Fracture sealing property quantitative evaluation method based on fault rock pore medium static balance

Abstract

The invention discloses a fracture sealing property quantitative evaluation method based on fault rock pore medium static balance, and the method comprises the steps: determining the internal structure of a fracture system, and starting from the analysis of the internal microstructure of the fracture system, dividing the internal structure of the fracture system; fault rock static equilibrium analysis is introduced into a Terzaghi model, a fracture vertical closing coefficient is defined according to fault rock section positive pressure, fault rock pore fluid pressure and fault rock compressive strength parameters, and the change rule of fracture sealing performance in the fracture evolution process is dynamically described; comprehensive fracture lateral sealing performance evaluation is carried out, the fault mudstone ratio SGR is calculated, and finally fracture sealing performance changes of different positions of the fracture are evaluated. According to the invention, the problem of low precision of an existing closure evaluation method for a complex fracture structure is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of fracture sealing prediction, and relates to a fracture sealing quantitative evaluation method based on static balance of fault rock pore media. Background Art

[0002] In actual drilling, when drilling into fault zones, accidents such as drilling fluid leakage and drilling tool falling occur frequently, and the quality of fault sealing seriously restricts the success rate of drilling. On the other hand, theoretically, the quality of fault sealing is directly related to the ability to seal oil and gas, but in the process of fault evolution, the sealing of the fault will change with the changes in the basin stress field, the changes in the sedimentary environment, and the oil and gas accumulation events. Therefore, accurate and dynamic evaluation of fault sealing is not only of great significance to oil and gas accumulation, but also has a timely effect on reducing the risks of actual drilling work.

[0003] The existing technology for evaluating the closure of faults mainly includes two aspects, namely vertical closure and lateral closure. For the evaluation of vertical closure, there is currently mainly the cross-section normal pressure method, that is, the relative size of the normal pressure perpendicular to the fracture surface is calculated to evaluate the closure. The greater the normal pressure, the more difficult it is to open the fracture surface, that is, the better the closure. Generally speaking, the nature of the fault is directly related to the closure of the fault. For example, the closure of thrust faults is generally better than that of extensional faults. On the other hand, the evaluation of the lateral closure of the fault mainly includes qualitative and quantitative methods. The docking relationship between the lithology of the two plates of the fault is used to qualitatively judge the closure, and then the parameters related to mudstone smearing (CSP, SSF, SGR, etc.) are calculated for quantitative evaluation.

[0004] At present, the main problems in fault closure evaluation are as follows: (1) It is only applicable to conditions such as simple basin environment and single fault nature, but it is ineffective in most cases for complex fault systems; (2) The current methods for fault closure evaluation are all static and macroscopic models, which are difficult to reflect the microstructure and oil and gas sealing mechanism within the fault system; (3) There are few exploration wells in low-exploration areas, and how to use seismic data to accurately evaluate fault closure has always been a difficult problem. Summary of the invention

[0005] The purpose of the present invention is to provide a quantitative evaluation method for fracture sealing based on static balance of fault rock pore media, which solves the problem of low precision of existing sealing evaluation methods for complex fracture structures.

[0006] The technical solution adopted by the present invention is to use a quantitative evaluation method for fracture sealing based on the static balance of the porous medium of fault rocks, clarify the internal structure of the fracture system, and divide the internal structure of the fracture system based on the analysis of the internal microstructure of the fracture system; introduce the static balance analysis of fault rocks into the Terzaghi model, define the vertical sealing coefficient of the fracture according to the normal pressure of the fault rock section, the pore fluid pressure of the fault rock, and the compressive strength parameters of the fault rock, and dynamically describe the change law of the fracture sealing during the fracture evolution process; then comprehensively evaluate the lateral sealing of the fracture, calculate the fault mudstone ratio SGR, and finally evaluate the change of the fracture sealing at different positions of the fracture.

