ZHAO Wenzhi; WEI Guoqi; LIU Delai and ZHANG Junfeng

, 2003, 30(2): 282-0.

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Salt structures are widespread in North America, Africa, Europe, Southeast and Middle-east Asia, which are among the hottest topics of tectonic research and exploration for oil and gas during the annual meeting of AAPG in 2002. According to the latest researches, five stages have been found in the growth and development of salt structures, including early-stage diapir, local salt migration, coeval transformation of linear salt-walls, late-stage evolution of the mature diapirs and active diapiric episodes. During the evolution of the salt structures, eight types of structural styles can be recognized, such as salt walls, salt stock canopies and nappes, mini-basins, thrusts and strike-slip faults. With the applications of 3-D seismic and numerical modeling techniques, the growing stages and the tridimensional variation of salt structures should be able to be restored and recognized. Salt structures related with traps that are likely oil-bearing have been discovered recently in the Mexico Bay, Africa and Middle-east, which means that salt structures are closed are promising exploration areas of oil and gas, and they will play an important role in the growth of reserves.

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Analysis of the faults in the northern Ordos Basin, Northwest China

YAO Zhonghui; ZHANG Mingshan; ZENG Lingbang; WANG Rensheng and HE Tianyi

, 2003, 30(2): 283-0.

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The Ordos basin has been being thought as a stable craton basin for a long time by many Chinese researchers, in which none of the faults were developed yet. Hovewer, the recent studies of seismic profiles and processed data show that some of the faults with a fault throw ranging from 40m to 240m developed in the northern part of the Ordos Basin. Overeally, the area from Tianhuanbei to Suligemiao, Wushenzao to reach Dongsheng are the location with many faults developed in NS direction, where the faults cut off Ordovician weathered crust and Coals of Taiyuan and Shanxi Formation (in age of Permian), that mainly composted of the group of reflect wave. The faults usually formed simple thrust fault, ramp faults, back thrust faults and reverse faults. The faults were formed by the extremely extruded near the rim or edge of Ordos Basin in the middle and later Yanshan movement, and they are also the by-products of the transformation of foreland basin.

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Oil and gas sources of Laojunmiao structural belt in Jiuxi basin,Northwest China

LI Wei; LIU Baojun; Lü Tao; BAI Shuyan and Fu Jiankui

, 2003, 30(2): 284-0.

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Most researchers in China thought that the oil and gas sources should come from the Qingnan depressed, since these oil fields of Yaerxia, Laojunmiao, Shiyougou and Liugouzhuang have discovered in the Jiuxi Basin, Northwest China. But the authors think that the most parts of the oil and gas in the Laojunmiao and Shiyougou oil-fields come from the underlain lower Cretaceous source rocks below the plate of Laojunmiao Thrust Nappe, based on comprehensive analyses of the oil physics property, the pyrrolic nitrogen compounds, structural attitude of Laojunmiao Thrust Nappe, the ratio of proved reserves and resource extent, and the advance for the exploration of oil and gas recently.

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The distribution and features of reef in Tazhong Area of Tarim Basin，Northwest China

OUYANG Rui; JIAO Cunli; BAI Lihua; CHANG Heng and WANG Yuchang

, 2003, 30(2): 285-0.

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There are many different kinds of reef in Tazhong Area of Tarim Basin, Northwest China in age of Medium-Upper Ordovician. The main reef-building organisms are Sponges, Calathium, Stromatoporoids, Corals, Crytalgaes, Bryozoans, Blue-green algae, Chorophyte and Rhodophyte in Solenoporaceae. The reef can be divided into calcilutite mound, framework reef and baffle reef. The analyzing on the reef encountered during the drilling shows that the calcilute mound is mainly formed in continental shelf and inner zone of the shelf margin, while framework reef and baffle reef are mainly in the shelf and the shelf margin. And by studying the sedimentary facies and the features of seismic reflection in this area, it can be predicted that reef with the distribution shapes of belt and discontinuous belt can be found in the shelf margin area of Tazhong Uplift and in the middle area of northern slope of Tazhong Area. Especially, the areas at the west end of No. 1 fracture of Tazhong in west Shutuoguole block, up to now six anomaly reflection bodies have been found. Depending on the characters of environment and features of interior reflection they are very likely the reef mounds. It will have great effects on the oil and gas exploration of this area in case of that more play would have been processed.

