WO2022193655A1 - 一种基于井壁力学失稳垮塌的地应力大小评价方法 - Google Patents

一种基于井壁力学失稳垮塌的地应力大小评价方法 Download PDF

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WO2022193655A1
WO2022193655A1 PCT/CN2021/125957 CN2021125957W WO2022193655A1 WO 2022193655 A1 WO2022193655 A1 WO 2022193655A1 CN 2021125957 W CN2021125957 W CN 2021125957W WO 2022193655 A1 WO2022193655 A1 WO 2022193655A1
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stress
collapse
data
magnitude
calculation
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PCT/CN2021/125957
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French (fr)
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梁利喜
何坷培
刘向君
熊健
丁乙
张文
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西南石油大学
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    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B49/00—Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells
    • E21B49/006—Measuring wall stresses in the borehole
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F30/00—Computer-aided design [CAD]
    • G06F30/20—Design optimisation, verification or simulation
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F30/00—Computer-aided design [CAD]
    • G06F30/20—Design optimisation, verification or simulation
    • G06F30/28—Design optimisation, verification or simulation using fluid dynamics, e.g. using Navier-Stokes equations or computational fluid dynamics [CFD]
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F17/00—Digital computing or data processing equipment or methods, specially adapted for specific functions
    • G06F17/10—Complex mathematical operations
    • G06F17/11—Complex mathematical operations for solving equations, e.g. nonlinear equations, general mathematical optimization problems
    • G06F17/12—Simultaneous equations, e.g. systems of linear equations
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F17/00—Digital computing or data processing equipment or methods, specially adapted for specific functions
    • G06F17/10—Complex mathematical operations
    • G06F17/16—Matrix or vector computation, e.g. matrix-matrix or matrix-vector multiplication, matrix factorization
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B2200/00—Special features related to earth drilling for obtaining oil, gas or water
    • E21B2200/20—Computer models or simulations, e.g. for reservoirs under production, drill bits
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V20/00—Geomodelling in general
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V2210/00—Details of seismic processing or analysis
    • G01V2210/10—Aspects of acoustic signal generation or detection
    • G01V2210/12—Signal generation
    • G01V2210/123—Passive source, e.g. microseismics
    • G01V2210/1234—Hydrocarbon reservoir, e.g. spontaneous or induced fracturing
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V2210/00—Details of seismic processing or analysis
    • G01V2210/60—Analysis
    • G01V2210/62—Physical property of subsurface
    • G01V2210/624—Reservoir parameters
    • G01V2210/6242—Elastic parameters, e.g. Young, Lamé or Poisson
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F2119/00—Details relating to the type or aim of the analysis or the optimisation
    • G06F2119/14—Force analysis or force optimisation, e.g. static or dynamic forces

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  • the invention relates to the technical fields of geomechanics, oil and gas well engineering, and oil and natural gas exploitation, in particular to a method for evaluating the magnitude of in-situ stress based on the mechanical instability and collapse of the borehole wall.
  • In-situ stress is an important basic parameter required for the design and implementation of deep underground engineering, especially in the field of oil and gas drilling and production. Sand prediction and establishment of safe mining operation system are of great significance.
  • deep in-situ stress evaluation is mainly carried out through drilling core stress test, stress analysis of mine data such as fracturing and drilling, and in-situ stress profile logging calculation.
  • the traditional method needs to calibrate and constrain the stress obtained by stress test or mine data analysis to ensure the reliability of the logging in-situ stress calculation results; the method of hydraulic fracturing data analysis of in-situ stress is suitable for large-scale stimulation fracturing construction. There are many influencing factors of the obtained data, and it is difficult to meet the needs of scientific evaluation of in-situ stress; borehole collapse and drilling-induced fractures are another important information that can be used to evaluate deep in-situ stress, but it is mainly limited to the evaluation of deep in-situ stress direction. Analysis, although Mark D.
  • Zoback proposed a theoretical model for calculating the in-situ stress based on borehole collapse, due to the heterogeneity of deep formation rocks, the irregularity of actual borehole collapse, and the parameters related to borehole collapse required by the model. It is restricted by factors such as acquisition. At present, the theoretical model is still difficult to be effectively applied to the calculation and evaluation of the in-situ stress in the deep. Therefore, the present invention proposes an evaluation method of the in-situ stress based on the mechanical instability and collapse of the wellbore to solve the problem in the prior art. problems in .
  • the purpose of the present invention is to propose a method for evaluating the magnitude of in-situ stress based on the mechanical instability and collapse of the borehole wall.
