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26 October 2018, Volume 8 Issue 5
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  • Reservoir Geology
    Study on quantitative way for recombination of series of strata of reservoir in offshore with thin interbed
    Xiang Hong,Tang Hai,Su Yanchun,Zhang Zhang,Lyu Dongliang
    2018, 8(5):  1-7. 
    Abstract ( 198 )   HTML( 151 )   PDF (1416KB) ( 151 )   Save
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    PL oilfield, which belongs to the offshore reservoirs with thin interbeds, has long treatment interval and high thin layers. During the development, due to the serious interlaminar interference caused by the commingling production and serious interlayer interference in the earlier stage, the vertical balance level and the overall development effect are poor. In order to improve the oilfield development effects, it is necessary to reorganize the development layer. Firstly, we established the mathematic model of effective judgment of combination series of strata. Then, the chart boards of the relation between the oil price and average accumulative production of single adjustment well, and the relation between the current oil price and the thickness of the minimum layers adjusted by the original oil saturation were established by means of numerical simulation which was based on the characteristics of PL oilfield. Meanwhile, the equation of lower thickness limit of layers was acquired based on the research of correction curve of the influence of development stage, net/gross ratio and mobility difference on the minimum thickness of layers. The application in PL oilfield can make the recovery increased by 6.1 %. This new quantitative way for recombination of series of strata proposed can guide the efficient development of PL oilfield and similar oilfields.

    Reservoir Evaluation
    Contrastive analysis on reservoir adaptability of four kinds of oil-displacement systems of Sazhong oilfield
    Liu Jinxiang,Sun Xuefa,Lu Xiangguo,Zhang Yunbao,Xiao Long,Xie Kun,Wang Tingting,Zhao Jinyi
    2018, 8(5):  14-22. 
    Abstract ( 149 )   HTML( 139 )   PDF (3622KB) ( 139 )   Save
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    For the success of the implement of chemical flooding in Daqing oilfield, the viscosity, molecule coil size and molecular configuration of polymer solution, polymer/surfactant compound system, strong base alkali-surfactant-polymer(ASP) system and weak base ASP system, and the permeability range of the shale core and its influencing factors were studied under the same condition. The results showed that under the same condition, the viscosity and molecule coil size were in a descending order as: polymer/surfactant dual system, polymer solution, weak base ASP system, and strong base ASP system. While for the core permeability limit, the order was: polymer/surfactant dual system, strong base ASP system, polymer solution, and weak base ASP system. The reason was the bigger the molecule coil size was, the higher the core permeability that the oil-displacement systems could get through and the greater the permeability limit would be. But the strong base ASP system could react with the minerals in the cores, which resulted in the blocking of the core pores and the increase of permeability limit. The viscosity and permeability range of four kinds of oil-displacement system decreased with the increase of the shear strength, but the shearing action led to the oriented arrangement of the polymer molecules, the change law of polymer molecules in the oil-displacement system after shearing action was unobvious.

    Analysis and discussion on cause of OWC differentiation of complex faulted reservoir in Bohai area: A case study of well block 7 in W oilfield of Liaozhong sag
    Zheng Hua,Li Yunpeng,Chen Jianbo,Chen Dayong,Song Hongliang
    2018, 8(5):  23-28. 
    Abstract ( 449 )   HTML( 283 )   PDF (6357KB) ( 283 )   Save
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    According to the classical theories of the oil and gas accumulation, oil and gas are always gathering in the trap of high position. However, the phenomenon of OWC differentiation occurrs occasionally during the actual exploration and development of the oil field. W oilfield located in the concave inversion zone of the middle section in Liaozhong sag of Bohai Sea is a complex fault block reservoir. For the developed wells in the strike slip zone of the oilfield, we analyze the causes of the OWC differentiation. On the basis of the stratification and contrast, the reasons are mainly from the aspects of structure, accumulation and reservoir. It shows that OWC differentiation is due to the poor accumulation condition and sand body superimposition. According to the research on tracking of sand body and deposition characterization, it is considered that Dong-3 segment of this area shows the retrogradation phenomena, while the Dong-2 segment shows the progradation phenomenon. Besides, the Dong-2 segment's sand strata ratio is higher than that of Dong-3 segment. The mudstone of Dong-3 segment is relatively developed with good longitudinal plugging. Meanwhile, the progradation and retrogradation patterns are corresponding to the superposition relation of different sandbody. Then, a difference in oil-water interface appeared.

