, Volume 38 Issue 2

    

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油气勘探
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  Control of salt structures on hydrocarbons in the passive continental margin of West Africa

  Liu Zuodong and Li Jianghai

  , 2011, 38(2): 1848-0.

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  Salt basins along the passive continental margin of West Africa are becoming one of the most attractive areas for hydrocarbon exploration. The oil and gas discovered recently are related to salt structures. The salt structures are widespread in Anglo-Cameroon, the depth of salt is up to 1500 m and the average width is 300 km. These basins can be divided into two parts in horizontal direction: extensional zone and compressional zone, which extend 100-150 km and 100-200 km respectively. The extensional zone includes sealed titled zone, growth fault zone and diapir zone and is characterized by rollover structure and turtle structure anticline. The compressional zone is characterized by salt sheet, salt tongue, thrust fault and small folds. Oil and gas are distributed in both the zones, oil and gas reserves in the extensional zone are a little more than those in the compressional zone. During the evolution of the salt structures, several types of trap can be recognized, such as salt anticline, salt diapir and fault related trap, unconformity and structural-lithologic traps. Salt anticlines are the most potential exploration targets.
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  Further discussion on the connotation and significance of the natural gases relaying generation model from organic materials

  Zhao Wenzhi; Wang Zhaoyun; Wang Hongjun; Li Yongxin; Hu Guoyi and Zhao Changyi

  , 2011, 38(2): 1913-0.

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  The gases relaying generation model (abbreviated as relay model) of organic materials focuses on the potential of gas generation and resource formation derived from the dispersed liquid hydrocarbons retained in source rocks during high to over mature stage (Ro>1.6%). It means the gas generation converts from thermal degradation of kerogen to oil cracking gas with the increase of thermal maturation, and it forms relaying gas generation processes at different thermal maturation. According to the supplementary kinetic studies and anatomization of discovered gas reservoirs, it was found that source rocks still contain a fair number of liquid hydrocarbons within oil window even after expulsion, which can serve as effective gas source kitchen during the high to over mature stage. The maturity for gas largely generated from oil cracking is greater than 1.6% vitrinite reflectance (Ro), and the content of methyl cyclohexane can be utilized as a specific index for identification of such natural gas. Conventional natural gas reservoirs with considerable scale could be formed due to the existence of migration pathway, driving force and process under high diagenetic environment. The significance of the natual gas relay model is reflected at the following three aspects: (1) focusing on natural gas accumulations of dispersed liquid hydrocarbons retained in source rocks, (2) determination of the main gas-generation periods of retained liquid hydrocarbons, and (3) evaluation on the conventional gas accumulation potential by cracking of the detained liquid hydrocarbons outside of source kitchen during the high to over mature stage.
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  Lacustrine carbonates in the southwest of Qikou Sag, Huanghua Depression, Bohai Bay Basin

  Pu Xiugang; Zhou Lihong; Xiao Dunqing; Hua Shuangjun; Chen Changwei; Yuan Xuanjun; Han Guomeng and Zhang Wei

  , 2011, 38(2): 1914-0.

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  The southwest of the Qikou sag is a flexural gentle slope formed by the deformation of a drape structure due to its underlying basement lifting. The sedimentary period of the Lower Member 1 of Shahejie Formation was the maximum extensional time of the Paleogene lacustrine basin. Debris from source areas was in shortage. In the broad littoral-shallow lake, thousands of square kilometers of lacustrine carbonates deposited and were distributed stably. The main lithologies of sediments are biolithite and dolomite (micritic dolomite and dolomitic limestone), and the dolomites are mainly middle-late buried dolomite and penecontemporaneous dolomite. Their distribution area is more than 1650 m2, the cumulative thickness is between 5 and 45 meters, and the average thickness is about 10 meters. Intercrystal pores, intergranular pores, corrosion pores and frequent fissures are developed in the medium porosity and low permeability dolomite reservoirs. The dolomites alternate with oil shale and dark mudstone, favorable for the charge of low-mature hydrocarbons and the formation of large-scale accumulations. Drilling exploration practices show that the lacustrine dolomite reservoirs are characterized by medium burial depth and regional petroleum accumulation and are a new exploration area for Paleogene oil and gas.
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  An integration porosity forecast model of deposition, diagenesis and structure

  Zhang Ronghu; Yao Genshun; Shou Jianfeng; Zhang Huiliang and Tian Jiqiang

  , 2011, 38(2): 1915-0.

