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Table of Content
26 February 2019, Volume 9 Issue 1
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  • Reservoir Geology
    Analysis on main controlling factors of tight oil reservoirs in Chang-8 reservoir of Fu County, Ordos Basin
    Liu Xiuchan,Chen Xipan
    2019, 9(1):  1-7. 
    Abstract ( 360 )   HTML( 372 )   PDF (3011KB) ( 372 )   Save
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    Based on the massive analytical data of core, we comprehensively researched on the main controlling factors of the tight oil reservoir according to the property and the storage space of the tight oil formation in Chang-8 reservoir of Fu County in Ordos Basin. Fine sandstone in Chang-8 reservoir contained the movable tight oil with low density and low viscosity, and mostly concentrated in micron-sized pore throats. The accumulation of tight oil was mainly controlled by three factors that were the source rocks of Chang-7 and Chang-9 reservoirs, the main accumulation mode of "the reservoir existed in the resource, and the resource existed in the reservoir", and the high quality reservoir with composite superimposed sedimentary sand body formed in the underwater distributary channel microfacies environment. Based on the controlling factors above, and combined with the current exploration results, we predicted 6 potential blocks of Chang-8 tight oil reservoir in Fu County, and provided the basis for the further exploration.

    Reservoir Evaluation
    Experimental study on seepage flow patterns of fine controlled fractured thin and poor reservoirs
    Yu Qiannan,Liu Yikun,Yao Di,Liu Xue,Yu Yang
    2019, 9(1):  15-22. 
    Abstract ( 366 )   HTML( 519 )   PDF (2379KB) ( 519 )   Save
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    Experiments for seepage flow patterns in thin and poor reservoirs could be carried out by the plate models made by artificial core designed based on the similarity theory. Pressure gradient distribution in fractured thin and poor reservoir by fine controlling was revealed based on the pressure data, and the sketch maps of seepage flow sections were drew to study on seepage flow patterns of fine controlled fractured thin and poor reservoir qualitatively and quantitatively. Experiment results showed that seepage flow patterns in thin and poor reservoirs were greatly influenced by permeability, heterogeneity and fine controlled fracturing cracks while the thin and poor reservoirs had low permeability and strong homogeneity. Fine controlled fracturing could reduce the negative influence of low permeability and strong heterogeneity. Thin and poor reservoirs could be divided into the non seepage flow section, the nonlinear seepage flow section and the quasi linear seepage flow section. The non seepage flow section was reduced by over 72 % after fine controlled fracturing, the area for fluid flowing through increased correspondingly, and the proportion of quasi linear percolation area which was more conducive to fluid flow raised by at least 86 %.

    Influence of stress sensitive differences on natural well productivity in fractured reservoirs
    Cao Jun,Tang Hai,Lyu Dongliang,Wu Jinwei
    2019, 9(1):  23-28. 
    Abstract ( 257 )   HTML( 301 )   PDF (1428KB) ( 301 )   Save
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    In order to study the productivity characteristics of low permeability reservoirs with natural fractures, we established a prediction model of natural fractured reservoir productivity considering stress sensitivity differences between matrix and natural fractures based on the theory of plane radial flow. After that, we derived the productivity equation of natural fracture reservoir considering the difference of matrix and natural fracture stress sensitivity. Then taking the basic data of the low permeability oilfield as an example, we calculated and analyzed the influence of fracture parameters, matrix stress sensitivity coefficient and crack stress sensitivity coefficient on productivity by the productivity equation above. The results showed that with the increase of matrix stress sensitivity coefficient, the oil well productivity decreased. When the crack width was small, the stress sensitivity of fractures had a significant impact on the oil production. Therefore, in the low permeability reservoirs with natural fractures, increasing the length of the fractures and linking more microcracks would be beneficial to the increase of production.

    Parameter analysis of SRV fracturing effect of tight reservoirs based on finite element numerical simulation
    Feng Fuping,Lei Yang,Chen Dingfeng,Hu Chaoyang,Wang Huzhen,Huang Rui
    2019, 9(1):  29-33. 
    Abstract ( 349 )   HTML( 442 )   PDF (2418KB) ( 442 )   Save
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    In general, complex fracture network was formed after SRV fracturing operation in tight reservoirs, and the horizontal well yield was increased by changing the seepage field near the fracturing wells. At present, there was few weight analysis about the influence of SRV fracturing influence parameters of tight reservoirs on fracturing effect at different periods after the production of horizontal wells. By establishing the two-phase finite element equation which was applicable to the tight oil reservoir and water, finite element numerical simulation of complex fracture network was carried out, and the orthogonal experiment and grey correlation method were adopted to analyze the influence degree of horizontal well volume fracturing influence parameters on productivity of oil wells within 10 years. The results showed that the fracture conductivity determines the initial fracturing productivity of horizontal wells, and the fracture length determined the decline rate of daily production of horizontal wells and the level of steady production in the later stage. With the continuous production of fracturing wells, the fracture length replaced the fracture conductivity and became a key factor affecting the yield. The research on the influence degree of each influence parameter on the fracturing effect in different periods in which horizontal wells could provide theoretical support for the construction and design of SRV fracturing horizontal wells in tight reservoirs.

