Table of Content

10 October 2020, Volume 42 Issue 5

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GEOLOGY EXPLORATION

Characteristics and Main Controlling Factors of the Middle Permian Qixia Formation Reservoir in Shuangyushi Structure

PENG Xian, PENG Jun, ZHANG Lianjin, LIN Pan, LAN Xuemei

2020, 42(5):  1-12.  DOI: 10.11885/j.issn.1674-5086.2019.04.29.03

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For the characteristics and main controlling factors of dolomite reservoir in Qixia Formation of Shuangyushi structure in northwestern Sichuan Basin, based on field outcrop, core and well logging data, combined thin section analysis, casting thin section, SEM, cathodoluminescence, this paper analyzes the development characteristics and main controlling factors of dolomite reservoirs in this area. The results show that the reservoirs are distributed in the NE-SW direction along the front of the Longmenshan mountain, with a thickness between 10 and 40 m. The reservoirs which develop in the shoal of platform margin facies are mainly crystalline dolomites, followed by a small amount of grain dolomites; The reservoir spaces are dominated by dissolution pores (vugs), followed by a small amount of cracks; The porosity of Qixia Formation reservoirs ranges from 1% to 4%, the permeability ranges from 0.001 mD to 10.000 mD; the reservoir types are mainly fracture-pore (vug) type. The development and distribution of reservoirs are controlled by sedimentary facies, sedimentary paleogeomorphology, diagenesis, and late tectonic fracture. Sedimentation provides the material basis for reservoir development and sedimentary highlands of paleogeomorphology control the distribution of high-energy shoal area; Penecontemporaneous atmospheric water eluviation not only forms a large number of secondary dissolution pores (vugs), but also provides migration pathway for the fluid of dolomitization; The early pores (vugs) are maximally inherited and preserved during the stage of the shallow burial dolomitization; The cracks formed by the late tectonic fracture further connect the pores (vugs) system.

Sedimentary Facies Distribution and Exploration Significance of the Middle Permian Qixia Formation in the Sichuan Basin

BAI Xiaoliang, YANG Yueming, WEN Long, LUO Bing, HONG Haitao

2020, 42(5):  13-24.  DOI: 10.11885/j.issn.1674-5086.2019.03.04.03

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Through analysis of the seismic and logging data, we established standard lithology and Paleozoic stratigraphic profiles, and identified facies markers. Sedimentary facies were divided into the open platform facies, platform margin facies, slope facies, and basin facies. The slope facies and the basin facies were identified in the Pingwu-Maowen-Xiaojin area. A zone of platform margin facies had developed in the Western Sichuan Area. The Western Sichuan-Central Sichuan uplift is a developmental belt of the intra-platform beach subfacies of the open platform facies. The Northern Sichuan-Southern Shu low uplift is the open-sea and intra-platform beach subfacies of the open platform facies. The Eastern-Sichuan area is the intra-platform shallow-swamp subfacies of the open platform facies. Regional stratigraphic correlation and the distribution of sedimentary facies indicate that the pre-Permian sedimentary paleo-geomorphology controlled the sedimentary pattern of the Qixia Formation, while the development of the Caledonian uplift and the Western Sichuan rift Basin jointly controlled the distribution of the platform margin facies of the Qixia Formation in Western Sichuan. The platform margin facies belt of the Qixia Formation developed a facies-controlled dolomite reservoir, which formed a good source-storage match with the lower Cambrian high-quality hydrocarbon source layer. The platform margin facies belt of the Qixia Formation is a key exploration area for deep marine carbonate rocks. The Devonian-Permian has the same source-storage matching relationship, providing geological conditions for the development of large-scale tectonic-lithologic trap gas reservoirs. The large-scale concealed structural highs developed in the lower part of the nappe, which is an important zone favorable for overall exploration and three-dimensional exploration.

