Table of Content

10 April 2021, Volume 43 Issue 2

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GEOLOGY EXPLORATION

Characteristic and Developmental Controlled Factors of Pre-salt Lacustrine Carbonate, Santos Basin

JIA Huaicun, KANG Hongquan, LIANG Jianshe, CHENG Tao, ZHANG Shixin

2021, 43(2):  1-9.  DOI: 10.11885/j.issn.1674-5086.2019.07.18.02

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The lacustrine carbonate of pre-salt in Santos Basin is rich in oil and gas resources, a hotspots of exploration in the world. Based on analysis of cores, thin sections from 41 wells, we determine two types of carbonate developed including microbial reef strobitolites limestone and bioclastic bank coquinas. The lacustrine carbonate is porous limestone reservoir, medium porosity and permeability. The main pore type is primary pore, which had undergone reconstruction from later dissolution. Analysis of C-O isotope data and Ostracoda materials leads to the conclusion that three main elements, paleo-salinity of water, paleo-structure, sedimentary facies, are the main control factors lacustrine carbonate reservoir development. Genesis types of carbonate reservoir is controlled by paleo-salinity of water. Distribution of reservoir is controlled by paleo-structure. And physical property of reservoir is controlled by sedimentary facies. Eastern uplift zone and lower horsts of central depression zone is the favorable area to develop lacustrine carbonate reservoir, helpful to direct exploration deployment.

Characteristics and Controlling Factors of Tight Sandstone Reservoirs in Bagung Formation in North Qiangtang Depression

CHENG Leli, BAI Linkun, WEI Shaoxiao, XIONG Ting, YIN Senlin

2021, 43(2):  10-22.  DOI: 10.11885/j.issn.1674-5086.2019.08.28.02

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The Upper Triassic Bagung Formation clastic rocks in the North Qiangtang Depression are the key strata of reservoirs in the Qiangtang Basin. The study shows that the overall compositional maturity and structural maturity of the sandstone in the Bagung Formation are medium and low, the dissolution pores are the main reservoir space, and the pore structure is characteristic of small pore throat radius, poor sorting and poor connectivity. Dissolved pore space is the main pore type, and the pore structure shows poor sorting, fine roaring channel and poor connectivity. Sedimentary factors are the main factors controlling the quality of the reservoir. The sands formed in the microphase of the diversion channel are formed with strong hydrodynamic force and transported far away, and their thickness is larger and the primary pores are more developed, and the acidic dissolution is more developed in the later stage because of the strong compaction resistance and more intergranular pores are retained. The chlorite lining inhibits the formation of intergranular siliceous cement, the fracture development improves the reservoir properties, and the unique acidic medium environment of the coal system also promotes the formation of secondary pores.

Fine Characterization of Reef Limestone Reservoirs in Pearl River Mouth Basin, South China Sea

XIE Ribin, LI Haitao, YANG Yong, LIU Yuanzhi, QU Changwei

2021, 43(2):  23-35.  DOI: 10.11885/j.issn.1674-5086.2019.12.18.01

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The reef limestone reservoir of L Oilfield is characterized by strong heterogeneity with the development of fractures and dissolution pores, which brought out big challenge for reservoir evaluation and production. Logging while drilling (LWD) image logging can provide resistivity images with high resolution, which can give decision-makers an in-depth understanding on the sedimentary and structural characteristics of reservoirs. The high-resolution resistivity image is utilized for the first time to identify reef limestone category, evaluate fracture, analyze secondary dissolution porosity and investigate productivity controlling factors. The results show that rock types of reef limestone can be distinguished accurately by high-resolution resistivity image data. Moreover, fracture types and characteristics can be evaluated precisely by LWD image. Furthermore, qualitive and quantitative analysis of dissolution pores are carried out based on LWD image logging. In addition, the main control factors of reef limestone reservoir productivity are discussed based on all the interpretation results. All related evaluation results are consistent with the operation output of oilfield production and water control technology. The comprehensive analysis of highresolution resistivity imaging not only achieve the objective of fine characterization of reef limestone reservoir, but also provide a strong reference for the design of reef limestone reservoir completion plan and give decision-makers a specific interpretation model for similar oil/gas field.

