Stratum maximum horizontal principal stress calculation method suitable for tectonic extrusion state

Abstract

The invention relates to a method for calculating the maximum horizontal principal stress of a stratum in a tectonic extrusion state, belongs to the technical field of oil and gas field exploration, and particularly relates to the field of new energy exploration such as shale gas exploration and geothermal exploration. On the basis of a Huangrongvessel model for conventional crustal stress calculation, the internal correlation between the maximum difference stress and the extrusion structure is found, a correction term related to the maximum difference stress is introduced, an improved calculation formula is provided, the precision and adaptability of the Huangrongvessel model are improved, and the calculation efficiency is improved. And the maximum horizontal principal stress field in the extrusion state can be reflected more accurately.

Description

Technical Field

[0001] The present invention relates to the field of oil and gas field exploration technology, in particular to the field of new energy exploration such as shale gas exploration and geothermal exploration, and specifically to a method for calculating the maximum horizontal principal stress of a stratum suitable for a structural compression state. Background Art

[0002] Geostress calculation is an important part of geophysical exploration and is of great significance for revealing the stress distribution of underground rock masses and the laws of geological tectonic activity. With the continuous advancement of geophysical exploration technology and numerical simulation methods, geostress research has gradually developed from qualitative analysis to quantitative calculation, which can more accurately reflect the stress state under complex geological conditions. The current research focus is to combine a variety of detection methods with theoretical models to conduct a systematic analysis of the stress field deep in the crust, thereby providing a scientific basis for oil and gas exploration, shale gas exploration, geothermal development, and earthquake prediction.

[0003] The research on geostress calculation methods aims to gain a deeper understanding of the stress state of rock mass in the crust, which is crucial to engineering construction, mineral mining, earthquake prediction and other fields. At present, the commonly used geostress calculation models include Huang Rongzun model (Huang's model), Anderson model and combined spring model. Huang's model is based on the principle of static equilibrium and proposes a method to calculate the stress distribution in the crust. It can better explain the changes in the direction of principal stress and stress gradient, and has high application value in practical engineering. Anderson model reveals the stress action mechanism under different tectonic environments by analyzing the three main stress states of the crust, especially in areas with frequent tectonic activities. Combination spring model starts from the elastic theory and compares the stress transfer and deformation process of rock mass to the combined action of spring elements, so that it can adapt to complex geological conditions and heterogeneous strata.

[0004] The introduction and continuous improvement of these models not only provided important theoretical support for the calculation and analysis of geostress, but also promoted the development of the field of geological engineering and provided more scientific tools for stress prediction and prevention in complex geological environments. Summary of the invention

[0005] 1. Analysis of the advantages of the present invention over conventional technologies

[0006] The present invention improves the conventional Huang Rongzun model (Huang's model) for calculating geostress by adding a correction term, thereby improving the accuracy of calculating the maximum horizontal principal stress of the strata in a tectonic compression state; and designs a set of calculation processes suitable for exploration applications in new energy fields such as shale gas and geothermal exploration.

[0007] (II) The core content of the present invention

[0008] The present invention proposes a method for calculating the maximum horizontal principal stress of a formation suitable for a tectonic compression state. In the original Huang's model, the influence of factors such as pore pressure and tectonic stress under compression environment is not fully considered, which often leads to deviations in the calculated maximum horizontal principal stress and large errors. In order to solve this problem, the present invention improves the accuracy and adaptability of the original Huang's model by introducing a maximum differential stress correction term, so that it can more accurately reflect the stress field under compression state.

[0009] The derivation process of the core calculation formula of a method for calculating the maximum horizontal principal stress of a formation suitable for tectonic compression state is as follows:

[0010] According to the effective stress principle, the relationship between the effective stress of rock and the overlying stratum pressure and stratum pressure is:

[0011] (1) In the formula, is the overlying formation pressure, unit: ; is the formation pore fluid pressure, unit: ; is the rock skeleton stress of the formation, unit: .

[0012] For the stress model of the formation under compression, the maximum horizontal principal stress is greater than the vertical stress, so the maximum differential stress can be obtained: is the difference between the maximum horizontal principal stress and the vertical stress, that is:

[0013] (2) In the formula, is the maximum horizontal principal stress, in units of: ; is the vertical stress, in units of: .

[0014] Based on Fan Taoyuan et al. (Geo-stress Analysis of Tectonic Mineralization: Research Status and Thinking, Modern Geology, 2024), “In a compression environment, when the pore fluid is in a hydrostatic pressure state, the maximum differential stress at 5 km is about 160 ”, substituting into formula 2, we can get the maximum horizontal principal stress at this time is 285 .

[0015] Substitute the parameters into the Huang model proposed by Huang Rongzun:

[0016] (3)

[0017] (4) In the formula and are the minimum and maximum horizontal principal stresses, ; is the vertical in-situ stress, ; is the Biot coefficient; is the pore pressure, ; is Poisson's ratio, dimensionless; and is the tectonic stress coefficient in the direction of maximum and minimum horizontal principal stresses, dimensionless.

[0018] Taking Poisson's ratio as 0.25, the tectonic stress coefficient in the direction of the maximum horizontal principal stress is is a constant, and its value varies in different regions. The present invention obtains is 0.283, and substituting it into formula 4, the maximum horizontal principal stress can be calculated to be about 96 .

[0019] In an overpressure environment, based on Fan Taoyuan et al. (Geostress Analysis of Tectonic Mineralization: Research Status and Thinking, Modern Geology, 2024), "When there is overpressure fluid inside the rock, in a compression environment, as the pore overpressure increases and the maximum differential stress decreases, the maximum differential stress decreases by about 2.12 times the increase in pore fluid pressure", that is:

[0020] (5) In formula 5 is the reduction of the maximum differential stress, is the increase in pore fluid pressure.