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Unconformity types and the relationship of unconformity and hydrocabon accumulation

XIAO Qianhua; LI Meijun; PENG Suping and LIU Jiguo

, 2003, 30(2): 286-0.

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Unconformity plays an important role in hydrocarbon accumulation. Various unconformities are widely occurred in Dongbu sag, Liaohe depression. The regional distribution of unconformity and the lithological change upon unconformity surface are studied by the analysis of numerous data. It reveals that different unconformity types and different lithological changes upon unconformity surface impact differently on hydrocarbon accumulation. Hydrocarbons can be accumulated on the type Ⅰ1 and Ⅰ2 unconformities with mudstone below and sandstone upon. Unconformity reservoir can be formed under the type Ⅳ1 truncation unconformity with sandstone below and mudstone upon. Stratigraphic onlap reservoir can be formed in the onlap unconformity stratiraphies. Type Ⅱunconformity with sandstone below and upon is favorable pathway for hydrocarbon migration. Type Ⅴunconformity with mudstone below and upon can be served as regional seal bed in hydrocarbon accumulation.

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The research and application of technology of progressive exploration and development in the Dongying Sag, Shengli Oilfield

YU Zhengjun; HAN Hongwei and WANG Fuyong

, 2003, 30(2): 287-0.

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The research and application of technology of progressive exploration and development in the Dongying Sag, Shengli Oilfield

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Distribution of the fracture within the low permeability sandstone reservoir of Baka oilfield, Tuha Basin, Northwest China

WANG Fachang; MU Longxin and ZHAO Houyin

, 2003, 30(2): 288-0.

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Sandstone reservoir of Middle Jurassic in Baka oil field is of lowest permeability, which is fracture and pore, and the average permeability is only 0.3×10－3μm2 on the ground. According to a test, the matrix permeability is 0.16×10－3μm2 and matrix porosity is 7.4% in the underground basement. There are 6 styles main fractures, i.e., normal orthogonal fracture，diagonal orthogonal fracture，tectonic bedding fracture and plumose fracture. Generally, the wide of fracture is 0.3-3.2mm，and long is 0.1-0.8m in vertical direction, 0.2-2.1m in horizon. Most of fractures are semi-filled，whose distribution are controlled by lithology，thickness of strata and tectonic characters, moreover, the fraction presents banded vertically. Fracture growth relates to tectonic setting. The size of matrix rock is decided by the fracture frequency. Most matrix rocks distributed in a NWW trend, which is identical with tectonic axes.

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Reservoir synthetic evaluation based on new loging technology

KUANG Lichun; MAO Zhiqiang; SUN Zhongchun and ZHANG Youping

, 2003, 30(2): 289-0.

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The geological applications of log data have been greatly opened up by new development of modern loging technology. The combination of NMR and wire-line formation testing logs can be used in evaluation of oil and gas reservoir, such as researches on control factor and determination of pressure system. A synthetic evaluation technique of oil and gas reservoir based on new logs has been presented with some case studies from various reservoirs in Junggar basin, Northwest China.

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Geologic factors influencing the water-drive development of sandstone reservoirs and their comprehensive evaluation using Grey System Theory

GAO Xingjun; SONG Ziqi; CHENG Zhongping; YU Xinghe; YANG Chundong and LI Honghai

, 2003, 30(2): 290-0.

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The geologic factors, which influence the development effect of water-derived sandstone reservoirs, include rock pore structure, percolation property, sensitivity of reservoir, distribution of reservoir, natural energy of reservoir, property of crude oil. The Grey evaluation index system, criteria, and weight factors for studying the factors as mentioned above were set up. Furthermore the corresponding software was developed. Three different types of water-drive sandstone pool in Liaohe Oilfield were evaluated with this method, and the results accorded with the data of production and development effect of these reservoirs.

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The effect of temperature on the relative permeability and residual oil saturation

YANG Long; SHEN Dehuang; WANG Xiaodong and ZHAO Limin

, 2003, 30(2): 291-0.