Accumulation Model of the Secondary Oil Reservoir in Southern Slope, Weixi'nan Sag and the Implications for Future Exploration

LI Anqi, YE Qi, HU Desheng, GAI Yonghao, XU Xuefeng

2021, 43(2):  36-45.  DOI: 10.11885/j.issn.1674-5086.2019.08.14.03

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In order to reveal the oil and gas accumulation rule and accumulation model of the secondary reservoir in the southern slope of Weixi'nan Sag, the study of oil-source correlation, oil reservoir characteristics, tectonic evolution, the accumulation model of secondary oil reservoirs were analyzed. The results show that before late Miocene the structure shape of southern slope was high in west and low in east, and primary hydrocarbon accumulation was formed in the western anticline trap. The "bottom calcium layer" formed by the hydration of clastic rocks and the decarboxylation of organic matter near the oil-water interface was an effective indicator to determine the oil-bearing range of paleo-reservoirs. Dongsha movement in late Miocene destroyed paleo-reservoir in the western anticline trap and leaded to the redistribution of oil and gas, and formed secondary oil reservoirs in the eastern reversal anticlines. The main exploration objects of the southern slope should be the low-rising anticlines in the eastern part.

An Analysis of Shallow Oil and Gas Sources and Exploration Enlightenment in Xiaermen Area of Biyang Depression

JIN Yunyun, SHI Zhengyong, REN Xiaoyu

2021, 43(2):  46-53.  DOI: 10.11885/j.issn.1674-5086.2019.06.25.01

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In order to find out the source of shallow oil and gas and the genesis of natural gas in Xiaermen Area of Biyang Depression, a comprehensive geochemical profile of source rock evaluation in Xiaermen Area is established by using various organic geochemical evaluation methods, and the relationship between oil and gas sources is analyzed. The composition and stable carbon isotope of natural gas are analyzed. The results show that the source rocks of Hetaoyuan Formation in Xiaermen Area are rich in organic matter, mainly of type I-Ⅱ₁, with a maturity threshold of about 2 200 m, the shallow source rock is dominated by low maturity, H₃ is in the mature stage; the shallow low maturity crude oil is dominated by the hydrocarbon generated by the upper H₃ source rock moving upward along the fault, and the mixed source oil formed by the infection of the shallow low maturity source rock; the natural gas is the bio-thermal catalytic transition zone gas. To clarify the source of oil and gas is conducive to guiding the next exploration and deployment in Xiaermen Area.

Organic Geochemical Characteristics and Oil Source Comparison of Bitumen from Huanglong Formation of Huaying in Eastern Sichuan Basin

HE Lei, YANG Ping, XIE Yuan, WANG Zhengjiang, LIU Jiahong

2021, 43(2):  54-64.  DOI: 10.11885/j.issn.1674-5086.2019.09.27.01

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The void of the dolomite of Huanglong Formation in section of Xikou town of Huaying are filled with a large amount of bitumen, in the field, samples of asphalt and source rocks of different strata were collected in the study area and adjacent areas to explore the organic geochemical characteristics and sources of bitumen.The results show that the content of organic carbon in the bitumen-bearing dolomite of Huanglong Formation is high, the value of R_o is 1.45% to 1.48%, the value of carbon isotope is -28.90‰, the content of saturated hydrocarbon and aromatic hydrocarbon are low, mainly non-hydrocarbon; the main peak carbon of paraffins is C₂₀, the value of Pr/Ph ratios from 0.78 to 0.79, the content of tricyclic terpanes C₂₃ > C₂₄ > C₂₁, the ratio of tricyclic terpanes to pentacyclic terpanes are from 0.82 to 1.06, in Sterane, the content of C₂₇ > C₂₉ > C₂₈, C₂₇ gonane is dominant, these parameters indicate that the sedimentary environment is reductive. The value of terpane parameters and Ts/(Tm+Ts) all indicate high maturity of bitumen. The value of DBT/P is from 1.48 to 1.88, indicating that the parent rock may be Marine marl deposit. According to the comprehensive comparison of biomarkers and bituminous isotopes, it is considered that the solid bitumen of Huanglong Formation comes from the earlier mature shale of Longmaxi Formation, the extraction of chloroform bitumen "A" has the characteristics of mixed source, which may contribute to the shale of Longmaxi Formation.

