Typical fractured hot dry rock compressibility evaluation method based on dominant rock mass quantitative characterization

Abstract

The invention discloses a typical fractured hot dry rock compressibility evaluation method based on dominant rock mass quantitative characterization. The method comprises the steps that a crack development index and a crack strike index are obtained through a micro-resistivity scanning imaging logging technology and a far exploration acoustic logging technology; obtaining the maximum horizontal principal stress and the minimum horizontal principal stress by utilizing a geophysical logging technology, and then obtaining a horizontal stress difference; and obtaining a comprehensive evaluation index of the compressibility of the dominant lithofacies based on the parameters, thereby evaluating the comprehensive quality of the compressibility of the stratum. According to the method, stratum sensitive parameters beneficial to improvement of stratum flow conductivity and heat exchange capacity are searched from the aspects of congenital fracture development condition of opening of a hot fluid channel and postnatal mechanical transformation, a multi-parameter fused dominant rock mass comprehensive index is established, the compressibility of typical fractured hot dry rock geothermal resources in a research block is quantitatively evaluated, and the compressibility of the typical fractured hot dry rock geothermal resources in the research block is evaluated. Formulating of a fracturing development measure scheme can be effectively guided, and successful operation of the enhanced geothermal system in the later period is guaranteed.

Description

Technical Field

[0001] The invention belongs to the technical field of geophysical exploration well logging data evaluation, and particularly relates to a typical fractured hot dry rock compressibility evaluation method based on quantitative characterization of dominant rock mass. Background Art

[0002] At present, the development of hot dry rock geothermal resources is to enhance the construction of geothermal systems and adopt the methods of "one injection and two extractions" and "cold injection and hot extraction" to extract the heat inside the formation to meet the needs of power generation and comprehensive utilization. The core technical difficulty is to select favorable target formations and form an effective fracture connection network based on the formation stimulation by hydraulic fracturing, thereby improving the heat exchange capacity during the injection and extraction process.

[0003] Domestic research on hot dry rock geothermal resources started late and is still at a stage where research mainly focuses on basic geological characteristics. A complete logging evaluation technology system has not yet been formed, especially for the later enhanced geothermal system fracturing development. It mainly focuses on qualitative analysis of the formation and has not formed a complete quantitative evaluation system. Therefore, it cannot meet the next step of development needs of hot dry rock geothermal resources. Summary of the invention

[0004] In order to solve the above problems, the object of the present invention is to provide a typical fractured hot dry rock compressibility evaluation method based on the quantitative characterization of the dominant rock mass.

[0005] In order to achieve the above object, the typical fractured hot dry rock compressibility evaluation method based on the quantitative characterization of the dominant rock mass provided by the present invention comprises the following steps performed in sequence:

[0006] Step 1: Use microresistivity scanning imaging logging technology and remote detection acoustic logging technology to obtain the fracture development index and fracture trend index to evaluate the development of congenital fractures;

[0007] Step 2: Use geophysical logging technology to obtain the maximum and minimum horizontal principal stresses, and then obtain the horizontal stress difference, which is used to evaluate the acquired mechanical transformation capability;

[0008] Step 3: Based on steps 1 and 2, a comprehensive evaluation index of the compressibility of the dominant lithofacies is obtained, thereby evaluating the comprehensive quality of the compressibility of the formation.

[0009] In step 1, the calculation formula of the crack development index F1 is:

[0010]

[0011] Where: p1 is the density of fractures around the well obtained by using the micro-resistivity scanning imaging logging system, 1 / m; p2 is the development of fractures around the well obtained by using the remote detection acoustic logging system, 1 / m;

[0012] The calculation formula of the crack trend index F2 is:

[0013]

[0014] Where: g i is the crack strike angle within a certain range in the crack statistics diagram, deg; f i is the distribution frequency of a certain range in the fracture statistics diagram, %; n is the total share in the fracture statistics diagram; the fracture statistics diagram is obtained by statistically analyzing the fracture occurrence after picking the fractures using the micro-resistivity scanning imaging logging system.

