Table of Content

10 February 2024, Volume 46 Issue 1

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GEOLOGY EXPLORATION

Application and Prospect of Fluid Mobility in Oilfield Development

TAN Fengqi, MA Chunmiao, LI Xiankun, JING Yuqian

2024, 46(1):  1-20.  DOI: 10.11885/j.issn.1674-5086.2022.06.18.02

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The study on fluid mobility in micro-pore-throat is of great significance for accurate evaluation and efficient development of the reservoir, and it is also the necessary basis for enhanced oil recovery of oil-gas reservoir. According to the differences of research objects, the research methods of fluid mobility in pore throats are divided into three dimensions: mineral composition, pore structure and fluid production. NMR technology can quickly and accurately determine the commonly used movable fluid parameters such as movable fluid saturation, movable fluid porosity and irreducible water saturation, and then effectively evaluate and predict the productivity of various oil and gas reservoirs. At present, the major oil fields at home and abroad have adopted the method of combining NMR with other experimental means to determine the production law of fluid in the reservoir, and have achieved good application results in different types of reservoirs such as tight glutenite, carbonate rock, coal seam and oil shale. In addition, in order to achieve effective exploration and development of different types of oil and gas resources, it is necessary to clarify the control factors of fluid mobility in the reservoir. Based on the existing research results, the control factors of fluid mobility can be divided into macro and micro aspects. The macro factors include sedimentary environment, diagenesis and lithofacies type, while the micro factors include pore throat structure, reservoir physical properties, mineral composition, water film thickness and other factors. At present, although the research methods of fluid mobility have been abundant and have achieved good application results in the evaluation of different types of oil and gas resources, further research and exploration are needed for greater accuracy and wider coverage in its application. In the future development, new ideas and methods such as pore network model, reservoir numerical simulation, multi parameter evaluation index, simultaneous geochemical parameters and so on can be comprehensively applied so as to deeply reveal the percolation mechanism of movable fluid in the micro-pore-throat, and continuously improve the accuracy of comprehensive evaluation of movable fluid, to provide geological basis for the rational formulation of reservoir development plan, and to promote the efficient development of the petroleum industry.

Diagenetic-pore Quantitative Evolution of the Reservoir from Lower Huagang Formation in the South-central Xihu Sag

ZHAO Xiaoming, DAI Maolin, LIU Shu, GE Jiawang, ZHAO Tianpei

2024, 46(1):  21-34.  DOI: 10.11885/j.issn.1674-5086.2022.07.01.03

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The Lower Huagang Formation in Xihu Sag is rich in tight gas resources, which is a hot spot for oil and gas exploration and development in this area. Based on observation of rock slices, scanning electron microscopy, physical property testing of the core and X-ray diffraction, the basic reservoir characteristics, the diagenesis and the pore evolution of the reservoir are studied. The results show the reservior porosity is mainly between 7% and 10%, the permeability mainly between 0.10 to 0.50 mD, and the fracture undeveloped, so the reservoir belongs to a kind of tight sandstone reservoir. The reservoir has experienced the early diagenesis stage A and B and the middle diagenetic stage A, and is currently in the middle diagenesis stage B, and the reservoir are greatly influenced by compaction, dissolution and cementation. The results of pore quantitative evolution show that the compaction reduces porosity by 29.67%, which is the main reason for the undeveloped primary pores; the dissolution increases porosity by 15.14%, which is the key factor for the development of deep reservoirs; with the influence of cementation, the reservoir porosity reduces by 13.55%, which is an important reason for the deterioration of reservoir pore structure. Based on the relationship between pore evolution results and oil-gas charging time, the Lower Huagang Formation in the south-central of the Xihu Sag is a kind of tight reservoir that denses before the accumulation of oil and gas.