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The relative permeability curves and residual oil saturation are important parameters that describe multi-phase flow in multiple media and they can also offer base information of each phase's flow in oil reservoir. Whether the temperature could affect the relative permeability and residual oil saturation was discussed in this study. Simulating the reservoir condition with samples of unconsolidated sandstone and crude oil helps determine the temperature effects on relative permeability and residual oil saturation. Water flooding tests were conducted under 60℃, 120℃, 200℃ with crude oil samples from Du32, Qi 40 Liaohe Oilfield of eastern China and Area 6,Kelami Oilfield of northwest China, and whereupon the experiment results are processed and analyzed. The conclusion is that the temperature has little effect on the relative permeability curve and residual oil saturation.

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The reservoirs’ well pattern optimizing techni-ques in the deeper interval of Qianliyuan sag, Dongpu Oilfield

HUANG Xinwen; ZHU Xueqian; ZHOU Qi; ZHANG Xingyan and FENG Yongsheng

, 2003, 30(2): 292-0.

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In order to solve the problem between well pattern thickening and invest increasing, on the base of uniting of benefits and effects, the study uses numerical simulation and hydraulic-power fracture model, inducts ground stress research results, at the same time, fully thinks about the influence of fracturing fractures for flooding development, makes optimum design to well-pattern density and injection-production pattern, forms a series of deeper interval and low permeability reservoirs' well pattern optimizing techniques. The research results have been well used and lead to notable effects in the Qianliyuan sag of Dongpu Oilfield.

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Research on the high temperature and salt resistance (TS series) polymers

OUYANG Jian; ZHU Zhuoyan; WANG Guijiang and SUN Guang-hua

, 2003, 30(2): 293-0.

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Based on the design theory of molecular structure, the high-temperature and salt resistance (TS series) polymers have been synthesized, which consist of acrylamide , hydrophobic monomer, the negative charged monomer with strong hydrophilic group. The experimental results show that they are higher temperature-resistance and salt-tolerance than ordinary polymer such as polyacrylamide. They can be used with produced water in polymer flooding. The oil displacement efficiency of the polymer flooding is about 6% higher by using the polymer than that of by using polyacrylamide (the viscosity average molecular weight is about 25 million) in the same condition. The results have been achieved in laboratory.

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Industrial application in large-scale multiple water plugging and profiling technology

YUAN Mou and YIN Wenjun

, 2003, 30(2): 294-0.

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In the research of anisotropy sandstone reservoir developed by water injection, how to enhance oil recovery of the ultra-high water-cut oilfields is an project for internationally reservoir engineering. The study introduces the application of multiple water plugging and profiling technology, with a large-scale example from the Shengtuo Oil Field, which can be used in the ultra-high water-cut oilfields (entering a critical stage now). The authors analytically sum up the support technology of the industrial application in the large-scale water plugging and profiling. The result of this study may be applicable to other reservoir similar conditions.

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Gas-solid phase behavior of high waxy retrograde condensate gas

LIU Henian; LUO Kai; HU Yongle; ZHAO Wenzhi; ZHONG Taixian and TIAN Changbing

, 2003, 30(2): 295-0.

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In recent years, more high-pressure underground fluids have been discovered within deeper traps targeted by exploration activities. Retrograde condensation usually occurs at high reservoir temperature conditions. More importantly, the formation fluids may exhibit gas-solid phase transition due to the presence of high molecular weight paraffin. This unusual phase change is investigated by high-temperature and high-pressure solid detection system. The experimental results show that the solid deposition pressure increases with decreasing temperature. In addition, this phenomenon is explained theoretically in terms of thermodynamics.

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A study of oil-base fracturing fluid

LIU Min; ZHOU Fujian and XIONG Chunming

, 2003, 30(2): 296-0.

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A new oil-base fracturing fluid has been studied and reported, which can be used for developing of reservoirs under the conditions of low pressure, low permeability and water sensitivity. According to the component of crude oil, a thickener synthesized, which can be reacted with crude oil and be mixed into thickened oil. Through a cross-linking reaction, a gel system is formed. The viscosity of gel can be controlled by the concentrations of thickener and cross-linker. Crude oil is used as a substitute of diesel and kerosene in this oil-base fracturing fluid, so the cost of fracturing fluid is decreased sharply. At the same time, thermo stability and shearing strength are increased. The cross-linking time can be controlled in 2 hours. After gel-breaking reaction, the viscosity of fracturing fluid is decreased, which is correspond to that of crude oil. The new oil-base fracturing fluid can be used economically and easily in some low-permeability oil fields. A pilot test is conducted successfully in Qinghai Huatugou oil field, Qinghai Province, northwest China.

