Table of Content

10 August 2023, Volume 45 Issue 4

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SPECIALIST FORUM

Development Status of High-efficiency Rock-breaking and Speed-increasing Technologies for Deep Shale Gas Horizontal Wells

ZHU Xiaohua, LI Rui, LIU Weiji, LI Zhilin, LU Dengyun

2023, 45(4):  1-18.  DOI: 10.11885/j.issn.1674-5086.2021.04.05.01

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At present, China has basically formed the economic exploitation of shallow shale gas engineering technology system, and is moving towards deep layer (more than 3 500 m) exploitation. Deep shale gas has great development potential with rich reserve. But the problems of slow drilling speed and high cost caused by high hardness, high plasticity and high abrasiveness of deep rock are very prominent. Therefore, the efficient rock breaking methods and influencing factors in deep shale gas drilling are introduced. We analyze and summarize the efficient transmission technology of reducing friction and torsion in deep shale gas horizontal wells to improve bit breaking power; and we analyze and summarize new technologies of bit and tooth with strong attacking power and longer service, technology of rock breaking parameter enhancement by using speed-raising tool to assist bit and speed-raising tool-bit parameter matching technology that is suitable for deep shale gas, and briefly describe several new non-mechanical and efficient rock breaking methods, aiming to providing a reference for future economic and efficient exploration and development of deep shale gas.

GEOLOGY EXPLORATION

Thin Reservoir Prediction and Exploration Area Selection of Qixia Formation in Longnvsi Structure, Central Sichuan Basin

LIU Hong, WANG Shuangqin, TAN Lei, TANG Song, CHEN Cong

2023, 45(4):  19-30.  DOI: 10.11885/j.issn.1674-5086.2021.09.26.01

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In recent years, a number of wells in central Sichuan have drilled high-yield industrial airflow in Qixia Formation, showing the great exploration potential of the strata. However, compared with the northwestern margin of Sichuan, the carbonate beach body of Qixia Formation in Longnvsi Area is smaller in scale and thinner in reservoir thickness, which is far lower than the seismic longitudinal resolution, and has not achieved good reservoir prediction effect, which seriously restricts the oil and gas exploration and development in the vast area of the platform. Therefore, in view of the difficulty in thin reservoir prediction in the platform, the reservoir control factors and prediction geological model of Qixia Formation in Longnvsi Area of central Sichuan are studied by comprehensively utilizing core and thin section, combined with logging and seismic data, and the idea of close combination of geology and geophysics. The results show that the reservoir of Qixia Formation in this area is mainly beach dolomite reservoir, and the reservoir rocks are mainly grain dolomite and dolomitic limestone. The main reservoir space is intergranular (dissolved) pores and caves, and a small amount of cracks are visible. The main factors controlling the formation of relatively high-quality reservoirs in Qixia Formation are the position of paleogeomorphology, sedimentary microfacies and fracture development in Qixia Period. Based on this, a thin reservoir prediction geological model of Longnvsi Qixia Formation in “Qixia Period paleogeomorphology highland+ shoal core and Shoal margin microfacies+fracture development area” is established, and on this basis, the favorable areas for reservoir development are optimized. The research results provide important support for the optimization of favorable zones for oil and gas exploration deployment in the platform of Qixia Formation.

Log Interpretation and Evaluation of Hydrocarbon Source Rocks of Xujiahe Formation in the North of Central Sichuan Basin