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  Taking the Cretaceous Bashijiqike sandstones in the Kuqa foreland basin as an example and beginning from the analyses of the tectonic evolution, ancient stress, sedimentary system distribution, diagenesis type and intensity of the basin, the authors studied the porosity formation mechanisms and changes of the main pay zones in the Quqa depression and built a porosity forecast model integrating deposition, diagenesis and structure based on a large number of experimental data (cuttings, thin core slices, mineral composition, ancient tectonic stress, particle size) and logging test data and using a multi-disciplinary knowledge of geology, mathematics and statistics. The predicting results of the model in the sandstones of the Bashijiqike Formation matches well with the logging integration porosity, providing a basis for the space evaluation and forecast of deep, effective, high-quality reservoirs of different pore types in the Kuqa depression.
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  Structural styles and hydrocarbon accumulation of the northern piedmont belt in the Taibei sag, Turpan-Hami NW Basin

  Liu Bo; Huang Zhilong; Tu Xiaoxian; Zhang Jinxue and Mu Kexun

  , 2011, 38(2): 1916-0.

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  The northern piedmont belt of the Taibei sag is one of the oil-rich structural belts in the Turpan-Hami Basin. Based on the interpretation of seismic cross section and the analyses of discovered hydrocarbon accumulations, the geologic structure can be divided into six structural styles, thrust-imbricate structures, imbricate fan structures, thrust-opposite structures, forward setting structures and duplex structures. According to the study of the distribution regularity of the structural styles, the fold-thrust belt controlled by three levels tectonic transform zones is characterized by zonation from the south to the north, segmentation from the west to the east, and it can be classified into thrust-nappe zone, faults zone and thrust-fault zone by mechanism of tectonic deformation. The leading edge with two accumulation forming models which are the leading edge pop-up model and the leading edge imbricate fan model is the most favorable hydrocarbon enriched belt in the northern margin of the Taibei sag. The thrust-opposite structures in the rear edge of the deformable zone have good preservation, potential source kitchen on the footwall, higher fault dip, and good communication of sandbodies. They are the next favorable exploration structures.
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  Distribution of source-reservoir-cap rock assemblages within the sequence framework from the Devonian to the Middle Triassic in the Sichuan Basin

  Xu Shenglin; Chen Hongde; Chen Anqing; Lin Liangbiao; Li Junwen; Yang Junbin and Gao Shan

  , 2011, 38(2): 1917-0.

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  Guided by the sequence framework, the characteristics of source rocks, reservoir rocks and source-reservoir-cap rock assemblages were discussed in detail for the Devonian to the Middle Triassic in the Sichuan Basin. Combined with the existing results of hydrocarbon exploration, a diagram of the source-reservoir-cap rock combinations within the supersequence framework was established. Two sets of regional source rocks and three sets of regional reservoir rocks are developed under the supersequence framework. The carbonatite and dark mudstone which contain much organic matter are developed in the transgressive systems tracts of SS5 and SS6, and the hydrocarbon generating centers are developed in the cratonic depression and deep shelf. The main controlling factor of the SS4 transgressive systems tract reservoir is karst paleogeomorphology. The SS5 highstand systems tract reservoir rock is mainly developed in the platform margin reef/beach, and then the secondary controlling factors are karst paleogeomorphology and tectonic movement. The SS6 transgressive systems tract- highstand systems tract reservoir rock is mainly developed in the platform margin reef/beach. In all, three source-reservoir-cap combinations occur in the Sichuan Basin from the Devonian to the Middle Triassic, including composite, highstand and transgressive. Regional source rocks are developed in the transgressive system of the supersequence. Regional reservoir rocks developed in the highstand system of the supersequence. The distribution characteristics of the regional cap rocks are similar to the characteristics of the regional source rocks
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  Paleo-reservoir bitumen of Middle Protozoic Jixian System in the southwest margin of the Ordos Basin, China

  Li Rongxi; Liang Jiwei and Weng Kai

  , 2011, 38(2): 1918-0.

