Table of Content

10 February 2021, Volume 43 Issue 1

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SPECIALIST FORUM

Geological Characteristics and Exploration Prospect of Carbonate Source Rock Gas in Sichuan Basin

GUO Tonglou

2021, 43(1):  1-16.  DOI: 10.11885/j.issn.1674-5086.2020.10.20.03

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By means of thin section observation, petrophysical property analysis, scanning electron microscope, X-ray diffraction, isotope analysis and other laboratory test methods, combined with logging data analysis, seismic profile interpretation and other research, starting from the determination of geochemical evaluation parameters and indicators of carbonate source rock gas, taking stable high production gas reservoir in Nanchuan area as an example, this paper makes full use of the original samples such as outcrop, drilling core, cuttings, dissects the characteristics of source rock, petrophysical property, petroelectrical property, gas bearing property and hydrocarbon generation potential of carbonate rocks in the first member of Maokou Formation in Sichuan Basin, and discusses the positive role of supergene sedimentary environment, early diagenesis, especially the evolution series of magnesium rich clay minerals on the enrichment of organic matter, generation and accumulation of carbonate gas in carbonate rocks, so as to clarify the main control factors of stable high production of gas reservoirs and implement the characteristics and distribution of "sweet spot", and indicate the prospect of exploration and development in this field.

GEOLOGY EXPLORATION

Karst Identification and Influencing Factors on Carbonate Reservoir in Bozhong 22-1 Buried Hill Structure

HOU Mingcai, CHEN Yang, WANG Yuechuan, GAO Kunshun

2021, 43(1):  17-29.  DOI: 10.11885/j.issn.1674-5086.2019.11.25.01

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The basic characteristics, karst identification and influencing factors of carbonate reservoir in buried hill were studied by means of core, thin section, imaging logging and other data. The results show that the lithology of the study area is mainly dolomite, limestone and transition rock. The reservoir space is dominated by dissolution holes, holes and fractures with an average porosity of 4.1%. The reservoir is mainly controlled by sedimentary facies, fractures and karsts. The sedimentary microfacies influence the dissolution degree, and the restricted platform facies and open platform facies are developed in the study area, among which the in-platform beach microfacies and cloud lagoon microfacies matrix pores are developed, which are conducive to the occurrence of dissolution. The improvement of reservoir space by fault and fracture system formed by tectonics is the early channel of karst. Karstification is the key to the formation of reservoirs. The karst structure in Well Ke2 was identified by core and imaging logging, and the influence depth of epigenic karst reaching 180 m below the unconformity surface. Under the control of karst cycle, there are four vertical percolation-horizontal subsurface flow zones, and the best physical property is the horizontal subsurface flow zone, which is a high-quality reservoir development zone.

Anastomosed Shallow-water Delta of the Lower Member of Minghuazhen Formation in Huanghekou Sag

LIU Wenchao, SHEN Xiaoxiu, WANG Shaopeng, LAI Youchun, MIAO Feifei

2021, 43(1):  30-40.  DOI: 10.11885/j.issn.1674-5086.2019.05.06.03

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In order to understand the sedimentary model of anastomosed shallow-water delta during the shrinking period of a lake basin, the study analysed the lower Member of Minghuazhen Formation of the Huanghekou Sag integrating well logging, mud logging, core, grain size analysis and seismic data. The results indicate that the sand body of the anastomosed shallow-water delta in the lower Member of Minghuazhen Formation of the Huanghekou Sag is mainly a product of vertical accretion. The river channel is net-like and interlaced, with a small width-to-depth ratio and a strong stability, and sand bodies are moderately developed. It's formed in the low slope where network channels develop both in the delta plain and the delta front facies. The channels are flower-like, and the sedimentary microfacies. The natural levees, floodplains and sheet sands account for most sediments. The formation process is the model of "channels flower-like" dominated by overbank sediments. From the formation mechanism, natural levees are developed on both sides of the anastomosed shallow-water delta, which increase lateral stability, and the diversion is the main mechanism for the forming of new channels.