[0007] The present invention is also characterized in that

[0008] The quantitative evaluation method of fracture sealing based on static balance of fault rock pore medium is implemented in the following steps:

[0009] Step 1: Divide the internal structure of the fracture system;

[0010] Step 2: Construct the Terzaghi model and introduce the static equilibrium analysis of fault rocks into the Terzaghi model. The fault closure includes vertical closure and lateral closure. The lateral closure is evaluated by the fault mud ratio (SGR); the vertical closure is quantitatively evaluated by defining the closure coefficient.

[0011] Step 1 is as follows: study and divide the internal structure of the fault system, divide a complete fault into component units such as surrounding rock, upper plate crushing zone, fault core, lower plate crushing zone, fault rock, sandstone lens, etc. The core of evaluating the closure of the fault is to look at the permeability difference between fault rock and surrounding rock.

[0012] Step 2 is as follows:

[0013] Step 2.1, respectively calculating the normal pressure of the fault rock section, the pore fluid pressure of the fault rock, the compressive strength parameter of the fault rock, and the vertical sealing coefficient of the fracture to quantitatively evaluate the vertical sealing property;

[0014] Step 2.2, calculate the fault mudstone ratio SGR, comprehensively evaluate the lateral sealing of the fault, and finally evaluate the changes in the fracture sealing at different locations of the fault;

[0015] Step 2.3: Combined with the seismic velocity inversion data, five parameters, namely, section normal pressure, vertical section fluid pressure, fault rock compressive strength, vertical sealing coefficient, and lateral SGR, are calculated to comprehensively evaluate the sealing property of the fault.

[0016] Step 2.1 is as follows:

[0017] Step 2.1.1: For a certain depth point perpendicular to the cross section, the normal pressure perpendicular to the cross section is the resultant force of the horizontal tectonic stress on the fault rock and the pressure of the overlying strata at the same depth, that is:

[0018] P vs =P ov +P tm =0.0098H(ρ r -ρ w )cosα+δ h sinβsinα (1)

[0019] Among them, P vs is the normal pressure perpendicular to the cross section, MPa; P ov is the overlying formation pressure at the same depth, MPa; P tm is the horizontal tectonic stress, MPa; H is the depth, m; ρ r is the density of fault rock, g / cm 3 ρ w Density of formation water, g / cm 3 ; α is the inclination angle of the fault plane, °; δ h Maximum principal stress, MPa; β is the angle between the fault strike and the structural principal stress direction, °;

[0020] Step 2.1.2: The direction of the fault rock pore fluid pressure is upward, and the pressure is calculated according to the improved Phillippone formula, that is:

[0021]

[0022] Among them, P f is the fluid pressure, MPa; V int is the formation velocity at a certain depth, m / s; V max is the maximum formation velocity, m / s; V min is the minimum formation velocity, m / s; P ov is the overlying formation pressure at the same depth, MPa.

[0023] In actual calculation, the fluid pressure is decomposed to the vertical section, that is:

[0024] P vf =P f cosα (3)

[0025] Among them, P vf is the fluid pressure perpendicular to the cross section, MPa; P f is the fluid pressure, MPa; α is the section inclination, °.

[0026] The effective stress perpendicular to the cross section is:

[0027] σ=P vs -P vf (4)

[0028] Where σ is the effective stress perpendicular to the cross section, MPa; P vs is the normal pressure perpendicular to the cross section, MPa; P vf is the fluid pressure perpendicular to the cross section, MPa.

[0029] Step 2.1.3: The compressive strength of the rock is calculated by fitting the velocity, and the total compressive strength of the fault rock is determined by the sand particles and the mud particles, that is:

[0030] δ=δ S +δ m (5)

[0031] Among them, δ is the total compressive strength of fault rock, MPa; δ S is the compressive strength of sand particles in fault rock, MPa; δ m is the compressive strength of muddy particles in fault rock, MPa;

[0032] Step 2.1.4: Define the vertical closure coefficient of the fracture based on the effective stress and rock compressive strength, that is:

[0033] ΔF=σ-δ (6)

[0034] Among them, ΔF is the vertical closure coefficient of the fault, MPa; σ is the effective stress perpendicular to the cross section, MPa; δ is the total compressive strength of the fault rock, MPa.

