Petroleum Exploration and Development

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Formation model of multi-stage fracture reservoirs inside the buried hills in Liaohe Depression

XIE Wenyan; MENG Weigong; ZHANG Zhanwen; LI Xiaoguang and CHEN Zhenyan

, 2006, 33(6): 1397-0.

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It has been accepted that reservoirs can be formed in the weathering crust at the top of buried hills. But whether they can be formed in the deep side of buried hills remains unknown. This paper focuses on the buried hill in the Xinglongtai area of west sag in Liaohe Depression. The development of the multi-stage fracture reservoir is discussed from such aspects as buried hill lithology, tectonic movement, and hydrocarbon generation system and transport mode. A formation model of multi-stage fracture reservoirs is established. Under the guide of it, Well Xinggu 7 was drilled and a large reservoir about 1000 meters high in the deep side of buried hill was found. It paves the way for the exploration into the deep side of buried hills in Liaohe Depression and around the country.

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Age of oil accumulation

LI Mingcheng; MA Chenghua; HU Guoyi and SHAN Xiuqin

, 2006, 33(6): 1398-0.

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Miller (1992) and Macgregor (1996) studied the era distribution of global petroleum reserves and large oil field reserves. They estimated their average median ages at 29Ma and 35Ma and their existent ages at 41Ma and 55Ma, respectively. In this paper, the concept of natural age is put forward (natural age means the reservoir die-out time caused simply by permeation and molecular diffusion). The average natural ages of large and medium gas-oil fields are estimated at 70Ma and 120Ma. Whatever age is short relative to geologic era. Continual hydrocarbon sources or conditions of various late-period accumulations are the preconditions for Paleozoic oil-gas accumulations being conserved during the geological history. This is very important to evaluating oil-bearing perspectives of Paleozoic basins.

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Advances in oil-shale resources: development and utilization

LI Danmei; TANG Dazhen and YANG Yufeng

, 2006, 33(6): 1399-0.

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Oil shale is one of the significant alternative energy resources in the 21st century because of its enormous reserves, convenient development and utilization. Statistics show that the natural resources of oil shale around the world is about 10×1012t (40% more than coal), in comparison with shale oil about 4750×108t (50% more than traditional petroleum). Over 200 years, the development technology and the comprehensive utilization of oil shale have been mature, from primary direct recovery to advanced subsurface-conversion technology and from simple energy application to multiple-purpose application. These result in energy utilization ratio increasing, cost and environmental pollution reducing dramatically. Also the severe energy crisis and continued high-oil-price have boosted the oil shale industry. China has enormous potential resources of oil shale, the proven reserves (about 315×108t) being the fourth in the world. In order to reasonably develop and utilize these resources, it is necessary to strengthen the research of geology and resources distribution and use the foreign advanced experiences for reference.

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Sealing and preservation conditions for large and medium gas fields of China

FU Guang and LIU Jiangtao

, 2006, 33(6): 1400-0.

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Based on the analysis of the sealing and preservation characteristics of 46 large and medium gas fields in different types of basin, the sealing ability of the caprocks was examined using comprehensive evaluation parameters. The gas sealing ability in foreland basins,followed by rift basins,is the best, and that in cratonic basins is the worst. The preservation conditions of the fields were studied according to the gas accumulation time. The gas accumulation in rift basins is relatively late, and their preservation conditions are good. The preservation conditions in foreland and crationic basins are poor. The gas accumulation efficiency of foreland basin is the highest, followed in turn by rift basin and cratonic basin. According to the relationship between accumulation efficiency and sealing and preservation conditions, to form highly efficient large and medium gas fields, the minimum sealing parameter value for cratonic basin should be about 3.1×109m/s, for rift basin about 7.0×109m/s, and for foreland basin 9.7×108m/s.

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Controlling of petrophysical fractures on extra-low permeability oil and gas reservoirs in Ordos Basin

DI Lingjun

, 2006, 33(6): 1401-0.