A Dynamic Matching Feature Wavelet Picking Seismic Event Technology

PENG Renyan, XU Zhenwang, LIU Wenfeng, YU Feng, DONG Xuguang

2021, 43(2):  65-74.  DOI: 10.11885/j.issn.1674-5086.2019.06.12.04

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Traditional seismic data interpretation or velocity analysis usually depends on manual identification and picking up, which not only has heavy workload, but also has very low efficiency. Therefore, the industry began to use a variety of algorithms are used in production to automatically identify and pick up seismic events, but these algorithms have many defects and low accuracy. Seismic profiles can be regarded as the convolution of seismic wavelet and reflection coefficient. The existence of wavelet and noise makes it difficult to pick up profiles automatically. Through feature extraction of seismic wavelet and sparse expression of seismic profiles, the influence of wavelet and noise on automatic pickup is reduced, and the number of data sampling points is reduced to improve the calculation efficiency. By introducing vector distance and combining with dynamic waveform matching algorithm to calculate the minimum distance of characteristic vector data, the automatic tracking of events. The validity and anti-noise ability of the method proved by the test of theoretical data and the validity of the method in this paper have been proved by the automatic pickup of the actual data in an eastern exploration area.

Application of Azimuth Anisotropic Fracture Detection Technology in Niudong Buried Hill Zone

WANG Pan, ZHANG Menglin, WANG Xin, ZHAO Zhipeng, LIU Xing

2021, 43(2):  75-83.  DOI: 10.11885/j.issn.1674-5086.2019.03.18.01

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The carbonate reservoir in the Niudong buried hill are mainly fracture-cave reservoirs, with strong heterogeneity and rapid lateral change. The prediction accuracy of cracks by conventional seismic attribute analysis methods is low due to the obvious attenuation of amplitude, frequency and velocity affected by the cracks. As a result, fracture prediction of azimuthal anisotropy is carried out in this area as the accurate identification of fracture reservoirs is the key to the hydrocarbon exploration. The results of imaging logging show that steep fractures are mainly developed in the study area, which has the characteristics of HTI medium. The azimuth angle dataset is obtained by determining the offset range and dividing the four azimuth ranges, which based on the forward modeling carrying out on the longitudinal wave reflection coefficient formula. The main direction of the fracture in the study area is determined to be NE by outlining the fracture development zone combined with the orientation and density of the features, which are calculated by azimuth seismic attributes of longitudinal wave extracted by the data volume. It is proved that AVAz technology has a good practical application value for reservoir prediction of high and steep fractures in carbonate reservoir by the use of imaging logging data in actual drilling, which verified the prediction results, and obtained a good match.

Three-dimensional Prediction of In-situ Stress in Oil and Gas Field Based on Intelligence Algorithms

YUAN Duo, WU Chao, LU Yunhu, ZHANG Dongqing

2021, 43(2):  84-92.  DOI: 10.11885/j.issn.1674-5086.2019.03.27.03

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Complex sedimentary and tectonic environment results in the difficulty of predicting in-situ stress quantitatively. Two new three-dimensional in-situ stress prediction methods for different working conditions based on intelligence algorithm are proposed using the relationships between interval velocity, in-situ stress and post stack seismic information. With abundant well logging and test data, in-situ stress is predicted by the rock physics and mechanics method based on spatial velocity information obtained using BP neural network algorithm. With sparse well points and a small number of data, simulated annealing algorithm is utilized to directly search for the stress solution vector with the best match of synthetic and actual seismic records. These methods have been applied in an oilfield in eastern China and achieves high accuracy and resolution prediction results, which proves the feasibility of these methods.