[0035] Step 2.1 is as follows: the condition for fracture closure is that the effective stress of fault rock is greater than the compressive strength of rock, that is, ΔF>0; the condition for fracture opening is that the effective stress of fault rock is less than the compressive strength of rock, that is, ΔF<0; and the fracture is in the critical condition of closure and opening, that is, ΔF=0; the normal pressure perpendicular to the section will change continuously, that is, the effective stress will change continuously. If the effective stress is greater than the compressive strength of fault rock, the particles in the fault rock will be compressed and the fracture closure will tend to become stronger; otherwise, the fracture closure will weaken.

[0036] In step 2.2, the fault mud ratio SGR is used to evaluate the lateral sealing of the fault. The docking relationship of the lateral lithology of the fault directly affects the lateral migration of the fluid in the fault zone, namely:

[0037]

[0038] Among them, SGR fault mud ratio, %; h i The thickness of the fault-displaced formation i; is the mud content of fault-displaced stratum i, %; H is the total vertical throw of the fault.

[0039] In step 2.3, from the definition of the vertical closure of the fault, it can be seen that the fluid pressure and the compressive strength of the fault rock are obtained by velocity calculation. In order to achieve continuous evaluation of the fault, high-precision seismic velocity inversion data are used to calculate the relevant parameters. The seismic information is compensated by the frequency division method, and the missing low-frequency velocity in the seismic data is supplemented from the well logging data, so that the frequency spectrum is close to the frequency spectrum of the well data, and the accuracy of the seismic velocity is improved.

[0040] The beneficial effects of the present invention are as follows: the present invention is based on the method for quantitatively evaluating the sealing properties of faults based on the static balance of the porous medium of fault rocks, based on the static balance model of the porous medium of fault rocks, defines a new vertical sealing coefficient of the fault, uses high-precision seismic velocity inversion data, and comprehensively considers parameters such as the normal pressure of the section, the pore fluid pressure of the fault rock, the compressive strength of the fault rock, the vertical sealing coefficient of the fault, and the mudstone-mud ratio of the fault zone; combined with the evaluation of seismic data, the sealing properties of the faults in complex structural areas can be evaluated more precisely, providing a basis for favorable areas for oil and gas exploration. The method for quantitatively evaluating the sealing properties of faults based on the static balance of the porous medium of fault rocks of the present invention can evaluate the sealing integrity of the cracks in the injection and production wells of gas storage reservoirs and is applicable to the injection and production wells of gas storage reservoirs with complex fractures, aquifers, and salt caverns. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a schematic diagram of the internal structure of the fracture system of Example 3 of the present invention;

[0042] Figure 2 This is a static balance analysis diagram of the porous medium in Example 3 of the present invention;

[0043] Figure 3 This is a force analysis diagram of the fracture surface of Example 3 of the present invention;

[0044] Figure 4 This is a relative velocity profile of Line 1040 of Example 4 of the present invention;

[0045] Figure 5 It is a low-frequency velocity profile of Line 1040 of Example 4 of the present invention;

[0046] Figure 6 It is the absolute velocity profile of Line 1040 in Example 4 of the present invention;

[0047] Figure 7 This is a normal pressure distribution diagram of the vertical section of the F2 fault in Example 4 of the present invention;

[0048] Figure 8 This is a pore fluid pressure distribution diagram of F2 fault rock in Example 4 of the present invention;

[0049] Fig. 9 This is the compressive strength distribution diagram of F2 fault rock in Example 4 of the present invention;

[0050] Fig.10 The vertical closure coefficient ΔF distribution diagram of the F2 section in Example 4 of the present invention;

[0051] Fig.11 This is a distribution diagram of the lateral sealing mud ratio of the mudstone in the F2 section in Example 4 of the present invention;

[0052] Fig.12 is a graph showing the change of fluid pressure over time during the fracture evolution process in Example 4 of the present invention;

[0053] Fig.13 This is an intersection diagram of the vertical closure coefficient and depth of the F2 fracture in Example 4 of the present invention. DETAILED DESCRIPTION

