Sand production possibility prediction and calculation method applied to deep sandstone stratum

Abstract

The invention provides a sand production possibility prediction and calculation method applied to a deep sandstone stratum. The sand production possibility prediction and calculation method comprises the steps that 1, stratum rock mechanics characteristic parameters, original ground stress data and stratum data are obtained through experimental testing; 2, calculating the actual stress state around the well according to the well wall mechanical model; step 3, calculating maximum and minimum principal stresses according to the actual stress state around the well; 4, the critical sand production pressure difference is calculated; step 5, calculating the shear strength of the rock according to the rock mechanical parameters and the original crustal stress data; and 6, according to the critical sand production pressure difference and the rock shear strength, the stratum sand production possibility is judged and analyzed. According to the sand production possibility prediction and calculation method applied to the deep sandstone stratum, the well periphery stress state change of the deep stratum along with the depth is considered in calculation, the reservoir depth of sand production of the deep stratum can be predicted, and a basis is provided for sand production prediction of an oil field production site.

Description

Technical Field

[0001] The present invention relates to the technical field of oil extraction, and in particular to a method for predicting and calculating the possibility of sand production in deep sandstone formations. Background Art

[0002] Deep earth exploration is a crucial component of the national science and technology innovation strategy and a major scientific and technological project of strategic, fundamental, forward-looking, and critical importance. The drive for oil and gas exploration into the Earth's depths is primarily driven by ensuring national energy security. After years of exploration and development, my country's shallow oil and gas resources are insufficient to meet the needs of national economic development, and the discovery of large-scale gas fields in shallow areas is becoming increasingly difficult. Deep oil and gas development also presents a series of new challenges, with sand production being a particularly prominent example. Unlike shallow oil and gas reservoirs, deep formations with loose, low-strength rock are prone to sand production, leading to production losses. Deep oil and gas production in the southern margin of the Junggar Basin in my country has encountered severe sand production problems despite dense and high-strength reservoirs, impacting oil and gas production. Traditional sand production prediction methods assume that sand production in this area is nonexistent or that the critical sand production pressure differential is higher than the actual production pressure differential. This is inconsistent with actual production conditions and cannot guide rational development in this area. Therefore, developing a method to predict the potential for sand production in deep sandstone formations is crucial for development and production.

[0003] In the Chinese patent application with application number: CN202011271394.6, a method for predicting sandstone reservoirs in coal-bearing strata is involved, which belongs to the technical field of sandstone reservoir prediction in coal-bearing strata. The invention utilizes the frequency attenuation difference of seismic waves propagating through sandstone and mudstone in coal-bearing strata. First, the corresponding pre-stack gathers are obtained by forward modeling the well logging data of the well containing sandstone reservoirs; then the logging data of the sandstone section in the well is replaced with mudstone logging data, and the replaced data is used to perform forward modeling again to obtain the corresponding pre-stack gathers; the pre-stack gathers obtained before and after the replacement are subjected to frequency analysis to determine the attenuation of the reflected wave of the sandstone section; the pre-stack gathers of the target area to be predicted are obtained, and sandstone prediction is performed on the target area based on the attenuation of the reflected wave of the sandstone section. This invention does not require complex post-stack data processing, reduces the errors caused by data processing, and improves prediction accuracy.

[0004] Chinese patent application number CN201080047410.1 discloses a system and method for predicting sand production in a geomechanical reservoir system. The sand production prediction calculations may include solving a system of partial differential equations that simulate the geomechanical reservoir system. Furthermore, a system and method are provided for operating the geomechanical reservoir system based on the sand production predictions, thereby controlling sand production in the geomechanical reservoir system.

[0005] Chinese patent application number CN201110176362.2 describes a technology for addressing sand production in loose sandstone heavy oil reservoirs. The technology first conducts theoretical research on the sand production mechanism of loose sandstone heavy oil reservoirs. Then, based on the sand production mechanism, sand production predictions are made for these reservoirs. Furthermore, experimental research is conducted on the macropores formed by particle migration during production in loose sandstone heavy oil reservoirs to understand the formation patterns of these macropores. Finally, a high-temperature foaming agent is injected into the loose sandstone heavy oil reservoir to block heat carrier crossflow channels. This invention not only reduces steam mobility, blocks steam crossflow channels, and increases steam sweep volume, thereby preventing particle migration from forming macropores, but also reduces the rate of water cut increase.

