Table of Content

10 April 2020, Volume 42 Issue 2

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Identification of the Complex Lithology of Mixed Rock

CHEN Gongyang, WANG Pengyu, GAO Yang, ZHANG Fang, YIN Senlin

2020, 42(2):  1-14.  DOI: 10.11885/j.issn.1674-5086.2019.04.08.01

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The Permian Lucaogou Formation in the Jimsar Sag is a set of terrigenous clastic and carbonate mineral mixed rock layers with complex and diverse mineral types. Currently, controversy still exists surrounding the naming conventions for the lithology of the Lucaogou Formation, which has greatly affected the efficiency of lithology identification at drilling sites. In this paper, X-ray fluorescence (XRF) and X-ray diffraction (XRD) were applied to the comprehensive analysis of the relationship between rock mineral composition and elemental content. By adopting the element cross-plot method, we established six types of lithological identification plots, including feldspar lithic sandstone, fine sandstone, mudstone, mudstone dolomite, sandy dolomite, and dolomitic sandstone. Comparative analysis revealed that the coincidence rate can reach 80%. This provides a good method for in situ lithology and sweet-spot identification of tight oil mixed rock, which could effectively guide lithology identification and geosteering of horizontal wells on site.

Seismic Sedimentary Study on the Fan-delta of the Baikouquan Formation on the Western Slope of the Mahu Sag

LI Quan, LI Peijun, NI Zhen, LIU Jun, LIU Hechong

2020, 42(2):  15-26.  DOI: 10.11885/j.issn.1674-5086.2019.01.29.01

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Fan-delta front glutenite exhibits wide variation in physical properties, making it difficult to predict high-quality reservoirs. Aiming to address this key issue, we identified and described the sedimentary facies distribution characteristics and filling process of the fan-delta in Baikouquan Formation in the Fengnan region on the western slope of the Mahu Sag (Junggar Basin). The study was guided by seismic sedimentology theory, and was done by means of seismic lithology, seismic geomorphology, and stratigraphic slicing techniques with logging and seismic data. In this study, we first established a high-precision sequence stratigraphic framework of the Triassic Baikouquan Formation on the western slope of the Mahu Sag, and delineated six fourth-order sequences. Then, we identified the sedimentary microfacies of the diversion channels, river channels, fan-delta front subaqueous diversion channels, estuary dams, and sheeted sands, as well as the corresponding logging characteristics of the Baikouquan Formation in the study area. We also indicated the correspondence between reservoir sand bodies and seismic amplitude by lithology calibration. Finally, with the help of slicing techniques in a fourth-order sequence grid, we clarified the filling-evolution process of the fan-delta sedimentary system in the Baikouquan Formation and pointed out the distribution range of high-quality reservoirs in the fan-delta front and the consequent prospecting direction.

The New Understanding and Exploration Significance in Triassic Baikouquan Formation of Eastern Mahu Sag

QIAN Haitao, YOU Xincai, WEI Yun, BAI Yu, WU Jun

2020, 42(2):  27-36.  DOI: 10.11885/j.issn.1674-5086.2018.10.21.01

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The oil and gas in the lower part of the second member of the Triassic Baikouquan Formation in the eastern Mahu Sag, Junggar Basin keep showing activity, and the industrial oil flow has been obtained in many Wells. However, there has been a dispute over the horizon of the gray sand conglomerate and the oil and gas layer. In order to further expand the exploration results of the Baikouquan Formation, we utilize the core, logging and seismic data, through the Paleogeomorphic restoration, waveform classification, and seismic attributes, to reclassify Baikouquan Formation, and analyze the paleogeomorphology, sedimentary facies belt and sedimentary model of the first Member of Baikouquan Formation. The results show that the Baikouquan Formation in this area is divided into 4 sections, which are superimposed step by step from bottom to top, and distributed in retrogradation and overlay; controlled by paleogeomorphology, three major provenance systems developed in the first Member of Baikouquan Formation, the front subfacies of fan-delta developed widely in the platform area of two flanks of the trench and the center of the sag; The three sets of oil layers developed from the bottom to the top, the lateral distribution being stable, and the closer to the center of the lake basin, the earlier of the oil and gas reservoir is formed; The reservoir of the first member of Baikouquan Formation is overlapped with the second member of Baikouquan formation reservoir of the high position of DA13 well block, which is characteristics of large area oil content. On the basis of the above new understanding, we pointed out that the first member of Baikouquan Formation is an important oil-bearing series in the study area, which is an important exploration area to find reservoir with economic sacle in the Baikouquan Formation.