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In geological survey and core observation in Ordos Basin, structures as echelon joints, X-conjugated joints, fractures, micro-fractures and local ruptures were found well developed in the reservoir sandstones. It cannot be explained by the traditional tectonics theory based on Ultra-steady Block. The tectonic movement direction, the petrophysical property of sandstone, and the oil and gas distribution were subjected to the successive activities of deep and big faults in the basin basement. The regional tectonic stress field also influences them. The low permeability reservoir reflected by the matrix does not represent the real permeability of the reservoirs. The oil and gas distribution is subjected to the reservoir petrophysical fractures, reflected by the features of a series of shear deformation derived from the base ruptures and late tectonic activities. The emphasis should be put on understanding how tectonic factors control the diagenesis, the acidic liquid transporting, and the formation of secondary solution pores in the future exploration.

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Influence of pore structures on electric properties and well logging evaluation in low porosity and permeability reservoirs

ZHANG Longhai; ZHOU Cancan; LIU Guoqiang; XIU Lijun; LI Changxi and LIU Zhonghua

, 2006, 33(6): 1402-0.

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Recent investigation indicates that the accuracy of reservoir productivity evaluation and well logging identification of oil, gas and water zones in low porosity and permeability reservoirs are affected by their pore structures. This paper analyzed the characteristics of pore structures in low porosity and permeability reservoirs and their influence on productivity and electric properties. It was found that for net water layers, the better the reservoir pore-throat conductivity was, the lower the formation resistivity, if the other affecting factors were the same; the worse the pore-throat conductivity, the higher the formation resistivity. The resistivity of some water-bearing layers with poor pore structure was even higher than that of oil-bearing layers, resulting in decrease of the identification capacity of formation resistivity method and increase of difficulty in well logging interpretation. Good results can be obtained in evaluating oil and water zones by calculating their oil saturations with the changeable m value, which can raise the consistency of well logging interpretation of the reservoirs from 64% to 85%.

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Geochemical characteristics and origin of tar mats in Eastern Block 25 in Wenliu Oilfield, Dongpu Depression

ZHU Zhanjun; YUAN Jingju; LIN Renzi and YAO Shanglin

, 2006, 33(6): 1403-0.

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Three tar mats separating reservoirs are identified in high porosity and permeability reservoirs in the east of Block 25 of Wenliu Oilfield using thin layer chromatogram – flame ionization detector (TLC-FID) and whole hydrocarbon gas-chromatography. The tar mats have similar logging characteristics of oil-bed and are rich in polar composition (over 40%), which is far higher than that in oil sand. Similar clan constitutions in tar-mats, oil sand and crude oil indicate their common origins. The GC/MS analysis of saturated hydrocarbon shows that n-alkane and biomarkers are similar in constitutions, proving that they come from the same source rocks, have similar thermal evolution histories and are not biodegraded sharply. Both geochemistry and well log data indicate that long-term formation water washing and oxidation action are main causes of tar mats existing in the oil-water interface.

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Application of hydrocarbon-generating chemical kinetics in the Puguang gas field, NE Sichuan Basin

ZHAO Zhe; ZHONG Ningning; LI Yanxia and ZHANG Ping

, 2006, 33(6): 1404-0.

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The Puguang gas field is a gas field with the largest scale, buried depths and oil-gas reserves in the Sichuan Basin. Based on the relations of the contribution of different source rocks, the key hydrocarbon-generating period and the tectonic evolution, the model of hydrocarbon-generating chemical kinetics was established and kinetics parameters were calibrated. The hydrocarbon-generating and oil-cracking processes were described quantitatively using the data of the source rock parameters, the basin burial and geothermal histories. The chief source rock is the Lower Silurian mudstone in the Puguang area, the chief kerogen-formed oil period is from the late Early Permian to the late Early Triassic (286-240Ma), the chief kerogen-formed gas period is in the Middle Triassic (240-230Ma), the main origin of natural gas is the late-stage oil-cracking gas, and the chief period of oil-cracking is Early Cretaceous (144-97.5Ma). The formed pattern of the gas field is of the multi-stage hydrocarbon accumulation, the transformation from oil to gas, and the late-stage finalization.

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Hydrocarbon generation of Lower Cretaceous lacustrine carbonate in Jiuxi Depression

XIONG Ying; CHENG Keming and MA Liyuan

, 2006, 33(6): 1405-0.