OIL AND GAS ENGINEERING

Determination of Gas-water Relative Permeability in Dongping Bedrock Gas Reservoir

LUO Pei, YANG Yun, CHAI Xiaoying, YANG Huijie, WANG Jiong

2021, 43(2):  93-100.  DOI: 10.11885/j.issn.1674-5086.2020.03.07.01

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The lithology of the bedrock reservoirs in Dongping is different and heterogeneous. The rock is loose and complete core cannot be drilled in zones where pores and fractures are well developed, while the tight zone is almost impervious. So, the relative permeability curve cannot be obtained through displacement experiment. It has become a difficult problem for gas reservoir dynamic analysis and prediction. In order to solve this problem, a calculation method of water saturation of formation at different development time is established based on the principle of water drive gas reservoir material balance. This will improve the accuracy of water saturation by avoiding the uncertain factors in the calculation method of water influx. Based on the fractal dimension of the pore structure and the historical fitting of the water-gas ratio data, the gas-water relative permeability calculation method is established. The fractal dimension limit of pore structure is determined by classifying capillary pressure curve of this gas reservoir, the fractal dimension of reservoir pore structure was determined by historical water-gas ratio data fitting method, and the relative permeability curve of gas and water is calculated. This method can effectively overcome the difficulty in determining the fractal dimension due to the diversity of capillary pressure curves, and the obtained relative permeability curves can better represent the overall seepage characteristics of heterogeneous gas reservoirs. This method not only provides an effective way for gas reservoirs that cannot obtain relative permeability curve through core displacement, but also has reference significance for other bedrock gas reservoirs and seriously heterogeneous gas reservoirs.

Technical Policy Study of Single Well N₂ Injection for EOR in Complex Fracture-cavity Carbonate Reservoirs

Lü Xinrui, Lü Tie, XIAO Fengying, ZHANG Hui, ZHANG Yun

2021, 43(2):  101-109.  DOI: 10.11885/j.issn.1674-5086.2020.04.13.01

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Fractured-cavity carbonate reservoirs in Tahe Oilfield have complex geological conditions and strong heterogeneity. The oilfield test of single well inject N₂ for EOR has been successful, but the effect are quite different between wells due to the difference of each well and the injection and production parameters need further optimized action. In this paper, we propose specific reproduce N₂ injection technology policy for each well in this kind reservoir. Takeing Well TA1 as an example, based on reservoir identification and prediction, we build reservoir development pattern, reproduce reservoir development process and characterize the distribution characteristics of remaind oil; based on the actual reservoir model, we optimize the injection timing, gas injection mode and inject-production parameters. The results show that there are more than 50 000 t of remaining oil in the top cave of Well TA1. N₂ injection can form a secondary gas cap, which can better utilize the attic oil on the top of cave and further improve the recovery degree of the reservoir. We determined the optimal parameters based on the model that the best, injection time is when the water cut is 93%, and best injection mode is gas water mixed injection, cycle gas injection volume is 600 000 m³, gas injection speed is 150 000 m³/d, well soak time is 10 d, and liquid production intensity is 40 m³/d. This technical policy provides important basis for the preparation and implementation of gas injection scheme. After implementation of the plan, the effect of increasing oil is remarkable.It has been applied to other injection wells with different karst background and achieved good results.

A Study on Optimized Method of Gas Injection Volume of the Oxygen-reduced Air Flooding in Deep Heavy Oil Reservior