Characteristics and Controlling Factors of Glutenite Reservoir in Permian Lower Urho Formation in the South Slope of the Mahu Sag

QIAN Haitao, ZHANG Xiang, BIAN Baoli, LIU Hailei, ZHANG Menggang

2021, 43(1):  41-50.  DOI: 10.11885/j.issn.1674-5086.2019.06.12.03

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Good prospects of exploration of the Permian Lower Uhro Formation on the south slope of Mahu Sag in Juggar Basin. Based on the core observation, the casting of the thin sections, SEM, as well as the analysis of reservoir physical properties, the characteristics and controlling factors of Lower Urho Formation have been researched. The results indicate that the type of reservoir rock in the Permian Lower Uhro Formation is mainly debris sandstone with muddy and zeolite cementation, and reservoir has lower maturity of structure and composition. There are various of pores of reservoir space, mainly the residual intergranular pores, volcanic material pores and zeolite pores. Influencing factors on physical properties of reservoirs are sedimentation, diagenesis and tectonism. The reservoir is controlled by sedimentary facies belt. The under-water distributary channel on the leading edge of the fan Delta is the most favorable sedimentary facies belt, followed by the fan Delta plain water diversion channel. The diagenesis is mainly compaction, cementation and dissolution. Average 24.0% pores are reduced by compaction, and the cementation reduction porosity is 4.9%. The dissolution is mainly turbid zeolite dissolution, and secondary pores formed by dissolution improve physical property.

Lithofacies Types of Longmaxi Formation and Its Influencing Factors on Pore Characteristics

XU Chuanzheng, FENG Shuo, TIAN Jijun, JIANG Liwei

2021, 43(1):  51-60.  DOI: 10.11885/j.issn.1674-5086.2019.05.04.01

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The main subjects of study for this paper are from Longmaxi Formation of Lower Silurian in northern Yunnan and Guizhou Province. Based on analysis of whole rock-mineral and observation of core slices, we divide shale lithofacies into 4 types of shale facies, in which the main developed lithofacies in the study area are the clayey shale facies and mixed shale facies. Based on scanning electron microscopy imaging and organic carbon content measurement, and the experiment of nitrogen adsorption at low temperature, we analyzed the pore structure characteristics of different shale facies. The results show that the larger pores in argillaceous shale facies reservoir are mainly flask-shaped pores, open pores and half-closed pores. The larger pore forms in mixed shale facies are mainly open pores with some half-closed pores; the smaller pores in the two facies are mostly half-closed pores. The content of TOC is favorable to the development of micropores and mesopores, while the content of argillaceous minerals is beneficial to the development of macropores. Because the clay mineral content of the clayey shale facies are higher than that of the mixed shale facies, as well as the effect of diagenesis, the macro-pore volume of the clayey shale facies is higher than that of the mixed shale facies, the pore volume of micro-pore and meso-pore is smaller than that of mixed shale facies.

Application of Weathering Correction in Organic Geochemistry of Source Rocks

MI Weiwei, WANG Teng, LI Na, GUO Xiaodan, XIE Xiaofei

2021, 43(1):  61-71.  DOI: 10.11885/j.issn.1674-5086.2019.07.04.02

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Through field profile observation and sample collection of the Lower Permian in Hami Depression, the laboratory test was carried out by using rock pyrolysis, organic carbon test, kerogen analysis, gas chromatograms of saturated hydrocarbonand other technologies. On the basis of a combination with existing analysis data, this paper gives systematic evaluation about abundance of organic matter, type and maturity grade of Lower Permian Hami Depression source rocks, discusses the primary sedimentary environment and source characteristics of organic materials. Relevant results show that Lower Permian Hami Depression source rocks are very good source rock. The major type of organic materials give priority is sapropel humus type (Ⅱ₂), with a small amount of humus types (Ⅲ); the organic materials are the low-medium period of highly mature stage with high grande of evolution; n-alkanes of source rocks present great changes in distribution, a twin-peak feature of low first and high later. The contrast with quite low light-heavy hydrocarbon ratio reflects that organic materials are significantly influenced by terrigenous organisms. The low Pr/Ph ratio shows strong phytane advantages. Sedimentary environment presents relatively strong reducibility with high salinity, so it is semi-closed water.