[0054] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0055] Example 1

[0056] The present invention is a quantitative evaluation method for fracture closure based on the static balance of the porous medium of fault rocks. The fundamental of fracture closure is the permeability of fault rocks. First, the internal structure of the fracture system is clarified. Starting from the analysis of the internal microstructure of the fracture system, the structure inside the fracture system is divided; the static balance analysis of fault rocks is introduced into the Terzaghi model, and the vertical closure coefficient of the fracture is defined according to the normal pressure of the fault rock section, the pore fluid pressure of the fault rock, and the compressive strength parameters of the fault rock, so as to dynamically describe the change law of the fracture closure during the evolution of the fracture; then the lateral closure evaluation of the fracture is integrated, the fault mudstone ratio SGR is calculated, and finally the change of the fracture closure at different positions of the fracture is evaluated; according to the comprehensive evaluation results of the fracture closure of the present invention, the effective closure part of the fracture is determined, and the favorable zone and the drilling target are selected. At the same time, the fracture opening part can be effectively avoided during the drilling process to reduce the drilling risk.

[0057] Example 2

[0058] The quantitative evaluation method of fracture sealing based on static balance of fault rock pore medium is implemented in the following steps:

[0059] Step 1: Divide the internal structure of the fracture system;

[0060] Step 2: Construct the Terzaghi model and introduce the static equilibrium analysis of fault rocks into the Terzaghi model. The fault closure includes vertical closure and lateral closure. The lateral closure is evaluated by the fault mud ratio (SGR); the vertical closure is quantitatively evaluated by defining the closure coefficient.

[0061] Example 3

[0062] The quantitative evaluation method for fracture sealing of fault rock pore medium based on static balance of the present invention is implemented in the following steps:

[0063] Step 1: Divide the structure inside the fracture system;

[0064] Step 1 is as follows: study and divide the internal structure of the fracture system, such as Figure 1 As shown in the figure, a complete fault is divided into component units such as surrounding rock, upper plate crushing zone, fault core, lower plate crushing zone, fault rock, sandstone lens, etc. The core of evaluating the closure of a fault is to see the difference in permeability between fault rock and surrounding rock.

[0065] Step 2: Construct the Terzaghi model and introduce the static equilibrium analysis of fault rocks into the Terzaghi model, such as Figure 2 As shown in the figure, the fault sealing includes vertical sealing and lateral sealing. The lateral sealing is evaluated by the fault mud ratio (SGR). The vertical sealing is quantitatively evaluated by defining the sealing coefficient. According to the Terzaghi model, combined with the fault evolution process and using high-precision seismic velocity inversion data, the pressure of the overlying strata of porous rocks is mainly borne by two parts, one is the effective stress borne by the rock particles, and the other is the pore fluid pressure borne by the pores.

[0066] Step 2.1, respectively calculating the normal pressure of the fault rock section, the pore fluid pressure of the fault rock, the compressive strength parameter of the fault rock, and the vertical sealing coefficient of the fracture to quantitatively evaluate the vertical sealing property;

[0067] Step 2.1.1: Figure 3 As shown in the figure, for a certain depth point perpendicular to the cross section, the normal pressure perpendicular to the cross section is the resultant force of the horizontal tectonic stress on the fault rock and the pressure of the overlying strata at the same depth, that is:

[0068] P vs =P ov +P tm =0.0098H(ρ r -ρ w )cosα+δ h sinβsinα (1)

[0069] Among them, P vsis the normal pressure perpendicular to the cross section, MPa; P ov is the overlying formation pressure at the same depth, MPa; P tm is the horizontal tectonic stress, MPa; H is the depth, m; ρ r is the density of fault rock, g / cm 3 ρ w Density of formation water, g / cm 3 ; α is the inclination angle of the fault plane, °; δ h Maximum principal stress, MPa; β is the angle between the fault strike and the structural principal stress direction, °;

[0070] Step 2.1.2: The direction of the fault rock pore fluid pressure is upward, and the pressure is calculated according to the improved Phillippone formula, that is:

[0071]

[0072] Among them, P f is the fluid pressure, MPa; V int is the formation velocity at a certain depth, m / s; V max is the maximum formation velocity, m / s; V min is the minimum formation velocity, m / s; P ov is the overlying formation pressure at the same depth, MPa.

