Table of Content

01 October 2018, Volume 40 Issue 5

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Development History and Future Trends in Reservoir Architecture Research

CHEN Fei, HU Guangyi, HU Yuting, XIE Chao, WANG Haifeng

2018, 40(5):  1-14.  DOI: 10.11885/j.issn.1674-5086.2017.05.11.03

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Architecture research is both a popular and challenging topic in current reservoir research. This study discusses the formation history of this discipline, its practical importance through time, and summarizes the research history and trends in reservoir architecture. Methodology in reservoir architecture research has changed from conventional field outcrop descriptions and sedimentation analyses to new techniques, such as 3D seismology, ground penetrating radar, flume experiments, and numerical simulations. Notable improvements in methods include stratigraphic constraints, model fitting, multi-dimensional interactions, and seismic sedimentology. Research subjects have also changed from traditional meandering river sedimentation to delta, deep-water, and carbonate rock reservoirs. Reservoir architecture research has become progressively more sophisticated and quantitative. Finally, this study also introduces and discusses some hot topics in current reservoir architecture research, such as subsurface architecture analyses, seismic responses of architecture and associated mechanisms, composite sand body architecture, and well-to-well distances in well placement.

Reservoir Plane Heterogeneity Characterization Based on Reservoir Architecture Research

ZHANG Rui, LIU Zongbin, JIA Xiaofei, WANG Gongchang, TIAN Bo

2018, 40(5):  15-27.  DOI: 10.11885/j.issn.1674-5086.2017.05.02.03

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As shown by coring and drilling data from numerous infill and regulation wells, significant differences in water flooding have occurred along the plane of the Bohai Sea SZ Oilfield, and there has been uneven utilization of the plane residual oil. Current methods for quantitatively characterizing plane heterogeneity are insufficient for satisfying future exploitation demands. To mitigate plane differences and realize plane residual oil potential, research characterizing reservoir plane heterogeneities was conducted during the late exploitation stage in the Bohai Sea SZ Oilfield. The results indicate that current quantitative methods for this type of characterization have been primarily based on geostatistics, with fundamental parameters, i.e., reservoir indices, obtained from wells. Because they are measured in small individual layers, they can neither sufficiently present all different properties nor effectively describe issues, such as internal structural differences in reservoir layers between wells. By examining reservoir architecture, a more comprehensive characterization of reservoir plane heterogeneity is achieved. This is integrated with plane oil-water contact relationships in different facies units in the oilfield to obtain a new quantitative characterization index and non-connected thickness, for heterogeneous layers. This index uses well profiles as basic units, thus overcoming the limitation that internal structural differences in reservoir layers between wells are not depicted. Furthermore, plotting a plane distribution map of unconnected thicknesses provides a mechanism for semi-quantitatively characterizing internal structural differences in reservoir layers. The non-thickness index is applied to closely spaced wells in the Bohai Sea SZ Oilfield in a pilot test. The predictions based on the index are consistent with the actual production results, suggesting that the index is practically applicable.

Study on the Control Factors and Potential-tapping Strategies for the Remaining Oil of SZ Oilfield in the Bohai Sea

TIAN Bo, LI Yunpeng, JIA Xiaofei, ZHANG Xuefang, ZHANG Rui

2018, 40(5):  28-36.  DOI: 10.11885/j.issn.1674-5086.2017.10.31.02

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The recovery efficiency of SZ Oilfield in the Bohai Sea has greatly improved since the first infilling adjustment. However, with the oilfield transitioning to the high-water-content stage, the distribution of the remaining oil has become increasingly complicated and it has become more difficult to make further adjustments and realize the untapped potential; sustainable development of the oilfield necessitates new technical means and exploitation strategies. To cope with these challenges, a detailed description of the vertical and in-plane contact relationship of homogeneous sand bodies was carried out on the basis of the delta facies reservoir architecture theory, by comprehensively utilizing coring, seismic, and logging data. With this approach, the role of reservoir architecture in controlling the movement of oil and water was analyzed. The results showed that during the high-water-content stage, inter-stratum and inter-zone interference, intercalated beds, and joints between plane-architecture units were critical to controlling the remaining oil. To further improve the oil field development efficiency, three architecture unit-based strategies are proposed for tapping the potential of inter-stratum and intra-stratum horizontal wells and infilling densely spaced horizontal wells. A set of technologies was developed for tapping the potential of the delta facies oil reserves remaining after a comprehensive adjustment is made to the oilfield. The strategies and technologies were then applied, achieving good results.