  • the data and collapse data are classified, and the stress limit equilibrium equation based on the strain coefficient and the overdetermined equation based on the information constraint of the critical collapse formation are solved, and the maximum in-situ horizontal principal stress in the deep and the minimum in-situ horizontal principal stress in the deep are calculated and evaluated, and given.
  • the method for evaluating the rationality of in-situ stress results is developed, and the quantitative calculation and evaluation of the horizontal principal stress of the deep formation is realized, which provides the necessary basic parameters of deep formation mechanics for deep underground engineering, especially oil and gas well engineering and oil and gas production engineering.
  • the present invention is realized through the following technical solutions: a method for evaluating the magnitude of in-situ stress based on the mechanical instability and collapse of the borehole wall, comprising the following steps:
  • Step 1 Screening and classification of mechanically unstable collapsed well sections. According to the geological research results of the research area, screen well sections with relatively gentle stratigraphic structure, and calculate the borehole diameter expansion rate according to the following formula.
  • CER i , CAL i , and BIT i are the borehole expansion rate, borehole diameter and drill bit size at the i-th formation depth point of the analyzed well section, respectively.
  • Stratigraphic data points and then classify the stratigraphic data at each depth based on the data obtained by screening and the size of the diameter expansion rate;
  • Step 2 Use the construction strain coefficient Represents the magnitude of the in-situ horizontal in-situ stress in the deep, as follows:
  • the structural strain coefficient of the vertical wellbore when the wellbore angle is 90° or 270° is used. Represents the borehole wall stress, as follows
  • Step 3 Establish the equation of structural strain coefficient based on the limit equilibrium condition of borehole stress, select the rock strength criterion for judging the collapse of the bottom layer, and bring equations (5), (6) and (7) in step 2 into the selected rock strength criterion , the construction of the structural strain coefficients
  • the overdetermined system of equations as follows
  • Step 4 Use the least squares method to solve and calculate the horizontal maximum structural strain coefficient and the horizontal minimum structural strain coefficient of the example well section, and put them into equations (3) and (4) to calculate the horizontal maximum structural strain coefficient of the analyzed well section. Stress, horizontal minimum principal stress;
  • Step 5 Bring the obtained horizontal maximum structural strain coefficient, horizontal minimum structural strain coefficient and the corresponding parameters of the classified strata into formula (8) to calculate Fi, and carry out two kinds of calculation judgments. When the result does not satisfy any one of the judgments, Re-select the analysis well section and repeat steps 2 to 5 for calculation and analysis until the two criteria are satisfied.
  • a further improvement is that: in the first step of screening, according to the logging interpretation results of mud content, the formation sections with high clay content such as mudstone and shale are eliminated, and at the same time, structural planes such as fractures, bedding, and joints are eliminated.
  • the interval and the interval with relatively broken formation structure are used to exclude the hydration of the clay-rich formation and the wellbore instability and collapse formation dominated by the structure plane.
  • step 1 the deep formation data in step 1 is divided into three categories: 1 S-type formation data with stable borehole wall: 0 ⁇ CER i ⁇ 3%, no obvious diameter expansion, regular hole diameter data; 2 critical balance data A-class formation data: 3% ⁇ CER i ⁇ 7%; 3 B-class formation data with significant collapse: CER i >7%, data of well sections with significant diameter expansion.
  • a further improvement is: in the step two formulas (2), (3), (4) are the horizontal maximum structural strain coefficient and the horizontal minimum structural strain coefficient, respectively; DEP and Den are the formation depth and density, respectively; E and ⁇ are the elastic modulus and Poisson's ratio of the formation, respectively; ⁇ V is the vertical principal stress; The structural strain coefficients are The maximum horizontal principal stress and the minimum horizontal principal stress corresponding to the stratum at the time;
  • D mud is the density of the drilling fluid used for drilling
  • P w is the liquid column pressure of the bottom-hole drilling fluid
  • a further improvement is that: in the step 3, the rock strength criterion selects one of the Mohr-Coulumb strength criterion, the Drucker-Prager strength criterion, and the Hoek-Brown strength criterion according to the mechanical properties of the formation and the failure characteristics, which is used for the estimation of the horizontal in-situ stress. .
  • calculation judgment 1 for the well section with significant well diameter expansion
  • type B data that did not participate in the above calculation is brought into the formula (8), and the judgment is made.
  • a further improvement is that when both the calculation criterion 1 and the calculation criterion 2 are established, it means that the estimation results of the structural strain coefficient and in-situ stress are reasonable.