[0006] The above existing technologies are all significantly different from the present invention and fail to solve the technical problem we want to solve. Therefore, we have invented a new method for predicting and calculating the sand production possibility in deep sandstone formations. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for predicting and calculating the possibility of sand production in deep sandstone formations, which can predict the reservoir depth of sand production in deep formations and provide a basis for sand production prediction at oil field production sites.

[0008] The object of the present invention can be achieved by the following technical measures: a method for predicting and calculating the possibility of sand production in deep sandstone formations, the method for predicting and calculating the possibility of sand production in deep sandstone formations comprising:

[0009] Step 1: Obtain formation rock mechanical characteristic parameters, original ground stress data, and formation data through experimental testing;

[0010] Step 2: Calculate the actual stress state around the well according to the wellbore mechanical model;

[0011] Step 3: Calculate the maximum and minimum principal stresses based on the actual stress state around the well;

[0012] Step 4: Calculate the critical sand production pressure difference;

[0013] Step 5: Calculate the rock shear strength based on rock mechanical parameters and original ground stress data;

[0014] Step 6: Analyze the possibility of sand production in the formation based on the critical sand production pressure difference and rock shear strength.

[0015] The purpose of the present invention can also be achieved by the following technical measures:

[0016] In step 1, the rock mechanical characteristic parameters include the rock uniaxial compressive strength UCS, rock Poisson's ratio ν, rock Young's modulus E, rock internal friction angle Rock cohesion C0, original ground stress data including the minimum horizontal ground stress of the original rock in the formation σ h and direction, the original maximum horizontal stress of the formation σ H and direction, the original overlying rock pressure σ V , formation data include rock pore pressure coefficient α, rock pore pressure P p .

[0017] In step 1, a core uniaxial compressive strength test is carried out to obtain the experimentally measured rock uniaxial compressive strength UCS. The measured rock uniaxial compressive strength UCS is corrected and the three-dimensional wellbore stability is calculated until it matches the wellbore collapse image obtained by imaging, and the rock uniaxial compressive strength UCS, Poisson's ratio ν, and Young's modulus E are obtained.

[0018] In step 1, a triaxial compression test is carried out. The confining pressure setting should cover the confining pressure of the formation rock. The internal friction angle is obtained by testing. and cohesion C0.

[0019] In step 1, the minimum horizontal stress of the original rock in the formation σ is obtained by the rock acoustic emission Kaiser effect ground stress test method. h and direction, the original maximum horizontal stress of the formation σ H and direction, the original overlying rock pressure σ V .

[0020] In step 1, the formation data rock pore pressure coefficient α can be calculated according to the following formula:

[0021]

[0022] Wherein, pore pressure coefficient α, rock Poisson's ratio ν, rock Young's modulus E.

[0023] In step 1, the depth H can be obtained from the oil well field test. Kaiser The pore pressure P p .

[0024] In step 1, according to the minimum horizontal stress of the original rock σ measured in step 1 h , the original maximum horizontal stress σ H , the original overburden pressure σ V ; According to the depth H of the test sample Kaiser The ground stress at , the corresponding stress gradients in three directions can be obtained:

[0025]

[0026] Where D is the depth of the well in meters, γ v is the vertical stress coefficient, γ His the maximum horizontal stress coefficient, γ h is the minimum horizontal in-situ stress coefficient.

[0027] In step 2, according to the rock pore pressure P in step 1, p , the rock pore pressure gradient can be obtained:

[0028]

[0029] In step 2, according to the minimum horizontal principal stress σ obtained in step 1, h and direction, the original maximum horizontal principal stress σ H and direction, the original overlying rock pressure σ V , pore pressure coefficient α, rock pore pressure P p , converted into actual stress state parameters around the well, including radial principal stress σ r , circumferential principal stress σ θ , vertical principal stress σ z :

[0030]

[0031] In the formula, the rock Poisson's ratio ν, the original rock minimum horizontal principal stress σ h and direction, the original maximum horizontal stress of the formation σ H and direction, the original overlying rock pressure σ V , formation data include rock pore pressure coefficient α, rock pore pressure P p , bottom hole pressure P w , radial ground stress σ r , circumferential principal stress σ θ , vertical principal stress σ z , θ is the counterclockwise angle between a point around the well and the original maximum horizontal stress.

[0032] In step 2, the bottom hole pressure P w To calculate based on the crude oil density and production depth in the wellbore:

[0033] P w =0.0098ρD (5)

[0034] Where ρ is the density of crude oil, in kg / m 3 , D is the well depth, unit is m.