    A new method of liquid production rate prediction with different water cut
    Ling Haochuan,Zhou Haiyan,Shi Hongfu,Sun Qiang,Kong Chaojie
    2019, 9(1):  34-37. 
    Abstract ( 243 )   HTML( 377 )   PDF (1606KB) ( 377 )   Save
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    It is showed that the increasment of the differentid pressure for high liquid production rate of producing wells was one of the main techniques used to enhance oilfield production. In order to determine the reasonable liquid production rate at different water cut stages, we proposed the concept of dimensionless liquid production intensity based on the previous study of dimension less liquid production index, and obtained its theoretical plate according to relative permeability curves. The application showed that the plate of dimensionless liquid production intensity could be used to predict the reasonable liquid production rate and determine the relative values of differential pressure ratio of producing wells at different water cut stages without knowing the differential pressure.

    Petroleum Engineering
    Evaluation of OB-2 system for W/O emulsifier and displacement experiments research at high temperature reservoir in high water cut period
    Pu Wanfen,Mei Zilai,Yang Yang,Wang Duo,Shen Chao,Chen Pei
    2019, 9(1):  38-43. 
    Abstract ( 257 )   HTML( 158 )   PDF (1951KB) ( 158 )   Save
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    Aim

    ed at how to develop high temperature reservoir after water flooding, we proposed the in-situ emulsion flooding by injecting surfactant solutions to evaluate the emulsifying property and study on the oil displacement by the emulsion of the OB-2 system for the W/O(water in oil)emulsifier. The results showed that the emulsion viscosity firstly increased and then decreased along with emulsifier concentration. For oil in reservoir-X, the optimal emulsifier concentration was 0.3 wt% at which could make the interfacial tension reduce to 10 -2 mN/m order of magnitude. When the water-oil ratio was lower than 7∶3, the complete emulsification of oil-water happened and the W/O emulsion with high viscosity would form. The maximum emulsion viscosity appearde when the oil-water ratio was 7∶3, with the viscosity increasing rate of as high as 370 %. The results of emulsion flooding indicated that the recovery factor of the homogeneous core could increase another 26.15 % after water flooding by injecting 0.3PV OB-2 system. On the other hand, when the permeability ratio of parallel cores was lower than 7.6, applying the OB-2 system could achieve good mobility control and heterogeneity regulation.

    Study on water plugging effect and mechanism of starch graft copolymer gel
    Cao Weijia,Lu Xiangguo,Zhang Yunbao,Xu Guorui,Li Xiang
    2019, 9(1):  44-50. 
    Abstract ( 209 )   HTML( 524 )   PDF (2370KB) ( 524 )   Save
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    Bohai oilfield has the characteristics of loose cementation, serious heterogeneity, high viscosity of crude oil, high average permeability and large amount of water injection in a single well. The breakthrough phenomenon of water injection development was serious, and the injection water erosion also caused damage to rock structure. Then we formed inefficient and ineffective circulation between injection and production wells, seriously affecting the effect of water flooding development, and bringing great risks to subsequent chemical flooding development. In order to satisty the heavy oil reservoir of high water shutoff technology needs, based on the physical chemistry, polymer materials and reservoir engineering theory, and taking the chemical analysis, detection equipment and physical simulation as an experimental method, we took the reservoir rock and fluid in SZ-361 field of Bohai oilfield as the research object to study the water plugging effect and mechanism of starch graft copolymer gel. The results showed that when the water plugging agent group was "starch(4 %)+ acrylamide(4 %) + crosslinking agent(0.036 %) + initiator(0.012 %) +anhydrous sodium sulfite(0.002 %)", the reasonable slug size of water plugging agent was between 0.025PV and 0.075PV. For the model of "edge water and vertical oil well", the oil recovery of water flooding decreases with the increase of crude oil viscosity. After water plugging in the oil well, the liquid production rate decreases when the water content drops. The higher the viscosity of crude oil is, the greater the decline of water content and the recovery rate will be, but the ultimate recovery is still lower. Compared with the model of "single water and vertical oil well", the model of "multilateral water and vertical oil well" had higher water flooding recovery, and the effect of water plugging and oil increasing was better. For the high water cut development period of reservoir, due to the impact of early water flooding and chemical flooding profile control and other measures, the remaining oil saturation near the water wells borehole area was low, but the residual oil saturation in low permeability reservoirs near the wellbore was higher. Therefore, the effect of water plugging measures on increasing oil and precipitation was much better than that of profile control measures.