Variation Between Platform Margin and Open Platform Reef-shoal Reservoirs of the Lianglitage Formation in the Western Tarim Basin

WEI Huadong, SHI Guipeng, ZHU Xiuxiang, ZHANG Yunfeng, WANG Zhenyu

2020, 42(5):  25-38.  DOI: 10.11885/j.issn.1674-5086.2019.04.23.01

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Based on the characteristics and evolutionary variation of platform margin and intra-platform reef-shoal reservoirs in the Upper Ordovician Lianglitage Formation in the western Tarim Basin, data on rock core, thin slices, logging, and geochemical analysis were used to compare and analyze the differences in the basic characteristics, diagenesis, and pore evolution of the two reservoirs. A reservoir development model and proposed corresponding exploration strategies are established. In terms of the reservoir characteristics, the reservoir space of the platform margin reef-shoal reservoir shows the coexistence of fabricselective and non-fabric-selective characteristics. The reservoir is vertically stacked in multiple layers and is laterally aligned. The reservoir space of the intra-platform reef-shoal is in the form of non-fabric selective fracture-holes, mainly distributes in the middle and lower parts. Its vertical thickness and lateral continuity are lower than those of the platform margin. The evolution and distribution of high-quality reservoirs in the platform margin are controlled by penecontemporaneous meteoric dissolution, early diagenesis near-surface karstification, and burial dissolution, whereas the intra-platform reservoirs are controlled by fractures and burial karstification. In terms of exploration strategies for platform margin reef-shoal reservoirs, priority should be given to the three-stage karst and tectonic rupture superimposed development zone. For intra-platform reservoirs, attention should be paid to the jointly controlled zones of fault and burial dissolution.

The Internal Characteristics of Carboniferous in Ke-Bai Fault Zone in the Northwest Margin of Junggar Basin

QIU Zhengke, LI Ting, YANG Xing, HU Zongfang, HU Geling

2020, 42(5):  39-47.  DOI: 10.11885/j.issn.1674-5086.2019.03.04.02

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In recent years, high-yield oil flow has been produced in exploration wells and evaluation wells drilled in carboniferous system of Ke-Bai fault zone in the northwest margin of Junggar Basin, which shows great exploration potential. The carboniferous thrust of the fault zone is over the Permian, Triassic and Jurassic strata. Under the action of long-term compressive, torsional and rotational stress, the carboniferous inner strata are easy to release stress along the low-density plastic strata, forming anticlines, synclines and faulted anticlines. The work area evolves from imbricate structure to recoil structure from south to north, with imbricate and recoil in the middle and thrust rock mat in the north; explosive tuff is developed in carboniferous system, followed by overflow basalt and andesite. The oil test results show that all kinds of lithology contain oil, and the oil content is mainly related to petrophysical properties and the occurrence degree of fractures. The fracture development position is also the development position of various micro-fractures. The enrichment of oil and gas along deep and large faults and associated secondary faults will be the favorable exploration area for carboniferous system in this area.

3D Geometrical and Kinematic Characteristics of the Boundary Fault in Nanyang Depression

LI Zhi, ZHANG Zhiye, HE Dengfa, LUO Xi, XIONG Jian

2020, 42(5):  48-62.  DOI: 10.11885/j.issn.1674-5086.2019.07.18.01

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Xinye Fault is a boundary fault in the south of Nanyang Depression, Nanxiang Basin. It is very important to study its 3D geometrical and kinematic characteristics in analyzing the formation and evolution of Nanyang Depression. Based on 2/3D seismic, drilling and logging data, guided by normal fault related fold theory and structural restoration theory, the 3D geometrical and kinematic characteristics of Xinye Fault are analyzed in this paper. According to plane strike, combined with dip angle and fault distance changes, Xinye Fault is divided into three segments, i.e. west, central and east. The fault plane, which could be subdivided into 11 subzones by 2 vertical axial planes and 4 transversal axial planes, is a curved surface consisting of several dip domains. Based on the balanced geologic cross-sections, we established that the west and east segments of this fault developed in the late Cretaceous; the central segment formed in the sedimentary period of Dacangfang Formation in the Eocene, then the three segments linked into one fault. The rotation degree of the fault weakens from east to west. The largest reverse degree appears on the east segment, followed by the central segment and the west segment. The seat-type normal fault form developed in the west segment; the central segment is a turning normal fault instead of listric form and listric in the east segment. The differential subsidence along fault strike and the difference of section shape are important controlling factors for the formation and evolution of Nanyang Depression.