[0015] In step 2, the calculation formulas for the maximum and minimum horizontal principal stresses are as follows:

[0016]

[0017]

[0018] Then the maximum and minimum horizontal principal stresses are subtracted to obtain the horizontal stress difference F3, and the calculation formula is:

[0019] F3=(FK1-FK2)(PO-α*PP) (3)

[0020] Where: H is the maximum horizontal principal stress; σ h is the minimum horizontal principal stress; υ is the Poisson's ratio of the formation, dimensionless; FK1 is the static mode tectonic stress coefficient 1, with an implicit value of 1.0; FK2 is the static mode tectonic stress coefficient 2, with an implicit value of 0.4; PP is the formation pore pressure, MPa; PO is the overlying rock pressure, MPa; α is the Boit constant, dimensionless; the horizontal stress difference F2 should be between the tensile strength and the shear strength, and the smaller the horizontal stress difference, the more conducive it is to the formation of a network of fractures.

[0021] In step 3, based on step 1 and step 2, a comprehensive evaluation index of the compressibility of the dominant lithofacies is obtained, and the specific method for evaluating the comprehensive quality of the compressibility of the formation is as follows:

[0022] 1) Calculate the reservoir heat source security index to quantitatively characterize the heat source security effect;

[0023] The well temperature of the formation is continuously measured by the log IQ high temperature and high pressure logging system, and then the reservoir heat source security index G1 is calculated using the following formula:

[0024]

[0025] Where: WTBH is the continuous well temperature measured by the logIQ high temperature and high pressure logging system, °C; WTBH井底 is the well temperature measured at the bottom of a single well, °C;

[0026] 2) Calculate the dominant heat reservoir indicator parameters and dominant fracture trend index to quantitatively characterize the quality of formation heat reservoir;

[0027] Combined with the reservoir porosity and the fracture development index F1 obtained in step 1, the dominant heat reservoir indicator parameter G2 is calculated using the following formula: When the natural fracture strikes at an angle of 30° to the maximum horizontal principal stress, G2 ≥ 1, which helps to obtain the maximum fracture network area in the later stage; when the angle between the natural fracture strike and the maximum horizontal principal stress is far greater than 30°, 0 < G2 < 1;

[0028] G2=φ*F1 (5)

[0029] Where: φ is the reservoir porosity value obtained using the conventional logging system, %;

[0030] Combining the maximum horizontal principal stress direction and the crack trend index F2 obtained in step 1, the dominant crack trend index G3 is calculated using the following formula:

[0031]

[0032] Where: β is the maximum horizontal principal stress direction obtained by using the microresistivity scanning imaging logging system, deg;

[0033] 3) Calculate the optimal horizontal stress difference index to quantitatively characterize the formation ability of the mesh seam;

[0034] Combining the formation tensile strength, shear strength, and the horizontal stress difference F2 obtained in step 2, the optimal horizontal stress difference index G4 is calculated using the following formula:

[0035]

[0036] Where: To and So are the formation tensile strength and shear strength obtained by the cross-dipole acoustic logging system, MPa;

[0037] 4) Calculate the dislocation degree of the fracturing stimulation seams to characterize the difficulty of forming the network seams;

[0038] The calculation formula of the dislocation degree value G5 of the fracturing transformation seam is as follows

[0039]

[0040] Where: ν is the formation Poisson's ratio; E is the Young's modulus, 10 4 MPa;

[0041] 5) Calculate the comprehensive evaluation index p of the compressibility of the dominant lithofacies by using the above reservoir heat source guarantee index, dominant heat reservoir indication parameter, dominant fracture strike index, optimal horizontal stress difference index, and the misalignment degree value of the fracturing transformation fracture, and then classify the formation accordingly;

[0042] The calculation formula of the comprehensive evaluation index p of the compressibility of the dominant lithofacies is as follows:

[0043]

[0044] Where: is the reservoir property data set, including the reservoir heat source guarantee index G1, the dominant heat reservoir indication parameter G2, the dominant fracture strike index G3, the optimal horizontal stress difference index G4, and the misalignment degree value G5 of the fracturing transformation fracture; A T =(0.2, 0.3, 0.2, 0.15, 0.15) is the reservoir property weight data set, selected by combining regional experience; Combining field experience, when p > 0.2, it is evaluated as Class I formation; when 0.1 < P < 0.2, it is evaluated as Class II formation; when P < 0.1, it is evaluated as Class III formation.