Mixed Sedimentation Characteristics and Evolution of Lower Member 3 of the Shahejie Formation in the KL Oilfield

HAN Jianbin, TIAN Xiaoping, KANG Kai, SHEN Chunsheng, WANG Libing

2018, 40(5):  37-46.  DOI: 10.11885/j.issn.1674-5086.2017.05.05.02

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There is still limited understanding of the formation conditions, sedimentation characteristics, and modes of the terrestrial debris-carbonate rock mixed sedimentation in the lower sub-member of Member 3 of the Shahejie Formation in the KL Oilfield in the southern slope of the Laizhou Bay Depression. In this study, data from side-wall cores from the area, thin sections, and scanning electron microscopy were obtained and integrated with contextual information, including tectonic evolution, paleoclimate, and paleogeomorphology. The sedimentary and sedimentary characteristics were analyzed within a sequence stratigraphic framework. The results reveal that mixed sedimentation developed in the study area due to wide and gentle slopes, humid subtropical climate, and periodically varying lake surfaces, water sources, and hydraulic conditions. This mixed sedimentation includes two sedimentation modes, gradual mixing along the facies edges and in situ mixing; two mixing modes, rhythmic bedding and compositional mixing; and four mixing patterns. The two mixed sedimentation modes differ in their mechanisms, while the mixing modes and mixing patterns show relatively significant variations, which has resulted in different microscopic characteristics in the reservoir.

Humid Fan-delta Sedimentation Characteristics in the Badaowan Formation in the Northwestern Junggar Basin

QIU Zhengke, WANG Hui, LI Ting, TAO Wulong, PU Bo

2018, 40(5):  47-58.  DOI: 10.11885/j.issn.1674-5086.2017.07.18.01

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There are abundant oil and gas resources in the Jurassic Badaowan Formation at the northwestern margin of the Junggar Basin, but they are mostly located in the sand-conglomerate reservoirs on the southeastern side of the Ke-Wu fault belt. Recent exploration reveals that there are plentiful oil and gas reserves and higher exploration potential in the basin area far away from the fault belt. There is, however, little knowledge of the types and distributions of the sedimentary facies in the study area. Based on an integrated analysis of data obtained from well drilling and logging, core samples, and geophysical measurements the Badaowan Formation is divided into two three-fold stratigraphic sequences and various facies, including fan-delta facies, braided river facies, braided river delta facies, and lake facies, are identified. Fan-delta facies dominate the lower sequence of the Badaowan Formation, while the upper sequence is characterized by braided river and braided river delta facies. The fan-delta facies in the study area formed in humid environments. They are widely distributed, fine-grained, thick at the facies fronts and oil-rich in the plains. These facies are clearly different from the arid fan-delta facies developed in the Paleogene rift basins in Eastern China.

Karst Reservoir Characteristics and Main Controlling Factors of the Yingshan Formation in the Tarim Basin Central Uplift

XIAO Bo, BAI Xiaoliang, LÜ Haitao

2018, 40(5):  59-70.  DOI: 10.11885/j.issn.1674-5086.2017.04.19.02

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The main factors controlling the development of carbonate karst reservoir of the Yingshan Formation, Tarim Basin Central Uplift are discussed here to provide a theoretical basis for exploring lithological hydrocarbon reservoir traps of the Yingshan Formation. Results of rock core and thin section observation and physical data analysis, along with borehole imaging interpretation suggest that the carbonate rocks of the Yingshan Formation form a low-porosity, low-permeability karst reservoir. The reservoir space mainly comprises dissolution pores, fractures, and dissolution cavities. The mid-lower Ordovician carbonate reservoir is classified into several types such as fracture-pore, fracture, dissolution pore, and karst cavity. The development process of the karst reservoir is described in detail, and the factors controlling the development are also discussed:(1) mid-Caledonian phase I led to the uplift of rock layers and formation of a broad anticline structure. Carbonate rocks generally experienced leaching and corrosion parallel to the strata. Extrusion fold and faulting from tectonic activities formed numerous structural fractures, resulting in increased vertical permeability and horizontal connectivity of the limestone strata; (2) micritic limestone, dolomite-containing limestone, and dolomitic limestone are more compact lithologically, and only corroded along fractures to form dissolution pores-expanded dissolution cracks during the karst process. Limestone-containing dolomite and calcite dolomite have good porosity and permeability, and a section of the underlying dolomite strata is exposed to the surface. This enabled surface water to easily flow through dolomite strata, thereby forming a large number of pores; (3) dolomitization in general enhances the porosity and permeability of the dolomite strata (due to favorable structure and high dolomite content), providing the basis for the karst process.