FENG Linjie, JIANG Yuqiang, CAO Jixiang, YANG Changcheng, SONG Linke

2023, 45(4):  31-42.  DOI: 10.11885/j.issn.1674-5086.2021.09.22.01

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Based on the geochemical experiment results and logging data of source rocks, by fitting the sensitive logging values of geochemical parameters, a reliable logging interpretation model of total organic carbon content and hydrocarbon generation potential is established. At the same time, combined with the actual situation of the study area, the corresponding hydrocarbon source rock classification evaluation standards are formulated, and their plane distribution is preliminarily characterized. The results show that: 1) the source rocks of the Xujiahe Formation in the northern of central Sichuan Basin have high natural gamma, high acoustic transit time, high resistivity, and low compensation density response characteristics on logging curves; 2) the response of acoustic transit time and resistivity curves to the total organic carbon content and hydrocarbon generation potential of source rocks is relatively sensitive. Based on multiple regression between the two and measured geochemical parameters, a more reliable interpretation model for the total organic carbon content and hydrocarbon generation potential of source rocks can be obtained; 3) the total organic carbon content of the source rocks of the Xujiahe Formation in the study area is mostly 0.75% to 1.50%, and the hydrocarbon generation potential is mostly 0.60 mg/g to 1.00 mg/g, mainly composed of poor hydrocarbon source rocksl; 4) vertically, the Xu5 Member is the main source rock development zone of the Xujiahe Formation, followed by the Xu2 Member; Horizontally, the thickness of the source rock in the Xu 5 Member has a trend of thinning from west to east, while the thickness of the source rock in the Xu 2 Member has a trend of thinning from northwest to southeast.

Mesozoic Faults and Their Control on Oil Reservoirs in Ordos Basin

LUO Anxiang, LIU Guanglin, LIU Zhengpeng, SHEN Tiandan, MA Shuang

2023, 45(4):  43-54.  DOI: 10.11885/j.issn.1674-5086.2021.10.25.05

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Aiming at the problems of complex fault system and unclear reservoir distribution in Gufengzhuang Area, Yanchi County, northwest of Ordos Basin, using three-dimensional seismic and balanced profile restoration technology, we identify the fault distribution, delineate the morphology of the fault plane and restore the opening and closing state of the fault, and clarify the formation stage of the faults and favorable reservoir forming conditions. Three fault systems are developed in Gufengzhuang Area. Indosinian faults are mostly normal faults, distributed in en echelon arrangement in NWW direction, opened in the early Cretaceous, and played a role in connecting oil sources and efficiently transporting oil and gas. Yanshanian faults are developed in the west of the area, showing a nearly NS direction, mostly thrust faults, with strong structural deformation, which is not conducive to reservoir preservation. Himalayan faults are in NEE direction, distributed in parallel in the work area, mostly normal faults, formed after reservoir formation, adjusted or destroyed the primary reservoir. The reservoir forming conditions in the fault development area are as follows: the faults communicating with oil source opened in the reservoir forming period; the traps had good conditions and located near the convex ridge of the fault plane (reservoir forming above the source) or near the concave ridge (reservoir forming below the source). The research results have certain guiding significance for oil and gas exploration in fault system development areas.

Characteristics of Seismic Facies of High-quality Source Rocks and Prediction of Their Distributions in the Zhu III Depression, Pearl River Mouth Basin

YOU Junjun, LEI Mingzhu, LIU Yi, ZHAI Yanan, JIANG Li

2023, 45(4):  55-71.  DOI: 10.11885/j.issn.1674-5086.2022.03.11.03

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The source rocks developed in different sedimentary environments have different geochemical characteristics and contributions to petroleum accumulation. However, the spatial distribution of the source rocks of different facies is unknow, which restricts the following petroleum exploration. Based on the comprehensive analysis of rock debris, well logging, geochemistry and seismic data, the characteristics of seismic facies of high-quality sources within the Enping Formation and Wenchang Formation as well as their distribution modes are systematically investigated. The results demonstrate that: 1) the seismic facies of the source rocks of the Wenchang Formation deposited in the semi-deep and shallow lake in the Wenchang B Sag as well as the source rocks of Enping Formation deposited in the shallow lake are featured by strong amplitude-low frequency-parallel-moderately continuous reflection, weak amplitude-low frequency-parallel-weakly continuous reflection, and moderate and weak amplitude-low frequency-parallel-moderately continuous reflection (or chaotic reflection). 2) the highquality source rocks deposited in the semi-deep lake in the Wenchang B Sag are widely distributed in the sag center and steep slope zone, whereas the source rocks deposited in shallow lake are primarily distributed in the sag center and gentle slope; however, the source rocks deposited in the semi-deep lake are only located in the sag center in the Wenchang A Sag, and the source rocks deposited in the shallow lake are well developed around the sag. Thus, source rocks deposited in the semi-deep lake and shallow lake within the Wenchang Formation in the Wenchang B Sag and that deposited in the shallow lake in the Wenchang A Sag are the primary source rocks.