  • the present invention solves the stress limit equilibrium equation based on the strain coefficient and the overdetermined equation based on the information constraint of the critical collapse stratum by screening the wellbore stress instability collapsed well section data and the collapse data classification, and the calculation is evaluated.
  • the maximum in-situ horizontal principal stress in the deep and the minimum in-situ horizontal principal stress in the deep, and the rationality evaluation method of the in-situ stress results is given, which realizes the quantitative calculation and evaluation of the horizontal principal stress in the deep strata, which is very useful for deep underground engineering, especially oil and gas wells.
  • Engineering, oil and gas extraction engineering, etc. provide the necessary basic parameters of deep formation mechanics.
  • Fig. 1 is a flow chart of the estimation method of the present invention.
  • FIG. 2 is a schematic diagram of screening well caliber and rock mechanics-related parameters of a well section according to an embodiment of the present invention.
  • FIG. 3 is a schematic diagram of formation data of excluding high-content clay intervals according to an embodiment of the present invention.
  • FIG. 4 is a schematic diagram of estimation results of in-situ stress at each depth point according to an embodiment of the present invention.
  • FIG. 5 is a schematic diagram of a calculation and discrimination result of Fi according to an embodiment of the present invention.
  • this embodiment provides a method for evaluating the magnitude of in-situ stress based on the mechanical instability and collapse of the borehole wall, including the following steps:
  • Step 1 Screening and classification of mechanically unstable collapsed well sections. According to the geological research results of the research area, screen well sections with relatively gentle stratigraphic structure, and calculate the borehole diameter expansion rate according to the following formula.
  • CER i , CAL i , and BIT i are the borehole expansion rate, borehole diameter and drill bit size at the i-th formation depth point of the analyzed well section, respectively.
  • step 5 From the data of type A, select the data whose depth span is not more than 15 meters for the analysis of step 2 to step 5.
  • the well section with relatively gentle stratigraphic structure is screened as shown in Figure 2 of the description; according to steps (2) and (3), the well section shown in Figure 3 of the manual is screened for the formation section and the borehole expansion rate is calculated. , the results are shown in Figure 3 of the description.
  • the formation is divided into three types, and the type A data is selected and analyzed from the type A data according to the above method. The results are shown in Table 1.
  • Step 2 Use the construction strain coefficient Represents the magnitude of the in-situ horizontal in-situ stress in the deep, as follows:
  • (3), (4) are the horizontal maximum structural strain coefficient and the horizontal minimum structural strain coefficient, respectively; DEP and Den are the formation depth and density, respectively; E and ⁇ are the elastic modulus and Poisson's ratio of the formation, respectively; ⁇ V is the vertical principal stress; The structural strain coefficients are The maximum horizontal principal stress and the minimum horizontal principal stress corresponding to the stratum at the time;
  • the structural strain coefficient of the vertical wellbore when the wellbore angle is 90° or 270° is used. Represents the borehole wall stress, as follows
  • D mud is the density of the drilling fluid used for drilling
  • P w is the liquid column pressure of the bottom-hole drilling fluid
  • Step 3 Establish the equation of structural strain coefficient based on the limit equilibrium condition of borehole stress, select the rock strength criterion for judging the collapse of the bottom layer, and select the Mohr-Coulumb strength criterion, Drucker-Prager strength criterion, and Hoek-Brown strength criterion according to the formation mechanical properties and failure characteristics
  • One of the strength criteria in the criteria is used to estimate the magnitude of the horizontal in-situ stress.
  • the formulas (5), (6) and (7) in step 2 are brought into the selected rock strength criteria, and the structural strain coefficients are constructed.
  • the overdetermined system of equations as follows
  • Depi , E i , ⁇ i , a i , C i are the depth, elastic modulus, Poisson's ratio, Biots coefficient, cohesive force and internal friction angle of the i-th formation depth point of the analyzed well section, respectively;
  • ⁇ Vi and P pt are the vertical direction of the i-th formation depth point of the analyzed well section, respectively stress, pore pressure;
  • Step 4 Use the least squares method to solve and calculate the horizontal maximum structural strain coefficient and the horizontal minimum structural strain coefficient of the example well section, and put them into equations (3) and (4) to calculate the horizontal maximum structural strain coefficient of the analyzed well section. Stress, horizontal minimum principal stress.
  • equation (10) is a binary first-order overdetermined equation system.
  • equation (11) the least squares solution of the equation is obtained, that is, the horizontal maximum structural strain coefficient ⁇ is obtained.