[0073] In actual calculation, the fluid pressure is decomposed to the vertical section, that is:

[0074] P vf =P f cosα (3)

[0075] Among them, P vf is the fluid pressure perpendicular to the cross section, MPa; P f is the fluid pressure, MPa; α is the section inclination, °.

[0076] The effective stress perpendicular to the cross section is:

[0077] σ=P vs -P vf (4)

[0078] Where σ is the effective stress perpendicular to the cross section, MPa; P vs is the normal pressure perpendicular to the cross section, MPa; P vf is the fluid pressure perpendicular to the cross section, MPa.

[0079] Step 2.1.3: The compressive strength of the rock is calculated by fitting the velocity, and the total compressive strength of the fault rock is determined by the sand particles and the mud particles, that is:

[0080] δ=δ S +δ m (5)

[0081] Among them, δ is the total compressive strength of fault rock, MPa; δ S is the compressive strength of sand particles in fault rock, MPa; δ m is the compressive strength of muddy particles in fault rock, MPa;

[0082] Step 2.1.4: Define the vertical closure coefficient of the fracture based on the effective stress and rock compressive strength, that is:

[0083] ΔF=σ-δ (6)

[0084] Among them, ΔF is the vertical closure coefficient of the fault, MPa; σ is the effective stress perpendicular to the cross section, MPa; δ is the total compressive strength of the fault rock, MPa.

[0085] The condition for fault closure is that the effective stress of fault rock is greater than the compressive strength of rock, that is, ΔF>0; the condition for fault opening is that the effective stress of fault rock is less than the compressive strength of rock, that is, ΔF<0; and the fault is in the critical condition of closure and opening, that is, ΔF=0.

[0086] During the evolution of the fault, the fluid pressure, cross-section normal pressure and effective stress in the fault rock are changing, so the vertical closure coefficient of the fault is also changing dynamically. The activity of the fault is periodic and cyclical, and it is always periodic and static. In this process, the normal pressure perpendicular to the cross section will continue to change, that is, the effective stress will continue to change. If the effective stress is greater than the compressive strength of the fault rock, the particles in the fault rock will be compressed, and the fault closure will tend to become stronger; otherwise, the fault closure will become weaker.

[0087] Step 2.2, calculate the fault mudstone ratio SGR, comprehensively evaluate the lateral sealing of the fault, and finally evaluate the changes in the fracture sealing at different locations of the fault;

[0088] In step 2.2, the fault mud ratio SGR is used to evaluate the lateral sealing of the fault. The docking relationship of the lateral lithology of the fault directly affects the lateral migration of the fluid in the fault zone, namely:

[0089]

[0090] Among them, SGR fault mud ratio, %; h i The thickness of the fault-displaced formation i; is the mud content of fault-displaced stratum i, %; H is the total vertical throw of the fault.

[0091] Step 2.3: Combined with the seismic velocity inversion data, five parameters, namely, section normal pressure, vertical section fluid pressure, fault rock compressive strength, vertical sealing coefficient, and lateral SGR, are calculated to comprehensively evaluate the sealing property of the fault.

[0092] From the definition of vertical closure of the fault in step 2.3, it can be seen that the fluid pressure and compressive strength of the fault rock are calculated from the velocity. In order to achieve continuous evaluation of the fault, high-precision seismic velocity inversion data are used to calculate the relevant parameters. The frequency division compensation method is used for seismic information to supplement the missing low-frequency velocity in the seismic data from the logging data, so that the spectrum is close to the spectrum of the well data, and the accuracy of the seismic velocity is improved. The core of the fault closure evaluation is the fault rock, and the permeability of the fault rock directly determines the closure of the fault. When the pore fluid is large, the permeability of the rock is better, and as the compressive strength of the rock increases, the permeability of the rock is better.

