Digital core resistivity numerical simulation and saturation model construction method under deep overpressure and high temperature conditions

Abstract

The invention relates to a digital core resistivity numerical simulation and saturation model construction method under deep overpressure and high temperature conditions, and relates to the technical field of oil-gas exploration, and the method comprises the steps: constructing a digital core under the overpressure condition, calculating the clay conductivity and formation water conductivity under the high temperature condition, and obtaining an overpressure and high temperature equivalent digital core model; based on an overpressure and high-temperature equivalent digital core model, through an electrical numerical simulation algorithm, the resistivity and the stratum factor F of water-saturated cores with different porosities phi are calculated, and an F-phi cross plot is constructed; and calculating digital core resistivity and resistivity increase coefficient RI of different water saturation Sw by using a numerical simulation algorithm, and constructing an RI-Sw cross plot. According to the method, a saturation model under the deep actual temperature and pressure conditions can be constructed through equivalence of pressure and temperature by utilizing a digital rock core numerical simulation technology.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas exploration, and in particular to a method for constructing a digital core resistivity numerical simulation and saturation model under deep overpressure and high temperature conditions. Background Art

[0002] In the field of oil and gas exploration and development, accurate evaluation of formation saturation is crucial. However, traditional rock electrical experiments are usually conducted under ground conditions, and the constructed saturation model does not correspond to the actual temperature and pressure conditions of the formation, resulting in inaccurate logging saturation evaluation and difficulty in popularization and application.

[0003] To solve this problem, people try to conduct rock physics experiments under overpressure and high temperature conditions to build a more accurate saturation model. However, this method faces challenges such as high experimental costs and difficult experimental conditions. When the temperature is higher and the pressure is greater, the pressure resistance and high temperature resistance of the experimental equipment and the complexity of the experimental operation are greatly increased, making it more difficult to promote this method.

[0004] At the same time, digital rock electrical numerical simulation technology, as an emerging research method, provides new ideas for the study of rock electrical properties under formation conditions. However, most of the existing numerical simulation methods do not consider the influence of temperature and pressure conditions, and the constructed saturation model is still based on normal temperature and pressure conditions, so it is difficult to meet the needs of overpressure and high temperature formation conditions.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for numerical simulation of digital core resistivity and construction of a saturation model under deep overpressure and high temperature conditions. By using numerical simulation technology, a more accurate saturation model can be constructed by considering the actual temperature and pressure conditions of the formation.

[0007] In order to solve the above technical problems, the basic concept of the technical solution adopted by the present invention is:

[0008] First, the digital core resistivity numerical simulation and saturation model construction method under deep overpressure and high temperature conditions include:

[0009] Through core CT, high-resolution digital cores can be constructed;

[0010] Based on the high-resolution digital core, the overpressure porosity experimental results are used for calibration to construct a digital core model under overpressure conditions;

[0011] Based on the digital core model under overpressure conditions, the conductivity of clay and formation water under high temperature conditions are calculated to obtain digital cores equivalent to overpressure and high temperature;

[0012] Numerical simulations were performed on digital cores with equivalent overpressure and high temperature, the resistivity and formation factor F of saturated cores with different porosities φ were calculated, and F-φ crossplots were constructed;

[0013] The digital cores with different water saturation were constructed by using mathematical morphology algorithm, the resistivity and resistivity increase coefficient RI of the digital cores with different water saturation Sw were calculated, and the RI-Sw cross plot was constructed.

[0014] According to the cross-plot, the relationship between the core formation factor F and the rock porosity φ, the resistivity increase coefficient RI of the digital core with different saturations and the water saturation Sw is analyzed, so as to construct a new conductivity equation and saturation model.

[0015] Furthermore, core CT is used to construct high-resolution digital cores, including:

[0016] Perform CT scanning on the core samples to obtain detailed structural information of the cores and obtain CT scanning images;

[0017] Preprocessing the CT scan image to obtain a preprocessed image;

[0018] According to the preprocessed image, the gradient information of the image is obtained, and the weak edges in the image are identified and segmented to obtain a segmented image;

[0019] Based on the segmented images, XRD experiments and porosity measurements are performed to obtain the mineral composition and porosity data of the core;

[0020] The CT scan image segmentation images, the core mineral composition and porosity measurement data are combined to construct a high-resolution digital core.

