, Volume 39 Issue 5
    

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    油气勘探
  • Strategic replacement situation and outlook of China oil-gas production area
    Zhang Kang
    , 2012, 39(5): 2067-0.
    Abstract ( ) Download PDF ( ) Knowledge map Save
    Sustainable development of petroleum industry depends on tactic and strategic replacement of production, in which the exploitation of new oil and gas production areas has a profound and lasting significance. After first and second strategic development, the existing oil and gas areas in China have been in a relatively stable and mature stage of their life cycles, there is an urgent need to start a new strategic replacement of oil and gas to guarantee stable and increasing production for China in the long term. Through production and research sponsored by government in the beginning of the 21 century, the targets of new oil and gas areas have been initially identified. They include: (1) the Upper Paleozoic of north China, especially the Carboniferous and Permian underlying the Mesozoic and Cenozoic; (2) Qiangtang block which features in Paleozoic and Mesozoic marine strata, and Cenozoic rift system which has simple petroleum accumulation conditions in Tibetan plateau; (3) Mesozoic marine strata covered by the Cenozoic in the south sea and east sea of China; (4) unconventional hydrocarbons, especially tight oil and gas, shale gas, shale oil and coalbed gas.
  • Distribution regularity and formation mechanism of gas and water in the western area of Sulige gas field, NW China
    Dai Jinyou; Li Jianting; Wang Baogang and Pan Rui
    , 2012, 39(5): 2068-0.
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    Serious water production and the confusion about the distribution regularity and formation mechanism of gas and water affect the progressive development in the western area of Sulige gas field. Making use of drilling, logging, and testing data, this comprehensive study determines the gas-water distribution regularity and formation mechanism, and establishes the evolution modes of gas-water distribution. The results show that, (1) the gas-water distribution appears complementarily, and relatively water-rich area is located in the northwest; (2) source rock, reservoir physical property and structure are the key controlling factors of gas-water distribution, and formation water is distributed in areas with less developed source rocks, areas of poor properties, and structural lows within connecting bodies; (3) source rocks play a key role in controlling the distribution of gas and water, source area of low maturity is rich in formation water, while source area of high maturity is rich in gas. This research gives direction for favorable areas and well site selection in the progressive development of the gas field.
  • Origin and accumulation mechanism of shallow gas in the North Baodao slope, Qiongdongnan Basin, South China Sea
    Huang Baojia; Li Li and Huang Heting
    , 2012, 39(5): 2069-0.
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    On the basis of geochemical characteristics and origins of gases in the North Baodao slope of the Qiongdongnan Basin, the gas migration and accumulation episodes and reservoir forming time are investigated and the reservoir forming model is built for the BD13 shallow gas pools. The chemical composition and carbon isotopic data of the shallow gas, are compared with the characteristics of BD19-2 high-mature gas from the south section of the same structural belt, which reveals that the shallow gas of the BD13 gas pools is a mixture of biogas/low mature gas and some mature gas. In combination with the associated condensate biomarkers and the inclusions data, it is inferred that the biogas and low mature gas in the BD13 gas pools came from the nearby immature to low mature source rocks of the Miocene to Oligocene and charged approximately 3 Ma ago; whereas the high-mature gas generated by the Yacheng Formation source rock in the Badao Sag migrated lately into the reservoirs. Geochemical and geological data show that the No.2 fault system acts as the key pathway for upward gas migration into the shallow reservoirs, and that the sand-bodies within the Miocene Meishan and Sanya Formations are the main conduits for lateral migration of the gas. This gas migration pattern implies that the Songdong-North Baodao slope has favorable gas exploration potential in the future gas exploration of the east shallow water area in the Qiongdongnan Basin.
  • Fluid identification method based on 2D diffusion-relaxation nuclear magnetic resonance (NMR)
    Hu Falong; Zhou Cancan; Li Chaoliu; Xu Hongjun; Zhou Fengming and Si Zhaowei
    , 2012, 39(5): 2070-0.