Characteristics and Sedimentary Facies Model of Wandering Braided Rivers

WANG Haikao, WANG Miao, YU Zhongliang, YU Chenglin, YIN Yanshu

2024, 46(1):  35-52.  DOI: 10.11885/j.issn.1674-5086.2022.01.13.04

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Aiming at the problem of unclear knowledge and unclear patterns of sandy braided river in Guantao Formation of Block Gao 104-5 in Jidong Oilfield, a classification study of sandy braided rivers was carried out, using criteria including regional geological background, paleoclimate, rock grain size, bedding structure and facies sequence, levee and mud drapes, and sand body morphology. The study area is determined to be a wandering braided river. Then, the architectural element analysis method from Miall is adopted to anatomize the wandering braided river. The two types of identification marks of braided belt boundary and 3 types of identification marks of river channel and mid channel bar are constructed to anatomize the wandering braided channel. The result shows that the scale of the channel belts are about 1 400.00 m wide, the width and length of mid channel bar are about 158.86 m and 414.47 m, respectively; the width of channel is 53.18 m. and the length/width of mid channel is about 2~4; the average width of mid channel bar and channel is 2.2. So the study area is categorized as the wide bar and narrow channel pattern. Finally, using depositional simulation methods, a wandering braided river sedimentary facies model in the study area was established to guide oilfield development.

Time Effects of Stress Sensitivity in Shale Reservoirs

KANG Yili, LAI Zhehan, CHEN Mingjun, WU Jianjun, LI Bing

2024, 46(1):  53-63.  DOI: 10.11885/j.issn.1674-5086.2022.10.31.01

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The effective stress and its action time are important external factors controlling the deformation of pores and fractures in rock. The characteristics of multi-scale pore structure and pore fracture configuration make the stress sensitive time effect of shale reservoirs special. However, the influence of effective stress loading and unloading time on the stress sensitive behavior of shale reservoirs has not been considered in previous studies. In this paper, the Longmaxi Formation shale gas reservoir in Weirong Gas Field, south Sichuan is taken as the research area. The shale samples with different development degrees of pores and fractures are drilled, and the experiment of the influence of variable loading and unloading sustained stability time on permeability of rock samples under variable effective stress is designed and tested. The results show that: 1) when the effective stress loading from 5 MPa to 35 MPa, the permeability of micro fracture sample and matrix sample decreases by 66.82% and 27.19%, respectively, 74.73% and 79.82% recovery rate of permeability during unloading. The lower the shale permeability is, the more significant the effective stress hysteresis effect is. 2) when the continuous stability time of constant effective stress loading is extended from 2.5 h to 10.0 h, and stress sensitivity index increases by 3.76%~80.17%. and the time effect is more significant when the effective stress is small. It is concluded that shale composition and multi-scale pore structure are the main reasons for the difference of pore deformation behavior. Based on the experimental results, the effective stress loading pretreatment time of shale samples is determined to be 6 h, and some suggestions are put forward to optimize the experimental scheme of shale reservoir sensitivity evaluation and optimize the working system of gas wells.

OIL AND GAS ENGINEERING

Research Progress on Functionalization Nanocarbons for Enhanced Oil Recovery

LIU Rui, CHEN Zezhou, GAO Shi, PU Wanfen, DU Daijun

2024, 46(1):  64-75.  DOI: 10.11885/j.issn.1674-5086.2022.06.13.02

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Owing to their amphiphilic, and high aspect ratio, functionalization nanocarbons display multifaceted properties of surfactant, molecular film, colloid, liquid crystal molecule and polymer, stimulating their unique advantages and application potential application in enhanced oil recovery. This paper summarizes the common and unique characteristics of the structures and properties of the nanocarbons composing of 1D carbon nanotube and 2D graphene, the preparation methods, and their functionalization routes. The lipophilic-hydrophilic tailoring modification for nanocarbons on harsh reservoir temperature and salinity is proposed. Guided by the universal problem of low sweep efficiency and low micro-displacement efficiency of water flooding reservoirs, the absorption and self-assembly mechanisms of functionalization nanocarbons at water/oil and water/rock interfaces are analyzed, and multi-dimensional characterizations and information-based physical simulations of functionalization nanocarbons are summarized. Based on the nano-scale molecular and cross-scale characteristics and water/oil/rock interface effects, the coupled enhanced oil recovery mechanisms of functionalization nanocarbons on enhancing sweep volume and improving displacement efficiency are elucidated. The papers ends with a critical and perspective outline on the existing problems in the large-scale application of functionalization nanocarbons and their route to the low-carbon cost for enhanced oil recovery.