Accumulation Conditions and Main Controlling Factors of Fengcheng Formation Reservoirs in the South Slope of Mahu Sag

BIAN Baoli, LIU Hailei, JIANG Zhongfa, WANG Xueyong, DING Xiujian

2023, 45(4):  72-84.  DOI: 10.11885/j.issn.1674-5086.2021.07.08.01

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Recently, breakthroughs have been made in oil and gas exploration of Fengcheng Formation in the south slope of Mahu Sag, the conditions of hydrocarbon accumulation such as source rock and reservoir rock need to be re-recognized, and the main controlling factors of pure oil reservoir in lithologic reservoir zone need to be identified. In view of the above problems, geochemical and sedimentary reservoir testing were carried out for exploration wells in recent years, and logging, and seismic data were integrated, and the results show: 1) recently drilled wells in the study area in the outer front of fan delta facies mature and good type II hydrocarbon source rock reach of certain thickness, revealing that Fengcheng Formation source rock also exist in study area. 2) the plain facies of fan delta develops massive glutenite, and there is no mudstone cap layer inside, and the front facies of fan delta develops mudstone cap layer inside, which can be used as local cap layer; reservoir rocks are extra-low porosity and extra-low permeability reservoirs. 3) four hydrocarbon accumulation belts are identified, and massive glutenite is distributed in plain facies reservoir belt, and downdip direction water hose is formed due to the unconformity of the plain facies reservoir zone cap layer sealing; pure oil layers in fan delta front reservoirs are controlled by regional mudstone cap rock development, and outer frontal shale cap rock develops generally. We thus select a 289 km² area favorable for exploration, guiding further exploration and deployment.

OIL AND GAS ENGINEERING

Study on Improvement and Effect Evaluation of Salt Resistance of “Drying Agent” in Tight Gas Reservoir

XIONG Yu, FU Xitong, ZHANG Liehui, SUN Yang

2023, 45(4):  85-93.  DOI: 10.11885/j.issn.1674-5086.2021.08.21.01

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At present, the high water saturation of the reservoir is the main reason for the low permeability of the tight gas reservoir. It has been pointed out that the desiccant which can react with the formation water to reduce the water saturation has been injected into the pores of the tight reservoir. However, the way of reducing water saturation by injecting desiccant may encounter the solid salting out produced by the reaction, resulting in pore blockage, so it is particularly important to reduce the formation of salting out on the basis of the previous study of desiccant. It is particularly important to improve the formula of desiccant. A metal carbonization complex LC containing lithium ion was used as a synergistic agent to participate in the drying reaction of the compound drying agent formula, which mainly improved the salt resistance effect of the drying agent formula, greatly reduced the formation of solid phase salting-out after the drying reaction, and analyzed the reaction heat of various chemical substances in the reaction. Combined with the experiment, the thermal effect and drying effect of the improved composite drying agent and the original drying agent were compared. Based on the results of XRD phase analysis of the salting out, EDTA and DTPA, which can complex with metal cations, were selected as salt resistance auxiliaries, and the salt resistance effects were studied under the experimental conditions of normal temperature, normal pressure and simulated formation high temperature and high pressure. the experimental results show that the desiccant system can achieve ideal salt resistance effect by adding synergist LC and salt resistance auxiliaries. That is to say, when the water consumption is the most, the solid salting out is the least, which makes the drying agent system more perfect.

Evaluation Method of Water Control Effect of Conformance Flow Water Control Technology

LIU Chenglin, REN Yang, PEI Bailin, ZHAO Wei

2023, 45(4):  94-102.  DOI: 10.11885/j.issn.1674-5086.2021.05.13.02

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The evaluation of conformance flow water control technology in newly commissioned horizontal wells is usually verified by a single comparison with the offsets, but the comparison results could be greatly unreliable. Water control effect evaluation methods based on the principles of such technology can complement the existing evaluation methods. Conformance flow technology equalizes the output flow profile in each production section of horizontal well, making the axial pressure profile along the wellbore unbalanced. A short shut-in results in the redistribution of axial pressure in the wellbore, and in the process of pressure balance, the fluid in the production section with high water saturation flows out and backflows into the production section with low water saturation. Therefore, there is a correlation between the effectiveness of such techniques and the occurrence of backflow. For example, in Well LFY13-2-A7, where the conformance flow technology water control technology was applied, the water cut was stable at 85% before the well was shut in, and after the well was opened again, the water cut gradually decreased from 90.81% to 85.69% and then remained stable and slightly decreased. This phenomenon, together with referring to the data of the existing adjacent well comparison method, is fully consistent with the mechanism of the conformance flow water control technology, so it proves that this technology has played a role in water control in Well LFY13-2-A7.