Cyclic Sequences and Microscopic Heterogeneity of Reservoirs in the Qigu Formation of the Fudong Slope Area

YU Jingwei, TANG Qunying, WU Jun, LU Ziyang, WEN Huaguo

2020, 42(2):  37-47.  DOI: 10.11885/j.issn.1674-5086.2018.11.28.03

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During the exploitation of Member 1 of the Qigu Formation in the Fudong slope area in the eastern part of the Jungar Basin, microscopic heterogeneity results in low oil and gas recovery and difficulties obtaining the residual oil. To solve these problems, this study investigated variations in the microscopic heterogeneity of (underwater) diversion channel reservoirs within cyclic sequences of different classes. Based on the sedimentary dynamics of the cyclic sequences and a stratigraphic framework with high-resolution sequences, quantitative evaluation of the heterogeneity of grains, filling materials, and reservoir pore and throat sizes was carried out mostly using mercury intrusion data of wells in the region. It is believed that the microscopic heterogeneity of the reservoirs with cyclic sequences of different classes differ. For short-term cycles, the microscopic heterogeneity of single (underwater) diversion channel reservoirs is strong at the bottom but weak at the top. For medium-term cycles, the microscopic heterogeneity of superimposed (underwater) diversion channel reservoirs is strong at the top but weak in the middle. Uplift or subsidence of cyclic sequences leads to changes in the relationships between available spaces and sediment sources. These are the main factors resulting in the differences microscopic heterogeneity of the reservoirs. And the heterogeneity of the original grains determines the heterogeneity of the reservoir pore and throat sizes.

Relationships Between Sulfur-containing Compound Types in Crude Oil and Causes of Thermochemical Sulphate Reduction in Tazhong Area

YUAN Yuyang, WANG Tiankai, CAI Chunfang, XU Chenlu, QIN Qirong

2020, 42(2):  48-60.  DOI: 10.11885/j.issn.1674-5086.2018.10.27.30

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Various sulfur-containing compounds, such as thiophene, tetrahydrothiophene, benzothiophene dibenzothiophene, and thioadamantane, were detected in crude oil extracted from the Ordovician reservoirs in the Tazhong Area. These compounds differ in their contents and isotopic values for single-atom sulfur. The analysis results show that modifications of crude oil by thermochemical sulphate reduction (TSR) may be the cause of the differences. There is less tetrahydrothiophenes and thioadamantanes in the crude oil not modified by TSR. As crude oil is increasingly modified by TSR, the total dibenzothiophene (DBT) concentration increases. This indicates that DBTs are probably formed during TSR. Meanwhile, non-TSR-modified crude oil samples were compared to highly TSR-modified condensate oil samples from Cambrian reservoirs for their sulfur isotopic values and total thioadamantane concentrations. It was found that TSR can also change the sulfur isotopic values of crude oil. The DBTs and thioadamantanes in the highly TSR-modified crude oil samples have sulfur isotopic values of from 36‰ to 40‰. In contrast, the DBTs in slightly TSR-modified and non-TSR-modified crude oil from Ordovician reservoirs are mainly from cracking of source rocks; thus, their sulfur isotopic values are relatively low (～20‰) near that of kerogen in the Cambrian reservoirs. Thus, it is believed that the crude oil extracted from the Ordovician reservoirs in the Tarim Basin is mainly from Cambrian source rocks and the crude oil with higher organic sulfur isotopic values is mostly caused by TSR modification.