  • the horizontal maximum structural strain coefficient of the example well section can be calculated Horizontal minimum structural strain factor They are 1.31413 ⁇ 10 -3 and 0.30406 ⁇ 10 -3 respectively. Substitute them into equations (3) and (4) to obtain the horizontal maximum principal stress and horizontal minimum principal stress of the analyzed well section. The results are shown in Figure 4 of the specification. Show.
  • Step 5 Calculate the obtained horizontal maximum structural strain coefficient Horizontal minimum structural strain factor and the corresponding parameters of the A-class strata are brought into formula (8) or formula (9) to calculate Fi, and the calculation and discrimination are carried out:
  • the in-situ stress estimation result can be considered unreasonable, and it is necessary to re-select the analysis well section and repeat steps 2 to 5 for calculation and analysis until the calculation criterion 1 and calculation criterion are reached. Both are established, and the in-situ stress results are reasonable.
  • the in-situ stress evaluation method based on the mechanical instability and collapse of the borehole wall constructs the stress limit equilibrium equation based on the strain coefficient and the overdetermined equation based on the information constraint of the critical collapse formation by screening the wellbore stress instability and collapse well section data and the classification of the collapse data. Solving, calculating and evaluating the deep in-situ horizontal maximum principal stress and the deep in-situ horizontal minimum principal stress, and giving a rationality evaluation method for the in-situ stress results, realizing the quantitative calculation and evaluation of the magnitude of the horizontal principal stress in the deep strata, which is the most suitable for the deep underground.
  • Engineering, especially oil and gas well engineering, oil and gas extraction engineering, etc. provides the necessary basic parameters of deep formation mechanics.

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Abstract

一种基于井壁力学失稳垮塌的地应力大小评价方法，包括力学失稳垮塌井段筛选及数据分类、基于构造应变系数表示深部地应力大小与井壁应力大小、基于应力极限平衡条件建立构造应变系数方程、基于最小二乘法求解构造应变系数并计算水平主应力、地应力估算结果合理性评价；该方法通过筛选井壁应力失稳垮塌井段数据、垮塌数据分类，构建基于应变系数的应力极限平衡方程以及基于临界垮塌地层信息约束的超定方程求解，计算出评价深部原地水平最大主应力和最小主应力，并给出了原地应力结果合理性评价方法，实现了深部地层水平主应力大小的定量计算评价，为地下深部工程尤其是油气井工程、油气开采工程等提供了所必需的深部地层力学基础参数。