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  Solid bitumen was found in outcrops of laminated dolostone of the Middle Protozoic Jixian System in the southwest margin of the Ordos Basin. Bitumen was distributed in the Jixian System and migrated upward into the overlying purple sandstone bedded with the mudstone of the Lower Cretaceous Luohandong Formation. Bitumen was distributed on rock bed surface or in rock pores and fractures as laminas and small veins. Distribution characteristics of chloroform bitumen A normal alkanes and the analysis of terpene and steroid biomarkers show that the bitumen is sourced from lower aquatic and algal organisms, and the laminated algal dolostone of the Middle Protozoic Jixian System is the most possible source rocks of the bitumen. The measured bitumen reflectance is between 2.7%-3.6%, which is very inconsistent with the thermal degree of coal beds of the Jurassic Yan’an Formation in the researched area (whose vitrinite reflectance (Ro) is 0.6%-0.8%), suggesting that it was controlled by local abnormally thermal events. The paleo-reservoir was destructed by the Tongcheng alkaline magma intrusion and the oil and gas inside the paleo-reservoir transformed to bitumen because of thermal cracking under high temperature. The study area has the material basis and accumulation conditions for the formation of oil and gas. The potential of hydrocarbon generation and exploration should be paid attention to and deserves further study in the Middle Protozoic Jixian System in the southwest margin of the Ordos Basin.
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  Modeling of the pressure evolution and hydrocarbon migration in the Moliqing fault-depression, Yitong Basin，NE China

  Cao Qiang and Ye Jiaren

  , 2011, 38(2): 1919-0.

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  Based on the drilling test data and seismic data, the basin modeling technique is applied to reconstruct the pressure evolution history and hydrocarbon migration in the Moliqing fault-depression in the Yitong basin. Three episodic accumulations and releases of pressure occurred in the Moliqing fault-depression, and the excess pressure evolution has a close relation to the three tectonic movements. The formation pressure distribution is characterized by normal pressure in almost the entire fault-depression with some residual overpressure locally. The difference of pressure distribution is mainly caused by the rock facies, sedimentation rate, hydrocarbon generation and fault activities. The hydrocarbon migration is more active during the release of the pressure, which mainly happened during the middle-late Oligocene and provided the driving force for hydrocarbon migration. The hydrocarbon migration was directed to the Shuangyang Formation within the Jianshan uplift and the Kaoshan depression. With the good conditions of hydrocarbon accumulation and the higher extent of hydrocarbon concentration, the northwest part of Kaoshan depression is considered as a favorable area for the oil and gas exploration in the Moliqing fault-depression.
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  Seismic facies prediction of lacustrine beach and bar reservoirs in the deep zone of the Bonan Subsag, Bohai Bay Basin

  Luo Hongmei; Zhu Yixiu; Mu Xing; Wang Changjiang; Xing Ya and Wang Qinghua

  , 2011, 38(2): 1920-0.

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  The lacustrine carbonates are developed in the Paleogene Sha 4 member of the Bonan subsag in the Zhanhua sag of the Bohai Bay Basin. This type of reservoirs is characterized by deep-burial, thin single bed, thin alternated bed deposition, complicated rock types, and a dramatic lateral change of lithofacies, so the main problem of its exploration is the identification of effective reservoirs. On the basis of analyzing rock facies and geophysical features, this paper develops a new technique for complicated lithofacies prediction based on sedimentary parameters. It begins from the normal seismic attributes analysis such as amplitude and frequency types, extracting the 3D seismic attributes and counting the sedimentary parameters such as the percent of the limestone, and sets up the relationship of the sedimentary parameters from wells and the seismic attributes along wells, and then computes the lateral features of many sedimentary parameters. At last, the cluster analysis is done to predict the sedimentary facies. This technology gets a preferable result in of the Sha 4 member of in the Bonan subsag, and it can provide some reference for other types of depositional system.
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  Study on sealing characteristics of the high pour-point oil reservoirs in the Archaeozoic buried hill of the Caotai area

  Li Junsheng; Pang Xiongqi; Ning Jinhua and Chu Zhenmiao

  , 2011, 38(2): 1921-0.