    Abstract ( ) Download PDF ( ) Knowledge map Save
    Based on current acquisition modes of MRIL-Prime NMR logging tool, 2D NMR signals could be obtained by the combination of logging data from different modes, then the fluid properties in complicated reservoirs could be distinguished by 2D diffusion-relaxation NMR logging data distribution of pore fluids, generated by multi-echotrain joint inversion. In comparison with 1D NMR logging, this method could increase fluid information in diffusion regime, separate oil, gas and water signals in 2D space and enhance the identification capacity of fluid properties from NMR logging. The 2D NMR logging in the multi-echowave interval was applied in the oil pays in Well A and the water layers in Well B in the Nanpu Sag by MRIL-Prime tool, and the interpretation matches the well testing result. It indicates that 2D NMR logging has advantages on the identification of light oil, and fluids in macropore reservoirs than 1D NMR logging.
  • Palaeo-fluid evidence for the multi-stage hydrocarbon charges in Kela-2 gas field, Kuqa foreland basin, Tarim Basin
    Lu Xuesong; Liu Keyu; Zhuo Qingong; Zhao Mengjun; Liu Shaobo and Fang Shihu
    , 2012, 39(5): 2071-0.
    Abstract ( ) Download PDF ( ) Knowledge map Save
    The multi-stage hydrocarbon charge process of Kela-2 gas field in the Kuqa foreland basin was studied from the perspective of palaeo-fluid evidence by the analyses of fluid inclusions, fluorescence spectroscopy, FE-SEM (field emission scanning electron microscopy) observation, core micro-CT scanning, and hydrocarbon geochemistry. The result shows that the Kela-2 gas field has experienced three periods of hydrocarbon charge process: (1) charged with oil at the early-middle period of the Miocence (N1), (2) charged with high maturity oil & gas at the sedimentary period of the Pliocence Kuqa Formation (N2) and then destroyed by intense tectonic compression, and (3) charged with high-over maturity coal-derived gas since the Quaternary. The widely distributed residual dry bitumen, the occurrence of gas-liquid two-phase hydrocarbon inclusions, the residual oils observed in the nanopores, the higher QGF and QGF-E index, and the higher S1, S2 values of rock pyrolysis detected in both current gas zone and water zone, are the evidence of early oil charges. The residual dry bitumen, the occurrence of gas-oil-solid (bitumen) three-phase hydrocarbon inclusions, the loss of light n-alkanes and the relatively high content of aromatic hydrocarbons in the condense oil, and the abnormally high content of diamondoid hydrocarbons, are the strong evidence of gas flushing and deasphalting.
  • Genetic types of Daxing conglomerate bodies and their controls on hydrocarbons in the Langgu Sag, Bohai Bay Basin, East China
    Liu Hui; Jiang Zaixing; Zhang Ruifeng; Zhou Haowei and Lu Zhenquan
    , 2012, 39(5): 2072-0.
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    The genetic types, porosity and permeability characteristics, as well as oil-gas production capacity of the Daxing conglomerate bodies in the lower and middle sections of Paleogene Sha 3 Member, in the Langgu Sag of the Bohai Bay Basin are studied by combining various data such as seismic, logging, core analysis and formation testing. Three genetic models of conglomerate bodies including faulted-trough gravity flow, grain flow dominated nearshore subaqueous fans, and debris flow dominated nearshore subaqueous fans are built based on core, seismic and logging phases figured out by analyzing the sedimentary settings. The conglomerate bodies generated due to faulted-trough flow are mainly composed of matrix supported conglomerates and grain supported conglomerates, in which various kinds of secondary pores are developed; the conglomerate bodies generated in grain flow dominated nearshore subaqueous fans primarily consist of grain supported conglomerates, of which the reservoir space is mainly dissolved pores within gravels, intercrystal pores and fractures; the conglomerate bodies generated in debris flow dominated nearshore subaqueous fans are mainly composed of matrix supported conglomerates and are dominated by dissolved pores within gravels. The conglomerate bodies with different genesis have different reservoir characteristics and oil/gas production capacities. Among them, the conglomerate bodies generated in grain flow dominated nearshore subaqueous fans have the best porosity, permeability and the highest oil/gas production, thus are the key targets for petroleum exploration.