GUO Xiaozhe, CAO Yufeng, TIAN Kai

2021, 43(2):  110-116.  DOI: 10.11885/j.issn.1674-5086.2020.01.15.01

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Lukeqin Oilfield adopts general gas injection in oxygen-reduced air flooding. There is no established method for optimizing gas injection, which results in great differences in oil production increase effects between different types of single wells. The pore volume multiples of gas injection in the dominant channel are determined through physical model experiments; numerical simulation experiments are carried out to propose the concepts of the gas injection/inlet coefficient α and β in the dominant channel, which are combined with the volume of the dominant channel to optimize the throughput. By simulating the oil exchange rate during the throughput of different gas injection volumes to verify the optimization results, an optimization calculation formula with theoretical guidance for the actual gas injection volume in the field is obtained. The experiments show that the optimal gas injection pore volume multiple is 0.20 PV, and the gas injection coefficient α of the dominant channel is 0.8, indicating that 80% of the gas enters the dominant channel, and the gas inlet coefficient of the dominant channel is 0.348, indicating that 1/3 of the well spacing to the production well is the distance the affected area covers. After the calculation of the gas injection volume optimization formula and the verification of the digital model, we conclude that the optimal gas injection volume of 4.5×10⁵ m³ is adequate. The optimization method combines the oil increasing mechanism of oxygen-reduced air throughput with the actual demand in the field, and has certain theoretical significance and field application value for the related design of oxygen-reduced oxygen throughput.

Strategy and Practice of High Efficient Water Injection in Deep Sea Turbidite Sandstone Oilfield

YUAN Zhiwang, YANG Li, YANG Baoquan, ZHANG Yingchun, CHEN Xiao

2021, 43(2):  117-127.  DOI: 10.11885/j.issn.1674-5086.2020.03.03.01

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The reservoir characteristics of turbidite channel and lobe in AKPO Oilfield, a deep-sea turbidite sandstone oilfield in the Niger Delta Basin, are analyzed. It also evaluates its dynamic production behavior based on the connectivity of sand bodies between injectors and producers to determine the water injection strategy during the zero water-cut production period. Based on time-lapse seismic imaging, after-breakthrough water control and plugging strategies are established from the flooding characteristics of different reservoir types. Thus, efficient water-flooding strategies at different production stages are constructed. In the zero water-cut production stage, the optimized water injection strategy focusing on controlling pressure is applied based on the connectivity of sand bodies between injector and producers. In the low and medium water-cut production stage, the water injection scheme focuses on increasing sweep efficiency based on sedimentation type. Therefore, hydro-dynamic method is implemented to improve the water-flooding sweep coefficient. Periodic injection scheme is applied for injector-producer well groups in the channel reservoir to increase the vertical sweep coefficient and the areal sweep coefficient for injector-producer well groups in the lobe reservoir is enhanced by changing the fluid flowing direction. In the high water cut production stage, "low-cost" sectional water control and plugging technique suitable for deep sea oilfield is applied to achieve economic and effective production development. Through the practice in the AKPO Oilfield, high efficient water injection strategy has achieved in the deep-sea turbidite sandstone oilfield. The stable production has continued for 7 consecutive years with a peak oil recovery rate at 5.5% and ultimate oil recovery rate at 53%. This water injection optimization strategy has worked well in the AKPO Oilfield and can be implemented to similar deep sea oil fields, which is convenient, economic and effective.

Analysis of Collapse Matrix and Weak Plane of Bedding Strata

LIU Hailong, XIE Tao, ZHANG Lei, CAO Wenke, GAO Jiajia

2021, 43(2):  128-137.  DOI: 10.11885/j.issn.1674-5086.2019.12.05.02

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There are a lot of hard brittle shale in deep strata of Bohai Bay, which is prone to cause wellbore instability. Taking hard and brittle shale as a kind of transversely isotropic medium, the stress calculation model of well circumference matrix and bedding plane is established. On the basis, influence of elastic anisotropy parameter, wellbore anisotropy and bedding formation on wellbore collapse is obtained. The results show that anisotropy has a significant effect on the stress distribution of the weak surface. The maximum error is about 31% compared with the isotropic model. With the increase of elastic modulus anisotropy, the risk of wellbore collapse increases. The direction of wellbore collapse is not only affected by the horizontal stress orientation, but also by the inclination and squint angle of weak bedding surface and well trajectory when drilling in a vertical well. With the increase of inclination and squint angle of weak bedding plane, the collapse shapes of the wellbore are as follows:matrix collapse only along the minimum horizontal stress direction, single diagonal collapse of bedding plane and double diagonal collapse of bedding plane. The collapse orientation of the matrix corresponds to the minimum in-situ orientation, and the collapse orientation of the bedding plane is consistent with the dip direction azimuth. The optimum drilling azimuth should be combined with the squint angle of bedding plane. When matrix failure and weak surface failure occur simultaneously, the collapse risk increases with the increase of well inclination. The collapse is the most serious along well deviation 30°~75°, near the maximum in-situ stress azimuth when drilling in a directional well. An example of a deep well in Bozhong structure is analyzed. The analysis results of wall collapse pressure are in good agreement with the actual situation. The research results have certain guiding significance for drilling operation in bedding strata.