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  The Caotai buried hill is shallow and lack of good overlying regional seals. Hydrocarbon accumulation was closely related to local sealing conditions. This study starts with the structural and stratigraphic characteristics of the Caotai buried hill, combines with logging and oil property data, and concludes after multidisciplinary analysis that except shale caprock seal, abnormal fluid pressure seal, fault seal and inclined dyke seal, there are three new seal types which are petrophysical seal, high pour-point oil self-seal and upstanding dike seal. Both single seal type and combination of multiple seal types can form hydrocarbon accumulation. According to the drilled wells in the study area, the sealing styles mainly include petrophysical seal, dyke seal, fault seal, and high pour-point oil self-seal. On the basis of this study, many progressive exploration wells have been arranged in this area and verified a promising result. This study is of significant reference value to buried hill reservoir exploration in the Liaohe fault depression and other areas.
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  K-Ar dating of authigenic illites and the hydrocarbon accumulation history of the Silurian bituminous sandstone reservoirs in the Yingmaili area, Tarim Basin

  Zhang Youyu and Luo Xiu-quan

  , 2011, 38(2): 1922-0.

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  The hydrocarbon charge history of the Silurian bituminous sandstone reservoirs in the Yingmaili area was investigated using an integrated approach by combining detailed petrographic analysis (thin section and SEM), clay mineral XRD characterization, and the modeling of authigenic clay minerals and subsequent K-Ar dating of authigenic illites. The result was correlated within the basin. The ordered mixed-layer illite/smectite (I/S) is dominant in the clay assemblages of the Silurian bituminous sandstones in the Yingmaili area except in local areas. They are authigenic illites. The authigenic illite ages of the Silurian bituminous sandstone reservoirs range from 255 Ma to 293 Ma, mainly from 277 Ma to 293 Ma, corresponding to the late Carboniferous to early Permian, indicating that the primary Silurian oil pools were formed mainly during the late phase of the Early Hercynian to the Late Hercynian. The authigenic illite ages of the Silurian bituminous sandstone reservoirs in the Yingmaili area are consistent with the general characteristics of the age distribution within the basin. The palaeo structural framework and the distribution of hydrocarbon supply center might be one of the key controlling factors for the difference in accumulation times within different areas. The long distance of the Yingmaili area from the hydrocarbon supply center might be one of the main controlling factors for the accumulations occurring relatively late in this area.
油气田开发
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  Calculation on reasonable production/injection well ratio in waterflooding oilfields

  Zou Cunyou; Chang Yuwen; Wang Guohui and Lan Lifeng

  , 2011, 38(2): 1923-0.

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  According to the accurate definition of the reasonable production/injection well ratio and injection/production ratio for waterflooding oilfields, the formula of the reasonable production/injection well ratio under the same or different formation pressures between oil well and injection well is derived based on principle of extreme value in this paper. The formula can be used in balanced and in unbalanced injection-production system such as reservoirs in high water cut stage or low-permeability reservoirs. All the previous formulas have flaws: the method of “infectivity, productivity indexes” is based on balanced injection-production system; the method of “infectivity, productivity indexes and injection/production ratio” ignores the influences of crude oil properties; and there is no theoretical and practical significance in the method of “infectivity index to liquid productivity index ratio and injection-production pressure difference”. The method presented in this paper is applied and verified in the Chaoyanggou Oilfield of Daqing. The daily fluid rate of the oilfield can reach maximized value 5 155.8 t when the reasonable production-injection well ratio is 3.28.
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  An improvement of design method of optimal horizontal wellbore length

  Zeng Xiaojing and Tong Dengke

  , 2011, 38(2): 1924-0.