Performance Study on the Preparation of Fracturing Proppants Based on Oil-based Drilling Chips

BAI Yang, CHANG Shuang, LIU Yucheng, LIU Xinguo, LUO Pingya

2024, 46(1):  76-88.  DOI: 10.11885/j.issn.1674-5086.2022.04.14.03

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In view of the difficulty in treating deoiled drilling cuttings after thermal analysis and lack of treatment method choices, the research on preparing non-burn fracturing proppant from oil-based drilling cuttings residue was carried out. The research explored the effects of drilling cuttings/cement ratio, CMC addition, gypsum addition and curing days on the performance of non-burn fracturing proppant. The results show that under the condition of excellent raw material ratio, the preparation process is as follows: the drilling cuttings/cement ratio is 0.67 (mass ratio), the gypsum content is 6%(mass fraction), the CMC content is 4%(mass fraction), and the curing time is 28 days. The volume density of fracturing proppant particles prepared under this condition is 1.47 g/cm³, the apparent density is 2.52 g/cm³, and the particle crushing rate under 35 MPa is 1.57%. Through the analysis of scanning electron microscope and X-ray diffraction, it is found that at this time, the internal structure of the fracturing proppant is compact, the pores are closed, and the hydration products C-S-H gel and anorthite are conducive to improving the comprehensive physical properties of the fracturing proppant. It provides a new direction for the utilization of deoiled drilling cuttings residue.

Research on Production Allocation Method of Gas Well Based on Production Loss Rate

LUO Jianxin, ZHAO Maolin, ZHANG Liehui, LIU Jizhu, FAN Zixuan

2024, 46(1):  89-96.  DOI: 10.11885/j.issn.1674-5086.2022.09.19.02

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Production allocation plays a very important role in gas well production. The existing production allocation are generally done based on 1/6~1/3 of the open flow rate. On the basis of studying the non-Darcy effect of gas in the formation, the concept of production loss rate was proposed. By quantifying the production loss caused by the non-Darcy effect, a chart of gas well production loss rate and dimensionless production was established. For each production allocation, the corresponding yield loss rate can be obtained. Therefore, reasonable production allocation can be carried out based on the yield loss rate. For certain high-pressure gas reservoirs, due to high formation pressure and high gas compression, the non-Darcy effect is not strong under formation conditions, and the rate of production loss is relatively low. This type of gas wells can increase production by a certain amount. This production allocation method can quantify the non-Darcy flow loss of reservoir gas and achieve reasonable production allocation of gas wells. This research achievement can further optimize the reasonable production allocation system of gas wells on the basis of conventional production allocation methods, better meet the long-term stable and efficient development needs of gas wells, and provide useful reference for gas reservoir development.

Segmented Water Control Strategy for Small-angle Swallowtail Sidetracked Horizontal Wells in the Same Layer

TANG Xiaoxu, PEI Bailin, ZHAO Wei

2024, 46(1):  97-104.  DOI: 10.11885/j.issn.1674-5086.2021.08.31.01

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In Bohai Oilfield, the number of wells with high water cut, low production and low efficiency has gradually increased, and the production of some blocks has declined rapidly. Sidetracking in the same layer with segmented water control completion was an effective method to tackle high water cut, low production and inefficient wells. Whereas, the effect of water control was not significant for small-angle swallowtail sidetracked horizontal wells with segmented water control technique. The theoretical model was build to find the reason why the effect of water control failed and it was found out that the original wellbore of this type of wells played the main role in this failure. After considering factors such as feasibility and economics, adjusted on existing drilling and completion method, a comprehensive drilling and completion improvement strategy featuring horizontal section extension and piping optimization for completion string was proposed, and the effectiveness of this strategy was verified in the field. The water control effect was much better than expected, no water production has been witnessed 164 d after commissioning, and the cumulative oil production in water free was as high as 15 000 m³. The target well adopting the new strategy achieved significant water control effect, while the cost of single well construction increased by only 8.8%. It provides ideas and technical reserves for the follow-up treatment of similar low production and low efficiency wells.