Effect of Thermal Conductivity Anisotropy on Heat Accumulation of Hot Dry Rock

HU Ming, LENG Wenxiang

2021, 43(1):  72-80.  DOI: 10.11885/j.issn.1674-5086.2019.06.11.01

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In recent years, the exploration and development of hot dry rock has become a hot spot in academic circles. In order to understand the mechanism of heat accumulation and conduction in hot dry rocks, an experiment of rock triaxial thermal conductivity was carried out by sorting out and summarizing previous research results and combining theoretical methods such as structural geology, heat transfer, geothermal science and mineral petrology. The results show that there is a difference in the triaxial thermal conductivity of rocks, which leads to the anisotropy of the conduction of underground heat flow in rocks. Therefore, the anisotropic index of rock thermal conductivity and the heat transfer formula of hot dry rock are proposed, and the heat transfer law and aggregation characteristics of hot dry rock are analyzed, and the vertical structural combination of heat source, heat channel, hot dry rock reservoir and cap layer is beneficial to the heat enrichment of hot dry rock.

A Predition Quantitative Study on the Sealing of Secondary Fault in Complex Fault Block Reservoir

CAO Long, QIN Runsen, ZHOU Liye, CUI Longtao, WU Qiongyuan

2021, 43(1):  81-90.  DOI: 10.11885/j.issn.1674-5086.2019.05.10.01

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Due to the small scale, regional geological characteristics and differences in hydrocarbon accumulation conditions, the height of the oil column and distribution of oil and water in secondary fault in developed oilfields with yielding fault sealing evaluation method doesn't conform to the actual drilling. In order to improve prediction accuracy, this study establishing a depth-pressure model with drilling, fluid pressure and other materials, and by fitting the shale gouge ratio (I_SGR) with across fault pressure difference (△p), we determine the quantitative evaluation relationship consistent with regional characteristics, and identify the lower limit of the I_SGR of the fault sealing according to the failure area of the fitted graph envelope. And quantitative judgment of fault sealing ability is made rough comnination of the two methods. The study of the fault block in Area 4 of K Oilfield reveals that the south block in I Formation and the middle block in the upper and lower section of Ⅱ Formation are the same oil and water system. The research are supported by the dynamic of the reservoir.

OIL AND GAS ENGINEERING

Advances of Enhanced Oil Recovery Method and Theory in Tight Reservoirs

WEI Bing, LIU Jiang, ZHANG Xiang, PU Wanfen

2021, 43(1):  91-102.  DOI: 10.11885/j.issn.1674-5086.2020.03.10.01

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The advancement of EOR methods in tight reservoirs in last ten years was comprehensively reviewed to promote the theoretical understanding. Moreover, the feasibility of these EOR methods was analyzed based on the mechanisms, and the technical issues and problems existing in lab scale and field scale investigations were presented. Finally, the research focus and development direction of tight reservoir EOR were prospected. After many years of exploration, a series of EOR methods, such as gas injection, chemical methods, smart water, solvent methods, and nanofluid, have been preliminarily formed for tight reservoirs. Among EOR methods, CO₂, natural gas and surfactant hold the most promising potential for application. There are wide gaps and even contradictory conclusions between core scale and field scale studies, which makes it impossible to precisely predict the performance. Therefore, the future researches should be focused on the key scientific questions, such as the interactions between injectants, formation fluids and formation, the multiscale seepage behaviors of oil, gas and water in complex fracture systems, and the mass exchange between tight matrix and fracture, to promote the development of EOR techniques in tight reservoir integrating informative technology.