[0045] The typical fracture-type hot dry rock compressibility evaluation method based on the quantitative characterization of the dominant rock mass provided by the present invention has the following beneficial effects:

[0046] (1) By looking for formation-sensitive parameters that are conducive to improving the formation's diversion ability and heat exchange ability from the congenital fracture development of the thermal fluid channel opening and the subsequent mechanical transformation, the present invention establishes a comprehensive index of the dominant rock mass with multi-parameter fusion, quantitatively evaluates the compressibility of the typical fracture-type hot dry rock geothermal resources in the research block, can effectively guide the formulation of fracturing development measures, and ensure the successful operation of the enhanced geothermal system in the later stage. And it strengthens the understanding of the formation and improves the evaluation system of geothermal resources;

[0047] (2) Relying on the multi-dimensional high-precision imaging logging technology, the present invention comprehensively evaluates the fracture development of the formation heat reservoir and the mechanical engineering quality, aims to find the characteristics that are conducive to improving the formation's diversion ability, combines various sensitive parameters, and establishes a comprehensive index of the dominant rock mass with multi-parameter fusion, innovatively forming a method for quantitatively and intuitively characterizing the compressibility of typical fracture-type geothermal resources, which can guide the formulation of fracturing development measures and ensure the successful operation of the enhanced geothermal system in the later stage. It breaks through the original technical bottleneck, has a solid theoretical foundation, intuitive and clear effects, and strong practicability. Brief Description of the Drawings

[0048] Figure 1 It is the evaluation result diagram obtained by using the method of the present invention in the embodiment. Detailed Embodiment

[0049] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0050] The typical fractured hot dry rock compressibility evaluation method based on the quantitative characterization of the dominant rock mass provided by the present invention comprises the following steps performed in sequence:

[0051] Step 1: Use microresistivity scanning imaging logging technology and remote detection acoustic logging technology to obtain the fracture development index and fracture trend index to evaluate the development of congenital fractures;

[0052] Hot dry rock is mainly granite, and its temperature is usually higher than 150℃, and can reach up to 230℃. Under high temperature and high pressure, the hot dry rock will undergo thermal fracture behavior, causing the volume to expand and produce a large number of natural cracks, thus forming the material basis for typical fracture-type hot dry rock fracturing development. Therefore, accurate understanding of natural cracks is crucial for increasing the effective heat exchange area in the later stage.

[0053] By using the micro-resistivity scanning imaging logging system and the remote detection sonic logging system, the electrical and acoustic characteristics are integrated to accurately evaluate the development degree of the fracture zone around the well and the development of the far-end fractures beside the well, so as to predict the heat exchange capacity on the injection and production profile.

[0054] Among them, the calculation formula of the crack development index F1 is:

[0055]

[0056] Where: p1 is the density of fractures around the well obtained by using the micro-resistivity scanning imaging logging system, 1 / m; p2 is the development of fractures around the well obtained by using the remote detection acoustic logging system, 1 / m;

[0057] The calculation formula of the crack trend index F2 is:

[0058]

[0059] Where: g i is the crack strike angle within a certain range in the crack statistics diagram, deg; f i is the distribution frequency of a certain range in the fracture statistics diagram, %; n is the total share in the fracture statistics diagram; the fracture statistics diagram is obtained by statistically analyzing the fracture occurrence after picking the fractures using the micro-resistivity scanning imaging logging system;

[0060] Step 2: Use geophysical logging technology to obtain the maximum and minimum horizontal principal stresses, and then obtain the horizontal stress difference, which is used to evaluate the acquired mechanical transformation capability;

[0061] Accurate evaluation of formation mechanical parameters can objectively reflect the engineering quality of the formation and provide basic data support for the selection of parameters such as fracture pressure in the later development of enhanced geothermal systems, thereby improving the success rate of geothermal system operation. The cross-dipole array acoustic logging system in geophysical logging technology extracts and processes three waves: longitudinal wave, shear wave, and Stoneley wave, and calculates formation mechanical parameters such as Poisson's ratio and Young's modulus in combination with the compensated density curve, effective porosity, and mud content curve in conventional logging. On this basis, rock mechanical strength analysis of formation tensile strength, shear strength, maximum and minimum horizontal principal stresses is carried out to provide basic mechanical parameters for the development and transformation of geothermal systems.