Composite Controls on Oil and Gas Accumulation by Fractures in Source Rocks and Ordovician Reservoirs in the Tazhong Uplift

SHEN Weibing, CHEN Jianfa, LUO Guangping, HE Liwen

2018, 40(5):  71-83.  DOI: 10.11885/j.issn.1674-5086.2017.11.26.01

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In this study, existing oil, gas and water exploration results and information on reservoirs and fractures were used and various methods employed, including conventional borehole logging, seismology, geochemistry, and mathematical statistics. The goal of this synthesis of methodology and data was to examine the distributions and accumulation characteristics of oil and gas in the target layers in the study area. The results reveal that the Ordovician reservoirs are mainly composed of reef beach sediments. There are numerous karst caves and fractures, which control the relatively high-permeability accumulation of oil and gas. As porosity and permeability of a reservoir increase, capillary force differences between the reservoir and its surrounding rocks increase. Consequently, there is a higher probability that the reservoir contains oil and gas, and the degree of oil saturation increases. The critical capillary force for oil and gas accumulation is 2.5 MPa. Fractures in Ordovician source rocks show complicated distributions. They intersect each other to form ten oil and gas filling points, and control oil and gas accumulation near these filling points. When far away from these points, oil and gas filling becomes less intense and their yield decreases. The geochemical properties of oil and gas show regular variations. The critical distance for oil and gas accumulation is 20 km from a filling point. Under the joint control from reservoirs and fractures in source rocks, oil and gas show an accumulation mode characterizing "relatively high permeability near filling points" in which reserves are first formed near filling points in high-permeability reservoirs.

Micropore Characteristics and Adsorption and Desorption Properties of Shales in the Yibin Region

YUE Changtao, LI Shuyuan, XU Xinyi, MA Yue, YANG Fei

2018, 40(5):  84-94.  DOI: 10.11885/j.issn.1674-5086.2017.07.26.04

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Shales of the Silurian Longmaxi Formation in the Yibin Region, Sichuan, were investigated and their geological parameters, including total organic carbon (TOC) contents and clay mineral contents, were measured. Scanning electron microscopy, high pressure mercury injection, low temperature nitrogen adsorption-desorption, and carbon dioxide gas adsorption methods were employed to qualitatively and quantitatively analyze pore structure characteristics. The mass method was utilized to conduct isothermal adsorption and desorption experiments on shale samples at different temperatures and adsorption and desorption processes were explained using the adsorption potential theory. The results demonstrate that these shale samples have relatively high TOC contents, and pore structures are dominated by micropores, followed by mesopores and macropores. Connected micropores and mesopores increase surface areas of shales, and provide more adsorption spaces, thus facilitating adsorption of shale gas. The isothermal adsorption curves of the shale samples reveal that as the pressure increases, the adsorption volume increases rapidly at first and then levels off gradually. The desorption curves resemble the adsorption ones, but show some delays. The TOC contents indicate relatively good positive correlations with the adsorption performances of shales. The zero-potential point of the absorption potential curve is generally consistent with the turning point of the adsorption curve. The occurrence of shale gas during adsorption and desorption can be explained by variations in adsorption potentials.

Design and Effect of Fracture-flooding in Class III Oil Reservoirs

HE Jingang, WANG Hongwei

2018, 40(5):  95-104.  DOI: 10.11885/j.issn.1674-5086.2017.12.25.03

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The efficient exploitation of the Class Ⅲ reservoir in the Daqing Oilfield is necessary for realizing a high and stable yield of oil. To solve the problems encountered in the Sazhong Development Zone, such as the multiple sand body types present, poor physical properties of the reservoir, low recovery, scattered distribution of remaining oil, high adsorption, and the difficulty in chemical flooding during oil extraction, a "fracturing flooding" technique is proposed. In this method, a high-speed channel is formed by a long fracture to quickly deliver high-efficiency oil displacement agents to sites with enriched remaining oil. Filtration loss happens along the way as the channel is formed by fracturing to reduce the contact duration and distance between the chemical agents and strata. Hence, the decrease in the effectiveness of the chemical agents during the injection process is minimized, and their usage efficiency and flooding effect are improved. Field tests show that the injection of oil displacement agents through a fracture is technically possible for the Class Ⅲ reservoir. Satisfactory flooding results are seen in the wells where trial injections are performed. This method could be applied to Sapu Class Ⅲ reservoir and Gaotaizi Class Ⅲ reservoir of the Sazhong Development Zone to realize production and injection enhancement for the rapid tapping of scattered remaining oil in the wells.