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Lower Cretaceous Chijinpu and Xiagou Formations in the Jiuxi Depression mainly consist of laminated argillaceous dolomites and dolomitic mudstones deposited in lacustrine environments. The argillaceous dolomite contains highly heterogeneous organic laminas (algal-lamina). The distribution of organic laminas in source rocks is positively related with hydrocarbon genetic potential, which shows a genetic relationship between them. During oil-source correlation, the biological markers showed that the oil in this area is predominantly originated from the algal-laminated argillaceous dolomites of the Lower Cretaceous Xiagou Formation with evidences from parental materials, sedimental environments and thermal maturation, etc. The rocks rich in organic laminas can not only work as good source rocks, but also enhance the formation of micro-fractures between gaps and help the hydrocarbon expulsion during the hydrocarbon generation and expulsion processes thanks to the laminated distribution of organic materials.

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Overpressured fractured mudstone reservoir in salt-mud interbed—A case from Wenliu structure in Dongpu Sag

LENG Jigao; LIU Xiaofeng; PANG Xiongqi and SONG Dongyong

, 2006, 33(6): 1406-0.

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The overpressured fractured mudstone reservoir is a special type of reservoir, which has the following characteristics of formation: both hydrocarbon generation and accumulation occur in the same reservoir; mudstone fractures are developed in the section with abnormally high pressure; hydrocarbons collect in the vicinity of fault belts. The overpressured fractured mudstone reservoir in Wenliu is developed mainly in the second member of third section of Paleogene Shahejie Formation,where major sediments are deposited in deep and half-deep lacustrine environments.The lithology is salt-mud interbeds and sandstone is immature. It takes dark and thick rock rich in carbonate and organic matter as its source. The reservoir is related to the local tectonic deformation caused by fault, abnormal fluid pressure and salt plastic flow. The sealing of salt beds up and down the source rock made autogenous and in-situ-stored fractured mudstone reservoirs come into being.

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Hydrocarbon generation potential of Upper Paleozoic in eastern part of North China

HU Zongquan; ZHOU Xinke and ZHU Jianhui

, 2006, 33(6): 1407-0.

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In the eastern part of North China, the "secondary hydrocarbon generation" potential of the Upper Paleozoic source rock is mainly determined by burial, thermal and hydrocarbon generation histories. The Upper Paleozoic source rock has 4 types of burial history: shallow burial in early stage - uplift in middle stage - deep burial in late stage, shallow burial in early stage - shallow burial in middle stage - deep burial in late stage, middle burial in early stage - deep burial in middle stage - shallow burial in late stage, and deep burial in early stage - uplift in middle and late stages. The modeling of hydrocarbon generation indicates that the secondary hydrocarbon generation of the Paleozoic source rock in Dongpu Sag concentrates in the Paleogene period and the genetic potential is high in late stage; in Jiyang Depression, it occurs mainly since the Paleogene period and the genetic potential is high in late stage; in Linqing Depression, it occurs in the Jurassic and Cretaceous periods, the genetic potential is low in late stage. The Upper Paleozoic sandstone reservoir is controlled by sedimentary facies and burial depth, the sandstone reservoir with a high quartz content and coarse granularity has high porosity and permeability, and the maximum depth limit of effective reservoir is deeper. The minimum depth limit of "secondary hydrocarbon generation" and the maximum depth limit of effective reservoir are combined to construct a model to evaluate the gas-pool forming condition of the Upper Paleozoic, showing that the gas-pool forming conditions of Jiyang Depression and Dongpu Sag are much better than that of Zhoukou Depression and Linqing Depression.

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Accommodation change and its relationship to hydrocarbon accumulation in the Silurian, Tarim Basin

LIU Jinhua; ZHANG Shiqi; WEI Chuigao; LIU Jingxin and JIANG Lin

, 2006, 33(6): 1408-0.

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Influenced by tectonic movements, the accommodation, the center of sedimentation and the formation thickness changed in the Silurian of Tarim Basin. Two models of the accommodation changes are established based on the north-south and west-east sections, one is the single-basin model; the other is the double-basin model. According to the change of the accommodation, the stratum is divided into increase zone, decrease zone and transitional zone. Based on the north-south and west-east sections and the stratigraphic sedimentary model, the accommodation zones are analyzed and the accommodation changes in vertical and horizontal directions are identified. The relationship of the accommodation change zones and reservoirs is analyzed in terms of the hydrocarbon accumulation of single well, showing the increase zone is also a good zone for the accumulation of oil and gas.

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Sedimentary facies and model of Kangkelin Age, western Tarim Basin

WANG Lidong; YU Bingsong; ZHANG Yongwang and MIAO Jijun

, 2006, 33(6): 1409-0.