A Study on the Threshold of Infiltration Adjustment of Tight Sandstone Gas Reservoir in the Middle and Late Stages of Development

LIU Yan, LIU Lu

2023, 45(4):  103-110.  DOI: 10.11885/j.issn.1674-5086.2021.06.15.01

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Infiltration adjustment is one of the main methods to improve recovery in the middle and late stages of gas reservoir development, but the adjustment effect is not ideal at present due to the inadequate understanding of threshold of adjustment implementation. Taking the typical tight sandstone gas reservoir of Xinchang JS₂ as an example, we study the economic and technical threshold for infiltration adjustment of different reserve areas through economic evaluation, dynamic analysis and numerical simulation, and put forward specific technical suggestions. In type I reserve area adjustments should be made to both vertical and horizontal wells when the formation pressure is greater than 59% of the original formation pressure; when the reserve abundance is greater than 4.96×10⁸ m³/km², adjustments should be made to horizontal wells; when the formation pressure is at 47%~59%, adjustments should be made to vertical wells only. In type II reserve area, when the formation pressure is greater than 67% and reserve abundance is greater than 2.03×10⁸ m³/km², adjustments can be made to both vertical and horizontal wells; when reserve abundance is less than 2.20×10⁸ m³/km², adjustments should be made to vertical wells, and when reserve abundance is greater than 2.34×10⁸ m³/km², adjustments should be made to horizontal wells; when the formation pressure is at 51%~67%, adjustments should be made to vertical wells only. In type III reserves area, adjustments can be made only to horizontal wells when the formation pressure is greater than 88%of the original formation pressure and reserve abundance is greater than 1.30×10⁸ m³/km². Ti is estimated that recoverable reserves can increase by 4.02×10⁸ m³ and recovery by 0.67% through infiltration adjustment.

A Study on Evolution Law of Complex Flow Pressure in Ultra-deep Wells with High Temperature and High Pressure

DENG Hu, TANG Gui, ZHANG Lin

2023, 45(4):  111-120.  DOI: 10.11885/j.issn.1674-5086.2022.09.17.01

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Due to the high temperature, high pressure, high stress and complex formation environment during the drilling of ultra-deep wells, gas invasion is prone to occur. If not discovered in time, the bottom hole pressure will continue to decrease, and gas invasion will intensify, leading to a vicious circle that increases the risk of well control. The key technology of wellbore pressure control lies in the study of complex multiphase flow laws in ultra-deep wells, but the current research is not deep enough. This study focuses on the high-temperature and high-pressure rheological characteristics of the fluids in the ultra-deep wellbore, and establishes a complex mathematical model of the full wellbore flow based on the drift flux model. The model is solved, verified and analyzed using the example of Well ST8 for pure overflow and simultaneous overflow and leakage. Research results show that the calculated standpipe pressure and casing pressure from this model are basically consistent with the field operation data, and the calculation accuracy is high, which can be used to describe the evolution law of complex flow pressure. Under the same working conditions, the pressure drop of the coexisting overflow is higher than that of the overflow condition, and the consequences are more serious. Both density and flow rate have an effect on the bottom hole pressure, in which the density mainly affects the hydrostatic column pressure, and the displacement mainly affects the flow friction.