    Design and property evaluation of a novel supermolecule temporary plugging agent DMF
    Xu Kun,Li Da,Guo Yujie,Fan Xiliang,Zhao Liqiang
    2019, 9(1):  51-55. 
    Abstract ( 307 )   HTML( 379 )   PDF (1639KB) ( 379 )   Save
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    Sulige gas field is a typical tight-gas reservoir whose ultralow permeability comes to a problem to a noble stimulation technology with its name refracturing coupling with SRV fracturing, owing to the failure of injection by conventional plugging agent, which aims to plug existing fractures and create more multistage fractures. So we designed the novel supermolecule temporary plugging agent--DMF and conducted a series of tests including gelling, break gelling, and temporary plugging steering. The results had demonstrated that the new plugging agent DMF was responded to high temperature, about 100 ~ 110℃, transforming into high viscosity supramolecular gel from low viscosity liquid at low or normal temperature, plugging existing fractures. When the temperature got higher, the gel of DMF turned into liquid automatically. Then, the DMF showed a better performance(122.92 MPa/m) of temporary plugging steering than that of conventional plugging agent, demonstrating a more desirable diversion agent for tight-gas reservoirs.

    Optimization research and application of lifting technology of electric submersible reciprocating pump
    Qian Kun,Hu Wenrui,Sun Yanan,Shi Guochen,Du Weishan,Li Jinan,Ge Weitao,He Yan
    2019, 9(1):  56-60. 
    Abstract ( 303 )   HTML( 430 )   PDF (1663KB) ( 430 )   Save
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    Electric submersible reciprocating pump is a rodless oil extraction device for low-permeability reservoirs. As one of the new technologies of high efficiency and energy saving lifting, its application scale is expanding year by year. In the light of problems of oil field production: we creatively proposed an optimization method for submersible linear motors, including the motor's lifting capacity and control methods; then we developed a new double-acting load shedding pump for deep oil wells or large displacement oil wells; after that we researched and developed new aluminum alloy submersible oil cables to reduce one-time investment costs. It is applied of 90 oil wells, then we found that the average pump inspection period increased from 452 to 693 days, the longest pump inspection period exceeded 1 037 days, and the average electricity saving rate reached 45.6 %. The applications showed that the new optimized and upgraded technology had better reliability, adaptability and economy, which was beneficial to the large-scale application of electric submersible reciprocating pumps. It also provided a basis for in-depth study of variable frequency control of long line submersible oil cables and monitoring of downhole working conditions.

    A boundary modification for water and electricity analogy experiment of fractured horizontal wells
    Li Linlin
    2019, 9(1):  61-64. 
    Abstract ( 249 )   HTML( 147 )   PDF (1268KB) ( 147 )   Save
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    When we studied the relation between the fracture spacing and production rate by water and electricity analogy experiments, if the boundary range was small, the influence of the distance between the fracture and the boundary on the production would be difficult to be neglected. Actually, this relation was affected by both the fracture spacing and the distance between fractures and boundary. In order to overcome this shortcoming, we proposed a new method to extract this influence by experimental measurement and formula correction, then, to eliminate the influences of fracture and boundary distance on fracture production rate. This method reflected the real relation between the fracture spacing and the production rate, and provided effective guidance for fracturing designs.

    Optimization method for injection intensity of multi thermal fluid huff and puff in multiple cycles
    Feng Xiang,Gong Ruxiang,Li Jinsong
    2019, 9(1):  64-67. 
    Abstract ( 262 )   HTML( 323 )   PDF (1410KB) ( 323 )   Save
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    As one of the offshore heavy oil thermal exploitation technology, the multi thermal fluid stimulation technology had been carried out in the development of heavy oil in Bohai oilfield. By the theoretical analysis and numerical simulation method, we reasonably characterized the mechanism of multi thermal fluid huff and puff, introduced the concept of coefficient of variation, and obtained the main factors affecting the effect of multiple rounds of throughput, which were the injection strength, shift opportunity, injection temperature, and periodic increasing rate. Based on the reservoir characteristics of the typical oil field, and with the evaluation index of the rate of cycle output and input, we got the sample data of different cumulative oil production and gas retention conditions, and regressed the optimum injection strength in multiple cycles of multi thermal fluid huff and puff wells. Then we corrected the optimization by using the main factors influencing the thermal recovery effect, drew the optimized version to obtain the reasonable injection parameters accurately and efficiently, and improved the thermal recovery effect of huff and puff in multiple rounds.