[0035] In step 3, the radial principal stress σ in the actual stress state at different depths is analyzed. r , circumferential principal stress σ θ , vertical principal stress σ z The maximum principal stress σ maxand the minimum principal stress σ min .

[0036] In step 4, the critical sand production pressure difference σ can be calculated based on the maximum and minimum principal stresses around the well, rock mechanical parameters, formation data and Mohr-Coulomb shear failure criterion. cri :

[0037]

[0038] Where UCS is the uniaxial compressive strength of rock, σ min is the minimum value of the principal stress, is the internal friction angle of rock.

[0039] In step 5, the rock shear strength τ cri It can be calculated according to the following formula:

[0040]

[0041] Where, rock shear strength τ cri , conversion angle θ; the minimum horizontal stress of the original rock σ h , the original maximum horizontal stress σ H ; Maximum principal stress σ max , the minimum principal stress σ min , cohesion C0.

[0042] In step 6, the possibility of sand production in the formation is analyzed based on the critical sand production pressure difference and the rock shear strength. When the critical sand production pressure difference is greater than or equal to the rock shear strength τ cri , then the formation produces sand, that is, if the following formula is satisfied, then the formation produces sand:

[0043] σ cri ≥τ cri (8)

[0044] The depth corresponding to the condition that satisfies formula (8) is the critical depth D cri , above this depth, the reservoir is at risk of sand production.

[0045] The purpose of the present invention can also be achieved through the following technical measures: a sand production possibility prediction and calculation system applied to deep sandstone formations, which uses a sand production possibility prediction and calculation method applied to deep sandstone formations to predict the reservoir depth of sand production in deep formations.

[0046] The present invention discloses a method for predicting and calculating the possibility of sand production in deep sandstone formations. The method obtains rock mechanical characteristic parameters, original geostress data, formation data, a wellbore mechanical model, and the Mohr-Coulomb shear failure criterion through experimental testing to compare the critical sand production pressure difference and the rock shear strength, and analyzes the possibility of sand production in the formation. The calculation takes into account the change in the wellbore stress state of the deep formation with depth, and can predict the reservoir depth of sand production in the deep formation, providing a basis for predicting sand production at the oil field production site. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is a flow chart of a specific embodiment of the method for predicting and calculating sand production possibility applied to deep sandstone formations of the present invention;

[0048] Figure 2 A schematic diagram of Kaiser test acoustic emission and stress-strain data in one embodiment of the present invention;

[0049] Figure 3 is a schematic diagram of a uniaxial compression stress-strain curve in a specific embodiment of the present invention;

[0050] Figure 4 A schematic diagram of a stress-strain curve of a triaxial compression test in a specific embodiment of the present invention;

[0051] Figure 5 A schematic diagram of the calculation of the Mohr-Coulomb criterion parameters in one embodiment of the present invention;

[0052] Figure 6 A schematic diagram of a stress-strain curve of a triaxial compression test in a specific embodiment of the present invention;

[0053] Figure 7 Schematic diagram of the change of rock stress on the well wall with depth in a specific embodiment of the present invention;

[0054] Figure 8 Schematic diagram of a template for judging the critical strength of shear failure in the near-wellbore zone in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0055] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0056] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations and / or combinations thereof.

[0057] like Figure 1 As shown, Figure 1 This is a flow chart of the method for predicting and calculating the possibility of sand production in deep sandstone formations according to the present invention. The method for predicting and calculating the possibility of sand production in deep sandstone formations includes:

[0058] Step 1: Obtain formation rock mechanical characteristic parameters, original ground stress data, and formation data through experimental testing;

[0059] Step 2: Calculate the actual stress state around the well according to the wellbore mechanical model;

[0060] Step 3: Calculate the maximum and minimum principal stresses based on the actual stress state around the well;

[0061] Step 4: The critical sand production pressure difference can be calculated based on the maximum and minimum principal stresses around the well, rock mechanical parameters, formation data, and the Mohr-Coulomb shear failure criterion;

[0062] Step 5: Calculate the rock shear strength based on rock mechanical parameters and original ground stress data;

[0063] Step 6: Analyze the possibility of sand production in the formation based on the critical sand production pressure difference and the rock shear strength. When the critical sand production pressure difference is greater than or equal to the rock shear strength, the formation is sanding.