Description

一种基于井壁力学失稳垮塌的地应力大小评价方法 技术领域
本发明涉及地质力学、油气井工程、石油与天然气开采技术领域，尤其涉及一种基于井壁力学失稳垮塌的地应力大小评价方法。
背景技术
原地应力是地下深部工程设计、实施所需的重要基础参数，尤其在油气钻采领域，深部原地应力大小评价对井眼轨迹设计、井壁稳定评价、完井优化、增产压裂、出砂预测以及安全开采作业制度建立等都具有极其重要意义，目前深部原地应力评价主要通过钻井岩心应力测试、压裂与钻井等矿场资料应力分析、地应力剖面测井计算等；
传统的方法需要用应力测试或矿场资料分析得到的应力大小进行标定、约束才能保证测井地应力计算结果的可靠性；水力压裂资料分析地应力的方法对于大型增产压裂压裂施工，所获取的资料影响因素众多，难以满足地应力大小科学评价的需求；井壁垮塌、钻井诱导缝是可用于评价深部原地应力的又一重要信息，但主要局限于深部原地应力方向的评价分析，尽管Mark D.Zoback提出了基于井眼垮塌计算地应力大小的理论模型，但由于深部地层岩石的非均质性、实际井壁垮塌的不规则、模型所需的井壁垮塌相关参数无法获取等因素制约，目前，该理论模型尚难以有效实际应用于深部原地应力大小的计算评价，因此，本发明提出一种基于井壁力学失稳垮塌的地应力大小评价方法以解决现有技术中存在的问题。
发明内容
针对上述问题，本发明的目的在于提出一种基于井壁力学失稳垮塌的地应力大小评价方法，该基于井壁力学失稳垮塌的地应力大小评价方法通过筛选井壁应力失稳垮塌井段数据、垮塌数据分类，构建基于应变系数的应力极限平衡方程以及基于临界垮塌地层信息约束的超定方程求解，计算得到评价深部原地水平最大主应力、深部原地水平最小主应力，并给出了原地应力结果合理性评价方法，实现了深部地层水平主应力大小的定量计算评价，为地下深部工程尤其是油气井工程、油气开采工程等提供了所必需的深部地层力学基础参数。
为实现本发明的目的，本发明通过以下技术方案实现：一种基于井壁力学失稳垮塌的地应力大小评价方法，包括以下步骤：
步骤一、力学失稳垮塌井段筛选和分类，依据研究工区地质研究成果，筛选地层构造相对平缓的井段，并根据井径测井数据，按下式计算井壁扩径率
Figure PCTCN2021125957-appb-000001
CER i、CAL i、BIT i分别为所分析井段第i地层深度点的井壁的扩径率、井径以及钻头尺寸，选择井壁垮塌分布在水平最小主应力方位±15°范围内的地层数据点，再基于筛选得到的数据和扩径率大小对各深度地层数据进行分类；
步骤二、用构造应变系数
Figure PCTCN2021125957-appb-000002
表示深部原地水平地应力大小，如下式
Figure PCTCN2021125957-appb-000003
Figure PCTCN2021125957-appb-000004
Figure PCTCN2021125957-appb-000005
不考虑井周地层的渗流效应，在圆柱坐标系中，将直井井壁在井周角为90°或270°时用构造应变系数
Figure PCTCN2021125957-appb-000006
表示井壁应力大小，如下式
Figure PCTCN2021125957-appb-000007
Figure PCTCN2021125957-appb-000008
Figure PCTCN2021125957-appb-000009
步骤三、基于井壁应力极限平衡条件建立构造应变系数的方程，选择判定底层坍塌的岩石强度准则，将步骤二中的式(5)、(6)、(7)带入选择的岩石强度准则中，构建关于构造应变系数
Figure PCTCN2021125957-appb-000010
的超定方程组，如下式
Figure PCTCN2021125957-appb-000011
其中，函数
Figure PCTCN2021125957-appb-000012
的表达式取决于所选择的强度准则；
步骤四、利用最小二乘法求解计算实例井段水平最大构造应变系数和水平最小构造应变系数，并将其带入式(3)和式(4)即可计算得出所分析井段的水平最大主应力、水平最小主应力；
步骤五、将求解得到的水平最大构造应变系数、水平最小构造应变系数及分类地层的相应参数带入式(8)中计算Fi，并进行两种计算判别，结果不满足任意一种判别时，重新选择分析井段重复步骤二 至步骤五进行计算分析，直至满足两种判别即可。
进一步改进在于：所述步骤一中筛选时根据泥质含量测井解释结果，剔除掉泥岩、页岩等粘土含量较高的地层层段，并同时剔除掉裂缝、层理、节理等结构面发育层段以及地层结构相对较为破碎的层段，以排除富含粘土地层水化作用以及结构面主导的井壁失稳垮塌地层。
进一步改进在于：所述步骤一中深度地层数据分成三类：①井壁稳定的S类地层数据：0＜CER i≤3％，无明显扩径、井径规则井段数据；②临界平衡的A类地层数据：3％＜CER i≤7％；③显著垮塌的B类地层数据：CER i＞7％，扩径显著井段数据。
进一步改进在于：所述步骤二式(2)、(3)、(4)中