Sedimentological Characteristics and Shale Gas Exploitation Potentials of the Foreland Basins of Xuefeng Mountain

LIU Chensheng, WANG Hui, SHI Le, FENG Ning

2020, 42(2):  61-74.  DOI: 10.11885/j.issn.1674-5086.2018.10.10.01

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The Silurian foreland basins of Xuefeng Mountain are distributed in the central and northwestern parts of Hunan and the Sichuan Basin and are the dominant basin type on the upper Yangtze Plate. However, at present, there are few studies the sedimentological characteristics and shale gas exploitation potentials of these foreland basins. Based on field survey and well logging data and test results, the sedimentological history and shale gas exploitation potentials of the foreland basins in the central and northwestern parts of Hunan were determined. The results show that the foredeep zones of the foreland basins in the central part of Hunan are dominated by turbidite fans and shallow marine continental shelf deposits. Meanwhile, there are various sedimentological facies in the post-uplift basins in the northwestern part of Hunan. These include tidal, shallow marine continental shelf, littoral, delta, and carbonate platform facies. Although the foredeep zones and the post-uplift basins significantly differ in their sedimentological facies and sedimentation thickness, the division of their sedimentation cycles is consistent. Hence, it is concluded that the foredeep zones and the post-uplift basins are interconnected and Xuefeng Mountain caused limited shielding effects on the basins along its two sides. Numerous geochemical analyses demonstrate that the organic carbon content and the organic matter type of the shales in the post-uplift basins of the study area are less than those of Jiaoshiba in the Sichuan Basin. The Silurian shales in the southern part of Hunan have relatively low values for various geochemical indexes mainly because the area has no black carbonaceous shales of the first sedimentation cycle found in the Longmaxi Formation.

A Study on the Development of Sand-body Flow Barriers in Deep-water Turbidity Channels

LI Chenxi, YUAN Zhiwang, YANG Xipu, BU Fanqing, ZHAO Xiaoming

2020, 42(2):  75-84.  DOI: 10.11885/j.issn.1674-5086.2018.10.11.01

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Deep-water turbidites, due to their genesis, often display dramatic lateral variations, which makes the internal connectivity of the reservoir relatively complex. In deep-water exploration, flow barriers play a very important role in not only connectivity, along with other main factors, but also in effects of water injection between wells. Therefore, it is important to study how to depict flow barriers inside a reservoir between channels, and to characterize connectivity within a sand-body to optimize well locations and improve efficiency of water injection. Through a comprehensive study of the outcrops of gravity flow in the Gannan Area of China, along with logging, seismic, and production data of the Z group in the AKPO Oilfield in Nigeria, we analyze the formation of flow barriers, their distribution within sand bodies in complex water channels, and their effects on water injection. The results show that, for the injection and production well pairs, flow barriers that affect the sand-body connectivity exist in scatter, linear, and composite patterns. The patterns of the effects of injection and production can be linear, wavy, and scattering; the increase in water cut also differs in production wells of different injection and production patterns.

The Research Progress of Well Logging Evaluation of Marine Natural Gas Hydrate

ZHOU Jian, SONG Yanjie, JIANG Yanjiao, SUN Qinshuai, JING Yanqing

2020, 42(2):  85-93.  DOI: 10.11885/j.issn.1674-5086.2019.10.10.01

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More and more attention has been paid to natural gas hydrates with huge resources. Aiming to slove the present problem of logging evaluation of marine gas hydrate reservoirs, this paper introduces the lattice structures, physical properties, distribution form and formation conditions. According to the physical properties and reservoir characteristics of natural gas hydrates, the logging response characteristics of natural gas hydrates are analyzed. Based on the literatures investigation, the main methods of calculating the porosity and saturation of natural gas hydrate reservoir by logging method are obtained, the shale content and saturation of the natural gas hydrate reservoir in Shenhu of South China Sea are evaluated. It is suggested that the existence of shale should be considered in the study of natural gas hydrates by synthetic artificial core in laboratory. By summarizing the research results of well logging evaluation of marine gas hydrate, this paper provides an important basis for future large-scale prediction of marine gas hydrate reserves and exploration and development, and has important practical significance for effective exploitation of natural gas hydrate resources.