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Calculation of minimum oil production increment cutoff of oil well work-over

LIU Bin; REN Fangxiang and YI Weirong

, 2003, 30(2): 297-0.

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To enhance the investment effect of well work-over, reducing investment of no effect, making good use of work-over budget, the authors proposed the concept of minimum oil production increment cutoff of oil well work-over, giving the algorithm of calculating the minimum oil production increment cutoff of oil well work-over according to the theory of technological economics. We took 1737 instances of 10 categories of well work-over in SG Oil Production Plant of Liaohe Oilfield as examples showing that the calculation of the minimum oil increment cutoff can evaluate the economic result of the well work-over objectively and thoroughly. It can be used effectively for the screening of work-over plans, managing the reservoirs according to the norm that economics plays the key role in reservoir management.

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To Remove Gas Cloud Effects by Using PSDM in Qaidam Basin,Northwest China

Marcello Simoncelli and HUANG Zuxi

, 2003, 30(2): 298-0.

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In the central part of Qaidam Basin, Quaternary bio-genetic gas system has been proved for the shallow layers, which consist of six gas fields, i.e., Sebei-1, Sebei-2, Tainan, Taijinaier, Yanhu, Tuofengshan. Apparently, due to gas cloud effects, typical phenomena, such as pull-down, low frequency, and poor deep imaging, occur in time sections across the gas fields. Pre-stack depth migration (PSDM) is an effective interpretation tool for the explorationist, as image enhancement and depth sections provide new reliable insights. Image improvement is achieved by building an accurate velocity model, enabling reflective energy to be correctly positioned and thereby increasing signal-to-noise ratio. In Sebei Block (Qaidam Basin), the resulting depth sections removed velocity effects associated with time sections and allowed the interpreter to better understand the structural setting and timing.

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Causese of bedding fractures of tight sand gas-reservoir in Xinchang, West Sichuan region

WU Zhijun; TANG Hongjun and AN Fengshan

, 2003, 30(2): 324-0.

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Based on the studies of core description and electron microscope scanning of laser com-focus, the results have been presented that fissures with a low angle to horizontal one of Upper-Shaximiao formation are well developed, while its vertical and structural fissures are not well developed yet. The fissures with low angle to horizontal one are defined as the bedding ones. The formed causes of these fissures are: (1) natural gas must have been accumulated into the gas reservoir prior to the compaction of the formation and structural uplifting, and the effective enclosed system must have been formed within the reservoir formation and hydrocarbon source rock beds; (2) the compaction of the formation and structural uplifting must arrive to a certain degree, the value that the pressure gradient of enclosed system should be bigger than the value that is desired when the weak planes (bedding plane) of tight sand are fractured. The fracturing effect of natural fluid might be taken place on bedding plane of tight sand, then, the “bedding fissure system" could be formed. They will be good for improving and the permeability of reservoir. The area well developed bedding fissure system should be the region with high productivity of gas wells.

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Diffuse reflectance spectrum measurement of kerogen

LIU Wenbing; JI Junfeng; BIAN Lizeng and WANG Liangshu

, 2003, 30(2): 325-0.

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A linear relationship between slope of diffuse spectrum curve (600-1000nm) of kerogen and reflectance of vitrinite has been introduced, on UV/VIS/NIR Spectrograph based on the study of some kerogen samples (Ro=0.27%-0.67%) taken from Shahejie Formation (in the age of Tertiary), Shengli Oil Field, East China. The analysis result suggests that the method of diffuse spectrum of kerogen could become a new and quantitative technique for evaluating maturity of organic matter, with a simple, quick and ancillary character of identifying kerogen for oil and gas exploration.

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Basic features of petroleum geology in the superimposed petroliferous basins of China and their research methodologies

ZHAO Wenzhi; ZHANG Guangya; WANG Hongjun; WANG Shejiao and WANG Zecheng

, 2003, 30(2): 334-0.