Recovery Rate Model for Strong Bottom Water Drive Reef Limestone Reservoirs

LUO Donghong, ZHU Xu, DAI Zong, CHENG Jia, NING Yuping

2018, 40(5):  105-112.  DOI: 10.11885/j.issn.1674-5086.2017.11.07.01

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To realize rapid prediction of the recovery rate of offshore strong bottom water drive reef limestone reservoir L, a model for simulating the mechanisms of the various factors affecting the reservoir exploitation was developed. The model was developed by reviewing and analyzing the geological, fluid, and engineering parameters associated with the reservoir exploitation process. The functional relationships between the recovery rate and the various influencing factors were then determined on the basis of the model as well as a numerical simulation study, thereby yielding a list of the major factors affecting the recovery rate of the water drive reservoir. Through this approach, a model was then developed for quantitatively representing the recovery rate of water drive reef limestone reservoirs, by employing an orthogonal experiment design and multiple nonlinear regression theory. Field application results showed that the recovery rate model was capable of rapidly predicting the recovery rate of strong bottom water drive reef limestone reservoirs exploited using horizontal wells, with high accuracy and small error.

A Quantitative Method to Predict the Dynamic Variation in Permeability of Oil Reservoirs During Waterflooding and Oil Displacement

HONG Chuqiao, WANG Wenjuan, LU Ruibin, ZHONG Jiajun, REN Chaoqun

2018, 40(5):  113-121.  DOI: 10.11885/j.issn.1674-5086.2017.10.09.01

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Most of the marine sandstone oil fields in the western part of the South China Sea have entered the middle-and high-water cut stage. The permeability of these reservoir changes constantly under the long term scouring effect. Because it is difficult to quantitatively characterize and predict the dynamic variation in permeability of oil reservoirs during the extraction process by core displacement experiments, we analyzed the dynamic variation pattern of reservoir permeability during a waterflooding process. In this study, the flux at the preferred surface is used as an index to characterize the reservoir scouring strength. By analyzing the mechanism associated with the change in permeability and adapting it to rationalize the temporal variation in permeability of production and testing wells during the oil reservoir extraction process, we derived a logarithmic prediction formula that describes the change in permeability with varying surface flux. We further applied the equation in a wider range of applications and expanded the applicability of the logarithmic correlation. Finally, a high-ratio oil displacement experiment is designed and performed to validate the accuracy and scientific merits of the proposed logarithmic relationship between permeability and surface flux. This logarithmic relationship was found to work well in practical applications during the later stages of oil extraction in oil fields with high water content in the western part of the South China Sea.

Effect of Radial Well Guidance on Hydraulic Fracturing Crack Propagation Mechanism

GONG Diguang, CHEN Junbin, QU Zhanqing, GUO Tiankui

2018, 40(5):  122-130.  DOI: 10.11885/j.issn.1674-5086.2017.10.27.02

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To study the effect of radial well guidance on cracks and understand the pattern of hydraulic fracturing crack propagation, a fluid-solid coupled three-dimensional crack propagation model is constructed based on the extended finite element theory and further used to simulate the hydraulic crack propagation process induced by radial well guidance. In particular, the effect of three factors (radial well azimuthal angle, horizontal stress difference, and radial well radius) on the guidance of hydraulic crack propagation are discussed. The concept of a "guidance factor" is first proposed in this study and used as a quantitative parameter for evaluating the guiding performance of the radial well. The results revealed that the guiding performance in hydraulic crack propagation can be affected by all three factors, including radial well azimuthal angle, horizontal stress difference, and radial well radius. Specifically, a smaller radial well azimuthal angle, a larger horizontal stress difference, and a larger radius for the radial well can enable a strong guiding ability for the radial well and therefore realize a decent guiding performance, and vice versa. Finally, the accuracy of the numerical simulation results is validated by large-scale true triaxial hydraulic fracturing simulation tests.