Figure PCTCN2021125957-appb-000013
分别为水平最大构造应变系数、水平最小构造应变系数；DEP、Den分别为地层深度、密度；E、μ分别为地层的弹性模量、泊松比；σ V为垂向主应力；
Figure PCTCN2021125957-appb-000014
分别为构造应变系数为
Figure PCTCN2021125957-appb-000015
时地层对应的水平最大主应力、水平最小主应力；
式(5)、(6)、(7)中D mud为钻井所用钻井液密度；P w为井底钻井液的液柱压力，
Figure PCTCN2021125957-appb-000016
进一步改进在于：所述步骤三中岩石强度准则根据地层力学特性、破坏特征选择Mohr-Coulumb强度准则、Drucker-Prager强度准则、Hoek-Brown强度准则中的一个强度准则用于水平地应力大小的估算。
进一步改进在于：所述步骤五中两种计算判别为：计算判别一：对于井径扩径显著井段，将未参与前述计算的B类数据带入式(8) 中，并进行判断
Figure PCTCN2021125957-appb-000017
计算判别二：对于井径规则、井壁稳定井段，将未参与前述计算的S类数据带入式(8)中，并进行判断
Figure PCTCN2021125957-appb-000018
进一步改进在于：当计算判别一和计算判别二均成立时，表示构造应变系数及地应力估算结果合理。
本发明的有益效果为：本发明通过筛选井壁应力失稳垮塌井段数据、垮塌数据分类，构建基于应变系数的应力极限平衡方程以及基于临界垮塌地层信息约束的超定方程求解，计算得到评价深部原地水平最大主应力、深部原地水平最小主应力，并给出了原地应力结果合理性评价方法，实现了深部地层水平主应力大小的定量计算评价，为地下深部工程尤其是油气井工程、油气开采工程等提供了所必需的深部地层力学基础参数。
附图说明
图1为本发明估算方法流程图。
图2为本发明实施例筛选井段井径及岩石力学相关参数示意图。
图3为本发明实施例剔除高含量粘土层段的地层数据示意图。
图4为本发明实施例各深度点地应力大小估算结果示意图。
图5为本发明实施例Fi计算判别结果示意图。
具体实施方式
为了加深对本发明的理解，下面将结合实施例对本发明做进一步详述，本实施例仅用于解释本发明，并不构成对本发明保护范围的限定。
根据图1、2、3、4、5所示，本实施例提供了一种基于井壁力学失稳垮塌的地应力大小评价方法，包括以下步骤：
步骤一、力学失稳垮塌井段筛选和分类，依据研究工区地质研究成果，筛选地层构造相对平缓的井段，并根据井径测井数据，按下式计算井壁扩径率
Figure PCTCN2021125957-appb-000019
CER i、CAL i、BIT i分别为所分析井段第i地层深度点的井壁的扩径率、井径以及钻头尺寸，选择井壁垮塌分布在水平最小主应力方位±15°范围内的地层数据点，再基于筛选得到的数据和扩径率大小将各深度地层数据为三类：
①井壁稳定的S类地层数据：0＜CER i≤3％，无明显扩径、井径规则井段数据；
②临界平衡的A类地层数据：3％＜CER i≤7％；
③显著垮塌的B类地层数据：CER i＞7％，扩径显著井段数据。
从A类数据中，选择深度跨距不大于15米的数据进行步骤2至步骤5的分析。
按上述方法筛选地层构造相对平缓的井段如说明书附图2所示；按步骤(2)、(3)对明书附图3所示井段，进行地层段筛选、井眼扩径率计算，结果如明书附图3所示。计算根据扩径率大小，将地层分成三类，并从A类数据中按上述方法选择分析A类数据，结果如表1所示
表1用于分析的数据表(A类数据)
Figure PCTCN2021125957-appb-000020
筛选时根据泥质含量测井解释结果，剔除掉泥岩、页岩等粘土含量较高的地层层段，并同时剔除掉裂缝、层理、节理等结构面发育层段以及地层结构相对较为破碎的层段，以排除富含粘土地层水化作用以及结构面主导的井壁失稳垮塌地层。
步骤二、用构造应变系数
Figure PCTCN2021125957-appb-000021
表示深部原地水平地应力大小，如下式
Figure PCTCN2021125957-appb-000022
Figure PCTCN2021125957-appb-000023
Figure PCTCN2021125957-appb-000024
式(2)、(3)、(4)中
Figure PCTCN2021125957-appb-000025
分别为水平最大构造应变系数、水平最小构造应变系数；DEP、Den分别为地层深度、密度；E、μ分别为地层的弹性模量、泊松比；σ V为垂向主应力；
Figure PCTCN2021125957-appb-000026
Figure PCTCN2021125957-appb-000027
分别为构造应变系数为
Figure PCTCN2021125957-appb-000028
时地层对应的水平最大主应力、水平最小主应力；
不考虑井周地层的渗流效应，在圆柱坐标系中，将直井井壁在井周角为90°或270°时用构造应变系数
Figure PCTCN2021125957-appb-000029
表示井壁应力大小，如下式
Figure PCTCN2021125957-appb-000030