Predicting the Diffusive Front of Supercritical CO₂ in Tight Oil Reservoirs

WEI Bing, SHANG Jing, PU Wanfen, Kadet VALERIY, ZHAO Jinzhou

2020, 42(2):  94-102.  DOI: 10.11885/j.issn.1674-5086.2019.10.30.02

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Most of researchers claim that supercritical CO₂ diffusion is one of the key considerations for CO₂ huff-puff EOR in tight reservoirs. In this paper, a matrix-fracture model was designed and applied to measuring the diffusion coefficient of supercritical CO₂ in saturated oil cores using pressure decay method. The influence of reservoir conditions such as pressure and core petroproperties on the diffusion coefficient and concentration distribution of supercritical CO₂ was comprehensively investigated, and a method predicting CO₂ concentration field and diffusion front was established. The experimental results showed that the diffusion coefficient of supercritical CO₂ in the tight core (0.06 mD) is in the order of 10^-12 m²/s. The diffusion coefficient was found to increase with the increase of the initial gas injection pressure before finally leveling off after a certain pressure. The maximum diffusion coefficient occured around the critical pressure point. In addition, the diffusion coefficient increased with the increase of matrix permeability and porosity, whereas it decreased with the increase of core tortuosity. After 900 days, diffusion in tight reservoirs, the diffusion front only advanced 0.095 m. Therefore, it is rational to neglect the diffusing effect of CO₂ in the field operation cycle of CO₂ injection in tight reservoirs. In the later stage of diffusion, the concentration gradient of CO₂ became low leading to gradual decrease of diffusion.

Optimization of Injection Technique of Corrosion Inhibitor in CO₂-flooding Oil Recovery

ZHANG Deping, MA Feng, WU Yule, DONG Zehua

2020, 42(2):  103-109.  DOI: 10.11885/j.issn.1674-5086.2019.05.08.01

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Severe downhole corrosion occurred during Jilin CO₂ flooding in an oilfield in Jilin due to the high pressure of CO₂, high concentration of saline water and sulfate reducing bacteria (SRB) in the produced fluid. Currently, addition of corrosion inhibitors is one of the common methods to protect the oil well and tubes. Through studies of corrosion mechanism and main factor analysis, the effects of inhibitor type, concentration, and injection technique on their filed inhibition efficiency and long-term durability were investigated, aiming at lowering the cost of corrosion management. Then a suitable injection regulation of inhibitor is proposed based on the filed situation in order to improve the long-term efficacy of inhibitor. Injection optimization tests indicate that the corrosion rate has been decreased to <0.076 mm/a. This optimized injection technique of inhibitor not only increases the service life of downhole device and tubes but also decrease the cost of corrosion management.

A New Method for Rapid Evaluation of Shale Gas Content

LIANG Hongbin, ZHANG Liehui, CHEN Man, ZHAO Yulong, XIANG Zuping

2020, 42(2):  110-117.  DOI: 10.11885/j.issn.1674-5086.2019.03.29.02

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It is important to make clear the variation rule of shale gas content for make reasonable development plan of gas reservoir. However, it is difficult to obtain the characteristics of shale gas content as adsorbed gas flow with free gas after desorption during the development. Due to the influence of environment, equipment and human factors, the interpretation results based on the two common methods of logging interpretation and field desorption have great errors, which brings trouble to research on the development theory of shale gas reservoirs. Therefore, the physical model for shale gas isothermal adsorption experiment based on volume method is established by using Horsfield filling theory, and the method to determine the proportion of adsorbed gas and free gas is proposed. This method is verified to be feasible based on the measured data. Compared with well logging interpretation method and field desorption method, this method is more concise and accurate, and easier to calculate. Furthermore, the variation characteristics of adsorption gas and free gas can be quantitatively described by this method during the reservoirs development. The results show that when the reservoir pressure decreases significantly and the main gas source in the pore changes from free gas to adsorbed gas, the corresponding pressure of transition point is negatively linearly correlated with the porosity.