Advances in the Interface Detection of Gas-liquid Two-phase Pipe-flow Research

JIANG Junze, YONG Qiwei, QIAN Haibing, JIANG Xinsheng, HUANG Yanqi

2021, 43(2):  138-148.  DOI: 10.11885/j.issn.1674-5086.2020.03.05.02

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The accuracy detection of the interface is not only the basis of the mechanics analysis, but also a powerful measure for the investigation of two-phase flow. Gas-liquid occurs widely in the energy, power, chemical engineering, petroleum and aviation, and there is an obvious topological and transient interface which is difficult to be detected accurately. The paper has summarized the interface detection technology and numerical simulation method.The decetion technology includes capacitance, conductivity, optical, ray, heat acoustic, nuclear magnetic resonance; the WMS, PT and PIV technologies are developed in recent years which enhance the precision of the interface detection; the numerical simulation includes PIC, MAC, ALE, VOF, Level Set, and so on. The methods are compared and analyzed with the advantages and boundedness, and some strategy and tendency are proposed, which may provide some references for the two-phase flow investigation.

Study on Generalized Optimization Model of Star-tree Oil & Gas Pipeline Network Layout

ZHOU Jun, ZHOU Liuling, LIANG Guangchuan, CHEN Chuan, ZHOU Xuan

2021, 43(2):  149-157.  DOI: 10.11885/j.issn.1674-5086.2020.03.04.02

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Oil & gas pipeline network has a complicated structure and large investment, which is an important part of oil & gas field construction. Therefore, optimizing the gathering and transportation pipeline network is very important for the oil & gas field to reduce the development cost. The star-tree type pipe network is widely used in the gathering and transportation system. Star-tree pipe network is widely used in gathering and transporting system. In view of the optimal layout of the star-tree pipe network, this paper carries out a study on the mathematical optimization models of the star-tree pipe network layout, and mainly focuses on the star-tree that has restrictions on the processing capacity and gathering radius of the gathering station in the pipeline network. Q model, R model and QR model of mixed integer linear programming with a large number of discrete variables have been established. Taking a real gas field and an oilfield as examples, we adopted the branch and bound method to solve the above model as a whole, and obtained the optimal topology structure, the location of the station facilities, and the location of the central processing facility under each scheme. At the same time, the pipeline network investment also can be able to obtain, thus proving the correctness and reliability of the models, which can guide the engineering construction of oil-gas fields. We further solved the QR model with a hierarchical optimization strategy, and compared the investment of hierarchical optimized pipe network and overall optimized pipe network. It is proved that the overall investment to solving the star-tree pipe network model is lower, which can guide the oil and gas field engineering construction.