An Analysis of Main Controlling Factors of Production for Horizontal Shale Gas Well in Weiyuan Block

CHEN Xue, XU Jianliang, LI Jing, XIAO Jianfeng, ZHONG Sicun

2020, 42(5):  63-74.  DOI: 10.11885/j.issn.1674-5086.2019.07.01.01

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Pilot development in the Weiyuan national shale gas demonstration area in the Sichuan Basin but the test production rates of different wells show a great variety. In view of this, the research focuses on the main factors controlling the high production of horizontal shale gas wells in this area. Using the geological and logging date of coring wells confirm that Long I₁¹ sublayer of Longmaxi Formation is the best development strata. Combining detailed reservoir studies fracturing evaluation of horizontal wells, we establish the relationship between reservoir thickness, optimal target position, the drilling rate of Type I reservoirs and the production of gas wells, and confirm the natural fracture development and its impact on horizontal well productivity.The relationship between the effectiveness of the fracture network and fluid volume, sand volume and pipe rate was calculated. The results indicate:(1) there is a highly positive correlation between the thickness of the Long I₁¹ sublayer and production; (2) distance from the bottom of Long I₁¹ sublayer 0～4 m is the optimal target position; (3) the drilling rate of Type I reservoirs has a direct effect on the high production of gas wells; (4) the natural fracture development are highly relate to single well production; (5) the defines the comprehensive coefficient of fracture network is above 0.8, which can provide effective channel for shale gas flow after fracturing.

The Application of Image Logging in the Identification of Microbialite Facies in Dengying Formation, Sichuan Basin

TIAN Han, ZHANG Jianyong, LI Chang, LI Wenzheng, YAO Qianying

2020, 42(5):  75-85.  DOI: 10.11885/j.issn.1674-5086.2019.04.14.01

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The lithology identification is the basis of study of the sedimentary facies and reservoirs, and it is very important to identify well logging lithofacies for uncored wells. The carbonate of Dengying Formation of Sinian system in Sichuan Basin, has undergone strong digenesis that led to the low discrimination for log response characteristics of different lithofacie, poses great challenge for conventional logs to identify carbonate lithofacies. In order to establish an effective identification method of log facies, on the basis of previous classification, the wells with complete core, thin section and logging data of the fourth Member of Dengying Formation in Gaoshiti-Moxi Area were selected as key wells. We conduct fine description of cores, extract the different typical imaging features of lithofacies, and establish the transformation model of the image logging facies and lithofacies. Finally, we use multi-point geostatistics method to carry out the whole wellbole imaging process. We extract image features, combine the established lithofacies identification model to carry out the lithofacies identification, then apply the method sto other uncored wells in the study area. The results show that the lithofacies identification method based on image logging has a high identification rate, which can provide a strong support for the subsequent studies of sedimentary microfacies and reservoir development mechanism.

OIL AND GAS ENGINEERING

Research and Application of Volume Fracturing Technology Fracture Control in Ning 209 Area

YUE Hong, YANG Zhaozhong, FAN Yu

2020, 42(5):  86-98.  DOI: 10.11885/j.issn.1674-5086.2020.06.17.03

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In order to solve the problems in shale gas development, such as limited fracturing volume, rapid production decline and low reserve production ratio, this paper puts forward volume fracturing technology of fracture control reservoir. By reducing the cluster spacing and increasing the number of fractures, the technology can increase the fracture control area, form a continuous control area, develop the reservoir three dimensionally, and greatly improve the primary recoverable reserves. Optimize the process design of the technology, optimize the perforation location by fine segmentation, optimize the number of perforations by perforation throttling, optimize the cluster spacing by seepage and stress interference, optimize the nanometer fracturing fluid by gas water replacement and increasing the amount of sand, optimize the proppant by effective pressure, and optimize the amount of temporary plugging agent by experimental regression. The optimization results are 6 clusters, 1 cluster of 6 holes×60°×6 holes/foot, cluster spacing of 6～8 m, and segment length of 40～50 m; using nanometer fracturing fluid system, nanometer slippery water polishing, nanometer linear glue continuous injected sand, the added sand strength is greater than 3.0 t/m; a combination of 70/140 mesh quartz sand +40/70 mesh ceramsite (3:7) with a small particle size used; the proportion of quartz sand is appropriately increased. This technology has been applied in Well 209X-x of Changning area, and the gas production converted to 1 500 m horizontal section is 26.6×10⁴ m³/d, which is 103% higher than adjacent wells. This technology has obvious stimulation effect and can provide reference for shale gas well efficient development.