[0021] The decrease in the maximum differential stress with the increase of pore overpressure can be expressed as:

[0022] (6)

[0023] The maximum differential stress at this time 55 , substitute into formula 2, Replace with , we can get the maximum horizontal principal stress is 180 Similarly, substituting the parameters into Formula 4, the maximum horizontal principal stress can be calculated to be approximately 115 The Huang model is inconsistent with the calculation results of the effective stress principle.

[0024] This calculation example uses public calculation data and is only used to illustrate that the Huang model has a large error in calculating the ground stress of strata under tectonic compression.

[0025] Therefore, the present invention analyzes the geostress of multiple shale gas exploration areas and geothermal exploration areas with structural compression, and finds the intrinsic correlation between the maximum differential stress and the compression structure on the basis of Huang's model, and introduces the correction term related to the maximum differential stress. , where k is an adjustment coefficient, obtained by fitting experimental data, and an improved calculation formula is proposed. The improved Huang model can be written as:

[0026] (7)

[0027] Formula 7 is the core calculation formula for the maximum horizontal principal stress of the formation applicable to the structural compression state proposed by the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a technical flow chart of the present invention;

[0029] Figure 2 The maximum horizontal principal stress prediction diagram of shale gas formation in a certain area of ​​Sichuan based on well logging data is calculated by the method of the present invention. DETAILED DESCRIPTION

[0030] Example 1

[0031] A method for calculating the maximum horizontal principal stress of a formation suitable for a tectonic compression state, wherein the specific steps of calculating the maximum horizontal principal stress of a target layer segment based on well logging data include:

[0032] Step 1: Input the well data of the study area, the depth of the top and bottom interfaces of the target layer, and the average P-wave velocity of the target layer. , the average shear wave velocity , average density , the average formation pressure of the target layer , the average maximum horizontal principal stress , average Biot coefficient , the average density of the strata above the target layer ;

[0033] Step 2: Calculate the maximum differential stress in the target layer of the well. ,

[0034] (8)

[0035] (9) In the formula, The average density of the strata above the target layer, in Kg / m 3 , is the depth of the target layer, unit: m, is the acceleration due to gravity, unit: m / s²;

[0036] Step 3: Establish the maximum differential stress based on the measured data of the drilled well The average P-wave velocity of the target layer The quadratic fitting relationship between:

[0037] (10) In the formula, , , is the fitting coefficient;

[0038] Step 4: Calculate the structural stress coefficient of the target layer section in the well ,

[0039] (11)

[0040] (12)

[0041] Step 5, calculate the coefficient ,

[0042] (13)

[0043] (14) In the formula, is the maximum horizontal principal stress calculated by Huang’s model;

[0044] Step 6: Enter the depth of the target layer of the target well to start calculation and extract the P-wave velocity at the current depth. , shear wave velocity :

[0045] Step 6-1: Set the P-wave velocity at the current depth of the target layer Substitute into the relationship obtained in step 3 to calculate the maximum differential stress at the current depth point of the target layer segment ;

[0046] Step 6-2, calculate the rock physical parameter Poisson's ratio at the current depth ,

[0047] (15)

[0048] Step 6-3, calculating the maximum horizontal principal stress of the target layer segment at the current depth;

[0049] (16)

[0050] Step 7, change the calculated depth of the target layer and repeat step 6;

[0051] Step 8: output the maximum horizontal principal stress of the target layer segment of the target well.

[0052] Example 2

[0053] In order to illustrate the effectiveness and advancement of the core formula of the present invention, a well with measured formation pore pressure and ground stress data is used for analysis and explanation.

[0054] Figure 2 The first column is the natural gamma, unit: API; the second column is the longitudinal wave velocity, unit: m / s; the third column is the density, unit: Kg / m 3 ; The fourth column is the calculated maximum horizontal principal stress value, unit: MPa; there are two measured pressure points in the target layer, and the prediction errors are 0.4MPa and 0.3MPa respectively, both less than 0.5MPa, which is consistent with the prediction accuracy.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for calculating the maximum horizontal principal stress of a stratum applicable to a tectonic compression state includes the following specific steps: Step 1: Input the well data of the study area, the depth of the top and bottom interfaces of the target layer, and the average P-wave velocity of the target layer. , the average shear wave velocity , average density , the average formation pressure of the target layer , the average maximum horizontal principal stress , average Biot coefficient , the average density of the strata above the target layer ; Step 2: Calculate the maximum differential stress in the target layer of the well. , In the formula, The average density of the stratum above the target layer, in Kg / m 3 , is the depth of the target layer, unit: m, is the acceleration due to gravity, unit: m / s²; Step 3: Establish the maximum differential stress based on the measured data of the drilled well The average P-wave velocity of the target layer The quadratic fitting relationship between: In the formula, , , is the fitting coefficient; Step 4: Calculate the structural stress coefficient of the target layer section in the well , Step 5, calculate the coefficient , In the formula, is the maximum horizontal principal stress calculated by Huang’s model; Step 6: Enter the depth of the target layer of the target well to start calculation and extract the P-wave velocity at the current depth. , shear wave velocity : Step 6-1: Set the P-wave velocity at the current depth of the target layer Substitute into the relationship obtained in step 3 to calculate the maximum differential stress at the current depth point of the target layer segment ; Step 6-2, calculate the rock physical parameter Poisson's ratio at the current depth , Step 6-3, calculating the maximum horizontal principal stress of the target layer segment at the current depth; Step 7, change the calculated depth of the target layer and repeat step 6; Step 8: output the maximum horizontal principal stress of the target layer segment of the target well.

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