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Reef-beach bodies of Permo-Carboniferous are well developed in the western Tarim Basin and with good oil and gas potentials. Based on the studies of the sedimentary bodies of the Kangkelin Age in the area, the lithology, the lithofacies, the depositional sequence and the lithofacies spatial distribution rule are analyzed in detail, and the depositional model of carbonate rocks of Permo-Carboniferous is established. It is suggested that there are three types of sedimentary facies, i.e. platform marginal reef-beach, restricted platform and strandflat; in the western Tarim Basin, the depositional environments between the early and late Kangkelin Age are different, and the transfer of facies zones reflects the control of the sea-level change and the paleogeographic condition on depositional fabric；and the reef-beach bodies of the Kangkelin are well developed and have a good spatial continuity. It could be one of the most important reservoirs in the western Tarim Basin.

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Paleogene rift structure and its dynamics of Qiongdongnan Basin

LI Xuxuan; ZHONG Zhihong; DONG Weiliang; SUN Zhen; WANG Lianghu; XIA Bin and ZHANG Minqiang

, 2006, 33(6): 1410-0.

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Qiongdongnan Basin is a Tertiary basin developed on the northwest margin of the South China Sea; it experienced two stages of extension from Eocene to early Oligocene and during late Oligocene. Two styles of structures, halfgraben and graben, developed with zonation from north to south and segmentation from east to west. From the point of mechanics and lithospheric extension, both the sinistral rotational stress associated with the Indosinian plate extrusion and the SSE stretching stress caused by the subduction of the ancient South China Sea controlled the rifting of Qiongdongnan Basin from Eocene to early Oligocene, while the extension during late Oligocene was caused by the spreading of the subsea basin. The thermal situation of the lithosphere determined the stretching style of the upper crust. The northern depression developed halfgrabens controlled by synclined faults due to relative cold lithosphere extension, while the central depression is characterized by composite rift belts, which are composed of halfgraben and graben.

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Development technique for horizontal wells in Tarim Oilfield

XIANG Jianmin

, 2006, 33(6): 1411-0.

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Horizontal drilling is applied widely to different oil/gas reservoirs in Tarim Oilfield. Good effects have been gained in developing new oil reservoirs, readjusting old oil reservoirs, developing gas/condensate reservoirs, and flooding. Over the past decade, a complete set of horizontal drilling technologies have been developed in Tarim Oilfield, including fine reservoir description, well pattern allocation optimization, horizontal well optimization design, control while drilling, production evaluation, acid treatment, waterflooding mechanism and dynamical monitoring and so on. The successful experience and future development of horizontal drilling technology in Tarim Oilfield are pointed out, and it will be a guide to developing horizontal drilling technology.

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Productivity of horizontal wells with complex branches

WANG Xiaodong; YU Guodong and LI Zhiping

, 2006, 33(6): 1412-0.

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Using a horizontal well with multiple branches to enlarge the drainage volume is a newly developed recovery technology. It brings up complex problems in flow of fluid in porous media. After solving the mathematical model of fluid unsteady flow for a horizontal well in 3D circular-boxed media, a novel equivalent radius model was presented by asymptotic analyses to the solution. A productivity-evaluating procedure was presented based on the model and the principle of superposition. There is a reasonable branch number in local drilling design because, as the number properly increases, the productivity index of each branch declines while the total productivity index ascends, and when the number increases excessively, the growth of the total productivity index continuously declines. Both the branch length and the intersection angle between branches influence the distribution of the branch productivity index. If the index has to be taken as a balance, each branch length and intersection angle should be designed.

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Mechanism of HPAM-biodegradation and its application

LI Yiqiang; SHEN Chuanhai; JING Guicheng and HU Jinqiang

, 2006, 33(6): 1413-0.

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To develop a water block remover of low-cost, long-term effect, environmental protection and safety, and of being able to relieve the block caused by polymer near well-bore, the evaluation experiments were carried out indoors using the mixed strains separated from the polymer-bearing produced liquid in an oilfield. The mixed strains consist of pseudomonas sp. ML1, clostridia sp.ML2 and ML3. The static experiments with HPAM biodegradation, the oil-displacement experiments in the emulation micro-models, and man-made cores indicated that the microbes could degrade the long-chained high-molecular polymer, release the block near well-bore, improve the communication of the pores and channels and increase the productivity, thus improving the single-well production. The final oil recovery was increased by 11.9% on what has already been achieved with polymer flooding. The field test demonstrated that after the damage removal by using the microbes, the injection pressure of injectors reduced, the liquid production of producers increased, and the effective period was up to more than 540 days.