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The continental plates of China have undergone a long history of several geologic evolution cycles since Phanerozoic, which have caused the formation of superimposed sedimentary basins characterized with the terrestrial facies of Mesozoic to Cenozoic sitting upon the marine and marine-to-terrestrial facies of Paleozoic sequence. The superimposed basins can be divided into three basic types according to their development features occurring during different geological ages, namely: the successive, gradually-transformed, and transformed types. Specific petroleum exploration concepts and technology are generated in this paper to determine the potential petroleum distribution, because some of the petroleum geologic phenomena of the superimposed basins has exceeded the range of present petroleum geology theory. Under deeply buried and overpressured conditions, the mechanism of hydrocarbon generation and expulsion, the formation of traps and the distribution of hydrocarbons are not confined or explained by over-late reservoir formation under source kitchen control's theory and annealing geological background, hence the distribution of large oilfields does not follow the existed model which called source kitchen control's theory. The properties of reservoirs at the deep interval with the features of early formation of hydrocarbon accumulation and late burial as well as the formation of secondary pores, fractures and dissolved cave and cavern are much better than that we predicted on the basis of common theory of petroleum geology. To understand the formation and distribution of hydrocarbon accumulations in superimposed basins requires integrated research that takes the process-oriented study as the key component. The exploration technologies should be chosen according the stage of exploration and the required results, and should be used in a complementary manner. In this way we can achieve difficult objectives with the best efficiency.

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Some thoughts on petroleum exploration in marine sedimentary basins of China

ZHANG Kang and WANG Darui

, 2003, 30(2): 335-0.

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Based on the analyses of discovered oil and gas fields generated in the marine sedimentary strata of China, the prescribed minimum amount of total organic carbon (TOC) in efficient source rocks should be at least higher than 0.5%, and the coal measures formed in littoral facies could be an important contributor to hydrocarbon generation. The efficient reservoir space within carbonate rocks should be mainly fracture, cavities, and secondary porosity. Karstification would be also a very important factor for generation and development of these types of reservoirs. In terms of the degree of porosity and permeability development (from weaker to stronger), the carbonate reservoirs can be classified as Naxi (irregular and independent reservoir), Tahe (net-like transitional type), and Weiyuan-Renqiu (horizon-like and block-like type, which are well-connected reservoir). Within the net-like reservoir, there are extremely uneven characters and the reservoir lacks a unified basal water and pressure system. The controlling and key factors for alteration of the marine sedimentary reservoirs are most likely tectonic cycles with multiple opening-closing. The retention conditions should be a direct controlling factor for guiding explorations to find commercial oil and gas traps and reservoirs within marine deposits. On the purpose of petroleum exploration, the targets should be selected by taking into consideration the relative activities of stable landmasses and their conditions for developing and generating of source rocks and reservoirs. It is important to double-check the effective marine source rocks, based on the standard that the content of total organic carbon should be 0.5% or higher. The exploration in marine strata should start from shallow secondary oil traps and major petroleum reservoirs. It should attach importance to lithologic traps and exploration of gases. The conveyance and series exploration technologies, with the goals mentioned above, must be developed in near future.

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Evolvement sequence of Tertiary volcanic rocks in the Nanpu sag，Eastern China

DONG Yuexia; XIA Wenchen and ZHOU Haimin

, 2003, 30(2): 338-0.

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Deep dynamic processes and evolution of a rift basin could be determined by studying the magmatic evolvement within it, and establishing active sequences of volcanic rocks and to tracing their geochemical characters should be one of the efficient and useful tools for studying the dynamics of an extensive rift basin. According to the comprehensive analyses and studies of the distribution, type and geochemical characters of the Tertiary volcanic rocks in the Nanpu sag, two types of the evolvement could be identified, that should be a local rift type of evolvement sequences of and a regional extensive volcanic rock, representing the differences of decrease of lithosphere and evolvement process.

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Depositional system and sequence stratigraphy of the Shashi Formation in Jiangling depression in Jianghan basin, South China

LIU Lijun; XIAO Jianxin; LIN Changsong; WANG Dianfu and LU Mingguo

, 2003, 30(2): 339-0.