    Water control diagnostic plots of carbonate reservoir based on the influence of casing channeling: A case of Rumaila complex multilayered carbonate reservoir of Ahdeb oilfield in Iraq
    Cheng Liang
    2018, 8(5):  29-36. 
    Abstract ( 404 )   HTML( 267 )   PDF (2080KB) ( 267 )   Save
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    In order to guarantee the fast and professional solution about types of water production and mechanism of water invasion in the Rumaila complex multilayer carbonate reservoir of Ahdeb oilfield with casing channeling, high permeability zone and situation of commingled production, a fine reservoir model which can characterize the pure aquifer zone, oil-water transition zone and pure oil zone was built. On this basis, combined with analysis of water invasion velocity in each reservoir, the various simulation curves would be calibrated by the actual typical production curves to obtain the different typical water control diagnostic plots including casing channeling with bottom aquifer coning, bottom aquifer coning with later casing channeling, single casing channeling and the section of perforation located in the oil-water transition zone with later casing channeling(including different position of casing channeling: pure aquifer zone, oil-water transition zone and pure oil zone) with dimensionless time, which would be used to distinguish and analyze the reservoir water-producing type and rules. The results showed that the water control diagnostic plots could accurately obtain the water production type and rules, decrease the downhole PLT, SWFL and other tests, and provide reliable basis for the stabilizing oil and controlling water of vertical wells.

    Influence of scale effect on oil displacement efficiency by natural gasiscible-flooding
    Yang Xue
    2018, 8(5):  37-41. 
    Abstract ( 128 )   HTML( 202 )   PDF (1440KB) ( 202 )   Save
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    In order to study the influence of the scale effects on the oil displacement efficiency of natural gas miscible-flooding, we proposed to take the volatile reservoir with mid-low permeability of the third section of the Shahejie formation of some block in Zhongyuan oilfield as an example, and carried out the small scaled physical simulation experiment of natural gas flooding by the combination of natural cores with different length to revealed the mechanism of enhanced oil recovery by long core miscible flooding. And then we researched the gas driving development effects with large size by the numerical simulation method based on the actual geological model. The results show that the recovery rate of the natural gas recovery with the core length of 1 800 mm, 950 mm and 500 mm respectively are 90.88 %, 82.89 % and 64.8 %. It is found that the oil displacement efficiency of the long core is about 25 % higher than that of the short one, that is to say, along with the increase of the injection volume at the same injection rate, the miscible section of the long core is longer, the miscible contact is sufficient and there are time lags in gas breakthrough. Meanwhile, it is verified by numerical simulation that the best well spacing range is 300 ~ 350 m. Within this range, the larger the well spacing is, the better the displacement effect will be. But as the well spacing increases, the increasing degree of the recovery efficiency and the economic effect all get worse. Based on this study, the influence of size effect on natural gas displacement is further clarified, which is of great practical significance for the optimization of injection and production parameters and the development of similar reservoirs.

    Petroleum Engineering
    Experimental study on influence factors of proppant placement in main fracture of channel fracturing process
    Liu Pingli,Li Zhenming,Song Yuchun,Zhao Liqiang,Guo Yujie,Li Jun
    2018, 8(5):  42-47. 
    Abstract ( 188 )   HTML( 345 )   PDF (1957KB) ( 345 )   Save
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    The polymer is easily trapped in the gap between the proppant particles, so the conventional hydraulic fracturing technology of the uniform sand production has limitation for the transformation of the low permeability, ultra-low permeability and shale gas reservoirs. The channel hydraulic fracturing technology can effectively increase the oil and gas production by forming a high diversion channel by non-uniform sand deposition. The effects of channel fracturing technique are mainly determined by the channel size of the formed sand embankment. By the similarity criterion, we established the experimental method of visual simulation system of channel fracturing to systematically analyzed the influence of the fracturing fluid viscosity, proppant concentration, fiber addition, pore arrangement, pulse time and construction displacement on the proppant placement pattern and channel ratio. Then we used the methods of the partial least squares regression and the importance of variable projection to analyze the influence degree of various factors on the channel rate. Under the experimental conditions, it is indicated that when the injecting volume is 4 ~ 6 m 3/min and the viscosity of fracturing fluid is 150 ~ 250 mPa·s, the concentration of proppant is lower, the concentration of fiber is higher, the pulse time is shorter, the perforation methods is more, and the higher viscosity is better. By means of partial least squares regression, importance analysis of variable projection, and Pearson product-moment correlation coefficient, the influence degree of each channel rate is in a descending order as: viscosity of fracturing fluid > perforation methods > pulse time > concentration of fracturing proppant > concentration of fiber > injecting volume.