Study on the Optimization of Shale Gas Well Spacing Based on Assessment of the Fracturing Performance

WANG Yanyan, WANG Weihong, HU Xiaohu, LIU Hua, GUO Yandong

2018, 40(5):  131-139.  DOI: 10.11885/j.issn.1674-5086.2017.10.24.03

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Determination of the optimum shale gas well spacing is to a large extent dependent on the assessment of fracturing performance. To tackle this problem, we explored the parameters associated with the reconstruction of horizontal wells used for multi-stage fracturing. Based on this exploration, we further optimized the shale gas well spacing. By establishing a mathematical model of seepage flow, we determined the flow regime existing in the formation of a shale gas well and furthermore developed a method to rationalize the fracturing parameters based on linear flow identification and the feature line diagnostic technique. The uncertainty associated with the parameter rationalization is also analyzed and discussed in this study. Finally, the optimum well spacing under uniform fracturing condition was determined by defining the total gas production over a 100-m stratum. The results demonstrate that the half length of the crack can be accurately determined without affecting the prediction of the production capacity of the gas well once the formation is under boundary control flow. The key factor in determining the well spacing is the half length of the crack. The relationship between these two parameters is affected by the relative physical properties and flow conductivity of the fracture inside and outside the SRV. These findings can provide guidance for performing well spacing optimization and policy-making associated with the extraction techniques.

Real-time Microseism Monitoring of Stability of Salt-cavern Gas Storage in Jintan

JING Gang, LI Long, BA Jinhong, LIU Tao, CHEN Jiasong

2018, 40(5):  140-146.  DOI: 10.11885/j.issn.1674-5086.2017.05.24.01

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To undertake the real-time monitoring of the cavity state in the process of water injection and brine displacement, gas injection and production of a salt-cavern gas storage, microseism technology is applied during continuous monitoring for 23 d. The 12-level detector is arranged using the in-well method, and the surface energy source is used for the spatial orientation of the detector. Moreover, the information of the P wave and S wave is combined for spatial orientation of the microseism events. Through a cross analysis on the number of microseism events and injection-production parameters, the influences of production technology on cavity stability are studied. The results show that 419 effective signals occurred during the 23 d monitoring process; sixteen microseism signals are detected in two cavity construction wells, without any obvious signal detected in injection and production wells. Many microseism signals are detected between two injection and production wells, which is considered as natural fracture activity through three-dimensional seismic data obtained with a b-value analysis. The microseism sources are detected as the joint action of shear stress and tensile stress after analytic monitoring, and the sources where tensile stress plays a leading role are more. It is believed that the current injection-production operation parameters meet the safe operation requirements of a salt-cavern gas storage; it is suggested to extend the monitoring time to enhance the microseism quantity and establish statistical laws for injection-production parameters in the follow-up studies, to strengthen the study on natural fracture activity among cavities, thereby ensuring the safe operation of a gas storage.

Study on Improving the Solution-mining Processes of Salt-cavern Gas Storage and Field Applications of the Improved Process Technology

WANG Yuangang, ZHOU Donglin, DENG Lin, FU Yaping, GUAN Di

2018, 40(5):  147-153.  DOI: 10.11885/j.issn.1674-5086.2017.09.06.04

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While the salt-cavern gas storage solution is becoming increasingly popular in the natural gas industry, engineering practice shows significant improvement opportunities for many solution-mining processes of the Jintan gas storage, the first commissioned salt-cavern gas storage in China. The solution-mining processes of the gas storage were analyzed to identify opportunities to improve solution-mining efficiency, minimize solution-mining energy consumption, and maximize the utilization of salt layers. The improvement opportunities identified are:employing reverse-circulation solution mining to increase greatly the salinity of the discharged brine; minimizing the number of underground operations and eliminating unnecessary interruptions to mining operations, thereby reducing solution-mining cycle time; installing a fiber-optic interface meter to enable real-time monitoring of the solution-inhibitor interface; optimizing the quantity of water injected to reduce energy consumption; and treating thick intercalated beds and expanding the overall cavern capacity to maximize the utilization of salt layers.

Experimental Study on the Transmission Behaviors of Supercritical CO₂ and CH₄ in Shale Nanopores