The Gas from Deflagration Fracture to Crack the Cement Test Sample Experiment

SUN Lin, HUANG Bo, YI Fei, ZHANG Jie

2020, 42(5):  99-106.  DOI: 10.11885/j.issn.1674-5086.2019.11.07.01

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In order to get better rock breaking effect, plugging removal effect and fracture forms, cement sample fracture experiment has been done, 9 cement samples by using ϕ244.5 mm casing with reserved perforation holes and ϕ1 600×1 000 mm external diameter. The ground experiment has taken common aerospace composite solid propellant and military dual-base powder. On the basis of experiments, a comparison between intra-layer explosion technology and repeated strong electric shock wave technology. The result shows that the gas from deflagration fracture can make fractures to all 9 samples with 2～4 fractures in centimeter level, and upper fracture width is more than middle part. The peak pressure, the number of fracture decrease and fracture width decreases by less powder. Its fracture mechanism and forms are different from these two above.

Mechanism Analysis of the Production Performance of Multi-stage Fractured Horizontal Well in Tight Gas Reservoir

ZHANG Boning, ZHANG Ruihan, WU Tingting, LU Youchang

2020, 42(5):  107-117.  DOI: 10.11885/j.issn.1674-5086.2020.04.10.01

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In order to accurately predict the production performance of multi-stage fractured horizontal wells in tight gas reservoirs under the nonlinear flow mechanisms and complex fracture distribution characteristics, the dual continuum discrete fracture coupling model is used to describe the flow characteristics of original tight reservoirs and hydraulic fractures, and a comprehensive flow mathematical model is constructed. The unstructured 3D tetrahedron mesh and control volume finite element method are used to establish the fully implicit numerical model, and the modified Peaceman method is used to establish the numerical well model of complex fractured horizontal wells, so as to obtain accurate numerical solutions. The influences of some key parameters such as water saturation, stress sensitive coefficient, opening degree and spatial asymmetric distribution of hydraulic fractures on the production performance of fractured horizontal wells in one block of X tight gas reservoir are analyzed. The results show that the simulation method in this paper can accurately predict the production performance of multi-stage fractured horizontal wells in tight gas reservoir, and provide theoretical support and calculation tools for efficient development of tight gas reservoir.

Numerical Simulation of Water Distribution of Bio-reef Gas Reservoir

YANG Lijuan, ZHANG Mingdi, WANG Bencheng, WEN Shanzhi, LIU Yuanyang

2020, 42(5):  118-126.  DOI: 10.11885/j.issn.1674-5086.2020.02.26.01

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The distribution of gas and water is usually very complicated in water-bearing bio-reef gas reservoir with strong heterogeneity. The correct understanding of gas and water distribution is the key to forecasting water production and plan adjustment in development of gas reservoir. There are some limitations for the existing methods of logging interpretation and seismic interpretation to stratigraphic water distribution. Numerical simulation, a technique that can fully combine geological static knowledge and production dynamic data, provides an important means for studying formation water distribution. Firstly, to analyze and quantify the active parameters of water intrusion, and study water intrusion mechanism based on three-dimensional model of gas reservoir considering reservoir heterogeneity, analyze the sensitivity of gas well production index to various parameters. Then identify the most possible situation of formation water state based on geological knowledge and production dynamic data. At the same time, describe the formation water distribution in detail by J function. Finally, a fine numerical simulation model that is more consistent with the actual gas reservoir is obtained. The research in this article has deepened the understanding of the formation water distribution of the Changxing complex reef gas reservoir in Yuanba. The research idea is also applicable to other types of water gas reservoirs with different degree of heterogeneity.