    Preparation and study of waste drilling fluid profile control water plugging agent
    Mu Yongqing,Wang Bo,Sun Zhixue
    2019, 9(1):  68-71. 
    Abstract ( 229 )   HTML( 190 )   PDF (1527KB) ( 190 )   Save
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    In order to deal with the waste drilling fluid in Jiangsu oilfield, we proposed to add additives to the waste drilling fluid, and made a kind of waste drilling fluid profile control agent. In the laboratory experiments, by the physical properties of waste drilling fluid and particle size, we filtered out the suitable profile control formula. Then we obtained the optimum dosage of each additive from the experiments: the suspension of 0.20 %, dispersant 0.30 % and curing agent 5.0 %. The developed waste drilling fluid profile control agent had good suspension stability, curing properties and plugging performance. It could not only solve the problemsof waste drilling fluid, but also reduced the production cost of plugging agent, moreover, it had great significance to the production of oil.

    Non-conventional Reservoir
    Research on productivity of fractured horizontal wells in shale gas reservoirs based on anomalous diffusion model
    Li Yongming,Wu Lei,Chen Xi
    2019, 9(1):  72-79. 
    Abstract ( 256 )   HTML( 237 )   PDF (1586KB) ( 237 )   Save
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    After the volume fracturing of shale gas reservoirs, due to the abrupt variations in the pore scale of the gas seepage and the severe difference between the characteristics of shale matrix and fractures, the seepage velocity field showed a sharp discontinuity, resulting in the failure of continuum assumption. In order to accurately understand the flow pattern of shale gas reservoirs and analyze the productivity, based on the trilinear flow model of fractured horizontal wells in shale gas reservoirs and coupled with the anomalous diffusion equation of fractal porous media, we established a fractured horizontal well productivity model of shale gas reservoirs. The dimensionless production was obtained by Laplace transform and Stehfest numerical inversion. Finally, we analyzed its result combining specific example and obtained a dimensional production curve. The analysis results showed that five flow regions for shale gas could be identified, including the linear flow stage of hydraulic fractures, the bilinear flow in hydraulic fractures and natural fractures, the linear flow stage of natural fractures, the bilinear flow in natural fractures and matrices, and the phase of matrix linear flow. Based on the production model, we also studied the influence of anomalous diffusion exponent, pseudo-permeability, storability ratio, fracture spacing and the like. on the production of shale gas reservoirs. The results indicated that the smaller abnormal diffusion exponent and the stronger matrix heterogeneity were, the more obvious decrease of productivity would be, and the natural fractures pseudo-permeability had great impact on the length of time in the linear flow of the natural fractures. Furthermore, the hydraulic fracture pseudo-permeability could influence the productivity in the whole middle-late production cycle. The larger the storability ratio was, the more obvious increase amplitude of productivity would be. The research provided a new idea and method for productivity analysis and evaluation of shale gas reservoirs.

    Reservoir Geology
    Application of reservoir parameters inversion method by using multi-attributes in M oilfield
    Zhang Jingyu,Fan Ting'en,Wang Zongjun,Yuan Ye
    2019, 9(1):  8-14. 
    Abstract ( 210 )   HTML( 144 )   PDF (3631KB) ( 144 )   Save
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    In order to satisfy the fine reservoir characterization at the development phase of the oilfield, we took a full use of reservoir information obtained by drilled wells to select several seismic attributes, and established the relation of the linear and nonlinear mapping between selected seismic attributes and inversion reservoir parameters to achieve the high-resolution spatial prediction of reservoir parameters. The application of seismic multi-attributes inversion in M oilfield showed that the vertical and lateral resolution of inversion result was significantly improved, and the predicted results agreed well with the drilling results.

    Non-conventional Reservoir
    Research and application of jet pump technology in drainage gas recovery of shale gas at atmospheric pressure
    Wang Yuhai,Xia Haibang,Bao Kai,Qiu Weidong
    2019, 9(1):  80-84. 
    Abstract ( 410 )   HTML( 285 )   PDF (1553KB) ( 285 )   Save
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    Pengshui block is a typical shale gas reservoir at atmospheric pressure which has lower coefficient of original formation pressure, and usually needs artificial lift recovery after fracturing. In the initial stage, we optimized the electric submersible pump for the drainage gas recovery. This technology was simple, meanwhile, the formation energy declined gradually, the formation liquid supply gradually decreased and the recovered fluid contained impurities such as sand and clay particle, so that it was hard to realize the stable continuous drainage and recovery, and had complex operation precess and high production cost. In order to solve these problems, we researched and applied the jet pump, and optimized the technology parameters and matching technology. At last, we formed a set of jet pump technology suitable for the drainage gas recovery of shale gas at atmospheric pressure to effectively guide the pressure of shale gas recovery.