Experimental Evaluation on the Cement Sheath Integrity of Unconventional Oil and Gas Well During Large-scale Hydraulic Fracturing

GUAN Zhigang, DENG Kuanhai, WU Yanxian, LIN Zhiwei, LIN Yuanhua

2023, 45(4):  121-132.  DOI: 10.11885/j.issn.1674-5086.2021.10.16.01

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Large-scale hydraulic fracturing of unconventional oil and gas wells will put the cement sheath in an extreme service environment, which is easily lead to the failure of the cement sheath barrier. The key to avoid the failure of the cement barrier is to investigate and understand failure mechanism of cement sheath under the alternating pressure induced by fracturing. Therefore, a self-developed experimental device is used to simulate the wellbore environment to carry out the physical test and evaluation of the sealing performance and interface mechanical performance of the full-scale“production casing- normal/high cement sheathintermediate casing” under alternating pressure. The sealing performance and interface mechanical performance of cement sheath were characterized by the number of seal failure cycles and interfacial bond strength, and the sealing performance results of ordinary cement sheath under four alternating pressures(0↗30↘0, 0↗50↘0, 0↗60↘0, 0↗70↘0 MPa) and high strength cement sheath under five alternating pressures(0↗30↘0, 0↗50↘0, 0↗60↘0, 0↗70↘0 and 0↗80↘0 MPa) are obtained. The influence of alternating pressure peak and cycles times on cement sheath integrity is analyzed, the failure mechanism and process of cement sheath integrity under alternating pressure are revealed, and the correlation between cement sheath sealing performance and interface mechanical performance is clarified. It is found that the sealing/channeling resistance and interface mechanical properties of high-strength cement sheath are obviously better than those of ordinary cement sheath. The results can provide an important basis for the optimization of cement slurry system and fracturing construction parameters in unconventional oil and gas wells.

Vortex Induced Forced Vibration of Euler-Bernoulli Pipe-in-pipe System

ZHAO Xiang, TAN Ming, LI Yinghui, SHAO Yongbo

2023, 45(4):  133-142.  DOI: 10.11885/j.issn.1674-5086.2021.02.23.01

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In order to solve the vibration problem of a Pipe-in-pipe (PIP) system under the action of seawater, the dynamic response of the vortex induced forced vibration of the PIP system is studied. Then the numerical analysis is carried out to study influences of the outer pipe diameter, axial load, and external excitation frequency on displacement responses of the PIP system under the action of vortex. Based on Euler-Bernoulli beams theory, Lamb-Oseen vortex model is used to establish the dynamic model the PIP system, and Green function method is used to obtain the steady-state response of the forced vibration of the PIP system. Results show that as the diameter of the outer pipe increases, the vortex excitation force increases, and the position of the maximum amplitude becomes farther from the outer pipe; the axial tension has a greater impact on the outer pipe, but has a smaller effect on the inner pipe; when the dimensionless external excitation frequency sets to 0.4, the displacement of the outer pipe exceeds the limit of allowable deformation, and periodic collisions between the inner and outer pipe can easily happen, which cause damage to the PIP system.

Mechanical Characteristics of Natural Gas Hydrate Production Riser

HUANG Xin, KOU Jian, MAO Liangjie, LI Juan

2023, 45(4):  143-154.  DOI: 10.11885/j.issn.1674-5086.2021.03.25.02

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The riser pipe is the key channel of gas hydrate exploitation in deep water, the force and deformation of the riser are more complicated due to the formation of multiphase internal flow due to the decomposition of gas hydrate in the pipeline, and the riser of gas hydrate exploitation is prone to failure accidents under the comprehensive action of internal and external flow. In order to analyze the mechanical characteristics of hydrate production riser, the decomposition and flow of hydrate in the pipe are considered in the model and introduced into the riser vibration equation. The dynamic model of hydrate riser in marine environment coupled with internal multiphase flow is established. Finite element method is applied to discretize and solve the model. The effects of slurry density, flow rate and outlet back pressure on the mechanical response characteristics of riser in hydrate mining are analyzed by taking solid fluidization test mining technology as an example. The results show that the mass of hydrate production riser decreases and the section tension of the riser increases due to the formation of multiphase flow from hydrate decomposition. The deformation displacement, bending moment and deflection angle of hydrate production riser are all smaller than those of pure liquid riser. The maximum displacement of hydrate production riser without buoyancy block appears below the midpoint of the riser, and the bending moment and deflection angle at the bottom of the riser are the largest. The displacement, bending moment and deflection angle of hydrate production riser increase with the increase of drilling fluid density, slurry discharge and outlet return pressure of riser. Appropriate increase of the tension at the top of the riser for hydrate exploitation or configure action of the buoyancy block, reduction of the drilling fluid density and displacement, and reduction of the outlet pressure of the riser are conducive to reducing the hydrate production riser bending deformation. The research results can provide theoretical guidance for protecting the safety of hydrate production riser.