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Based on the concept of sequence stratigraphic methodologies, the cyclic sequence of Shashi Formation in age of Paleogene the in Jiangling Depression is classified and correlated in detail, and the strata contrast frameworks of cyclic sequence is defined and established. It shows that Shashi Formation composite of shallow lacustrine and continent-source clastic rock and salt deposits that sedimented and developed in the half draught climate. The major deposit system is composed mainly of (1) fluvial-delta deposit system; (2) shore to shallow lacustrine deposit; (3) half-deep lacustrine sand deposit; (4) mudstone deposits and salt deposits. Lowstand systems tract is characteristiced by alternately developed incised valley, delta and draught salt lacustrine deposits, etc. High stand systems tract is characteristiced by delta deposits, shallow lacustrine deposits. The evolution of those three systems tracts suggests the changing of transgressive and regressive of fluvial -delta system and draught salt lake during the depositing. The sequences Sq3 and Sq4 formed the thicker reservoir sand beds, and they have the character of transgressive sequence structure. The reservoir sand mainly distribute in the high stand systems tract. Among these reservoir layers, the water-lain mouth bar and subaqueous channel deposits, which is developed in high stand systems tract of Sq1， are of the most important stratigraphical units of the reservoir.

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The type, distribution and controlling factors of the shallow gas-pool in the Block Sheng 3, Dongying sag, Shengli Oilfield in eastern China

LI Min; ZHAO Yong and FU Qing-xiang

, 2003, 30(2): 340-0.

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The basic characters, type, distribution and major controlling factors of the shallow gas pools in the Block Sheng 3, Dongying sag of the Shengli Oilfield in eastern China are characteristic of a shallow gas-pool. The gas pools in this area are mainly controlled by stratigaphic structure, fault-structure and lithologic type. The sequence of oil-oil/gas-gas reservoir formed successively from the Shahejie to Minghuazhen formations of Neocene age. Combined traps related with faults have a larger scale, then structurally formed ones. In most cases, “gas-potato" could be discovered within the lithologic traps, and their distribution is probably controlled mainly by sedimentary micro-facies. A better combination between the conditions of gas source, fault and trapping should be the key for forming the commercial gas-pools.

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Pooling mechanisms of “evaporating fractionation” of oil and gas in the Xihu depression, East China Sea

FU Ning; LI Youchuan; CHEN Guihua; CHEN Ming; GAO Weiyi and ZHANG Haiying

, 2003, 30(2): 341-0.

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According to the geochemical data and geological information of 30 samples taken from the Xihu depression, the geochemical characteristics of oil and gas, maturity, oil source and hydrocarbon pooling mechanisms have been synthetically analyzed and interpreted. The results suggest that the crude oil mainly originated from each district coal measure source rock in the Xihu depression because the oil has a character of short-distance migration from the source rock. The oil pools were formed before those of gas, and the pools were formed and trapped in two stages. The secondary condensate gas reservoirs were all formed as a result of the "evaporating fractionation effect", which is determined for the first time in this study and may be an important characteristic of the hydrocarbon pooling in this area.

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Identification of oil-water layers and evaluation of tight reservoir types

HUANG Lei; SHEN Pingping and SONG Xinmin

, 2003, 30(2): 344-0.

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To apply differential analysis and non-invasion line in low-permeability oil fields, this paper presents a method for identifying oil-water in reservoirs. The resistivity and porosity logging curves are related, thus in the oil formation the deep laterlog (or induction) and acoustic logs are both in high value, showing the characteristic “opposite direction." While in the water formation the resistively log has a low value, and the acoustic log high value, showing the characteristic “identical direction". Since there is a linear relationship between the induction log value (Ri) and 0.5m potential electrode log value (Ri) in the same coordinate system, the value of the induction log curve and 0.5m potential electrode log curve for the tight reservoir can make up a line, that is, the non-invasion line. By comparing the Ri/Rn ratio (Ri, Rn can be taken from any reservoir) to the non-invasion line, it is possible to distinguish between oil and water layer. Analyzing the mechanism of reservoir formation, we demonstratd that antidip faulting is the main control factor of hydrocarbon aggregation; the lithology also had an important impact on hydrocarbon aggregation. As a main style in Jilin Tuodong oil field, structural reservoir should be a focussed target for oil field development in the future.

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Micro-fractures distribution in extremely lower permeable sandstone reservoirs of Yanchang Formation and its geologic significance, Ordos Basin, Northwest China

WANG Jing; LING Shengjie and NAN Zhonghu

, 2003, 30(2): 345-0.