[0064] The following are several specific embodiments of the present invention:

[0065] Example 1

[0066] In a specific embodiment 1 of the present invention, the method for predicting and calculating the possibility of sand production in deep sandstone formations includes:

[0067] Step 1: Obtain formation rock mechanical characteristic parameters, original ground stress data, and formation data through experimental testing;

[0068] Step 2: Calculate the actual stress state around the well according to the wellbore mechanical model;

[0069] Step 3: Calculate the maximum and minimum principal stresses based on the actual stress state around the well;

[0070] Step 4: Calculate the critical sand production pressure difference;

[0071] Step 5: Calculate the rock shear strength based on rock mechanical parameters and original ground stress data;

[0072] Step 6: Analyze the possibility of sand production in the formation based on the critical sand production pressure difference and rock shear strength.

[0073] Preferably, the rock mechanical characteristic parameters in step 1 include the rock uniaxial compressive strength UCS, the rock Poisson's ratio ν, the rock Young's modulus E, the rock internal friction angle Rock cohesion C0, ground stress data including the minimum horizontal ground stress of the original rock in the formation σ h and direction, the original maximum horizontal stress of the formation σ H and direction, the original overlying rock pressure σ V , formation data include rock pore pressure coefficient α, rock pore pressure P p .

[0074] Preferably, the rock uniaxial compressive strength UCS, Poisson's ratio ν and Young's modulus E are determined with reference to the national standard "GB T 23561.7-2009 Coal and rock physical and mechanical properties determination method Part 7 Uniaxial compressive strength determination and softening coefficient calculation method", and a core uniaxial compressive strength experiment is carried out to obtain the experimentally measured rock uniaxial compressive strength UCS. The measured rock uniaxial compressive strength UCS is corrected and the three-dimensional wellbore stability is calculated until it matches the wellbore collapse image obtained by imaging, and the rock uniaxial compressive strength UCS, Poisson's ratio ν and Young's modulus E are obtained.

[0075] Preferably, the rock internal friction angle To obtain the rock cohesion C0 parameter, refer to the national standard "GB T23561.7-2009 Coal and rock physical and mechanical properties determination method Part 9 Coal and rock triaxial strength and deformation parameters determination method" and conduct triaxial compression tests. The confining pressure setting should cover the formation rock confining pressure. The rock internal friction coefficient μ and cohesion C0 are obtained by test.

[0076] Preferably, the in-situ stress data is obtained by referring to the literature "Jiang Yongdong, Xian Xuefu, Xu Jiang. Research on application of rock acoustic emission Kaiser effect in in-situ stress testing [J]. Rock and Soil Mechanics, 2005, 26(6):5. DOI:10.3969 / j.issn.1000-7598.2005.06.025.", and the minimum horizontal in-situ stress of the original rock in the formation σ is obtained by the rock acoustic emission Kaiser effect in-situ stress testing method. h and direction, the original maximum horizontal stress of the formation σ H and direction, the original overlying rock pressure σ V .

[0077] Preferably, the formation data rock pore pressure coefficient α can be calculated according to the following formula:

[0078]

[0079] Wherein, pore pressure coefficient α, rock Poisson's ratio ν, rock Young's modulus E.

[0080] Preferably, the formation data can be obtained from the field test of the oil well at a depth of H Kaiser The pore pressure P p .

[0081] Preferably, the minimum horizontal stress of the original rock σ measured by the rock acoustic emission Kaiser effect stress test method in step 1 is h , the original maximum horizontal stress σ H , the original overburden pressure σ V According to the depth H of the test sample Kaiser The ground stress at , the corresponding stress gradients in three directions can be obtained:

[0082]

[0083] Preferably, according to the rock pore pressure P in step 1 p , the rock pore pressure gradient can be obtained:

[0084]

[0085] Preferably, the actual stress state around the well in step 2 is calculated based on the minimum horizontal principal stress σ obtained in step 1. h and direction, the original maximum horizontal principal stress σ H and direction, the original overlying rock pressure σ V , pore pressure coefficient α, rock pore pressure P p , converted into actual stress state parameters around the well, including radial principal stress σ r , circumferential principal stress σ θ , vertical principal stress σ z :

[0086]

[0087] In the formula, the rock Poisson's ratio ν, the original rock minimum horizontal principal stress σ h and direction, the original maximum horizontal stress of the formation σ H and direction, the original overlying rock pressure σ V , formation data include rock pore pressure coefficient α, rock pore pressure P p, bottom hole pressure P w , radial ground stress σ r , circumferential principal stress σ θ , vertical principal stress σ z , θ is the counterclockwise angle between a point around the well and the original maximum horizontal stress.