A Study on the Effect of Shale-liquid Reaction on Casing Deformation

LI Gao, LI Ze, JIANG Zujun, YU Hao, HE Long

2021, 43(1):  103-110.  DOI: 10.11885/j.issn.1674-5086.2019.12.23.01

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The casing deformation after fracturing in shale is a serious problem, which has become a bottleneck restricting the development of shale resources. However, the cause of casing deformation is still unclear, and there is no effective prevention and control measures. In this paper, the effect of shale-liquid reaction on casing deformation and its prevention measures were studied by numerical simulation technology, according to the shale structure characteristics and mechanical properties. Results show that the weak deformation occurred because of the intergranular expansion in fractures in the reaction of shale and liquid. Due to the high mechanical strength and elastic modulus of shale, the weak deforamtion of shale will produce a strong force, and the force exerted on the casing will influence the casing safty. The reduction of elastic modulus of cement and the perforation can prevent casing deformation. The research results provide reference value for further understanding the causes of casing deformation and prevention measures.

Well Test Analysis of Multi-stage Horizontal Well with Varying Conductivity in Naturally Fractured Shale Oil Reservoir

YE Yiping, QIAN Genbao, XU Youjie, GAO Yang, QIN Jianhua

2021, 43(1):  111-119.  DOI: 10.11885/j.issn.1674-5086.2019.10.09.04

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Because of low-permeability property, horizontal well multi-stage fracturing technology is widely used to improve oil well production, and achieve economic value, such as tight and low-permeability oil and gas reservoirs. Based on the seepage mechanics, a mathematical model of multi-stage fractured horizontal well is stablished with consideration of stress sensitivity and varying conductivity. The model is solved by employing Laplace and Fourier integral transformation, pressure drop superposition principle and fracture discrete coupling method in Laplace domain. The Stehfest numerical inversion algorithm is used to calculate dimensionless wellbore pressure in real space and dimensionless pressure and its derivative log-log curve is drawn. The results show that if hydraulic fracture conductivity located at wellbore end-node fracture is higher than that of hydraulic fracture located at wellbore middle fracture, dimensionless pressure curve is lower during early bilinear flow and linear flow stage and production pressure difference is smaller. When the dimensionless conductivity decreases along the direction of the hydraulic fracture, the bigger the gradient is, the higher the dimensionless pressure curve is during the early stage, and the bigger the production pressure difference is. The larger the stress sensitive coefficient, the larger the creep amplitude of the dimensionless pressure and its derivative curve; the smaller the reservoir-capacity ratio, the earlier the cross-flow occurs, the longer the cross-flow duration. The larger the cross-flow coefficient, the earlier the channeling occurs. The results can provide guidance for well test data interpretation in fractured reservoirs.

An Experimental Study on Cyclical Thermal Stimulation to Enhance Permeability of Water-bearing Organic-rich Shale

YOU Lijun, LI Xinlei, KANG Yili, CHEN Mingjun, HAO Zhiwei

2021, 43(1):  120-132.  DOI: 10.11885/j.issn.1674-5086.2019.09.17.03

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Hydraulic fracturing can improve the production of shale gas wells, but its modification scale is mostly concentrated in millimeter-scale cracks. It is difficult to connect micro-nanopores and natural cracks, and a large number of fracturing fluids remained in formation tend to form water phase trapping damage. Organic-rich shale of the lower silurian Longmaxi formation in the Sichuan Basin was selected to simulate heat treatment of shale gas reservoir after hydraulic fracturing. Heating experiments on dry shales with the heating rate of 5℃/min and water-bearing shale with 10℃/min were carried out to monitor parameters such as color change, mass loss, seepage capacity, and wave velocity. Results have shown that color of organic-rich shale turns lighter when temperature rises. Gas permeability increases 3～5 times when dry shales are heated at 600～700℃. Permeability of water-bearing shale improves more significantly after heating at 200～300℃. Wave velocity decreases more after water-bearing shale heating than that of dry shales. Water-rock interaction, hot vapor pressure and spatial thermal stress change induced by heating rate are favorable conditions for reducing threshold temperature of shale.