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Based on the theoretical analysis of case studies, a rather systematic study of micro-fractures in the reservoirs of Yanchang formation has been completed by using the frequency analysis of abnormal value of permeability. The main reasons, which lead to the lower reservoir permeability and porosity, are the strong diagenesis, small aperture, and thin throat of the extra-lower permeable sandstone. The relative high permeability zones, existed in the reservoir, are closely related with the micro-fractures formed in the stratum. By using the frequency analysis of abnormal permeability, which takes the abnormal values as a clue, the well data as a base, and the area (the sedimentary body) as a unit, the matrix permeability of this area (the sedimentary body) is decided by much statistics data from core analysis, and the next step is to find out the abnormal value (bigger than the matrix permeability) and its changing law both in plane and section. Combined with the relative data of regional stress field, the interpretation of the plane distribution of micro-fractures should be presented. This method can be widely used and have a character of advantages of abundant data and lower cost. It is a meaningful discovery for studying the micro-fractures distribution patterns in the lower and the extremely lower permeable sandstone reservoirs.

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Predication of multi-wave and multi-component seismic exploration techniques on the Mesozoic reservoirs in the Lunnan, Tarim basin, Northwest China

WANG Shirui; PENG Suping; GOU Jingwei; LING Yun; WANG Enhua and HAN Long

, 2003, 30(2): 350-0.

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The multi-wave and multi-component seismic exploration has been used in the Lunnan area of Tarim Basin, Northwest China, including data collecting and processing and interpretation. In acquisition, to ensure the acquired converted wave data quality, a good mixture of charge sizes, offsets, etc. were necessaries and they were defined carefully. For the processing, plane-wave-based theory and plane-wave-based polarization and projection technique in anisotropy medium should be also considered and applied to separate P- wave and SV- waves data. And, for the interpretation, the P-wave sections were first interpreted and the characteristics of the waveforms were understood clearly. The VSP data and sonic logging data were used to calibrate the marker horizons of converted-wave sections, and to interpret the converted-waves sections and to generate the compressed-profile. The characteristics of the P and SV waveform sections were analyzed correspondingly on a purpose of identification for changing inner wave shapes and calculation of their characters. The application of above techniques in Lunnan area, Tarim basin shows an obvious difference of seismic dynamic characteristic of reflector between the Jurassic and Triassic reservoirs.

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The fine studies of depositional micro-facies on the middle-post development stages in Wennan Oilfield

XIONG Yunbin; YANG Jianwen; CHEN Yunying; TIAN Shicheng; HONG Yu and ZHANG Ling

, 2003, 30(2): 351-0.

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For a reservoir on the middle-post development stages, a fine study about micro-facies is very important for modeling a proper reservoir, getting a proper knowledge of remaining oil distribution and improving oil recovery rate. Based on the basis of comprehensive analyses of the features of the paleontology, geochemistry, depositional structure, petrology and granularity, the depositional environment of the sub-zone of No.2 member of the Shahejie Formation in age of Paleogene could be identified as an intermission fluctuating shore-shallow lake under a drought weather. The depositional facies should be swallow delta sedimentary system. A few of type of micro-facies are marked off, such as underwater channel, overflow bank sands, and so on. The nature of the micro-facies are described, it is clearly that the physical and storage properties of reservoirs, taken a sequence from the best to the worse, are underwater channel, overflow bank sands, respectively.

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Optimization of development scheme for gas-cap reservoir

YU Zhong; ZHAO Huijie; LI Weijing; LI Tao; ZHANG Yingshan; SHI Wensheng and YANG Jinfu

, 2003, 30(2): 358-0.

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Based on the studying and analyzing of distribution characteristics and edge-water energy of various kinds of gas-cap reservoirs, the aquifer influx, edge-water volume and reasonable elastic productivity were calculated. The appropriate development scheme for gas-cap reservoir was thus proposed. The successful application of this method in Block Gangshen 18-2,Tang Jiahe oilfield, Dagang Oil province have proved that gas-cap reservoir could be developed with high efficiency by using this kind development scheme.

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Study on N2 and solvent assisted steam stimulation in a super-heavy oil reservoir

GAO Yongrong; LIU Shangqi; SHEN Dehuang and LI Xiaoling

, 2003, 30(2): 359-0.