[0021] Furthermore, based on the high-resolution digital core, the overpressure porosity experimental results are used for calibration to construct the digital core under overpressure conditions, including:

[0022] According to the high-resolution digital core, a three-dimensional image of any shape and size is determined, and the pore space of the digital core is eroded and expanded to obtain the calculation result;

[0023] According to the calculation results, the porosity after overburden pressure is obtained;

[0024] The porosity of the digital core after overpressure is calibrated with the porosity of the core overpressure experiment to construct the digital core under overpressure conditions.

[0025] Furthermore, based on the digital core under overpressure conditions, the clay conductivity and formation water conductivity under high temperature conditions are calculated to obtain the digital core equivalent to overpressure and high temperature, including:

[0026] Based on digital core under overpressure conditions, clay mineral types and volume content are determined. To obtain the equivalent cation exchange capacity of clay minerals, CEC eq is the equivalent cation exchange concentration of clay minerals, V i is the volume content of the i-th mineral, i is the index, and n is the number of mineral types;

[0027] According to the equivalent cation exchange capacity of clay minerals, To obtain the cation solubility per unit volume Q v and core experimental porosity φ t , where ρ cl is the density of clay particles, Q v is the cation solubility per unit volume Q v ;

[0028] According to the cation solubility per unit volume, C cl =B T Q v The conductivity of clay under high temperature conditions is obtained, where C cl is the conductivity of clay minerals, B T It is the equivalent conductivity of exchange cations on the surface of clay particles at temperature T.

[0029] Furthermore, the calculation formula of formation water conductivity under high temperature conditions is:

[0030]

[0031] Among them, C w is the formation water conductivity, and are the formation water conductivity at temperatures T2 and T1 respectively, and α is the temperature coefficient of conductivity, where α is approximately 0.005 at 140°C.

[0032] Furthermore, the resistivity numerical simulation of the digital core equivalent to overpressure and high temperature is carried out, the resistivity of the saturated core with different porosity φ is calculated, and the F-φ cross-plot is constructed, including:

[0033] According to the digital core equivalent to overpressure and high temperature, the three-dimensional digital core finite element nodes are established and Get the energy of a pixel unit of the digital core, where σ pq is the conductivity tensor of the pixel unit, D rs is the stiffness matrix, e p and eq is the component of the electric field, u r and u s is the voltage component, E n is the energy of the pixel unit;

[0034] The energy of a pixel unit in the digital core is calculated to find the extreme value of the total energy, and the Calculate the voltage distribution of each pixel unit to realize numerical simulation of digital core, The partial derivative of energy with respect to the electric field component is 0, u m is the voltage component;

[0035] According to the numerical simulation of the digital core, the formation factor F of the core is obtained, and the Construct an F-φ cross plot to realize numerical simulation, where F is the formation factor of the core, R0 is the resistivity of the saturated core with completely different porosity φ, and R w is the resistivity of formation water, and φ represents the porosity of rock.

[0036] Furthermore, the mathematical morphology algorithm is used to construct digital cores with different water saturations, the resistivity and resistivity increase coefficient RI of digital cores with different water saturations Sw are calculated, and the RI-Sw cross-plot is constructed, including:

[0037] Numerical simulations were performed on digital cores with different saturations to obtain the core resistivity and resistivity increase coefficient RI. Construct the RI-Sw intersection diagram, where R t is the rock resistivity, R w is the resistivity of water, RI is the digital core resistivity increase coefficient of different saturations, S w is the water saturation;

[0038] Furthermore, according to the cross-plot, the relationship between the formation factor F of the core and the porosity φ of the rock, the resistivity increase coefficient RI of the digital core with different saturations and the water saturation Sw is analyzed, so as to construct a new conductivity equation and saturation model, including:

[0039] According to the cross plot, the relationship between resistivity and porosity, water saturation and formation water resistivity under overpressure and high temperature conditions is deduced. t =f(φ)g(S w )R w , to obtain a new conductivity equation, and transform the new conductivity equation to obtain the saturation model.