PETROLEUM MACHINERY AND OILFIELD CHEMISTRY

Safety Assessment and Management Strategy of Whole Life of Coiled Tubing

ZHONG Hong, HE Sha, LIU Shaohu

2021, 43(2):  158-166.  DOI: 10.11885/j.issn.1674-5086.2020.06.03.02

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Coiled Tubing (CT) is the "neural line" of the "universal working machine". The safe operation of CT is related to the entire construction process. The service life of CT is one of the important indicators of the safe operation. At present, there is little study on the safety assessment of the whole life of CT operation. Survival analysis was used to study 6 influencing factors of CT and 20 component variables. The Kaplan-Meier analysis method was used to describe the single-factor survival time of CT fatigue life, and the Cox proportional hazard model was used to perform multi-factor analysis in combination with the effective time of CT service. The comparison between the cumulative fatigue results and the Cox proportional hazard model calculation results shows that the model is feasible. The research results show that collinearity test and PH hypothesis are feasible for 399 samples survival analysis; among the classification variables:OD, wall thickness, corrosion, and welding have significant effects on the risk of CT; the risk rate of large-diameter CT (diameter>50.80 mm) is 1.484 times that of smalldiameter CT (diameter<50.80mm); the corrosion risk rate of H₂S environment is 2.509 times that of no corrosion risk rate; The risk rate of straight welds is 5.595 times that of no welds; the conclusions of the study are consistent with the statistical results of field CT failure. The four-level evaluation criteria proposed based on the cumulative survival rate and field failure statistical results have guiding significance for the safe operation of the CT in drilling, completion and gas lift.

Experimental and Numerical Simulation Research on Eccentric Flow Channel Erosion of Drilling Robot

XIAO Xiaohua, DAI Jiliang, ZHU Haiyan, ZHAO Jianguo

2021, 43(2):  167-177.  DOI: 10.11885/j.issn.1674-5086.2020.11.02.01

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In order to solve the problem of coiled tubing buckling drilling in extending reach in horizontal wells, a new coiled tubing drilling method of "drilling robot + power drilling tool" driven by drilling fluid was proposed. According to the dimensions, hydraulic pressure consumption, internal structure and manufacturing of the robot, a three-stage eccentric circular flow channel structure is designed. A numerical simulation-unit experiment-numerical simulation method was proposed for the erosion analysis of drilling robot's three-stage eccentric circular flow channel. Firstly, a numerical model for the fluid-structure coupling erosion of drilling robot's three-stage eccentric circular flow channel was established, and the influence laws of particle size parameters and velocity parameters on the erosion rate were analyzed. Secondly, the experiment of drilling robot eccentric channel erosion was carried out to calibrate the numerical model of drilling robot three-stage eccentric circular channel fluid-structure coupling erosion. Based on this, the numerical simulation research of drilling robot three-stage eccentric circular flow channel is further carried out. The results show that the optimal inclination Angle of the three-stage eccentric circular flow channel is 5°. When the flow channel wall thickness is 5 mm, the eccentric flow channel life is more than 300 h, which meets the working life requirements of general downhole tools. The position of main erosion point and erosion pattern of flow passage are in good agreement with the experiment. This provides a theoretical basis for the structural design and engineering application of the drilling robot and is of great significance for promoting the popularization and application of coiled tubing drilling technology in extended-reach horizontal wells.

Performance Evaluation and Self-aggregation Plugging Characteristic of Nano Microspheres as Profile Control Agent

YANG Zhiguo, YUE Xiang'an, SHAO Minglu, YUE Tianqi, HE Jie

2021, 43(2):  178-186.  DOI: 10.11885/j.issn.1674-5086.2020.04.05.01

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It is difficult to realize deep profile control because of the small pore-throats and complex structure of low-permeability reservoir, and there is contradiction between injection and plugging in traditional polymer microspheres. In order to solve this contradiction, a polymer microsphere plugging agent (CSA) containing amide groups on the surface of microspheres was prepared based on emulsion polymerization of styrene and acrylamide. The dispersed solution of CSA microspheres, whose particle size is much smaller than the diameter of pore-throats, was injected into the reservoir. When the microspheres migrated to the deep part of reservoir, these microspheres could automatically self-aggregate into large particle clusters because of the physical and chemical effects, so as to realize the plugging of the water channels. In this paper, the morphology, temperature resistance and self-aggregation properties of CSA microspheres were studied through transmission electron microscopy (TEM) and bottle test. The results showed that CSA microspheres exhibited heterogeneous core-shell structure, good dispersion, and outstanding thermal stability. The microspheres remain regular and uniform spheres at 100℃ after aging for 35 days. With the increase of the concentration of the cations, the self-aggregation time of CSA was gradually shortened, and the influence of bivalent cations was greater than that of monovalent cations. Core flooding experiments showed that CSA microspheres have good injection properties, CSA microspheres clusters can effective plug the water channels and migrate to the deep part of the reservoir for profile control.