[0093] The present invention studies the fracture sealing evaluation method in complex structural areas. Fractures are fractures without obvious displacement, which can also be evaluated. The static equilibrium equation of porous media is introduced into the fracture sealing evaluation, and a new fracture vertical sealing coefficient is defined based on the static equilibrium of fault rock; seismic data is introduced into the fracture sealing evaluation, and a comprehensive research method combining seismic and geological research is used to achieve quantitative and continuous fracture sealing evaluation; the critical sealing pressure of the fracture is proposed, and the critical sealing pressure is determined using the fracture sealing evaluation results, providing a method for clarifying the effective sealing position of the fracture.

[0094] Example 4

[0095] Embodiment 4 of the present invention is used for the Ordos western edge tectonic belt, a large fault fold belt starting from Guangkou, Inner Mongolia in the north and ending in Longxian, Shaanxi in the south, stretching more than 600 km from north to south and 50 to 100 km from east to west. The geological conditions in this area are extremely complex, tectonic movements occur frequently, and the structural styles are varied. The relationship between the discovered oil and gas reservoirs and the fault structures is very close, but the research on the nature, distribution characteristics, evolution law, trap effectiveness and control of the oil and gas reservoirs in this area is not clear, so the oil and gas exploration work in this area is seriously restricted.

[0096] The fault structures in the study area include four major faults mainly developed on the plane, which basically control the tectonic-sedimentary pattern in this area, extending more than 15 km, with a fault throw exceeding 1 km. The fault strike is mainly north-south, presenting mainly a "human" shape or an "entry" shape on the plane, and mainly showing fault combination patterns such as "Y" shape, reverse "Y" shape, "entry" shape, and flower structure longitudinally. Four major faults are selected as the targets. The small faults distributed around the main faults belong to the same fault system. The combination of these faults may control the migration and accumulation of oil and gas. In the low exploration area, there are few drilling, logging, coring, and analysis and testing data, so seismic data is processed for continuous evaluation of fault sealing.

[0097] In this Example 4, Colored inversion is used to obtain medium-high frequency seismic velocity data. Then, through acoustic velocity data and velocity spectrum data, combined with the interpretation results of the sequence stratigraphic framework, a low-frequency velocity model is made. Finally, the two types of velocities, high-frequency seismic velocity and low-frequency velocity, are merged to obtain the absolute seismic velocity.

[0098] The medium-high frequency seismic velocity in this area is mainly distributed between -800 and 1400 m / s. This velocity does not represent the true velocity of the formation, but the relative magnitude of the formation velocity. As Figure 4 shown, the low-frequency velocity represents the background velocity of the formation, mainly distributed between 1000 and 7000 m / s. As Figure 5 shown, it represents the trend velocity of the formation in this area. The absolute velocity is mainly distributed between 1000 and 7000 m / s. As Figure 6 shown, it represents the true velocity of the formation and is used to distinguish lithology.

[0099] Using the high-precision seismic velocity inversion data, five parameters on the fault section are calculated respectively according to the formulas in the principle and method part of the invention, namely the normal pressure perpendicular to the section, the pore fluid pressure of the fault rock, the compressive strength of the fault rock, the vertical sealing coefficient △F of the fault, and the ratio of fault gouge to mudstone. As Figure 7-Figure 11 shown, according to Figure 7 to Figure 11 the calculation results, the sealing properties of different parts of the fault have great differences, which is consistent with the heterogeneity of the geological body. From the evaluation results of the F2 fault, the shallow layer (above about 1000 meters) is mainly in an open state, and the deep layer is mainly in a closed state. From the lateral change, from north to south, the vertical sealing property of the fault generally first increases and then decreases, showing a non-uniform change. Therefore, when exploring for oil and gas in the fault zone, it is necessary to select the good and bad sealing properties of the fault and find the areas with better sealing properties, which are often the main areas for oil and gas accumulation.