[0088] Preferably, the bottom hole pressure P w Calculated based on the crude oil density and production depth in the wellbore:

[0089] P w =0.0098ρD (5)

[0090] Where ρ is the density of crude oil, in kg / m 3 , D is the well depth, unit is m.

[0091] Preferably, in step 3, the radial principal stress σ in the actual stress state at different depths is analyzed r , circumferential principal stress σ θ , vertical principal stress σ z The maximum principal stress σ max and the minimum principal stress σ min .

[0092] Preferably, in step 4, the critical pressure difference σ can be calculated according to the following formula: cri :

[0093]

[0094] Preferably, in step 5, the rock shear strength τ cri It can be calculated according to the following formula:

[0095]

[0096] Where, rock shear strength τ cri , conversion angle θ.

[0097] Preferably, in step 6, the formation produces sand if the following formula is satisfied:

[0098] σ cri ≥τ cri (8)

[0099] The depth corresponding to the condition that satisfies formula (8) is the critical depth D cri , above this depth, the reservoir is at risk of sand production.

[0100] Example 2

[0101] In a specific embodiment 2 of the present invention, the method for predicting and calculating the possibility of sand production in deep sandstone formations includes the following steps:

[0102] 1. Ground stress testing and analysis

[0103] Rock acoustic emission (AE) activity can "remember" the maximum stress previously applied to the rock, an effect known as the Kaiser effect. The Kaiser effect indicates that the frequency or amplitude of AE activity is related to stress. Under monotonically increasing stress, when the stress reaches the previously applied maximum stress, the AE signal increases significantly. The physical mechanism of the Kaiser effect can be considered to be microfractures in the rock after stress. The frequency of microfractures increases with increasing stress. The fracture process is irreversible, but frictional sliding on existing fracture surfaces can also generate AE signals. This frictional sliding is reversible, so AE signals can also appear when the stress during loading is lower than the previously applied maximum stress. These signals are caused by AE events induced by reversible frictional sliding. When the stress exceeds the previously applied maximum stress, new fractures occur, causing a sudden increase in the frequency of AE activity. This experiment was conducted on a press. Three rock samples were drilled at three 45-degree angles. The normal stresses corresponding to the Kaiser points in these three directions were measured. The maximum and minimum horizontal principal stresses within that horizontal plane, as well as their directions, were then calculated using theoretical formulas.

[0104] According to rock mechanics theory, the vertical in-situ stress, the maximum and minimum horizontal in-situ stresses, and the stress at the Kaiser point of the core along a specific direction have the following relationship:

[0105] For vertical ground stress:

[0106] σ V =σ ⊥ +βP0 (9)

[0107] The maximum and minimum horizontal stresses are:

[0108]

[0109] Where:

[0110] σ V is the overlying stratum stress;

[0111] σ H ,σ h are the maximum and minimum horizontal principal stresses;

[0112] σ ⊥ is the vertical core Kaiser point stress;

[0113] σ 0° ,σ 45° ,σ 90° The stress at the Kaiser point of the core at three horizontal directions: 0°, 45°, and 90°.

[0114] In this experiment, a GCTS-1000 rock mechanics testing machine was used to conduct in-situ stress testing. Cores were collected from the A1 well at a depth of 5730.51 m. One core was taken every 45° along the horizontal direction. A total of three cores were used to test acoustic emission and stress-strain data to calculate in-situ stress.

[0115] The in-situ stress test results of Well A1 are as follows: Figure 2 The direct data shown can be calculated according to formula (3-2-2) to obtain: the maximum horizontal ground stress is 146.82MPa, the minimum horizontal ground stress is 125.07MPa, and the vertical stress is 140.39MPa calculated based on the pressure of the overlying rock formation.

[0116] According to the above calculation, the test depth is 5730.51m, and the three-dimensional ground stress gradient can be obtained as follows:

[0117] σ V =0.0256H

[0118] σ H =0.0245H

[0119] σ h =0.0218H (11)

[0121] Where: H is the well depth in meters. Based on the in-situ stress gradient, this provides basic data for the calculation of the sand production pressure difference in Section 3.3.