Influence of EBIP Thickness Variation Modes on SAGD Production Characteristics in Super Heavy Oil Reservoirs

DUAN Yonggang, WU Zijian, WEI Mingqiang, REN Keyi, LU Chuan

2020, 42(5):  127-134.  DOI: 10.11885/j.issn.1674-5086.2020.06.15.02

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Steam assisted gravity drainage (SAGD) is a promising heavy oil development method, which has achieved good results in super heavy oil/oil sand development. Due to reservoir sedimentation, the effective reservoir thickness (EBIP) along the SAGD horizontal well section will change, which makes the development effect of SAGD well group significantly different. In order to make clear the influence of EBIP changing along horizontal well section to SAGD production, based on the geological characteristics of Long Lake oilfield in Canada, 3 typical EBIP thickness change modes are constructed. Subsequently, the SAGD numerical simulation mechanism model is established, and SAGD steam chamber breakthrough, daily oil production, cumulative gasoline ratio and recovery degree influenced by the EBIP change modes and thickness difference are analyzed and discussed. Finally, limits of on SAGD production which are influenced by the EBIP thickness are built. The results show that under the same total thickness of reservoir, the peak oil production speed and recovery degree of stepped EBIP change mode are the lowest, and the production characteristics of the other two modes are similar. Under stepped EBIP mode, the thickness difference 6 4 m is excellent, the thickness difference of 4～10 m is good, and the thickness difference >10 m is poor. Under two thick-one thin and two thin-one thick EBIP mode, the thickness difference <7 m is excellent, and the thickness difference >7 m has a great impact on SAGD production.

A Study on Calculation Model of Stress Field Around Wells Considering Rock Elastic-plastic Deformation

LI Xiaogang, LI Yunyun, HU Qiuping, ZHANG Xiang, YI Liangping

2020, 42(5):  135-144.  DOI: 10.11885/j.issn.1674-5086.2019.06.14.01

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Aiming at the elastic-plastic characteristics of coal, shale and other rocks, a calculation method for stress field of elastic-plastic formation is established, which divide the formation into the plastic softening, the plastic hardening and the elastic zone along the radial direction. In this new model the nonlinear hardening and softening deformation of rock and the percolation effect of the working fluid are considered. The analysis shows that the plastic zone range is positively correlated with the borehole fluid pressure, Poisson's ratio and the initial pore fluid pressure, and is inversely related to the strength of the rock. Compared with the elastic state, the plastic deformation of rock decreases the stress concentration effect, and the plastic deformation of the rock has a little influence on the radial stress of the formation while it can increase the circumferential stress of the formation.

Small Scale Factory Drilling Technology Optimization in Complex Fault Block of Desert Oilfield in Niger

ZHANG Haijun, ZHANG Nan, LIU Junbiao, QIAN Feng, KONG Xiangji

2020, 42(5):  145-152.  DOI: 10.11885/j.issn.1674-5086.2020.01.13.02

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The Agadem Oilfield of Niger is located in the Sahara desert area, and the bad natural environment, and drilling rig moving and material transportation difficulties lead to low drilling efficiency and high daily operation cost drilling investment. Based on the analysis of the reservoir new well plan characteristics, we put forward the application of small-scale factory drilling to reduce the well site construction cost, improve the efficiency of the drilling rig moving, so as to improve drilling efficiency and material utilization, achieve the purpose of reducing drilling cost through rig moving process optimization, cluster well site location optimization, well slot and borehole trajectory optimization, casing program optimization, drilling fluid system optimization and reutilization, PDC + motor one trip drilling and cementing quality security technology research. Actual construction application proves that small-scale factory drilling and matching technology apply successfully in the field with remarkable effect.

Pressure Relief Control Model of Rupture Disk for Annular Pressure Build-up in Deep-water Wells

SHI Yufan, TANG Yijia, MA Tianshou, HE Yufa

2020, 42(5):  153-160.  DOI: 10.11885/j.issn.1674-5086.2019.09.06.01

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Annular Pressure Build-up (APB) is caused by the thermal expansion for the sealed annulus, Heated by the high temperature fluid extracted from the bottom of the well. In order to ensure the safety of the wellbore, considering the development practice in the deep-water, the multi-annulus APB prediction model is proposed based on the semi-steady heat transfer method and coupled pressure and volume annular pressure calculation method. According to the working principle of the rupture disk, the threshold valve determination methods from inside to the outside and from the outside to the inside are established. Taking a Western African well as an example, the wellbore temperature and annulus pressure during production were predicted. Casing strength verification results show that the surface casing and technical casing have the risk of bursting during normal production. When the annular pressure relieved or the production casing annulus evacuated, the production casing is at risk of collapse. After adopting the rupture disk technology, all the casings meet the requirements of verification. Therefore, the rupture disk can effectively protect casing and is significant to safe exploitation of deep-water oil gas resources.