  • New insights into natural gas diffusion coefficient in rocks
    Liu Guangdi; Zhao Zhongying; Sun Mingliang; Li Jian; Hu Guoyi and Wang Xiaobo
    , 2012, 39(5): 2073-0.
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    Based on the analysis of measuring methods and results of natural gas diffusion coefficient in rocks and the measurement of methane diffusion coefficient in the Upper Paleozoic rocks of the Ordos basin, this paper clarifies the meaning of natural gas diffusion coefficient in rocks and discusses its application in gas diffusion simulation and some influencing factors. There are three methods for measuring natural gas diffusion coefficient in rocks, including free gas method, water-dissolved method, and time delay method. The meanings of diffusive concentration and the influencing factors are different for the natural gas diffusion coefficients measured by these three methods. The diffusion coefficient measured by the free gas method is 1 to 2 order of magnitude less than that measured by the water-dissolved method, and 2 to 3 order of magnitude less than that measured by the time delay method. The meanings of diffusive concentration in the diffusive volume calculation must be in line with that in the diffusion coefficient measurement during the process of diffusive volume calculation. Natural gas diffusion coefficient in rocks has a linear relationship with porosity and a dynamic relationship with temperature, and it logarithmically decreases with pressure.
  • Methods and key parameters of shale gas resources evaluation
    Chen Xinjun; Bao Shujing; Hou Dujie and Mao Xiaoping
    , 2012, 39(5): 2074-0.
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    Methods and key parameters of shale gas resources evaluation are studied so as to accurately assess the potential of shale gas resources. In much-explored areas, the volume method, followed by the analogy method, is recommended for evaluation; in less-explored areas, the analogy method is recommended. The concept of “gas-bearing shale system” is put forward and taken as an evaluation unit to calculate the thickness of shale. It refers to the lithologic assemblage sealed by upper and lower tight layers in one pressure system, composed of organic carbon-rich shale and the interbeds of sandstones and carbonates, featuring the logging responses of gas-bearing shale, with tight rocks at top and bottom, and the continuous thickness of gas-bearing interval being more than 30 m and no obvious water layer. According to exploration degree and available data, different methods may be selected to calculate the thickness of gas-bearing shale system. The logging data and the content of organic carbon are used in the areas with high degree of exploration and abundant data, while field geological profile, seismic profile, depositional characteristics and other data are considered in areas with low or ultra-low degree of exploration.
    • 油气田开发
  • Tight sand gas development technologies and practices in China
    Ma Xinhua; Jia Ailin; Tan Jian and He Dongbo
    , 2012, 39(5): 2075-0.
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    Tight sand gas is the main type of unconventional natural gas. According to the geologic characteristics of large-scale tight sandstone gas reservoirs discovered in China in recent years, tight sand gas reservoirs can be classified into three main types, multi-layer lens overlaid tight sand gas reservoir, multilayered tight sandstone gas reservoir and massive tight sand gas reservoir. A series of development technologies for the first 2 types of reservoirs have been formed, focusing on improving individual well producing rate and reducing development cost. They drive the scale development of tight gas. As to multi-layer lens overlaid tight sand gas, the specific technologies include well location optimization, multi-stage sand fracturing, down hole choking and low-pressure surface gas gathering system. As to multilayered tight sand gas, the specific technologies include sweet-spot prediction and evaluation, integrated horizontal well development technique, and drainage gas recovery technique. There are still great challenges in tight gas development from several aspects, such as the enhancement of reserve deployment ratio and recovery ratio, the improvement of individual well producing rate, the development of new and difficult-to-produce reserves as well as the rate maintenance, and gas well management in its later stage of life cycle.