[0122] 2 Rock mechanics parameter testing and analysis

[0123] Conventional rock mechanics parameters include uniaxial compression test, triaxial compression test, Brazilian splitting, and Boit coefficient test. They can calculate parameters such as the uniaxial compressive strength, elastic modulus, Poisson's ratio, tensile strength, cohesion, internal friction angle, and Boit coefficient of the rock, providing comprehensive data for analyzing the sand production mechanism.

[0124] (1) Uniaxial compression test

[0125] The cores used in this experiment are as follows: Figure 3 As shown in the figure, core sampling depths of 5730.34, 5735.60, and 5722.00 m were used. Uniaxial compression testing yielded stress-strain curves for three cores at different depths. The stress-strain curves indicate uniaxial compressive strengths ranging from 80 to 105 MPa, with an average of 93.4 MPa; elastic moduli ranging from 18 to 24 GPa, with an average of 20.26 GPa; and Poisson's ratios ranging from 0.17 to 0.21, with an average of 0.19. Specific parameters are shown in Table 1.

[0126] Table 1 Uniaxial compression rock mechanical parameters

[0127]

[0128] (2) Triaxial compression test

[0129] The triaxial test is a relatively mature mechanical test method used for geotechnical materials. The triaxial test usually refers to the conventional triaxial test, which measures the axial compressive stress at the time of failure. The conventional triaxial test of rock is to place a cylindrical regular specimen in a three-dimensional compressive stress state to study its strength characteristics. The strength and deformation parameters of rock under triaxial compression conditions are mainly: triaxial compressive strength (compressive strength), internal friction angle, cohesion, elastic modulus and Poisson's ratio. The indoor triaxial compression test is to place the specimen in a closed container, apply triaxial compressive stress until the specimen is destroyed, and measure the strain value under different loads during the loading process. Draw the stress-strain relationship curve to obtain the triaxial compressive strength (compressive strength), elastic modulus and Poisson's ratio of the rock. The stress and strain obtained by the triaxial compression experiment are as follows: Figure 4 As shown in the figure, the test confining pressure is 0, 30, 40, and 65 MPa. The variable confining pressure is used to test the cohesion and internal friction angle of the rock. Based on the Mohr-Coulomb criterion, the following can be calculated: Figure 5 The Mohr circle of the compressive strength-shear strength relationship of the reservoir rock is shown, based on which the internal friction angle of the rock can be calculated to be 34.98° and the cohesion to be 21.34 MPa.

[0130] According to the linear relationship between confining pressure and triaxial compressive strength, such as Figure 6 As shown. In order to calculate the sand pressure difference later, the relationship formula between the two can be obtained by fitting:

[0131] σ3=81.967+σ1·3.687 (12)

[0133] 3 Calculation of actual stress around the well

[0134] According to formula (3-1-16), the effect of well depth on liquid column pressure Pw can be analyzed, and the production pressure difference (P w -P p ) to the wellbore stress. The relationship between the fluid column pressure and depth in the well is as follows:

[0135] P w =0.0098ρD (13)

[0136] Where ρ is the density of crude oil, and the density of crude oil A is 0.6684 g / cm 3 , D is the well depth.

[0137] The relationship between in-situ three-dimensional ground stress and depth can also be established as follows:

[0138] σ V =0.022D

[0139] σ H =-20+0.025D

[0140] σ h =-10+0.02D (14)

[0141] According to the formation pressure gradient of oil field A, the pore pressure (formation pressure) can be calculated as follows:

[0142] P p =0.0185D (15)

[0143] According to the data A, the porosity is 8%, the Poisson's ratio ν is 0.25, and the effective stress coefficient α is 0.8. The minimum principal stress direction that is most prone to shear failure is calculated, and the following formula can be obtained:

[0144] σ r =10+65.45D

[0145] σ θ =-50+65.61D

[0146] σ z =-5-2.94D (16)

[0147] Substituting the relevant data of core A, we can calculate that as the well depth changes, there are Figure 7 As shown in the figure, the tangential stress is greater than the radial stress in shallow layers (less than 4700m). However, this strong opening is reversed with the change of depth, which means that the radial stress is greater than the tangential stress. At this time, for the wellbore rock, according to the Mohr-Coulumb shear failure criterion, when the rock confining pressure decreases, the corresponding failure stress also decreases. However, as the depth increases, the maximum principal stress radial stress σr of the rock further increases, the Mohr circle diameter increases, and the probability of shear failure of the rock increases. Therefore, depth is a key factor in reservoir shear sand production. The pressure difference also depends on the wellbore pressure that changes with depth, and depth is also a sensitive parameter to the critical production pressure difference. In the subsequent sections, we will further analyze the rock mechanical parameters and formation conditions in the study area.