[0062] The calculation formulas for the maximum and minimum horizontal principal stresses are as follows:

[0063]

[0064]

[0065] Then the maximum and minimum horizontal principal stresses are subtracted to obtain the horizontal stress difference F3, and the calculation formula is:

[0066] F3=(FK1-FK2)(PO-α*PP) (3)

[0067] Where: H is the maximum horizontal principal stress; σ h is the minimum horizontal principal stress; υ is the Poisson's ratio of the formation, dimensionless; FK1 is the static mode tectonic stress coefficient 1, with an implicit value of 1.0; FK2 is the static mode tectonic stress coefficient 2, with an implicit value of 0.4; PP is the formation pore pressure, MPa; PO is the overlying rock pressure, MPa; α is the Boit constant, dimensionless; the horizontal stress difference F2 should be between the tensile strength and the shear strength, and the smaller the horizontal stress difference, the more conducive it is to the formation of a network of fractures.

[0068] Step 3: Based on Step 1 and Step 2, a comprehensive evaluation index of the compressibility of the dominant lithofacies is obtained, thereby evaluating the comprehensive quality of the compressibility of the formation;

[0069] The hot dry rock geothermal resources successfully developed at home and abroad are mainly based on typical fractured formations. The high-temperature rock phase in this type of formation is the material basis for extracting heat from the formation; natural fractures are a prerequisite for increasing the effective heat exchange area; and mechanical quality is a necessary engineering factor for the subsequent water fracturing to produce shear displacement. Based on the parameters obtained in steps 1 and 2, a comprehensive evaluation index of the compressibility of the dominant rock phase is constructed to quantitatively analyze the transformation potential of hot dry rock reservoirs, which can provide an important basis for the fracturing development of geothermal resources.

[0070] The specific method is as follows:

[0071] 1) Calculate the reservoir heat source security index to quantitatively characterize the heat source security effect;

[0072] The main heat source of geothermal resources comes from the thermal conduction of deep lava. The well temperature of the formation is continuously measured by the log IQ high temperature and high pressure logging system, and then the reservoir heat source security index G1 is calculated using the following formula:

[0073]

[0074] Where: WTBH is the continuous well temperature measured by the logIQ high temperature and high pressure logging system, °C; WTBH 井底 is the well temperature measured at the bottom of a single well, ℃.

[0075] 2) Calculate the dominant heat reservoir indicator parameters and dominant fracture trend index to quantitatively characterize the quality of formation heat reservoir;

[0076] Combined with the reservoir porosity and the fracture development index F1 obtained in step 1, the dominant heat reservoir indicator parameter G2 is calculated using the following formula: When the natural fracture strikes at an angle of about 30° to the maximum horizontal principal stress, G2 ≥ 1, which helps to obtain the maximum fracture network area in the later stage; when the angle between the natural fracture strike and the maximum horizontal principal stress is far greater than 30°, 0 < G2 < 1;

[0077] G2=φ*F1 (5)

[0078] Where: φ is the reservoir porosity value obtained using the conventional logging system commonly used in the art, %.

[0079] Combining the maximum horizontal principal stress direction and the crack trend index F2 obtained in step 1, the dominant crack trend index G3 is calculated using the following formula:

[0080]

[0081] Where: β is the maximum horizontal principal stress direction obtained by using the microresistivity scanning imaging logging system, deg;

[0082] 3) Calculate the optimal horizontal stress difference index to quantitatively characterize the formation ability of the mesh seam;

[0083] Combining the formation tensile strength, shear strength, and the horizontal stress difference F2 obtained in step 2, the optimal horizontal stress difference index G4 is calculated using the following formula:

[0084]

[0085] Where: To and So are the tensile strength and shear strength of the formation obtained by using the cross-dipole acoustic logging system, in MPa; the optimal horizontal stress difference index G4 > 0, and the larger the value, the smaller the horizontal stress difference, and the more conducive to the formation of network fractures.