Figure PCTCN2021125957-appb-000031
Figure PCTCN2021125957-appb-000032
式(5)、(6)、(7)中D mud为钻井所用钻井液密度；P w为井底钻井液的液柱压力，
Figure PCTCN2021125957-appb-000033
步骤三、基于井壁应力极限平衡条件建立构造应变系数的方程，选择判定底层坍塌的岩石强度准则，根据地层力学特性、破坏特征选择Mohr-Coulumb强度准则、Drucker-Prager强度准则、Hoek-Brown强度准则中的一个强度准则用于水平地应力大小的估算，将步骤二中的式(5)、(6)、(7)带入选择的岩石强度准则中，构建关于构造应变系数
Figure PCTCN2021125957-appb-000034
的超定方程组，如下式
Figure PCTCN2021125957-appb-000035
其中，函数
Figure PCTCN2021125957-appb-000036
的表达式取决于所选择的强度准则。
若选择Mohr-Coulumb强度准则，则关于构造应变系数
Figure PCTCN2021125957-appb-000037
的函数方程组如下：
Figure PCTCN2021125957-appb-000038
其中
Figure PCTCN2021125957-appb-000039
Figure PCTCN2021125957-appb-000040
上式中，Dep i、E i、μ i、a i、C i、
Figure PCTCN2021125957-appb-000041
分别为所分析井段第i地层深度点的深度、弹性模量、泊松比、Biots系数、内聚力以及内摩擦角；σ Vi、P pt分别为所分析井段第i地层深度点的垂向应力、孔隙压力；
Figure PCTCN2021125957-appb-000042
为所分析井段第i地层深度点钻井所用钻井液密度。
步骤四、利用最小二乘法求解计算实例井段水平最大构造应变系数和水平最小构造应变系数，并将其带入式(3)和式(4)即可计算得出所分析井段的水平最大主应力、水平最小主应力。
对式(9)所示方程用矩阵进行表达，如式(10)所示
Figure PCTCN2021125957-appb-000043
当K≥2时，均可求解得到水平最大构造应变系数ε H1、水平最小构造应变系数
Figure PCTCN2021125957-appb-000044
通常K＞2，此时式(10)为二元一次超定方程组，通过进行式(11)所示的变换运算，求得该方程的最小二乘解，即得到水平最大构造应变系数ε H1、水平最小构造应变系数
Figure PCTCN2021125957-appb-000045
Figure PCTCN2021125957-appb-000046
将求解得到的水平最大构造应变系数
Figure PCTCN2021125957-appb-000047
水平最小构造应变系数
Figure PCTCN2021125957-appb-000048
代入式(3)、式(4)计算得到水平最大主应力、水平最小主应力。
按照上述步骤可计算实例井段水平最大构造应变系数
Figure PCTCN2021125957-appb-000049
水平最小构造应变系数
Figure PCTCN2021125957-appb-000050
分别为1.31413×10 -3、0.30406×10 -3，将其代入式(3)、式(4)可到所分析井段的水平最大主应力、水平最小主应力，结果如说明书附图4所示。
步骤五、将求解得到的水平最大构造应变系数
Figure PCTCN2021125957-appb-000051
水平最小构造应变系数
Figure PCTCN2021125957-appb-000052
及A分类地层的相应参数带入式(8)或式(9)中计算Fi，并进行计算判别：
计算判别一：对于井径扩径显著井段，将未参与前述计算的B类数据带入式(8)或式(9)中，并进行判断
Figure PCTCN2021125957-appb-000053
计算判别二：对于井径规则、井壁稳定井段，将未参与前述计算的S类数据带入式(8)或式(9)中，并进行判断
Figure PCTCN2021125957-appb-000054
当计算判别一和计算判别二均成立时，表示构造应变系数及地应 力估算结果合理。
若大部分结果数据不满足计算判别一或不满足计算判别二，则可认为地应力估算结果不合理，需重新选择分析井段重复步骤二至步骤五进行计算分析，直至计算判别一、计算判别二均成立、地应力结果合理。
基于上述判定对实例井段进行Fi的计算判别分析，利S数据的计算判别一以及利用B类数据的计算判别二结果如说明书附图5所示。可看出：除个别分析结果数据点外，利S数据的计算判别一结果普遍大于0且利用B类数据的计算判别二结果普遍小于0，因此地应力估算结果合理。
该基于井壁力学失稳垮塌的地应力大小评价方法通过筛选井壁应力失稳垮塌井段数据、垮塌数据分类，构建基于应变系数的应力极限平衡方程以及基于临界垮塌地层信息约束的超定方程求解，计算得到评价深部原地水平最大主应力、深部原地水平最小主应力，并给出了原地应力结果合理性评价方法，实现了深部地层水平主应力大小的定量计算评价，为地下深部工程尤其是油气井工程、油气开采工程等提供了所必需的深部地层力学基础参数。