Preliminary Study on the Mechanism of Abnormal High Pressure Formed by Oil and Gas Accumulation

HU Liming

2020, 42(2):  118-124.  DOI: 10.11885/j.issn.1674-5086.2019.04.17.01

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The formation mechanism of abnormal high pressure is very complex, and it is an unsolved academic problem, which needs to be further studied. By analyzing the characteristics of oil and gas migration, accumulation and reservoir drainage, the mechanism of abnormal high pressure formed by oil and gas accumulation is preliminarily explored from the aspects of "filling" power of oil and gas, quantitative calculation of abnormal high pressure, preservation and release of abnormal high pressure. The results show that the main driving force of oil and gas migration into reservoir is capillary pressure at the junction of reservoir and reservoir. The smaller the radius of pore capillary, the greater the power of oil and gas "filling" from reservoir to reservoir. The radius of pore capillary is one of the important factors affecting the maximum formation pressure coefficient in reservoir. The abnormal high pressure can be formed if the oil and gas volume of reservoir is slightly larger than the water discharged from reservoir; the abnormal high pressure in reservoir can be preserved by capillary pressure plugging; there is no capillary pressure at the reservoir-cap junction outside the oil and gas accumulation area, and the reservoir can release pressure through the drainage of caprock. The theory of abnormal high pressure formed by hydrocarbon accumulation can reasonably explain the fact that the pressure of most reservoirs is higher than that of hydrostatic column at the same depth, and that the formation pressure coefficient is slightly greater than 1.0, but high abnormal high pressure reservoirs is very few; it can also reasonably explain the cause of formation of high abnormal high pressure.

A New Method for Calculating Permeability of Sandstone Reservoir

YU Hua, LINGHU Song, WANG Qian, GUO Qingming, WU Ying

2020, 42(2):  125-132.  DOI: 10.11885/j.issn.1674-5086.2019.03.01.01

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Reservoir permeability is an important parameter in oilfield development. It is the basis for determining reasonable exploitation scheme, optimizing completion perforation scheme and selecting the optimal drainage position. The common core statistical analysis method is of errors in permeability calculation and is of a small scope of theoretical applicability. To solve this problem, based on the serial capillary model, the mathematical relationship between reservoir microstructure parameters and porosity, permeability and formation factors is theoretically derived. The mathematical and physical equations of pore throat diameter ratio are established, and the theoretical calculation model of permeability based on porosity, pore throat diameter ratio and throat diameter reservoir microstructure parameters is established, and the micro physical influencing factors of permeability are clarified. Based on core experiment, logging data and permeability theoretical model, a new permeability calculation method is established. The results show that the permeability calculation results are in good agreement with the core analysis results, and meet the needs of accurate evaluation of reservoir permeability. The results show that the permeability of reservoir is the macro characterization of the micro pore throat structure parameters from the mathematical and physical point of view, and the research results provide a new way for the permeability evaluation of reservoir development.

Influence of Time-varying Reservoir Physical Properties on Water Cone Change of Directional Wells in Heavy Oil and Bottom Water Reservoirs