A New Method for Inversing Mixed Water Resistivity in Water-flooded Zone

ZHANG Jiansheng, YANG Hongwei, SHI Xinlei, GUAN Yeqin, AN Yuhua

2021, 43(1):  133-141.  DOI: 10.11885/j.issn.1674-5086.2019.10.29.01

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The changes of electrical properties of water-flooded reservoirs are complex. Salinity of mixed water is influenced not only by the salinity of injected water and primary formation water, but also by the degree of flooding, which will lead to dynamic changes of resistivity of mixed water and electrical properties of rock and will bring great difficulty to the identification of water-flooded zones and the evaluation of remaining oil saturation. S oilfield in Bohai Area is taken as an example to illustrate how to solve the problems mentioned above. First of all, method of logging facies classification is proposed based on the theory of Multi-Resolution Graph-based Clustering and models of bound water saturation is established in different logging facies. Then the variation law of rock electricity parameters with the change of formation water salinity is analyzed on the basis of rock electricity experimental data, and the exponential relationship between m, n and salinity of mixed water in water-flooded zone is raised for the very first time. Finally residual oil saturation and resistivity of mixed water in water-flooded zone is calculated and quantitative evaluation of water-flooded Zone is realised. The main understandings are as follows:(1) logging facies can be effectively classified based on the theory of Multi-Resolution Graph-based Clustering and there is a much higher precise of bound water saturation by the method than the conventional model without logging facies; (2) with the increase of the salinity of mixed water, rock-electro parameters increase obviously in the low salinity area and the growth rate slows down in the high salinity area; (3) the quantitative interpretation results of water-flooded zone are in good agreement with actual production data and fluid yield profile logging results and the total coincidence rate is up to 92.3%, which shows that the evaluation accuracy of water-flooded zone is improved obviously.

Morphological Analysis of Cavern Leaching of Horizontally Butted Wells

ZHOU Donglin, JIAO Yujia, DU Yujie, WANG Lidong

2021, 43(1):  142-148.  DOI: 10.11885/j.issn.1674-5086.2019.05.20.01

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The shape of cavern leaching by horizontally directional butted wells can't be directly detected by the sonar detection equipment in service, and the unawareness of the shape is the main factor restricting the transformation and utilization of this kind of caverns. In order to solve this problem, sonar detection technology and leaching engineering technology are used, combined with the data of well drilling engineering, production data and salt layer insoluble content, the pit volume of the cavern is calculated, and the overall shape of cavern is constructed. The results show that the dissolution of horizontal directional butted wells mainly occurs in the vicinity of two wells, forming two cavities similar to single well dissolution. The free volume only exists near the two wells. There is only a narrow channel connecting the two wells. Most of the space are buried by insoluble substances, and the overall shape is U-shaped. The research results can guide the stability evaluation of cavern in horizontally directional butted wells and the design of transformation and utilization scheme, and effectively promote the transformation and utilization of this kind of cavern.

Sensitivity Analysis for Uncertain Factors of Gas Pipeline Leakage Model

AN Jianchuan

2021, 43(1):  149-156.  DOI: 10.11885/j.issn.1674-5086.2020.06.29.03

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The main cause for affects the uncertainty of pipeline leakage risk assessment is the analysis for uncertain factors of gas pipeline leakage model. For this purpose, on the one hand, four factors which were inlet pressure, leakage hole area, gas temperature and distance from the leakage hole to the pipe inlet were determined as the main uncertain factors affecting the calculation of gas pipeline leakage rate; on other hand, the multi-factor sensitivity analysis method was used to study the effects of uncertainty factors on the leakage rate by extracting twelve groups of samples with 500, 1 000, 2 000 and 3 000 samples. The results showed that:the rank of Spearman rank correlation coefficient of uncertain factors calculated under different sample sizes is basically consistent, that is, the leakage hole area has the greatest influence on the leakage rate; the gas temperature the second, the inlet pressure and the distance from the leakage hole to the pipe inlet has the third influence; within the existing value range of uncertain factors, the calculated results of the gas pipeline leakage model could meet the accuracy requirements of subsequent pipeline leakage risk analysis when the number of samples is greater than 500, because of the same rank trend of Spearman rank correlation coefficient among different samples.