[0148] 4 Sand production calculation example

[0149] According to the Mohr-Coulomb discriminant strength, in vertical wells, when the near-wellbore zone reaches the collapse pressure, the wellbore wall becomes unstable and there is a risk of shear failure and sand production. Substituting the parameters, the critical production pressure difference of reservoirs at different depths and different Biot coefficients can be calculated.

[0150] Table 2 Calculation parameters of shear-induced structural failure in the near-wellbore area

[0151]

[0152] Through calculations, we consulted the formation data of Oilfield A and found that parameters such as ground stress, rock strength, and formation stress coefficient are relatively stable. In the calculations, we also found that the reservoir Boit coefficient determines the pore connectivity in the reservoir rock and has a great influence on the shear failure of the wellbore. In the calculations, we considered different values ​​of the Biot coefficient α and obtained the following: Figure 8 The results are shown. The results show that the larger the Biot coefficient α value, the greater the shear strength of the rock mass in the near-wellbore area, and the critical pressure difference also increases synchronously. As the well depth increases, the two values ​​also tend to increase. When the critical pressure difference is greater than the shear strength, the near-wellbore area is prone to failure. When the Biot coefficient is 0.9, the critical depth for shear failure is 4300m, when the Biot coefficient is 0.8, the critical depth for shear failure is 4800m, and when the Biot coefficient is 0.7, the critical depth for shear failure is 5200m. According to the above experimental results, the Biot coefficient of reservoir A is 0.68-0.91, and the reservoir depth is about 5600m, which is prone to shear-induced structural sand production in the near-wellbore area. In shallow layers, the possibility of shear failure and sand production is small, which is relatively safe.

[0153] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art may modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features therein. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

[0154] Except for the technical features described in the specification, all other technical features are known technologies to those skilled in the art.

Claims

1. A method for predicting and calculating the possibility of sand production in deep sandstone formations, characterized in that: The sand production possibility prediction and calculation method applied to deep sandstone formations includes: Step 1: Obtain formation rock mechanical characteristic parameters, original ground stress data, and formation data through experimental testing; Step 2: Calculate the actual stress state around the well according to the wellbore mechanical model; Step 3: Calculate the maximum and minimum principal stresses based on the actual stress state around the well; Step 4: Calculate the critical sand production pressure difference; Step 5: Calculate the rock shear strength based on rock mechanical parameters and original ground stress data; Step 6: Analyze the possibility of sand production in the formation based on the critical sand production pressure difference and rock shear strength.

2. The method for predicting and calculating the possibility of sand production in deep sandstone formations according to claim 1, characterized in that: In step 1, the rock mechanical characteristic parameters include the rock uniaxial compressive strength UCS, rock Poisson's ratio v, rock Young's modulus E, rock internal friction angle Rock cohesion C0, original ground stress data including the minimum horizontal ground stress of the original rock in the formation σ h and direction, the original maximum horizontal stress of the formation σ H and direction, the original overlying rock pressure σ V , formation data include rock pore pressure coefficient α, rock pore pressure P p .

3. The method for predicting and calculating the possibility of sand production in deep sandstone formations according to claim 2, characterized in that: In step 1, a core uniaxial compressive strength test is carried out to obtain the experimentally measured rock uniaxial compressive strength UCS. The measured rock uniaxial compressive strength UCS is corrected and the three-dimensional wellbore stability is calculated until it matches the wellbore collapse image obtained by imaging, and the rock uniaxial compressive strength UCS, Poisson's ratio v and Young's modulus E are obtained.

4. The method for predicting and calculating the possibility of sand production in deep sandstone formations according to claim 2, characterized in that: In step 1, a triaxial compression test is carried out. The confining pressure setting should cover the confining pressure of the formation rock. The rock internal friction angle is obtained by testing. and cohesion C0.

5. The method for predicting and calculating the possibility of sand production in deep sandstone formations according to claim 2, characterized in that: In step 1, the minimum horizontal stress of the original rock in the formation σ is obtained by the rock acoustic emission Kaiser effect ground stress test method. h and direction, the original maximum horizontal stress of the formation σ H and direction, the original overlying rock pressure σ V .