  • A novel surface active polymer oil displacement agent
    Liu Pingde; Zhang Song; Yang Ning and Xiong Chunming
    , 2012, 39(5): 2076-0.
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    Based on the relationship between the molecule structure of monomers and their performance, two types of polymerizable monomers with low oil/water interfacial tension have been synthesized, which coplymerizes acrylamide to create a novel polymer oil displacement agent under complex initiator and low polymeric temperature. Its structure and distribution status in brine solution were characterized by infrared spectroscopy and freeze etching electron microscope. The results show that the polymer has good water solubility, viscosifying properties, salt-resistance and temperature-tolerance, shearing-resistance in brines. Due to the graft polymerization of acrylamide and the polymerizable surface-active monomer, the polymer overcomes chromatographic separation effect, and has low oil/water interfacial tension. Interfacial tension of 0.15% solution of the polymer (prepared in Daqing simulation brine) is around 10-1 mN/m in Daqing No.1 oil plant crude oil. Core flooding experiments show that the oil recovery of the novel surface active polymer is 5.2% higher than that of ordinary hydrolyzed polyacrylamide because of its better viscosifying performance and lower oil/water interfacial tension.
  • Formation mechanism and distribution law of remaining oil in fracture-cavity reservoirs
    Wang Jing; Liu Huiqing; Xu Jie and Zhang Hongfang
    , 2012, 39(5): 2077-0.
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    Drilling and dewaxing methods are used to create the quantitative model and stochastic model for fracture-cavity reservoirs respectively, which are used to investigate oil displacement in full diameter cores and to study the formation mechanism and distribution law of remaining oil in fracture-cavity reservoirs. The density difference between displacing phase and displaced phase and the connection position between fractures and cavities determine the fluid distribution in the cave. After the first water flooding, the remaining oil is composed of the following parts: the “attic oil” caused by the density difference between oil and water, the “occlusion oil” formed because the oil-to-water replacement is not instantaneous, the “corner oil” caused by the irregularity of the cave, the “blind cavity oil” formed because of the complex connection or low connectivity of the fracture-cavity system, and the “oil film” caused by the wettability of rocks. When the connection is higher, the amount of the “attic oil” is less. When the injecting velocity is lower and the viscosity of crude oil is lower, the amount of “occlusion oil” is less. The content of “corner oil” will become less when the cave figure is more regular, and the amount of corner is less. The amount of “blind cavity oil” is less when the connection is simple or the connectivity is high. In addition, on the water-wet rock surface, the content of “oil film” is less.
  • Fractal nature of acid-etched wormholes and the influence of acid type on wormholes
    Liu Ming; Zhang Shicheng and Mou Jianye
    , 2012, 39(5): 2078-0.
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    Two-scale (Darcy scale and pore scale) continuum wormholing models are built to study the fractal nature of the acid-etched wormholes in acidizing carbonate reservoirs and the influence of acid type on the conditions for wormholes to form. This model considers convection-diffusion mass transfer and reaction on the acid-rock interface, and the fractal dimension of dissolution patterns is calculated using box-counting method. The results show that wormholes are formed when convection and diffusion are equivalent in strength; when convection dominates, uniform dissolution is formed; when diffusion dominates, surface dissolution is generated. For the zones where the porosity is greater than 0.7, the fractal dimensions of the surface dissolution, wormholes and uniform dissolution are 1.46, 1.50 and 1.44, respectively, among which, the fractal dimension of the wormholes is approximate to the experimental results obtained by Daccord and Lenormand (1.6±0.1). The reaction between weak acid and rocks is controlled by reaction kinetics, the acid-etched wormholes are wide, and more acid is consumed. The reaction between strong acid and rocks is controlled by mass transfer, the acid-etched wormholes are narrow, and less acid is consumed. According to an example calculation, it is found that acidizing treatments should be performed in an isolated short section each time when the horizontal well is long.