    Reservoir Geology
    Experimental study on identification of influencing factors of igneous gas and water layer by longitudinal and shear wave velocities
    Jia Jun,Li Chang,Wang Liang,Zhao Ning
    2018, 8(5):  8-13. 
    Abstract ( 201 )   HTML( 181 )   PDF (1758KB) ( 181 )   Save
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    In order to reveal the link between the physical mechanism of identifying gas and water zones in igneous rock with longitudinal and transverse waves' velocity, and the internal factors of reservoirs, and guide the identification of fluid types in igneous rock, the Carboniferous igneous rock core of the Junggar Basin was selected, and its longitudinal and transverse waves' velocities were measured via the ultrasonic pulse method . The longitudinal and transverse waves' velocities of the core in the dry state and the water-saturated state were obtained. In addition, the influence of the internal factors of reservoirs like the fluid types, porosity, density and lithology on elastic wave velocity were analyzed. The research showed that the gas-bearing state of the formation would cause the significant decrease in both the longitudinal wave velocity and the ratio of longitudinal to transversal wave velocities, but had a small impact on transversal wave velocity. In formations with low porosity, it was difficult to identify the fluid types because the difference in the characteristics of the longitudinal and transverse waves' velocities in gas and water zones was weakened. Due to the complex lithology in igneous rock and the great influence of SiO2 content on elastic wave velocity, fluid types should be identified by different lithology. Based on the above conclusion and in order to highlight logging responses of fluids, VP/Vs-Rt crossplots were established by different lithology to identify gas and water zones in tested formations in the research area. For intermediate-basic rock and acid rock, the Vp/Vs values are 1.85 and 1.75, respectively, which can be used to distinguish the gas zone and the water zones effectively; however, due to the influence of low porosity, it is difficult to effectively distinguish between the gas zone and the gas-water coexistence zone.

    Petroleum Engineering
    A mathematical model for the effect of shearing action on the apparent viscosity of polymer injected by a different medium injection tool
    Huang Bin,Li Xiaohui,Fu Cheng,Wang Xin
    2018, 8(5):  48-55. 
    Abstract ( 209 )   HTML( 143 )   PDF (1833KB) ( 143 )   Save
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    Aiming at the low production level of the oil layer caused by the reservoirs with low permeability and the large contradiction between oil layers, we commonly use different medium injection tools in the oil fields to realize the match of polymer injection and polymer molecular weight to the oil layer. In order to reflect the effect of shearing on viscosity of polymer solution when it across the interstitial injection tools, a mathematical model about the impact on polymer apparent viscosity affected by shearing was established, and the influence of the structural parameters of interstitial injection tools and injection volume on the apparent viscosity of polymer was analyzed. The results showed that the apparent viscosity of the polymer solution went up when the length of contractile section, radius of cylindrical section, maximum diameter of dilated section and length of dilated section increased, while the apparent viscosity of polymer solution went down when the radius of the contractile section increased. And the length of cylindrical section had no effect on the apparent viscosity of polymer solution. The apparent viscosity of polymer solution decreased when the injection volume of the polymer solution increased. The calculation results can provide a theoretical reference for optimizing the structural parameters of the different medium injection tool.

    Feasibility analysis about taking CO2 as cushion gas for gas storage rebuilt upon depleted gas reservoirs
    Hu Shuyong,Hu Xinrui,Li Yongkai,Ma Junxiu
    2018, 8(5):  56-59. 
    Abstract ( 180 )   HTML( 182 )   PDF (1811KB) ( 182 )   Save
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    The underground gas storage is one of the major storage and peak-shaving means in the world. It needs the cushion gas to keep the reservoir pressure, prevent the water intrusion and ensure the stability of the gas storage. The cushion gas volume generally accounts for 30 % to 70 % of the total volume of the gas storage. If we just took the natural gas as the cushion gas, a considerable amount of natural gas would not be mined when the storage was abandoned, and a large amount of natural gas would be wasted. The study of thermodynamic properties and the mixed experiments of CO2 and natural gas show that taking CO2 as the cushion gas for gas storage rebuilt upon the depleted gas reservoirs is feasible, because CO2 is in the critical state under the operating pressure and temperature. Its physical properties of “high density” and “high viscosity” make itself separate from the natural gas, rather than mix.