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The Xinglongtai oil formation of Du32 block in Liaohe Oil field, eastern China, is a typical super-heavy oil reservoir. The LH-5 solvent developed in recent experiments has the property of effectively dissolving asphaltene and resin, with a good effect of reducing the viscosity, and good disperse in oil. Numerical simulation shows that the result of Huff and Puff with the solvent and nitrogen is better than that of conventional Huff and Puff. If the economic OSR is 0.25 in single cycle, one well can produce for 8 cycles, production time will be 920d, the cumulative oil will be up to 12,180t, the cumulative OSR is 0.54, the average daily oil production will be 13.2t/d, the recovery will be 14.3%. The economic analysis shows that if the price of the solvent is 2500 yuan (RMB)/t and the price of the nitrogen is 1 yuan(RMB)/m3, the cost of the incremental oil will be 436 yuan (RMB)/t.

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The formula of ASP flooding for the reservoir of Jing-11 in Huabei Oil Field

TANG Xianrong; YUAN Hong; CHEN Hong; WU Xingcai; WU Jie and LI Ming

, 2003, 30(2): 368-0.

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Considering the reservoir characteristics of the Jing-11 in Huabei Oil Field (the low viscosity and low acid value of crude, high content of clay and high water flooding recovery), the interfacial tension (IFT) between the ASP system and the crude oil, the adsorption of the surfactant on the core, the loss of alkaline and the effect of the environment factor on IFT were studied. The optimum ASP formula using low concentration weak alkaline was obtained for the reservoir of Jing-11. The formula consists of 0.15%2SY alkyl benzene sulfonate, 0.5% Na2CO3 and 0.15% HPAM. The experiment of physical simulation flooding shows that in the interval by rejecting 0.3PV ASP slug and 0.2PV 1.2g/L polymer protecting slug after the 98% watercut by water flooding, the oil recovery could reached up to over 21%OOIP.

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Generalization of well-bore effects in pressure transient analysis

ZHANG Yanyu and JIANG Haiyan

, 2003, 30(2): 369-0.

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Many factors, including well-bore storage, reservoir and fluid properties, flow behaviour, etc., could affect the pressure transient analysis of oil wells. Previous well testing analysis ignored the effects of mass and momentum changes in the pressure transient response. However, the temperature changes from the bottom hole to wellhead and the flow rate may increase or decrease during the testing. This may lead to a remarkable error if these factors were not taken into consideration. The study established new theoretic curves through Laplace transform, based on the W. B. Fair's model that considered momentum effect. And the effects of each factor on the dynamic pressure transient also were studied.

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Law of pore structure variety in reservoir during a long episode waterflooded development

LI Cungui and XU Shouyu

, 2003, 30(2): 392-0.

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Applying waterflooding experiment and core analytical data, the authors studied the law of pore structure variety in delta reservoir during a long episode waterflood development, that is in layer of 83 in second member of Shahejie formation (in age of Neogene) in Shengtuo oilfield of Shegnli region. The character of pore is obviously changed for a better condition after the water-flooded development. Shape factor of pore is fleshed out, the shape of pore is changed to more regular and smooth; the average specific surface of pore is diminished; the pore connectivity is alter for the better; and the isotrope degree is increment. The variety law of pore throat is complex. The radius of throat trends to aggrandize; sorting coefficient incline to decrease. The connectivity of pore throat has complex varying law, heterogeneity of pore throat in lower permeability trend to be buildup while homogeneity incline to boost up.

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The laboratorial evaluation of formation damage induced by asphalting precipitation

ZHAO Fenglang and YAN Jie-nian

, 2003, 30(2): 393-0.

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To prevent the formation damage induced by asphalting precipitation is one of the technical difficulties during development and production of heavy crude oil reservoir in the Bohai Sea. A laboratorial evaluation of formation permeability reduction was established by using the core flooding test device in which the reservoir situation of SZ36-1 field located in the Bohai Sea could be identified. In addition, the possibility of asphalting deposition for the Bohai Sea heavy oil was also predicted with the SARA method. It is indicated that the damage degree is related to the amount of asphalting precipitation and the initial formation permeability. The more the asphalting is precipitated and the lower the initial permeability is, the more serious the formation damage will be.

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, Volume 30 Issue 2