ZHANG Jilei, LUO Xianbo, HE Yifan, OUYANG Yuwei, XU Ya'nan

2020, 42(2):  133-140.  DOI: 10.11885/j.issn.1674-5086.2019.01.24.03

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In view of the existing water cone variation formulas of directional wells in heavy oil and bottom water reservoirs, the changes of reservoir physical properties caused by long term large fluid volume scour have not been considered, which lead to the large sweep volume of water flooding, pessimistic understanding of remaining oil and poor reserve production degree and so on. In order to describe more accurately the variation law of water cone and the distribution of remaining oil between wells in high water cut stage, the variation law of reservoir physical property under long term large fluid volume scour is considered synthetically. The equivalent percolation resistance is used to characterize the permeability of the reservoir inside and outside the water cone, and the equation of numerical variation of heavy oil and bottom water reservoir considering physical property time variation is derived. Through the analysis of practical examples, it is found that the influence of reservoir physical property time variation on water cone is very significant. Under the same water cone width, the water cone height calculated by the water cone formula, which does not take account of the time-varying physical properties, is reduced by 46.3%. Compared with the results of log interpretation, the relative error is only 5.3%. The field pilot test proves the reliability of the water cone change formula of the directional well in the bottom water reservoir considering the time variation of physical properties. This reseach provides technical support for accurate description of water cone change and residual oil distribution law of heavy oil bottom water reservoir in high water cut stage under long term large liquid volume scour.

Optimization Design of Well Pattern in Heterogeneous Gas Storage

LIU Pengcheng, YU Haojie, AN Hongyan, XU Wen, ZHU Yajun

2020, 42(2):  141-148.  DOI: 10.11885/j.issn.1674-5086.2019.05.29.04

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Gas storage well pattern design is very different from conventional gas field well pattern design. Under the same investment conditions, the conventional gas field well network design pursues the maximum recovery of gas field, while gas storage well network design pursues maximum working gas volume in one gas production cycle (3～4 months). Because of the great different of gas production capacity in different areas, one set of well pattern is not suitable for gas storage wells built on heterogeneous reservoirs. Taking Su A gas storage as an example, the area for gas storage network is divided into areas of high permeability and low permeability. We analyze the production capacity of gas wells in the two areas and the regional working gas volume variation with the number of gas wells. And we propose a non-uniform well pattern based on the maximization of working gas volume, and determine the reasonable well pattern density in high permeability zone and low permeability zone. When there are 11 wells in the gas storage, with non-uniform well pattern, the well pattern density in the high-permeability area is 1.7 wells/km², and that in the low-permeability area is 0.38 wells/km². The working gas volume of gas storage will be increased by 0.99×10⁸ m³ than that of uniform well pattern.

Impacts of Water Cross-formational Flow from Roof Rock on the Production Performance of Coalbed Methane Reservoirs

DU Jia

2020, 42(2):  149-157.  DOI: 10.11885/j.issn.1674-5086.2020.01.20.02

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Hydraulic fractures always penetrate into the roof rock. The water cross-formational flow from roof rock could apparently affect the production performance of CBM (coalbed methane) reservoirs. According to the crossflow effect on CBM production, two connection models are established to describe the geology relation between coalbed and top aquifer. Then, the effects of top aquifer on methane production performance is studied by numerical simulation under different hydraulic fracture conditions. Further, the production performance is plotted by dimensionless method and the water sources of well are judged in a case study. The results show that production schedule has a slight influence on water production when the water comes from the inner layer. For the top aquifer without a barrier, the fracture penetration ratio in aquifer will delay the gas production. Once the fracture penetrates the aquifer, the penetration ratio has less effect on production. For the top aquifer with a barrier, there exist two stages of gas production increase. When the penetration ratio is under 1/6, the gas production will increase first quickly and then slowly. When the penetration ratio is above 2/6, the gas production will increase first slowly and then quickly, and the production performance is less sensitive to penetration ratio.

Contact Forms of Casing with Centralizer and Its Effect on Friction

HU Xihui, LI Wei, XU Bihua, MA Jinglun, YUAN Bin

2020, 42(2):  158-165.  DOI: 10.11885/j.issn.1674-5086.2019.04.08.02

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During the running casing operation, the casing will be bent and contact the well wall due to the influence of gravity and well trajectory. Therefore, an additional friction is generated, which affects running casing when it is too large. In particular, a large number of centralizers are used to ensure displacement efficiency and cementing quality in horizontal wells, which brings greater difficulties to running casing operations due to the increase of friction coefficient. Aiming to this problem, the paper first points out the three contact forms of the casing and the well wall:free state, point contact and line contact. It is also points out that the friction is different under different contact form. Then, the casing tortuous equation and contact from judgment model are built. According to the model segmentation calculation method, the friction of the casing under different contact modes is accurately calculated. The field example analysis shows that the method can accurately predict the friction and has a good guiding significance for calculating the friction.