[0086] 4) Calculate the misalignment degree value of the fracturing and reconstruction fracture, which is used to characterize the difficulty of forming network fractures;

[0087] The relationship between the misalignment degree value G5 of the fracturing and reconstruction fracture and a single mechanical parameter is relatively complex and cannot be quantitatively described. However, generally, it has a positive correlation with the geometric relationship between the Young's modulus and the Poisson's ratio. The calculation formula is as follows

[0088]

[0089] Where: ν is the Poisson's ratio of the formation; E is the Young's modulus, 10 4 MPa. The larger the value of the misalignment degree value G5 of the fracturing and reconstruction fracture, the greater the shear misalignment degree of the fracturing and reconstruction fracture, and the more conducive to the formation of network fractures.

[0090] 5) Use the above reservoir heat source guarantee index, dominant heat reservoir indication parameter, dominant fracture strike index, optimal horizontal stress difference index, and misalignment degree value of the fracturing and reconstruction fracture to calculate the comprehensive evaluation index p of the compressibility of the dominant lithofacies, and then classify the formation accordingly;

[0091] The calculation formula of the comprehensive evaluation index p of the compressibility of the dominant lithofacies is as follows:

[0092]

[0093] Among them: is the reservoir property data set, including the reservoir heat source guarantee index G1, dominant heat reservoir indication parameter G2, dominant fracture strike index G3, optimal horizontal stress difference index G4, and misalignment degree value G5 of the fracturing and reconstruction fracture; A T =(0.2, 0.3, 0.2, 0.15, 0.15) is the reservoir property weight data set, which is selected in combination with regional experience. The higher the comprehensive evaluation index p of the compressibility of the dominant lithofacies, the higher the success rate of fracturing development of the enhanced geothermal system. Combining with on-site experience, when p > 0.2, it is evaluated as class I formation; when 0.1 < P < 0.2, it is evaluated as class II formation; when P < 0.1, it is evaluated as class III formation.

[0094] The following is based on the logging data of Well J in the Gonghe Basin of a certain province, and combined with the attached drawings, to further describe the practical effect of the present invention: Well J is a hot dry rock evaluation well, Figure 1 is the evaluation result diagram obtained by using the method of the present invention in the embodiment. From Figure 1It can be seen that at 2600-3200m and 3600-4000m, the comprehensive evaluation index p of the compressibility of the dominant lithofacies is significantly larger than that of other well sections, with an average value greater than 0.2. Therefore, it is evaluated as a Class I formation, which is an advantageous area for later EGS system fracturing transformation.

Claims

1. A typical fractured hot dry rock compressibility evaluation method based on quantitative characterization of dominant rock mass, characterized by: The typical fractured hot dry rock compressibility evaluation method comprises the following steps performed in sequence: Step 1: Use microresistivity scanning imaging logging technology and remote detection acoustic logging technology to obtain the fracture development index and fracture trend index to evaluate the development of congenital fractures; Step 2: Use geophysical logging technology to obtain the maximum and minimum horizontal principal stresses, and then obtain the horizontal stress difference, which is used to evaluate the acquired mechanical transformation capability; Step 3: Based on steps 1 and 2, a comprehensive evaluation index of the compressibility of the dominant lithofacies is obtained, thereby evaluating the comprehensive quality of the compressibility of the formation.

2. The typical fractured hot dry rock compressibility evaluation method according to claim 1, characterized in that: In step 1, the calculation formula of the crack development index F1 is: Where: p1 is the density of fractures around the well obtained by using the micro-resistivity scanning imaging logging system, 1 / m; p2 is the development of fractures around the well obtained by using the remote detection acoustic logging system, 1 / m; The calculation formula of the crack trend index F2 is: Where: g i is the crack strike angle of a certain range in the crack statistics map, deg; f i is the distribution frequency of a certain range in the fracture statistics diagram, %; n is the total share in the fracture statistics diagram; the fracture statistics diagram is obtained by statistically analyzing the fracture occurrence after picking the fractures using the micro-resistivity scanning imaging logging system.