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Mechanism of HPAMbiodegradation and its application

LI Yiqiang; SHEN Chuanhai; JING Guicheng and HU Jinqiang

, 2006, 33(6): 1414-0.

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To develop a water block remover of lowcost, longterm effect, environmental protection and safety, and of being able to relieve the block caused by polymer near wellbore, the evaluation experiments were carried out indoors using the mixed strains separated from the polymerbearing produced liquid in an oilfield. The mixed strains consist of pseudomonas sp. ML1, clostridia sp.ML2 and ML3. The static experiments with HPAM biodegradation, the oildisplacement experiments in the emulation micromodels, and manmade cores indicated that the microbes could degrade the longchained highmolecular polymer, release the block near wellbore, improve the communication of the pores and channels and increase the productivity, thus improving the singlewell production. The final oil recovery was increased by 11.9% on what has already been achieved with polymer flooding. The field test demonstrated that after the damage removal by using the microbes, the injection pressure of injectors reduced, the liquid production of producers increased, and the effective period was up to more than 540 days.

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Method of integrated studies for low permeability reservoir and its application

SUN Zhixue; LU Hongjiang; FENG Wenguang and SUN Zhilei

, 2006, 33(6): 1415-0.

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The exploration and development of oil reservoir are getting more difficult today, and the traditional methods of exploration and development can't meet the progressively complicated conditions. The Chang 63 Member of Yanchang Formation, Ordos Basin is a typical continental reservoir, with the features of high heterogeneity, low porosity and permeability, and low abundance. With the ideas of integrated reservoir studies, i.e. reservoir description and reservoir numerical simulation techniques, the paper tries to study the Chang 63 Member with dynamic and statistical information. First, the refined 3-D visual reservoir characteristics of the target layer were established by using the method of three-stage stochastic modeling. The reservoir numerical simulation model was developed from the refined 3-D geologic reservoir model by using the grids upscaling technology. The most reasonable oil reservoir model was achieved on the basis of the techniques of history matching and parameters adjustment. The practical production results indicate that the technology of integrated reservoir studies with reservoir description and numerical simulation can better resolve the complicated problems of oil reservoir.

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A dynamic modeling of underbalanced drilling multiphase-flow and numerical calculation

LONG Zhihui; WANG Zhiming and FAN Jun

, 2006, 33(6): 1416-0.

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Circulation flows in underbalanced drilling include downward flow in drill pipe and upward flow in annulus. The circulation flow system is studied according to the gas-liquid two-phase flow theory and a new dynamic model is established. The dynamic model is numerically solved by the finite difference method scattering time and the finite volume method scattering space. The often-encountered hole sizes in oilfields and the varied combination injection ratios of gas and liquid were inputted to the model, and the numerical calculation show that the dominant flow patterns are bubble flow and slug flow. Churn flow only exists in the annulus near to the surface. The steady-state flows in drill pipe and in annulus are analyzed and the variations of pressure, gas void fraction, and multiphase-flow density along the well depth are simulated. In the annulus flow, the pressures in deviated hole and the corresponding vertical hole vary with depth. The change of the annulus pressure in the non-steady multiphase-flow in closing choke valves is simulated. The calculation results of the model are validated by actually measured data, showing that the model can predict annulus pressure variation in drilling.

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Methods of determining proved reserves by SEC standard

ZHAO Wenzhi; LI Jianzhong; WANG Yongxiang and BI Ha-bin

, 2006, 33(6): 1417-0.

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There are two steps in determining proved reserves by the SEC standard, i.e. defining reservoir boundary and determining reserves boundary based on the well. Reservoir boundary consists of oil-gas-water contact, the boundaries of fault, stratum, and lithology, and the lowest known oil/gas (LKO/G) etc. The key issue in determining reservoir boundary by LKO/G is to estimate the hydrocarbon-water system so as to determine which one is reasonable among LKO, the cumulative net pay and the biggest net pay of monolayer. The upside boundary of reservoir should be determined only by the top of oil layer before a gas cap is proved not exist. Faults of all levels are categorized as fault boundary in the SEC standard. Determining reasonable development well spacing is the key in identifying the boundary of proved reserves. The drill platform is also an important factor for ocean oil/gas fields. The aim of determining the boundary is to make sure the higher certainty of the proved reserves and to protect stockholders’ interests.