CHEN Qiang, SUN Lei, PAN Yi, GAO Yuqiong

2018, 40(5):  154-162.  DOI: 10.11885/j.issn.1674-5086.2017.08.30.11

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Understanding the transmission behaviors of supercritical CO₂ and CH₄ in shale nanopores is fundamental for studying the supercritical CO₂ injection capacity of shale reserves and the temporal and spatial distribution of injected supercritical CO₂. Understanding these behaviors is also essential for improving the recovery rate of shale reserves. In the study, the transmission capacities of supercritical CO₂ and CH₄ in shale nanopores were compared and the difference in their transmission capacities was analyzed for the underlying reason. A core flow experiment was performed on organic-matter-rich shale matrix samples of the Longmaxi Formation (permeability smaller than 100 nD) by varying the pressure as well as the CO₂ and CH₄ concentrations in the CO₂/CH₄ mixture at the inlet and outlet of the core. The experimental results show that the pressure transmission rate of supercritical CO₂ in shale nanopores was clearly lower than that of CH₄. At the end of the experiment, the CH₄ content by percentage in the CO₂/CH₄ mixture significantly decreased at the inlet of the rock sample, demonstrating that the transmission capacity of supercritical CO₂ in shale nanopores is significantly lower than that of CH₄. This can be explained by certain properties of supercritical CO₂, such as its higher absorption capacity and lower diffusibility and permeability as well as its immiscible displacement and piston-like displacement behaviors owing to its super-high density characteristics. Based on this understanding, some fractured sections were selected for supercritical CO₂ injection, and other fractured sections were reserved for production. Compared with the single-well injection-soaking-production design, this configuration facilitates better displacement of free-state methane in shale nanopores.

Safety Analysis of Flange Joint Collapse in Deep Water Drilling Risers

LIU Qingyou, HE Junjiang, MAO Liangjie

2018, 40(5):  163-169.  DOI: 10.11885/j.issn.1674-5086.2017.07.25.02

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In deep water drilling, the flange joints of drilling risers are usually exposed to complex and harsh environmental loads while experiencing a high difference between internal and external pressure. Therefore, it is necessary to monitor the stress in these flange joints while drilling. In this study, a finite element model of a flange joint was developed for analyzing the stress distribution and critical collapse pressure of both a wear-free and a worn flange joint in a drilling riser under different external load conditions. The results showed that the flange joint satisfied the strength safety requirement under bolt preload and working load conditions. When applying an external load on a wear-free flange joint, the maximum stress inside the flange joint increased with increasing external load. Once the external load reached a certain threshold, a stress concentration formed on the T-shaped platform at the auxiliary pipeline junction in the upper flange joint. When applying an external load on a worn flange joint, the critical collapse pressure of the flange joint decreased with increasing depth of the wear.

Real Gas Correction on Gas Dynamics Function Method About Ejector

ZHOU Sanping, GU Ping

2018, 40(5):  170-180.  DOI: 10.11885/j.issn.1674-5086.2017.09.28.01

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The gas dynamic function method proposed by Sokolov is a classical method for designing injectors. However, its assumptions based on ideal gases make it error-prone when it is applied to real gases under high pressures. The gas thermodynamic method was used in this study. The real gas adiabatic indices at isentropic temperatures and isentropic volumes were introduced from the definitions of enthalpy and constant-pressure specific heat. Combined with the energy equations, the theoretical formula of the real gas dynamic function was derived. The basic equations of gas injectors and pneumatic delivery injectors based on real gases were then derived according to the laws of momentum conservation and mass conservation. A comparison with Sokolov's design method showed that, under the low-pressure working condition, the computational results obtained using the revised method based on real gases were consistent with results obtained with Sokolov's design method, indicating that the revised design method covered Sokolov's design method. However, under the high-pressure working condition, the results for these two design methods were significantly different. The real gas correction compensated for the limitations of Sokolov's design method and can be applied to injector design for the entire pressure range.

Response Surface Methodology Optimization of Bacterial Flocculation Treatment for Shale Gas Fracturing Fluids

FENG Xu, CHEN Kejin, GUAN Tongwei, WANG Shuxin, WEN Li

2018, 40(5):  181-188.  DOI: 10.11885/j.issn.1674-5086.2017.11.07.03

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A bacterial strain with flocculation activity, which was screened in our laboratory, was used to examine the effects of duration of fermentation on flocculation. Results showed that when strain H5 (Acinetobacter baumannii strain) was used for fermentation for 36 h, the flocculation was 65.7%. he flocculating bacteria and polyaluminium chloride (PAC) were used to treat shale gas fracturing flowback fluid, and response surface methodology was used for optimization of the treatment process, using COD removal rate as the response variable. According to the distribution of response values, the optimal flocculation conditions were as follows:Addition of 10 mg/L of flocculating bacteria H5, PAC concentration of 30 mg/L, slow stirring speed of 73 r/min, and a sedimentation period of 40 minutes. Under optimal flocculation conditions, the COD removal rate was 85.1% and turbidity removal rate was more than 95.0% when combined treatment was used on shale gas fracturing fluids.