Evaluation Method of Development Effect of Natural Gas Drive Reservoir Based on Fuzzy Evaluation Strategy

HU Shuyong, ZHENG Bingyang, YIN Yanfang

2024, 46(1):  105-114.  DOI: 10.11885/j.issn.1674-5086.2021.04.12.03

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Injecting natural gas to enhance oil recovery has a good application prospect, but at present, there is a lack of corresponding development effect evaluation index system and standard for natural gas flooding reservoirs, and it is impossible to evaluate the development effect correctly, objectively and scientifically. According to the industry standard of "oilfield development level classification" and the evaluation index system of water flooding and CO₂ miscible flooding development effect, 10 evaluation indexes for evaluating the development effect of natural gas flooding reservoirs are selected: recovery improvement range, oil exchange rate, production increase ratio, reserve utilization degree, reserve control degree, pressure maintenance level, gas storage rate, gas-oil ratio increase ratio, stage injection-production ratio and gas injection timing. Combined with the geological characteristics, production performance and gas injection development characteristics of W natural gas drive reservoir, the evaluation index system and evaluation standard of natural gas drive development effect are established. The development effect evaluation method of natural gas flooding reservoir based on fuzzy comprehensive evaluation decision is established by using analytic hierarchy process, fuzzy transformation principle and maximum membership degree principle. The traditional single index and qualitative development effect evaluation are transformed into multi-factor and quantitative development effect evaluation. The application example shows that the evaluation index system and evaluation method of natural gas flooding development effect are feasible and effective, and have certain guiding significance for the evaluation of the development effect of the same type of natural gas flooding reservoir.

A Study on the Hydraulic Isolation Property of Cement-casing and Cement-formation Interfaces by Oleophilic Cement Slurry

HUANG Sheng, ZHOU Can, LI Zaoyuan, YANG Chuan, LIU Yang

2024, 46(1):  115-125.  DOI: 10.11885/j.issn.1674-5086.2021.10.03.01

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When cementing with oil-based drilling fluid in shale gas wells, oil in casing and wellbore is easy to reduce the interface isolation performance and form channeling circulation channels, which will have a negative impact on subsequent production. Although the pre-fluid can effectively improve the interface wetting reversal, the oil film retention and adhesion will still occur due to the limitation of flushing efficiency. To this end, we add oil-wetting surfactants to cement slurry, and form oil-wetting cement slurry, giving cement oil-wetting ability. Contact angle, shear bonding strength and interfacial hydraulic isolation tests were used to evaluate the oil-wetting ability and interfacial isolation effect of the cement. It is found that the contact angle of non-polar solvent on the surface of oil-wetting cement is much lower than that on the surface of conventional cement, and the non-polar solvent has good oil-wetting performance. After oil-wet cement cementing with casing and shale core containing white oil and oil-base drilling fluid, the resistance to fluid cross-flow pressure of the cement-casing interface and cement-formation interface were increases by 5 times and 4 times, and the shear bonding strength increases by 205% and 122%, respectively. The addition of oil-wetting surfactant has no negative effect on the hydration degree of cement, mechanical properties of cement and basic engineering performance of cement stone. The results show that the addition of the oil-wetting surfactant can effectively improve the cement ring and oil-bearing interface, and has the potential to improve the cement sheath, casing and formation interface bonding and isolation performance under oil-based drilling fluid condition.