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Oil resource abundance of petroleum plays in Chinese basins and its prediction model

LIU Guangdi; HU Suyun and ZHAO Wenzhi

, 2006, 33(6): 1419-0.

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The petroleum resource abundance of different kinds of petroleum plays is very different in Chinese basins. It can be higher than 30×104t/km2 or lower than 5×104t/km2. The play with high petroleum resource abundance includes the buried hill, the structural play in steep slopes, and the central structure play in rift basins. The play with low petroleum resource abundance is the play in palaeozoic residual basins. Based on the results of the studies of petroleum plays in 6 basins of China, the relationships between oil resource abundance in place and some geological parameters were studied. It is showed that the oil resource abundance in place was mainly controlled by the generation intensity of source rock, the abundance of reservoirs and traps, and the number of unconformities in overlying strata. The quantitative model is established, which can be used for the prediction of oil resource abundance in different kinds of petroleum plays.

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Component and distribution of organic acid oil with high TAN, M Basin, Sudan

CHENG Dingsheng; DOU Lirong; LI Yingying and LI Zhi

, 2006, 33(6): 1420-0.

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M Basin has the most prolific hydrocarbons in central Sudan, even in the whole shear zone of the middle and western Africa. The effective hydrocarbon source rocks of the basin are believed to be the Lower Cretaceous lacustrine shales deposited during the synrift stage of the basin evolution. Most of the oils are normal oil with 20-34°API; the others are heavy oil with <20°API. All oils are with a low sulfur content, high asphaltene, high wax, high pour point, and high total acid number, especially in Bentiu reservoirs. The primary geochemical analyses indicate that biodegradation is the key genetic factor for high TAN crudes. Organic acid from high TAN crudes is mainly composed of naphthenic acid which is mainly distributed in the more than 300℃ fractions with mono-, bi-, tri- cycles. As fraction becomes heavier and acid value increases, the average molecular weight of naphthenic acid increases, its distribution gets wider and the carbon number range increases. The research results will be useful to crude transportation and processing.

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Low-pressure-water-injection development adjustment for the Greater Unity Oilfield with complex faults

YE Jigen; WU Xianghong; LIU Henian; GUO Rui and LUO Kai

, 2006, 33(6): 1421-0.

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Application of the large-scale corner point grid in geological modeling and reservoir simulation was discussed. Assistant software used to define completion layers in the corner-point system was developed and can be used to generate completion and schedule data easily for simulators according to geological model, perforation intervals and production data. It is helpful for efficiently carrying out a large-scale reservoir simulation study. The paper investigated the low-pressure-water injection development adjustment for the Sudanese Greater Unity Oilfield with complex faults and low GOR unsaturated oil. The optimal development decision for the oil field is that depletion is adopted at the early stage and low-pressure-water-injection is then carried out after the reservoir pressure decreases by about 35%. The flooding pattern and reasonable number of new wells are determined based on the calculation of limiting well number and well density and the simulation case study of well array and well number.

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Views on the inorganic origin of oil and gas in China

WANG Lansheng

, 2006, 33(6): 1422-0.

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This paper reviews the arguments of inorganic and organic theories of hydrocarbon generation. Based on the exact definition of commercial natural gas, some wrong understandings about inorganic origin in China are pointed out from the aspects of coexistence and symbiosis, artificial and inartificial nature, and gas and reservoir forming. For the coexistence and symbiosis, the inorganic origin supporters always testify symbiosis by the coexistence of hydrocarbon and nonhydrocarbon gases in natural gas and of hydrocarbon and nonhydrocarbon materials in crude oil. However, coexistence and symbiosis are not same. For the artificial and inartificial nature, petroleumlike material is generated from methane through the Fischer Tropsch reaction under experimental conditions. This process belongs to artificial nature. No direct evidence of the reaction has been found in nature, and inartificial nature is questionable. For the gas and reservoir forming, both of them are not equal although abiogenic methane gas exists, moreover, a gasforming process does not promise the forming of reservoir.

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, Volume 33 Issue 6