6. The method for predicting and calculating the possibility of sand production in deep sandstone formations according to claim 2, characterized in that: In step 1, the formation data rock pore pressure coefficient α can be calculated according to the following formula: Where, pore pressure coefficient α, rock Poisson's ratio v, rock Young's modulus E.

7. The method for predicting and calculating the possibility of sand production in deep sandstone formations according to claim 2, characterized in that: In step 1, the depth H can be obtained from the oil well field test. Kaiser The pore pressure P p .

8. The method for predicting and calculating the possibility of sand production in deep sandstone formations according to claim 2, characterized in that: In step 1, according to the minimum horizontal stress of the original rock σ measured in step 1 h , the original maximum horizontal stress σ H , the original overburden pressure σ V ; According to the depth H of the test sample Kaiser The ground stress at , the corresponding stress gradients in three directions can be obtained: Where D is the depth of the well in meters, γ v is the vertical stress coefficient, γ H is the maximum horizontal stress coefficient, γ h is the minimum horizontal in-situ stress coefficient.

9. The method for predicting and calculating the possibility of sand production in deep sandstone formations according to claim 8, characterized in that: In step 2, according to the rock pore pressure P in step 1, p , the rock pore pressure gradient can be obtained:

10. The method for predicting and calculating the possibility of sand production in deep sandstone formations according to claim 9, characterized in that: In step 2, according to the minimum horizontal principal stress σ obtained in step 1, h and direction, the original maximum horizontal principal stress σ H and direction, the original overlying rock pressure σ V , pore pressure coefficient α, rock pore pressure P p , converted into actual stress state parameters around the well, including radial principal stress σ r , circumferential principal stress σ θ , vertical principal stress σ z : In the formula, the rock Poisson's ratio v, the original rock minimum horizontal principal stress σ h and direction, the original maximum horizontal stress of the formation σ H and direction, the original overlying rock pressure σ V , formation data include rock pore pressure coefficient α, rock pore pressure P p , bottom hole pressure P w , radial ground stress σ r , circumferential principal stress σ θ , vertical principal stress σ z , θ is the counterclockwise angle between a point around the well and the original maximum horizontal stress.

11. The method for predicting and calculating the possibility of sand production in deep sandstone formations according to claim 10, characterized in that: In step 2, the bottom hole pressure P w To calculate based on the crude oil density and production depth in the wellbore: P w =0.0098ρD (5) Where ρ is the density of crude oil, in kg / m 3 , D is the well depth, unit is m.

12. The method for predicting and calculating the possibility of sand production in deep sandstone formations according to claim 1, characterized in that: In step 3, the radial principal stress σ in the actual stress state at different depths is analyzed. r , circumferential principal stress σ θ , vertical principal stress σ z The maximum principal stress σ max and the minimum principal stress σ min .

13. The method for predicting and calculating the possibility of sand production in deep sandstone formations according to claim 1, characterized in that: In step 4, the critical sand production pressure difference σ can be calculated based on the maximum and minimum principal stresses around the well, rock mechanical parameters, formation data and Mohr-Coulomb shear failure criterion. cri : Where UCS is the uniaxial compressive strength of rock, σ min is the minimum value of the principal stress, is the internal friction angle of rock.

14. The method for predicting and calculating the possibility of sand production in deep sandstone formations according to claim 1, characterized in that: In step 5, the rock shear strength τ cri It can be calculated according to the following formula: Where, rock shear strength τ cri , conversion angle θ; the minimum horizontal stress of the original rock σ h , the original maximum horizontal stress σ H ; Maximum principal stress σ max , the minimum principal stress σ min , cohesion C0.

15. The method for predicting and calculating sand production possibility in deep sandstone formations according to claim 1, characterized in that: In step 6, the possibility of sand production in the formation is analyzed based on the critical sand production pressure difference and the rock shear strength. When the critical sand production pressure difference is greater than or equal to the rock shear strength τ cri , then the formation produces sand, that is, if the following formula is satisfied, then the formation produces sand: s cri ≥τ cri (8) The depth corresponding to the condition that satisfies formula (8) is the critical depth D cri , above which the reservoir is at risk of sand production.

16. A sand production probability prediction and calculation system applied to deep sandstone formations, characterized in that: The sand production possibility prediction and calculation system applied to deep sandstone formations uses the sand production possibility prediction and calculation method applied to deep sandstone formations according to any one of claims 1 to 15 to predict the reservoir depth of sand production in the deep formation.

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