3. The typical fractured hot dry rock compressibility evaluation method according to claim 1, characterized in that: In step 2, the calculation formulas for the maximum and minimum horizontal principal stresses are as follows: Then the maximum and minimum horizontal principal stresses are subtracted to obtain the horizontal stress difference F3, and the calculation formula is: F3=(FK1-FK2)(PO-α*PP) (3) Where: H is the maximum horizontal principal stress; σ h is the minimum horizontal principal stress; υ is the Poisson's ratio of the formation, dimensionless; FK1 is the static mode tectonic stress coefficient 1, with an implicit value of 1.0; FK2 is the static mode tectonic stress coefficient 2, with an implicit value of 0.4; PP is the formation pore pressure, MPa; PO is the overburden pressure, MPa; α is the Boit constant, dimensionless; The horizontal stress difference F2 should be between the tensile strength and the shear strength, and the smaller the horizontal stress difference, the more conducive it is to the formation of the mesh seam.

4. The typical fractured hot dry rock compressibility evaluation method according to claim 1, characterized in that: In step 3, based on step 1 and step 2, a comprehensive evaluation index of the compressibility of the dominant lithofacies is obtained, and the specific method for evaluating the comprehensive quality of the compressibility of the formation is as follows: 1) Calculate the reservoir heat source security index to quantitatively characterize the heat source security effect; The well temperature of the formation is continuously measured by the log IQ high temperature and high pressure logging system, and then the reservoir heat source security index G1 is calculated using the following formula: Where: WTBH is the continuous well temperature measured by the logIQ high temperature and high pressure logging system, °C; WTBH 井底 is the well temperature measured at the bottom of a single well, °C; 2) Calculate the dominant heat reservoir indicator parameters and dominant fracture trend index to quantitatively characterize the quality of formation heat reservoir; Combined with the reservoir porosity and the fracture development index F1 obtained in step 1, the dominant heat reservoir indicator parameter G2 is calculated using the following formula: When the natural fracture strikes at an angle of 30° to the maximum horizontal principal stress, G2 ≥ 1, which helps to obtain the maximum fracture network area in the later stage; when the angle between the natural fracture strike and the maximum horizontal principal stress is far greater than 30°, 0 < G2 < 1; G2=φ*F1 (5) Where: φ is the reservoir porosity value obtained using the conventional logging system, %; Combining the maximum horizontal principal stress direction and the crack trend index F2 obtained in step 1, the dominant crack trend index G3 is calculated using the following formula: Where: β is the maximum horizontal principal stress direction obtained by using the microresistivity scanning imaging logging system, deg; 3) Calculate the optimal horizontal stress difference index to quantitatively characterize the formation ability of the mesh seam; Combining the formation tensile strength, shear strength, and the horizontal stress difference F2 obtained in step 2, the optimal horizontal stress difference index G4 is calculated using the following formula: Where: To and So are the formation tensile strength and shear strength obtained by the cross-dipole acoustic logging system, MPa; 4) Calculate the dislocation degree of the fracturing stimulation seams to characterize the difficulty of forming the network seams; The calculation formula of the dislocation degree value G5 of the fracturing transformation seam is as follows Where: ν is the formation Poisson's ratio; E is the Young's modulus, 10 4 MPa; 5) The dominant lithofacies compressibility comprehensive evaluation index p is calculated using the reservoir heat source security index, dominant heat reservoir indication parameter, dominant fracture trend index, optimal horizontal stress difference index and fracture dislocation degree value, and then the formation is classified based on the index; The calculation formula of the comprehensive evaluation index p of the compressibility of the dominant lithofacies is as follows: Wherein: is a reservoir property dataset, including the reservoir heat source guarantee index G1, the dominant heat reservoir indication parameter G2, the dominant fracture strike index G3, the optimal horizontal stress difference index G4, and the fracture misalignment degree value G5 of fracturing transformation; A T =(0.2, 0.3, 0.2, 0.15, 0.15) is a reservoir property weight dataset, selected by combining regional experience; Combining field experience, when p>0.2, it is evaluated as class I formation; when 0.1<P<0.2, it is evaluated as class II formation; when P<0.1, it is evaluated as class III formation.

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