Research on Strength Behavior of Casing Thread with Defects in High Pressure Wells

ZHU Xiaohua, GUO Yingchun, DONG Liangliang

2020, 42(2):  166-174.  DOI: 10.11885/j.issn.1674-5086.2018.09.25.01

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There are few studies on the influence of casing defects on the bearing capacity of connecting threads in high pressure gas wells, and the casing safety evaluation cannot be supported by theory and data. Based on the above problems, the typical API 177.8 mm×12.65 mm P110 steel grade round threaded casing is taken as the research object. Based on the elastic mechanics theory and the corrosion casing mechanics model, the casing-cement ring-formation finite element model under different corrosion forms is established, and the casing thread tooth under the casing-formation-cement ring system is analyzed and studied. The stress distribution law of the threaded connection part under the influence of the stress distribution state and the three corrosion defects. The results show that the uniform corrosion has greater influence on casing thread maximum equivalent stress of high pressure wells than on low pressure wells; influence of pitting and groove corrosion defects on casing thread maximum equivalent stress effects were similar; pitting and groove corrosion defects in the bottom casing thread engagement segments exert significant influence. We also acquire the critical corrosion defect depth of casing under different corrosion defects. The research work in this paper provides a theoretical basis for safety assessment of casing threads in high pressure wells.

Casing Damage Image Technology of Feature Pattern Recognition and Matching of Casing Damage Image and Its Application

HE Zhiming, WU Dong

2020, 42(2):  175-181.  DOI: 10.11885/j.issn.1674-5086.2019.03.29.01

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Aiming at the problem of casing damage and corrosion detection and recognition, four kinds of damage and corrosion types are defined, and the pattern matching recognition of damage and corrosion characteristics is studied. The traditional image contour tracking and extraction are optimized and improved. The casing damage image is transformed into three-dimensional one, and the feature pattern recognition technology of three-dimensional image is used to search a three-dimensional damage-corrosion closure volume, by constraining on distance thresholds between data points and numerical thresholds in casing damage data sets. Different three-dimensional damage-corrosion closure volume represent the different characteristic subsets of damage and corrosion shapes. The axial and radial features of the feature subset are extracted, and the extracted features are matched with the standard corrosion pattern features to accurately evaluate the damage-corrosion type of casing. Practical application shows that it can accurately detect ring corrosion, line corrosion, general corrosion and isolated corrosion, and solve the problem of identifying the corrosion type of casing damage at present.

Preparation and Performance Evaluation of W/O Emulsion Plugging Agent Based on Cottonseed Bottom Oil

DONG Ruiqiang, ZHI Keke, GUO Lianghui, HE Long, LI Entian

2020, 42(2):  182-188.  DOI: 10.11885/j.issn.1674-5086.2019.01.10.01

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Cottonseed oil is a by-product of cottonseed oil press. Waste cottonseed oil will cause serious environmental pollution and waste of resources. In this paper, emulsified cottonseed oil is first used as a selective plugging agent. The W/O emulsion of cottonseed bottom oil with high water content was prepared by using suitable compound emulsifier and its performance was evaluated. The viscosifying interval of emulsion was studied by rheometer. The results show that the maximum viscosifying interval can reach 80%. The stability of the emulsion was studied by oil fraction. The stability of the emulsion increased with the increase of water content. The temperature and salt resistance of the cottonseed oil emulsification system was evaluated. The cottonseed oil emulsion could withstand high temperature at 110℃ and 2×10⁴ mg/L. Calcium ion; Newtonian properties of emulsions with different water content were studied by flow behavior index. The results showed that the higher water content, the weaker pseudoplasticity; sand-filled tube displacement experiment showed that the water and oil plugging rates of cottonseed oil emulsions were 98% and 15%, respectively, with good plugging performance and oil-water selectivity.