    Optimization of amount of methanol injection in gas gathering station based on water dew point analysis: A case of gas gathering station of Zizhou gas field
    Zhang Yi,Shen Lei,Tian Xijun,Hu Junzhi,Liu Peng
    2018, 8(5):  60-63. 
    Abstract ( 200 )   HTML( 146 )   PDF (1368KB) ( 146 )   Save
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    During the transportation of the natural gas gathering station, due to the constantly change of the temperature and pressure, it is easily to occur the hydrate, resulting in the clogging of the pipeline and affecting the normal transportation of natural gas. The main way is injecting the methanol when the natural gas by the gathering station. According to the situation of Zizhou gas gathering station, we used the process model of "the separation at room temperature in small station, transportation as moisture vapor, and concentrated dehydrocarbon and dehydration in processing plant". In order to determine the reasonable methanol injection quantity and optimize the methanol injection system, firstly, we measured and compared the water dew point and the ambient temperature of the natural gas at the inlet and outlet of the separator at each level to determine whether methanol injection is needed. If the methanol was needed, we would take the maximum difference calculated between the gas dew point at each stage of the gas separator and receiver, and the corresponding ambient(pipeline) temperature as the maximum temperature difference that need to be optimized. Then, we used the industry standard dew point correction chart to establish the dew point correction model. Finally, based on the maximum temperature difference to be optimized, we determined the optimum methanol injection amount by the correlation analysis between the methanol injection volume and the temperature correction value in the gas gathering station of Zizhou gas field. The obtained methanol injection volume can effectively inhibit the formation of hydrate and save the cost. The final recommended table for methanol injection volume suitable for the gas gathering station in Zizhou gas field can be used to guide the production.

    Non-conventional Reservoir
    Study on effect and law of electric pulse hydraulic fracturing of low permeability coal
    Bao Xiankai,Duan Dongming,Cao Jiaxing,Wu Jinwen,Zhao Jinchang
    2018, 8(5):  64-69. 
    Abstract ( 175 )   HTML( 114 )   PDF (1723KB) ( 114 )   Save
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    In order to reveal the effect and rule of hydraulic fracturing by high voltage electric pulse on coal crack, the analysis and the experiment about high voltage electrical hydraulic fracturing was carried out based on the principle of electro-hydraulic effect. Then three specimens were made. In the case of constant hydrostatic pressure at 3 MPa, different voltages(9 kV, 11 kV and 13 kV) were applied. The coal samples before and after the experiment were respectively scanned by ultrasonic nondestructive testing techniques to analyze the distribution and expansion of the coal internal cracks, and establish the numerical model to analyze the crack propagation rule and the surrounding stress distribution under experimental conditions. The results showed that the changes of the head ultrasonic wave's time could reflect the change of the crack in the coal sample before and after the experiment. The effect of the pure hydrostatic pressure at 3 MPa on the crack was very slight. While with the increase of the discharge voltage in the water, the new cracks inside the specimen and the density of cracks increased, and the fissure area extended from the central drilling to the edge of the test piece, coal crack effect was obvious. During the loading process, the maximum stress increased gradually and changed with the crack propagation.

    Field application of tight oil factory fracturing in Mahu sag
    Yan Xiangyang,Wang Yandong,Wang Tengfei,Zhao Haiyan,Xu Yonghui,Wan Kai,Guo Nana
    2018, 8(5):  70-76. 
    Abstract ( 243 )   HTML( 285 )   PDF (1595KB) ( 285 )   Save
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    Reservoirs in the Triassic Baikouquan formation of Mahu sag in Xinjiang oilfield is a typically tight permeable formation. Considering the purpose of the development and comprehensive analysis, by the factory fracturing ideas of zipper fracturing and subdivision cutting volume fracturing by plug fracturing with multi-stages and multi-clusters, we explored and created a factory fracturing method that is used in 2 horizontal wells of 2 000 meters long in well area Ma131 by using pre-acid pretreatment, slick water multi-plug, low damage gel fracturing fluid which is causing a complex net volume on the role of stress interference. 26 and 22 stages fracture were respectively implemented in 2 wells with the fracturing fluid of 20 162 m 3 and 23 765 m 3 and proppant of 1 803 m 3 and 1 702 m 3, which leads to a good stimulation with the oil yield over 30 tons per day after hydraulic fracturing. The successful study and use of factory fracturing make a good foundation for the later stimulation of Mahu tight oil and provide safeguard for the scale effective development of tight oil in this area.

    Influence of fracturing parameters on development effects of shale gas wells in southeast Sichuan basin: A case of well LP-133HF
    Liu Xin,Zhang Lina,Zhang Yaozu
    2018, 8(5):  77-80. 
    Abstract ( 218 )   HTML( 130 )   PDF (1392KB) ( 130 )   Save
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    Before the design of the horizontal wells' fracture, we took the well LP-133HF in the half deep to deep layer of the overpressure shale gas reservoir in southeast Sichuan basin as the research object. And by the software--CMG, we established the numerical model of the single well to simulate the sensibility of the fracture parameters of the horizontal wells and analyze the potential production promoting factors. The results showed that four factors, that is, the fracture conductivity, fracture half length, fracturing length and well spacing, affected most on the development of the shale gas wells, while the single fracturing length had the minimal effect and negative correlation. Finally, we obtained a set of fracturing parameters suitable for well LP-133HF, which is proved to be credible in field application. This analysis method is reliable and applicable for the guidance of the fracturing design. It has certain promotion significance.