Prediction Method of Core Permeability and Fracture Aperture Based on Machine Learning

CHEN Lin, LI Pengwu, ZHANG Shaojun, LI Zhijie, DU Xiaoyong

2023, 45(4):  155-163.  DOI: 10.11885/j.issn.1674-5086.2021.04.30.04

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Stress sensitivity is one of the main reasons for the damage of tight sandstone gas reservoirs. The prediction of the change law of core permeability and fracture aperture under stress sensitivity damage is always the key point in the field of tight sandstone reservoir protection. Based on the stress-sensitive experiment and survey data, the core permeability prediction model and fracture opening prediction model were established by using machine learning multiple linear regression algorithm coupled with the confining pressure permeability relationship model and the K-p function parameter prediction model. The accuracy of the model was tested by correlation coefficient, root mean square error and relative error. The results show that the average correlation coefficient of the prediction results of the confining pressure permeability model in fractured and nonfractured cores is greater than 0.96. The prediction results of K-p function parameter prediction model show that the root mean square error in fractured cores is higher than that in non-fractured cores, but the relative error of fractured cores is lower than that of non-fractured cores. It shows that the permeability prediction model is more suitable for fractured cores. The coefficient of determination between the fracture opening prediction model and the measured value is 0.978, indicating a high prediction accuracy. The permeability prediction model and fracture aperture prediction model can provide guidance for the exploitation and protection of tight sandstone reservoir.

PETROLEUM MACHINERY AND OILFIELD CHEMISTRY

Effects of Catalyst and Environment Temperature on Heavy Oil Combustion

ZHAO Shuai, PU Wanfen, MIKHAIL A V, YUAN Chengdong

2023, 45(4):  164-173.  DOI: 10.11885/j.issn.1674-5086.2021.04.08.02

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To solve the problems of long low-temperature oxidation induction period and low combustion efficiency during insitu combustion of some heavy oil reservoirs, a set of porous medium thermo-effect cell (PMTEC) was designed and developed, and the effects catalyst type, mass percentage of catalyst, mixed catalyst, and environment temperature on heavy oil combustion were systematically evaluated using this cell. The results indicated that PMTEC could efficiently and quickly evaluate the influence of the catalyst on the combustion performance of crude oil, so as to screen out a suitable catalyst system. The mixed system [cobalt naphthenate (0.5% Co) + manganese naphthenate (0.5% Mn)] could reduce the initial temperature of combustion of heavy oil in A reservoir of Xinjiang Oilfield by 60 ℃, which meant that this catalyst system had good application prospects in catalyzing heavy oil combustion. The increase in environment temperature could significantly promote the occurrence of combustion. However, the influence of environment temperature on combustion intensity was limited.

Effect of Ion Composition on the Salt-tolerance Behavior of Medium-low Molecular Weight Polymers

WANG Lili, LIANG Yan, LI Wenhong, YUAN Guowei, CAO Miao

2023, 45(4):  174-184.  DOI: 10.11885/j.issn.1674-5086.2020.10.10.02

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In view of the practical problem of choosing the medium-low molecular weight salt-tolerance polymer for Changqing Jurassic reservoir with low permeability and high salinity, this paper systematically analyzed the influence of ion concentration and composition on the salt-tolerance behavior of three different medium-low molecular weight salt-tolerance polymers. The measurement results of viscosity, relaxation time, fluorescence and environmental scanning electron microscopy showed that, compared with the conventional salt-tolerance polymer SAV55 and the associative polymer EY-131 with lower molecular weight, the associative polymer BHXF-850 with higher molecular weight and associative monomer content had better viscosifying capacity. However, with the addition of Na⁺, Ca²⁺ and Mg²⁺, the viscosity retention rate, relaxation time and solution structure number of BHXF-850 were the lowest and the structural strength was also the weakest, and the solution microstructure was significantly affected by the addition of ions. At the same time, the salt-tolerance behavior of the polymer had no obvious difference between the addition of mono-valent and divalent ions. The findings can provide reference for the optimization of medium-low molecular weight salt-resistant polymers used for chemical flooding in reservoir fields.