以上显示和描述了本发明的基本原理、主要特征和优点。本行业的技术人员应该了解，本发明不受上述实施例的限制，上述实施例和说明书中描述的只是说明本发明的原理，在不脱离本发明精神和范围的前提下，本发明还会有各种变化和改进，这些变化和改进都落入要求保护的本发明范围内。本发明要求保护范围由所附的权利要求书及 其等效物界定。

Claims (7)

  1. 一种基于井壁力学失稳垮塌的地应力大小评价方法，其特征在于包括以下步骤：
    步骤一、力学失稳垮塌井段筛选和分类，依据研究工区地质研究成果，筛选地层构造相对平缓的井段，并根据井径测井数据，按下式计算井壁扩径率
    Figure PCTCN2021125957-appb-100001
    CER i、CAL i、BIT i分别为所分析井段第i地层深度点的井壁的扩径率、井径以及钻头尺寸，选择井壁垮塌分布在水平最小主应力方位±15°范围内的地层数据点，再基于筛选得到的数据和扩径率大小对各深度地层数据进行分类；
    步骤二、用构造应变系数(ε H1，ε h2)表示深部原地水平地应力大小，如下式
    Figure PCTCN2021125957-appb-100002
    Figure PCTCN2021125957-appb-100003
    Figure PCTCN2021125957-appb-100004
    不考虑井周地层的渗流效应，在圆柱坐标系中，将直井井壁在井周角为90°或270°时用构造应变系数(ε H1，ε h2)表示井壁应力大小，如下式
    Figure PCTCN2021125957-appb-100005
    Figure PCTCN2021125957-appb-100006
    σ r(ε H1，ε h2)＝P w  (7)
    步骤三、基于井壁应力极限平衡条件建立构造应变系数的方程，选择判定底层坍塌的岩石强度准则，将步骤二中的式(5)、(6)、(7)带入选择的岩石强度准则中，构建关于构造应变系数ε H1，ε h2的超定方程组，如下式
    F i(ε H1，ε h2)＝0  (8)
    其中，函数F i(ε H1，ε h2)的表达式取决于所选择的强度准则；
    步骤四、利用最小二乘法求解计算实例井段水平最大构造应变系数和水平最小构造应变系数，并将其带入式(3)和式(4)即可计算得出所分析井段的水平最大主应力、水平最小主应力；
    步骤五、将求解得到的水平最大构造应变系数、水平最小构造应变系数及分类地层的相应参数带入式(8)中计算Fi，并进行两种计算判别，结果不满足任意一种判别时，重新选择分析井段重复步骤二至步骤五进行计算分析，直至满足两种判别即可。
  2. 根据权利要求1所述的一种基于井壁力学失稳垮塌的地应力大小评价方法，其特征在于：所述步骤一中筛选时根据泥质含量测井解释结果，剔除掉泥岩、页岩等粘土含量较高的地层层段，并同时剔除掉裂缝、层理、节理等结构面发育层段以及地层结构相对较为破碎的层段，以排除富含粘土地层水化作用以及结构面主导的井壁失稳垮塌地层。
  3. 根据权利要求1所述的一种基于井壁力学失稳垮塌的地应力 大小评价方法，其特征在于：所述步骤一中深度地层数据分成三类：①井壁稳定的S类地层数据：0＜CER i≤3％，无明显扩径、井径规则井段数据；②临界平衡的A类地层数据：3％＜CER i≤7％；③显著垮塌的B类地层数据：CER i＞7％，扩径显著井段数据。
  4. 根据权利要求1所述的一种基于井壁力学失稳垮塌的地应力大小评价方法，其特征在于：所述步骤二式(2)、(3)、(4)中ε H1，ε h2分别为水平最大构造应变系数、水平最小构造应变系数；DEP、Den分别为地层深度、密度；E、μ分别为地层的弹性模量、泊松比；σ V为垂向主应力；σ H1(ε H1，ε h2)、σ h2(ε H1，ε h2)分别为构造应变系数为ε H1，ε h2时地层对应的水平最大主应力、水平最小主应力；
    式(5)、(6)、(7)中D mud为钻井所用钻井液密度；P w为井底钻井液的液柱压力，
    Figure PCTCN2021125957-appb-100007
  5. 根据权利要求1所述的一种基于井壁力学失稳垮塌的地应力大小评价方法，其特征在于：所述步骤三中岩石强度准则根据地层力学特性、破坏特征选择Mohr-Coulumb强度准则、Drucker-Prager强度准则、Hoek-Brown强度准则中的一个强度准则用于水平地应力大小的估算。
  6. 根据权利要求1所述的一种基于井壁力学失稳垮塌的地应力大小评价方法，其特征在于：所述步骤五中两种计算判别为：计算判别一：对于井径扩径显著井段，将未参与前述计算的B类数据带入式(8)中，并进行判断F i(ε H1，ε h2)＞0；
    计算判别二：对于井径规则、井壁稳定井段，将未参与前述计算 的S类数据带入式(8)中，并进行判断F i(ε H1，ε h2)＜0。
  7. 根据权利要求6所述的一种基于井壁力学失稳垮塌的地应力大小评价方法，其特征在于：当计算判别一和计算判别二均成立时，表示构造应变系数及地应力估算结果合理。
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