Research and Application on Optimization of Injection Production Process for Underground Gas Storage

GAO Jifeng, YIN Yongming, GONG Mingming, SUN Juan, WU Jiawei

2024, 46(1):  126-135.  DOI: 10.11885/j.issn.1674-5086.2022.05.17.03

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The construction of gas storage is of great strategic significance to the safe and balanced gas supply of the gas supply pipeline network, and plays a pivotal role in natural gas peak shaving. At present, there are some problems in the process of gas storage, such as the potential safety hazard of compressor unit venting to air emission, the exceeding of booster gas lubricating oil, the exceeding of light hydrocarbon of produced gas, emission of tail gas from glycol regeneration system to air, salt accumulation corrosion of gathering and transmission pipeline and so on. For the venting of the middle body, a venting ejection device is set to lead the emissions to the flare for centralized discharge, avoiding the hidden dangers of the accumulation of combustible gas in the station; For excessive lubricating oil content (volume ratio of 16×10^-6), set high-pressure degreaser to reduce the lubricating oil content of booster gas, and eliminate secondary pollution; by optimizing the absorption tower and regeneration device of the dehydration unit the foaming and deactivation of glycol is avoided; through the modification of the glycol regeneration gas system, the regeneration gas can be recycled, reducing environmental pollution and saving energy consumption.

A Study on the Law of Liquid Accumulation Influence in Southern Sichuan Wet Gas Pipeline

WU Kunyi, ZHANG Lulu, LIN Yu, LI Weixi, ZHOU Jun

2024, 46(1):  136-146.  DOI: 10.11885/j.issn.1674-5086.2022.07.23.01

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In order to solve the serious problem of liquid accumulation in the undulating wet gas gathering and transporting pipeline of a gas field in southern Sichuan, a liquid accumulation model is established based on OLGA simulation software. The influence of gas volume, infusion volume, pressure and temperature on the amount of liquid accumulation in the pipeline is taken into account, and the change rule of liquid accumulation in the pipeline with gas volume, pressure, infusion volume and ambient temperature is revealed. The map of liquid accumulation is drawn, and the change trend of liquid accumulation is displayed directly, which provides certain data support for analyzing the effect of liquid accumulation in gas fields. Due to the complexity of flow pattern variation in the pipeline with large drop fluctuation, the evolution process of flow pattern under different working conditions is analyzed. The results show that the liquid first forms annular flow in the long updip pipe section, and gradually accumulates upward to form slug flow with the increase of liquid accumulation until the pipe is full of liquid accumulation. Based on the law of liquid accumulation, the pigging operation under mixed and separate transportation conditions is established and simulated, and the feasibility of determining pigging period by the methods of minimum gas transfer efficiency, maximum liquid accumulation amount and maximum allowable pressure drop is studied. The results show that the pigging period of the maximum allowable pressure drop method is 4.5 days for mixed transportation conditions. The pigging period is determined to be 32.0 days by the method of maximum liquid accumulation.

Leakage Hazard Area of Natural Gas Stations Based on Scenario Cluster Analysis

XIAO Fei, YANG Lu, WANG Xiao, ZHAO Xueqing, XIE Zongbao

2024, 46(1):  147-155.  DOI: 10.11885/j.issn.1674-5086.2022.07.22.02

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Leakage hazard area can provide the basis for decision in maintenance management and emergency evacuation of natural gas stations. However, the relevant researches were mostly focused on the single leakage scenario with the highest probability of occurrence or the most serious loss. In view of the above problems, a method based on scenario cluster analysis for the leakage hazard area classification was developed, and a gas transmission station was selected for test. The typical 153 scenarios were selected via K-means cluster analysis, and the gas distribution for different leakage scenarios were calculated from CFD simulations. Finally, a leakage classification area was obtained with the consideration of scenario probability and its gas distribution. By comparison, the leakage hazard area in this paper solved the problems of single scenario, such as bad generality and flexibility. It also improved the efficiency of work by decreasing data redundancy.

An Analysis of the Impact of Energy Pricing on the Revenue of Natural Gas Network