[0100] During the evolution of the fault, its sealing property will change continuously, mainly manifested in the changes of basic parameters such as the normal pressure on the fault section, the pore fluid pressure, and the compressive strength of the rock. As Fig.12 As shown in the figure, during the geological history, the pore fluid pressure of the fault rock first increased, and before reaching the rock fracture limit, the rock mainly underwent plastic deformation; after reaching a certain pressure threshold, micro fractures began to appear in the stress concentration area, and the number continued to increase; after crossing the rock deformation pressure mutation point, the micro fractures gradually began to expand and converge, energy was released, and a large fracture was formed, that is, a fracture system; as the energy was released, the pressure gradually decreased, and finally the fracture closed and stopped activity. Therefore, when the fracture closed, there was a critical closure pressure P fmin , below the critical pressure, the fracture is closed, and above the critical pressure, the fracture is open. Fig.13 As shown in the figure, based on the sealing evaluation results of the F2 fault, the vertical sealing coefficient is intersected with the depth, and it is found that above 949.71m, the fault is in an open state, and below 949.71m, the fault is closed, and the deeper the fault, the better the sealing. Therefore, the critical sealing pressure can be determined to be 8.527MPa.

[0101] This example solves the problem of complex fault zone closure evaluation by evaluating the closure of the main fault in the Majiatan area on the western edge of the Ordos Basin, provides a new technical method and theoretical support for the evaluation of the closure of complex faults in the area, provides a basis and foundation for the understanding of the law of oil and gas accumulation, and reduces the risk of oil and gas exploration and development. The present invention is applicable to the evaluation method of the closure of the fracture system in complex structural areas to realize the evaluation of the closure of the fracture in complex structural areas, provides a comprehensive evaluation technology for the exploration of fault block oil and gas reservoirs in complex structural areas, and reduces the risk of drilling.

Claims

1. A quantitative evaluation method of fracture sealing based on static equilibrium of fault rock pore media. It is characterized in that The internal structure of the fault system is clarified, and the structure inside the fault system is divided based on the analysis of the internal microstructure of the fault system; the static equilibrium analysis of fault rock is introduced into the Terzaghi model, and the vertical closure coefficient of the fault is defined according to the normal pressure of the fault rock section, the pore fluid pressure of the fault rock, and the compressive strength parameters of the fault rock, so as to dynamically describe the change law of the fault closure during the fault evolution process; then the lateral closure evaluation of the fault is comprehensively evaluated, the fault mudstone ratio SGR is calculated, and finally the changes in the fracture closure at different positions of the fault are evaluated.

2. The method for quantitatively evaluating fracture sealing performance based on static equilibrium of fault rock pore media according to claim 1, It is characterized in that Follow the steps below to implement it: Step 1: Divide the internal structure of the fracture system; Step 2: Construct the Terzaghi model and introduce the static equilibrium analysis of fault rock into the Terzaghi model. The fault closure includes vertical closure and lateral closure. The lateral closure is evaluated by the fault mud ratio; the vertical closure is quantitatively evaluated by defining the closure coefficient.

3. The method for quantitatively evaluating fracture sealing performance based on static balance of fault rock pore media according to claim 2, It is characterized in that The step 1 is specifically as follows: studying and dividing the internal structure of the fault system, dividing a complete fault into component units such as surrounding rock, upper plate crushing zone, fault core, lower plate crushing zone, fault rock, sandstone lens, etc. The core of evaluating the closure of the fault is to see the difference in permeability between fault rock and surrounding rock.

4. The method for quantitatively evaluating fracture sealing performance based on static balance of fault rock pore media according to claim 3, It is characterized in that The step 2 is specifically as follows: Step 2.1, respectively calculating the normal pressure of the fault rock section, the pore fluid pressure of the fault rock, the compressive strength parameter of the fault rock, and the vertical sealing coefficient of the fracture to quantitatively evaluate the vertical sealing property; Step 2.2, calculate the fault mudstone ratio SGR, comprehensively evaluate the lateral sealing of the fault, and finally evaluate the changes in the fracture sealing at different locations of the fault; Step 2.3: Combined with the seismic velocity inversion data, five parameters, namely, section normal pressure, vertical section fluid pressure, fault rock compressive strength, vertical sealing coefficient, and lateral SGR, are calculated to comprehensively evaluate the sealing property of the fault.