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  To solve the problem of optimal horizontal length design, reasonable hypothesis and simplification were conducted for the flow in horizontal well in reservoir using filtration mechanic theory. Based on the model proposed by Fan zifei, et al., fully considering the effects of various drilling cost and petroleum price on horizontal length design, a new model to calculate the optimal length of horizontal section was derived. At the same time, productivity calculation error is introduced into Fan Zifei’s method, and according to case calculation, the effects of horizontal length, flow rate in well, wellbore coarse degree, fluid viscosity, reservoir permeability, wellbore diameter on horizontal well prodcution and productivity calculation error were analyzed. The results indicate that, for a certain reservoir, the main factors affecting horizontal well production and productivity error are horizontal length, wellbore coarse degree and wellbore diameter; for a particular horizontal well, the main factors affecting horizontal well production and productivity calculation error are fluid viscosity, reservoir permeabiltiy and flow rate in the well.
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  A model for predicting reservoir fracturing pressure of perforated wells after acid damage

  Guo Jianchun; Zeng Fanhui and Zhao Jinzhou

  , 2011, 38(2): 1925-0.

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  Acid damage is an effective technology to solve the problem of high fracturing pressure for the deep, tight, low-permeability sandstone reservoirs during fracturing or acid fracturing. A model for quantitatively predicting reservoir fracturing pressure of perforated wells with acid damage was established combing with damage mechanics, fracture mechanics and finite element theory. The model considered the effects of rock mineral composition, acid type, acid amount and temperature on fracturing pressure. The model was used to quantitatively predict the damage variable and fracturing pressure of the acid damaged formation in the Well DY1 in west Sichuan. The results showed that the higher the acid concentration, the higher the rock damage variable and the lager the rock strength reduction, and it will be more favorable for reducing fracturing pressure. The optimal 15%HCl＋3%HF acid was applied and the fracture pressure was reduced by 6.5 MPa successfully, which ensured “fracture network” acidation implementation subsequently. Field application results agreed with the prediction results, which verified the reliability of the model.
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  TPCT decreases heat loss of liquid within heavy oil well bores

  Zhang Yufeng and Wu Xiaodong

  , 2011, 38(2): 1926-0.

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  Considering the effect of the shear stress on steam-liquid interface in TPCT (two-phase closed thermosyphon) on the liquid film thickness and interface heat exchange coefficient, the average heat exchange coefficients of TPCT heat absorption interval and heat discharge interval were calculated, thus to improve the calculation method of wellbore TPCT fluid heat loss. At the same time, through laboratory physical simulation experiments, the heat loss of well bore TPCT was measured, and the influence rules of shear tress on steam-liquid interface on fluid heat loss was emphatically analyzed. The theoretical calculation and laboratory experiments show that wellbore TPCT can not only adjust the fluid temperature profile in wellbore, but also decrease wellbore fluid heat loss; shear stress on steam-liquid interface has the effects to carry fluid film upward, it can increase fluid film thickness and fluid film heat conduction resistance, thus decreasing fluid heat loss in wellbore; wellbore TPCT fluid heat loss is affected by wellbore fluid temperature and fluid rate, increases with increasing fluid temperature and decreases with increasing fluid rate.
石油工程
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  Numerical simulation of cutting-carrying ability of supercritical carbon dioxide drilling at horizontal section

  Shen Zhonghou; Wang Haizhu and Li Gensheng

  , 2011, 38(2): 1927-0.