CHEN Fei

2024, 46(1):  156-169.  DOI: 10.11885/j.issn.1674-5086.2021.09.23.02

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The proportion of natural gas in China's primary energy is increasing, and its value is mainly reflected in the heat generated during combustion. China still focuses on the volume measurement and pricing of natural gas, which is not conducive to the development of the domestic natural gas market and the integration with the international market. The implementation of energy measurement and pricing can better reflect the value of natural gas. This paper studies a variety of energy pricing methods, and carries out component tracking analysis based on SPS software. Taking the Sichuan-East gas transmission pipeline as an example, we calculate gas revenue of enterprises after the volume measurement method is changed to energy measurement method, analyze the influence of different energy measurement method on the gas revenue of enterprises, and determine the favorable energy measurement method, that is, 36.84 MJ/m³ is selected as the national reference calorific value. After studying the influence of different gas supply schemes from multiple gas sources on gas revenue, we suggest the gas supply scheme to maximize gas revenue: increasing daily gas supply of Yuanba Gas Field, taking Fuling Shale Gas as the main gas source, and Puguang Gas Field as the auxiliary gas source. The sensitivity analysis of the selection of the base calorific value to the gas revenue was carried out to clarify the influence of the base calorific value on the gas revenue, and the minimum influence of the base calorific value on the gas revenue was determined to be 36.52 MJ/m³ after the reform of pricing method.

PETROLEUM MACHINERY AND OILFIELD CHEMISTRY

The Influence of Cement Sheath Loss on Multi-layer Casing Stress in High Temperature and High Pressure Wells

SONG Lin, SHU Zhenhui, WU Yanxian, LIAN Zhanghua, SHI Junlin

2024, 46(1):  170-178.  DOI: 10.11885/j.issn.1674-5086.2021.12.21.01

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Due to the complex cementing conditions in high temperature and high-pressure wells, there will be a loss between casing and cement sheath, resulting in casing damage and major accidents, especially in the case of the multi-layer casing. Taking a high-temperature high pressure and high quantity gas well in the southern margin of Junggar Basin as the research object, Based on the finite element principle and method of nonlinear contact problem of the discontinuous medium, the axisymmetric finite element model of casing cement sheath loss casing cement sheath casing formation is established by using ANSYS finite element analysis software, In this model, the hydrostatic fluid element is used at the missing part of the cement sheath, the Extended Drucker Prager constitutive model is used for the rock and cement sheath, and the contact mechanics finite element model is used for all the interfaces. The research results show that: the newly established finite element of cement sheath loss can accurately analyze the stress of cement sheath loss casing under complex conditions, and solve the problems of fluid-solid coupling at the cement sheath loss where the previous model can not simulate; when there is the annular loss between Casing and cement sheath, The maximum stress occurs near the interface where the cement sheath is missing. The lack of cement sheath and the nature of the liquid have a great impact on the casing. In deep and ultra-deep wells, it is recommended to optimize the return height of the cement sheath so that the cement sheath does not return to the wellhead, reduce the length of cementing section, eliminate the problem of cement sheath loss and ensure its wellbore integrity. In addition, maintaining reasonable internal pressure during mining is also one of the effective measures to prevent and control cement sheath loss.

Research on Safety Evaluation Method of Casing in Geothermal Well

ZHANG Zhi, FENG Xiaoxiao

2024, 46(1):  179-188.  DOI: 10.11885/j.issn.1674-5086.2021.09.29.02

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Compared with traditional geothermal resources, deep geothermal resources have greater development potential. However, due to the higher bottomhole temperature of deep geothermal wells, the high temperature fluid in the development and exploitation causes the casing thermal expansion, which tends to cause casing yield deformation. At present, there are many challenges in theoretical research and technical practice for casing safety of deep geothermal wells. Therefore, according to the thick-walled cylinder theory and the basic theory of thermoelastic mechanics, the axial thermal stress of casing is reduced by applying thermal stress in advance, and the contact problem of formation-cement ring-casing after high temperature cement stone damage is considered. Based on the principle that the effective stress of casing is controlled within the minimum yield limit at the corresponding temperature, the safety factor of casing string is designed according to the strength of casing string, the safety performance of casing is evaluated, and the design method of casing preheating stress in deep geothermal wells is established to alleviate the problem of thermal damage of casing caused by high temperature. The analysis results show that the density of cement slurry has little effect on the damage factor, and the elastic modulus of cement ring plays a leading role in the damage factor. Under the water injection condition (water injection temperature at 65 ℃) preheat below 250 ℃ can meet the design conditions. Under the condition of geothermal production (geothermal temperature at 346 ℃), the safety design requirements is satisfied when preheat is above 200 ℃ to meet.