5. The method for quantitatively evaluating fracture sealing performance based on static balance of fault rock pore media according to claim 4, It is characterized in that The step 2.1 is specifically as follows: Step 2.1.1: For a certain depth point perpendicular to the cross section, the normal pressure perpendicular to the cross section is the resultant force of the horizontal tectonic stress on the fault rock and the pressure of the overlying strata at the same depth, that is: P vs =P ov +P tm =0.0098H(ρ r -r w )cosα+δ h sinβsinα (1) Among them, P vs is the normal pressure perpendicular to the cross section, MPa; P ov is the overlying formation pressure at the same depth, MPa; P tm is the horizontal tectonic stress, MPa; H is the depth, m; ρ r is the density of fault rock, g / cm 3 ρ w Density of formation water, g / cm 3 ; α is the inclination angle of the fault plane, °; δ h Maximum principal stress, MPa; β is the angle between the fault strike and the structural principal stress direction, °; Step 2.1.2: The direction of the fault rock pore fluid pressure is upward, and the pressure is calculated according to the improved Phillippone formula, that is: Among them, P f is the fluid pressure, MPa; V int is the formation velocity at a certain depth, m / s; V max is the maximum formation velocity, m / s; V min is the minimum formation velocity, m / s; P ov is the overlying formation pressure at the same depth, MPa; In actual calculation, the fluid pressure is decomposed to the vertical section, that is: P vf =P f cosα (3) Among them, P vf is the fluid pressure perpendicular to the cross section, MPa; P f is the fluid pressure, MPa; α is the cross-sectional inclination, °; The effective stress perpendicular to the cross section is: σ=P vs -P vf (4) Where σ is the effective stress perpendicular to the cross section, MPa; P vs is the normal pressure perpendicular to the cross section, MPa; P vf is the fluid pressure perpendicular to the cross section, MPa; Step 2.1.3: The compressive strength of the rock is calculated by fitting the velocity, and the total compressive strength of the fault rock is determined by the sand particles and the mud particles, that is: d=d S +d m (5) Among them, δ is the total compressive strength of fault rock, MPa; δ S is the compressive strength of sand particles in fault rock, MPa; δ m is the compressive strength of muddy particles in fault rock, MPa; Step 2.1.4: Define the vertical closure coefficient of the fracture based on the effective stress and rock compressive strength, that is: ΔF=σ-δ (6) Among them, ΔF is the vertical closure coefficient of the fault, MPa; σ is the effective stress perpendicular to the cross section, MPa; δ is the total compressive strength of the fault rock, MPa.

6. The method for quantitatively evaluating fracture sealing performance based on static balance of fault rock pore media according to claim 5, It is characterized in that The step 2.1 is specifically as follows: the condition for fracture closure is that the effective stress of the fault rock is greater than the compressive strength of the rock, that is, ΔF>0; the condition for fracture opening is that the effective stress of the fault rock is less than the compressive strength of the rock, that is, ΔF<0; and the fracture is in the critical condition of closure and opening, that is, ΔF=0; the normal pressure perpendicular to the cross section will continue to change, that is, the effective stress will continue to change. If the effective stress is greater than the compressive strength of the fault rock, the particles in the fault rock will be compressed and the fracture closure will tend to become stronger; otherwise, the fracture closure will become weaker.

7. The method for quantitatively evaluating fracture sealing performance based on static balance of fault rock pore media according to claim 6, It is characterized in that In step 2.2, the fault mud ratio SGR is used to evaluate the lateral sealing of the fault. The docking relationship of the lateral lithology of the fault directly affects the lateral migration of the fluid in the fault zone, namely: Among them, SGR fault mud ratio, %; h i The thickness of the fault-displaced formation i; is the mud content of fault-displaced stratum i, %; H is the total vertical throw of the fault.

8. The method for quantitatively evaluating fracture sealing performance based on static balance of fault rock pore media according to claim 7, It is characterized in that In step 2.3, it can be seen from the definition of the vertical closure of the fault that the fluid pressure and the compressive strength of the fault rock are obtained by velocity calculation. In order to achieve continuous evaluation of the fault, high-precision seismic velocity inversion data are used to calculate the relevant parameters; the seismic information is compensated by the frequency division method, and the missing low-frequency velocity in the seismic data is supplemented from the well logging data, so that the frequency spectrum is close to the frequency spectrum of the well data, and the accuracy of the seismic velocity is improved.

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