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  The density of supercritical carbon dioxide is relatively heavy, near to liquid density; its viscosity is small which is near to gas viscosity. In order to research the cutting-carrying ability of supercritical carbon dioxide drilling in horizontal section, a mathematical model was built describing cutting-carrying process in the horizontal eccentric annulus with supercritical carbon dioxide; at the same time, the physical model was built according to the characteristics of horizontal eccentric annulus. The cutting-carrying law in horizontal section at different viscosities and densities of supercritical carbon dioxide was simulated with CFD simulation software. The cutting-carrying ability of supercritical carbon dioxide increases with increasing density and viscosity, but there existed a critical density, when the density of supercritical carbon dioxide is smaller than that, the cutting-carrying ability will decrease apparently, and the smaller density of supercritical carbon dioxide is, the worst cutting-carried ability will be. We can control the back pressure of wellhead to change the density of supercritical carbon dioxide in the wellbore while drilling, to comply with the cutting-carrying request, but the ground pump pressure should be appropriate to avoid higher load.
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  Bearing capacity of bucket spudcan foundation for offshore jack-up drilling platform

  Zhang Puyang and Ding Hongyan

  , 2011, 38(2): 1928-0.

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  To compare the bearing capacities of the traditional spudcan and the bucket spudcan, the effects of t spudcan types on the rigidity of pile legs and the entire bearing capacity is analyzed in detail. Through the loading method of Swipe and constant displacement, this paper plots the spatial failure envelopes of the vertical-horizontal load, vertical-moment load, vertical-horizontal-moment load of the bucket spudcan and traditional spudcan under the mode of composite loading, as well as the spatial failure envelopes of the vertical static load-vertical cycling limit load, vertical static load-horizontal cycling limit load based on these two spudcans under the mode of cycling loading. Theoretical study showed that the skirt system of bucket spudcan can increase the effective embedded depth, consequently improving the foundation rigidity and entire stiffness of a jack-up drilling platform. It is found that the bearing capacity under horizontal load and moment of the new spudcan is increased by at least 10% than that of the traditional spudcan, especially horizontal load being up to 20% in cycling load. Under the action of limit storming loading condition including wind, wave and flow loads, the entire bearing capacity of the jackup rig in stiff clay is increased by about 46% with the bucket spudcan foundation compared to the traditional one.
综合研究
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  Technology of removing near wellbore inorganic scale damage by high power ultrasonic treatment

  Pu Chunsheng; Shi Daohan; Zhao Shushan; Xu Hongxing and Shen Hua’nan

  , 2011, 38(2): 1929-0.

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  The effects of ultrasonic treatment and the influence of ultrasonic parameters, process parameters and core physical parameters on the results of ultrasonic treatment for removal of near wellbore inorganic scale damage were studied using the self-developed dynamic simulation experimental apparatus of fluctuating oil extraction technology and the artificial cores damaged by inorganic scale. And the fundamental dynamical mechanism of ultrasonic treatment was also discussed. On the basis of the study, field experiments were conducted with the self-developed high power ultrasonic construction equipment. The results showed that transducer frequency, transducer power, ultrasonic processing time and core initial permeability all influence the plugging removal effect. The plugging removal effect gets better with the increase of transducer frequency and power. The optimal processing time is about 80-120min. Field tests carried out in the ShanBei low permeability reservoir and the Daqing Oilfield showed that ultrasonic treatment can increase the production and injection remarkably, confirming the laboratory results.
学术讨论
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  Carbon isotopic fractionations during the Fischer-Tropsch synthesis

  Ni Yunyan and Jin Yongbin

  , 2011, 38(2): 1930-0.

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  To understand the carbon isotope fractionation during the mineral-catalized Fischer-Traopsch synthesis of hydrocarbons under hydrothermal conditions, experiments on formic acid were carried out under 300℃ and 35MPa using gold tubes in the presence of Fe as a catalyst. The experiments were composed of two groups: with and without water. Due to the limited volume of gold tubes, only methane was available for isotopic analyses among all produced hydrocarbons. The results demonstrate that CO2 is the gas most enriched in 13C whereas methane is the gas most depleted in 13C. Moreover, methane became more and more depleted in 13C with the increase of reaction time. The carbon isotopic fractionation between CO2 and CH4 (a(CO2-CH4)) reached 1.052–1.059 at 144h, which is similar to those of microbial reduction of CO2 to CH4 by methanogenic bacteria (1.048–1.079). This implies that the carbon isotopic fractionation during Fischer-Tropsch synthesis is not only controlled by equilibrium but should be kinetic isotopic effects.