PETROLEUM MACHINERY AND OILFIELD CHEMISTRY

Multi-objective Optimization Design of Push System for Microsphere Focusing Logging Tool

REN Tao, FENG Bin, SUN Wen, ZHANG Chunlin, TANG Daolin

2021, 43(1):  157-166.  DOI: 10.11885/j.issn.1674-5086.2018.08.01.01

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The optimum design method of the pushback system based on the speed, acceleration and driving angle of the main driving mechanism of the pushback system is presented. According to the actual working conditions, the velocity and acceleration at the center of the polar plate in the push system are selected as the parameters to evaluate the driving performance of the push system through the motion analysis of the push system. Based on the result that the mean square root of the velocity difference and acceleration difference between the expected parameters and the moving velocity difference at the point of the center of mass of the pushing plate and the minimum mean square root of the transmission angle difference of the main drive mechanism of the system, the constrained multi-objective optimization model of the push system is established. An improved complex algorithm for population search in genetic algorithm and the information exchange method between individuals are introduced into the complex algorithm to solve the constrained multi-objective optimization problem. A log pushing system with high approximation to expected value and reasonable mechanism parameters is obtained. Finally, the optimization results are compared with the original design of the microsphere focusing logging system for dynamic performance analysis to verify the correctness and effectiveness of the optimization method. The results show that the optimization effect is obvious and the stability of motion and the force transfer performance of the pushing plate are greatly improved.

Optimization of Slips Structure for Preventing Upward Sliding of Drill Pipe Based on Experimental and Numerical Simulation

DONG Xuecheng, XIONG Kerui, WANG Guorong, WANG Pengcheng, KUANG Shengping

2021, 43(1):  167-175.  DOI: 10.11885/j.issn.1674-5086.2019.10.15.01

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There are few researches on prevention upward sliding of drill pipe, which is caused by high casing pressure after well shut-in, mature equipment to solve the problem have remained elusive. This problem can be solved effectively by the drilling pipe anti-jacking device designed in this paper. The slips used in the device bear a large clamping force during the working process, and the tooth tip is prone to wear, which directly affects the anchoring energy of the anti-jacking device. Through laboratory test and numerical simulation, this paper analyzed the working process of the slips, and analyzed the parameters such as the tooth rake angle α, tooth top round chamfer R and slips tooth tip distance d, which affect the stress distribution on the drill pipe, meanwhile, we obtained the Mises stress distribution and contact stress distribution of the drillpipe, the change law of axial displacement with each parameter. The results indicated that the tooth rake angle α=60° and tooth top round chamfer R=0.3 mm is the most reasonable slips tooth type, and this conclusion was well verified by laboratory experiments. The research results provide a theoretical basis for the optimal design of the slips structure of the anti-jacking device.

A Study on a Kind of Delayed Crosslinking Anti-high Temperature Weighted Guanidine Gel Fracture Fluid

DAI Xiulan, LIU Tongyi, WEI Jun, WANG Meng

2021, 43(1):  176-182.  DOI: 10.11885/j.issn.1674-5086.2019.05.05.04

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The problems of deep well reservoir, such as deep burial depth, tight lithology, high fracture pressure and fracture extension pressure, lead to high pressure and difficulty in fracturing, and low density of conventional fracturing fluid, which cannot guarantee the construction safety and effect of measures. In order to solve the above problems, a kind of organoboron crosslinking agent YGB-1 was synthesized in this paper, and the crosslinking ratio and the amount of regulator were optimized by the determination of crosslinking time. The thickening agent, weighting agent and other additives were optimized to form a fracturing fluid formula with density of 1.35 g/cm³, adjustable delay crosslinking time within 3～17 min, and suitable for 160℃ reservoir. Various properties of the fracturing fluid were measured through the temperature and shear resistance test, suspended sand test, resistance reduction test and demulsification test. The results showed that the enhanced guanidine gel fracturing fluid had excellent properties. The viscosity remained above 150 mPa·s after 2 h shear at 160℃ and 170 s^-1. At 90℃, when the sand ratio is 25%, the ceramsite (20～40 meshes) was suspended for 0.5 h without settlement. When the test line is 6 mm and displacement is 3.5 m³/h, the drag reduction rate of the weighted fracturing fluid is 61%. The surface tension of the broken glue solution was 24.8 mN/m, and the residue content was 398.2 mg/L. The anti-swelling rate of broken glue solution was 91%.