  • A quantitative model for evaluating the impact of volatile oil non-equilibrium phase transition on degassing
    Wu Keliu; Li Xiangfang; Wang Haitao; Guan Wenlong; Wang Xing; Liao Zongbao and Li Wuguang
    , 2012, 39(5): 2079-0.
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    To quantitatively evaluate the impact of non-equilibrium phase transition on degassing in an oil-gas system and accurately determine the bubble point pressure of the system with different oil rates, a model, which takes the influence of pressure drop and non-equilibrium phase transition into consideration, is established based on the Henry model to calculate the gas solubility. To measure the degassing speeds with non-equilibrium phase transition and equilibrium phase transition respectively, degassing experiments are done at different pressure drop speeds with the oil-gas system composed of transformer oil and carbon dioxide. A function characterizing the non-equilibrium nature of the oil and gas system is derived after calculation and matching, based on which, degassing speeds and bubble point pressures at different pressure drop speeds are calculated. The impact of non-equilibrium phase transition on degassing and the deviation degree of the bubble point pressure are evaluated quantitatively. The model considering the non-equilibrium phase transition has higher computational accuracy than the Henry model not considering the non-equilibrium phase transition. The computation results indicate that the non-equilibrium phase transition reduces the bubble point pressure in the reservoir and slows down the degassing process of the volatile oil during the development of volatile oil reservoirs. The extent to which the non-equilibrium phase transition impacts degassing depends on the speed of pressure drop and the value of pressure drop: the bigger the pressure drop value and the faster the pressure drop speed, the more significant impact the non-equilibrium phase transition exerts on degassing, the lower the bubble point pressure and the slower the degassing speed.
    • 石油工程
  • The theoretical radial stress solution and its experimental verification of expansion cement at annulus interfaces
    Yang Zhifu; Meng Qingyuan; Chen Xiaolou and Gao Lili
    , 2012, 39(5): 2080-0.
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    To determine the initial loading state of the casing and cement sheath during cement setting, the theoretical solution of radial stresses at the annulus interfaces during cement setting is derived considering volume expansion and material parameter variation. During the theoretical derivation, cement setting is divided into many time steps. In each step, the original radii of cement sheath without loading are calculated and the radial stresses are calculated according to the compatible deformation condition among the casing, cement sheath after free expansion and the stratum in this time step. The calculated radial stresses and radii of the cement sheath are used as initial data for the next step. The circumferential strains of casing and stratum are measured during cement setting process. The experimental result verifies the correctness of the theoretical solution. The calculated results and experimental data show that the radial stresses on both inner and outer boundaries of cement sheath are compressive stresses during the cement setting process, and their absolute values increase as the elastic modulus of the rock around the well increases. The higher the cement elastic modulus is, the larger the radial compressive stress on the wellbore will be, the radial compressive stress on the outer boundary of the casing will decrease on the contrary. The cement material with appropriate elastic modulus should be adopted according to different elastic modulus of stratum, so as to realize loading equilibrium of the oil and gas well structural systems.
  • Analyses on docking dynamic characteristics of the jack-up rig with two-piece units guide cable
    Shi Yongjin
    , 2012, 39(5): 2081-0.
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    To meet the requirements of deeper offshore oil and gas exploration, a two-piece units mode jack-up rig is employed to upgrade the existing cylindrical leg jack-up rig which works in shallow areas of 50 m deep. A set of mat support structure is added to the bottom of the cylindrical leg jack-up rig and the upper piece of rig and the bottom piece of rig are connected by a docking assembly, making the two pieces become a mat jack-up rig. This paper studies the equilibrium position and displacement response of the upper unit in docking procedure under different environmental condition and different ballast mode based on the three dimensional time domain linear potential flow theory and Morison theory, and analyses the dynamic response of the guide cable under different docking positions through physical models in laboratory. If the environment load acts from the stem direction, longitudinal oscillation affects mostly on the displacement of the guide cable. With the increment of water depth, the axial tension of the guide cable and the vertical angle of deviation decreases. Under the condition of separately floating, the guide cable is mostly affected by the mass of the platform; the forces acting on the guide cable of the lower unit is much smaller than that of the upper unit. Once one of the units was fixed, the towing force dropped obviously. The bearing force of the guide cable is obviously affected by the wave period and wave height and will increase with the increment of wave period and wave height in general.