PETROLEUM MACHINERY AND OILFIELD CHEMISTRY

Design and Experiment of a New Type of High Frequency Electric Dehydration Device

LU Dayan, ZOU Wanqin, LIANG Haibo, YANG Hai

2020, 42(5):  161-169.  DOI: 10.11885/j.issn.1674-5086.2019.10.15.04

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With the continuous growth of China's economy and the increasing demand for energy, oil supply has become a strategic issue affecting the country's economic development. The amount of offshore oil exploitation is also increasing. However, the crude oil produced by offshore platforms generally has a high water content, and even some crude oils can have a water content of more than 70%. It needs to be dewatered before being transported and refining. Aiming to solve the problems of limited dehydration treatment capacity and low dehydration efficiency of crude oil on offshore platforms, we make a study on the mechanism of high-frequency and high-voltage electric fields on oil and water. Using electric field simulation and experimental research methods, a novel non-uniform electric field model and high-frequency electro-dehydration dynamic experiment device is proposed that adopts a new-type different-diameter cylindrical electrode to construct an uneven electric field. At the same time, a dynamic experiment device is used to circulate the electric dehydration process of crude oil to realize the electric dehydration treatment of high water-containing crude oil. Experiments show that the electric dehydration efficiency of this dynamic electric dehydration device is higher than that of the device used currently with 0.7% water cut in the oil.

An Experimental Study on Vibration Characteristics of Horizontal Well Completion String

HUANG Liang, WANG Guorong, XU Jing, WEI Anchao, JIA Duping

2020, 42(5):  170-178.  DOI: 10.11885/j.issn.1674-5086.2019.10.16.03

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In order to explore the vibration response mechanism of the completion string under the action of gas, the horizontal well completion string vibration test was carried out under the open well condition. PE pipe was used to simulate completion string, transparent acrylic pipe was used to simulate completion casing, and Froude similarity criterion was used for dimension scaling. The horizontal and vertical vibration responses of completion string is tested based on strain gauge test technology, and the strain, displacement response and vibration modes of the string were analyzed by modal analysis method. Through the finite element software analysis of the natural frequency of the string and the comparison with the experimental vibration frequency, it is found that the vibration frequency of the string is close to the third-order natural frequency and resonance occurs. The response stress, displacement and vibration of the test string system are large in the bending section. The vibration frequency of the string in the horizontal direction and the vertical direction is consistent with the mode.

An Experimental Study on Viscosity Reduction of Water-cut Heavy Oil Under the Synergistic Action of Nano Catalyst and Microwave

LI Hanyong, GAO Hang, QIN Shouqiang, WANG Yecong

2020, 42(5):  179-186.  DOI: 10.11885/j.issn.1674-5086.2019.07.12.01

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Heavy oil has the characteristic of high viscosity, and with the increase of water cut, the viscosity of water-in-oil emulsion will increase further. To reduce the viscosity and improve its transportation capacity, the method of viscosity reduction by synergistic action of nano-catalyst and microwave is proposed. The response surface method is selected as the experimental design method and the influence factors include microwave heat power, temperature and nano-catalyst concentration. The viscosity-temperature curves under different experimental conditions are measured to calculate the viscosity reduction rate, to obtain the optimal viscosity reduction treatment method under different water cuts. The interaction between three factors and the influence of the change of water cut on the synergistic action on viscosity are explored. The experimental result shows that at the same water cut, the viscosity reduction rate increases with the increase of catalyst concentration, and increases first and then decreases with the increase of microwave power, and the variation of viscosity reduction rate with temperature is related to the water cut. In order to achieve the optimal viscosity reduction effect of different water cut, the required catalyst concentration increases first and then decreases. The required microwave power is similar, but the temperature is different. It shows that the viscosity reduction effect of water-in-oil emulsion with high water cut is better, which can provide theoretical basis for heavy oil viscosity reduction technology.