  • Key surface logging technologies in horizontal geosteering drilling
    Li Yichao; Wang Zhizhan; Qin Liming and Xu Hongze
    , 2012, 39(5): 2082-0.
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    In the drilling of horizontal wells, the core task of surface logging is to guide geosteering while drilling by using collected data including electrical property, lithology, petrophysics, and oil/gas-bearing properties. Surface logging in the horizontal geosteering drilling have two key technologies: one is stratigraphic correlation and prediction technology before encountering the zone of interest, the other one is geological interpretation and geosteering technology after encountering the zone of interest. Based on a systematic analysis of difficult points in the two aspects, in combination with application examples, this paper deeply analyzes how to accurately drill into horizontal section by in-depth stratigraphic correlation and timely model modification in the case of inaccurate horizon depth design; and how to improve drilling-encounter ratio of oil layer and well bore quality by accurate interpretation and guidance in the case of encountering non-target zone (e.g., borehole deviates from right track, sedimentary facies changes in the target zone, faults or mudstone interlayers are encountered.).
    • 综合研究
  • Key technologies for the fluvial reservoir characterization of marginal oilfields
    Wang Hui; Hu Guangyi; Fan Hongjun; Yu Lianyong and Liu Zhenkun
    , 2012, 39(5): 2083-0.
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    Fluvial reservoirs of the lower member of the Neogene Minghuazhen Formation in Q33-1 Oilfield, Bohai Bay Basin, are studied as examples to determine the distribution and characteristics of marginal reservoirs and develop offshore marginal oilfields effectively. Based on seismic, geological and logging data, three key technologies for the fluvial reservoir characterization of marginal reservoirs are proposed. The geometry and heterogeneity of fluvial sandbodies were studied through well-seismic calibration, 3D seismic interpretation and boundaries characterization. The geological knowledge database of fluvial reservoirs was established by the methods of width prediction outside wells and variogram analysis based on the high resolution 3D seismic data. Three types of well correlation modes of vertical facies changes, stacking sandbodies, incised channels, were constructed by integrating the analogous data from the oilfield with dense well pattern. According to the above three techniques of reservoir characterization, the most likely mode of reservoir distribution was established, based on which the oil field development plan was made and economic benefits have been gained.
    • 学术讨论
  • Further understanding on fluid flow through multi-porous media in low permeability reservoirs
    Dou Hongen and Yang Yang
    , 2012, 39(5): 2084-0.
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    This paper studies typical nonlinear models of fluid flow through multi-porous media in low-permeability reservoirs, analyzes hypothesis conditions, derivation process and the experimental data rationality, and clarifies some confusions in order to understand the fluid flow rules through multi-porous medium in low permeability reservoirs. There are three problems in establishing the models: first, hypothesis conditions cannot be proved, calculation values cannot be measured; second, wrong basic equation not only was used, but also wrong of derivation process, and derived equation is also a wrong equation; third, the threshold pressure gradients obtained from rock samples of low permeability reservoirs at the laboratory are too high, without rationality. The threshold pressure gradient does not exist in all of the low-permeability reservoirs, only when pressure coefficient of low-permeability reservoir is less than one, fluid flow through multi-porous media should need the threshold pressure gradient, threshold pressure gradient should not be considered in reservoir numerical simulation, productivity prediction and well testing in low permeability reservoirs development. To reveal flow rules of low permeability reservoirs and establish theory of low-permeability oilfield development it’s necessary to develop the digital rock technology, innovate experimental skills of modern petrophysics and so on.
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