[0040] Secondly, the digital core resistivity numerical simulation and saturation model construction system under deep overpressure and high temperature conditions includes:

[0041] The acquisition module is used to construct a high-resolution digital core through core CT; based on the high-resolution digital core, the overburden porosity experiment results are used for calibration to construct a digital core model under overpressure conditions; based on the digital core model under overpressure conditions, the clay conductivity and formation water conductivity under high temperature conditions are calculated to obtain a digital core equivalent to overpressure and high temperature.

[0042] The processing module is used to perform numerical simulation on digital cores equivalent to overpressure and high temperature, calculate the resistivity and formation factor F of water-saturated cores with different porosities φ, and construct an F-φ cross-plot; use mathematical morphology algorithms to construct digital cores with different water saturations, calculate the resistivity and resistivity increase coefficient RI of digital cores with different water saturations Sw, and construct an RI-Sw cross-plot; based on the cross-plot, analyze the changing relationship between the formation factor F of the core and the porosity φ of the rock, and the resistivity increase coefficient RI of the digital cores with different saturations and the water saturation Sw, so as to construct a new conductivity equation and saturation model.

[0043] According to a third aspect, a computing device includes:

[0044] one or more processors;

[0045] The storage device is used to store one or more programs. When the one or more programs are executed by the one or more processors, the one or more processors implement the method described.

[0046] In a fourth aspect, a computer-readable storage medium stores a program, and when the program is executed by a processor, the method described is implemented.

[0047] After adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art:

[0048] For the first time, the digital core electrical numerical simulation under formation conditions was realized, breaking through the digital rock physics simulation method under normal temperature conditions, and providing a new technical means for the study of rock electrical properties under formation conditions; through the numerical simulation method, the rock electrical experiment under formation conditions was realized, effectively replacing the traditional high-temperature and high-pressure rock electrical experiment, greatly improving the experimental efficiency, and significantly reducing the experimental cost; based on the numerical simulation of the electrical properties of digital rocks, the conductive mechanism under formation overpressure and high temperature conditions was deeply analyzed, and a saturation model that can reflect formation conditions was constructed, making the calculated saturation more accurate, providing more reliable data support for oil and gas exploration and development; it helps to have a deeper understanding of the electrical properties of rocks under formation overpressure and high temperature conditions, providing a favorable tool for geological research, oil and gas reservoir description and resource development, and helping to optimize development strategies and improve resource recovery.

[0049] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. Some specific embodiments of the present application will be described in detail in an illustrative and non-restrictive manner with reference to the drawings. The same reference numerals in the drawings indicate the same or similar components or parts. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale. In the drawings:

[0051] Figure 1 It is a schematic diagram of the method for numerical simulation of digital core resistivity and construction of saturation model under deep overpressure and high temperature conditions of the present invention.

[0052] Figure 2 It is a schematic diagram of the digital core resistivity numerical simulation and saturation model construction system under deep overpressure and high temperature conditions of the present invention.

[0053] Figure 3 It is a flow chart of digital core construction under overpressure conditions of the method for constructing a digital core resistivity numerical simulation and saturation model under deep overpressure and high temperature conditions of the present invention.

[0054] Figure 4 It is a finite element node model of the digital core resistivity numerical simulation and saturation model construction method under deep overpressure and high temperature conditions of the present invention.

[0055] Figure 5 It is the three-dimensional digital core before overburdening and the digital core after overburdening under deep overpressure and high temperature conditions of the present invention.

[0056] Figure 6 It is the F-φ relationship of the resistivity numerical simulation under deep overpressure and high temperature conditions of the digital core resistivity numerical simulation and saturation model construction method under deep overpressure and high temperature conditions of the present invention.

[0057] Figure 7 It is the RI-Sw relationship of the digital core resistivity numerical simulation and saturation model construction method under deep overpressure and high temperature conditions of the present invention, and the resistivity numerical simulation under deep overpressure and high temperature conditions.

[0058] Figure 8 This is a diagram of the logging interpretation results of the deep reservoir saturation of Well H in a certain depression in Region A according to the method for numerical simulation of digital core resistivity and construction of saturation model under deep overpressure and high temperature conditions of the present invention.

[0059] Fig. 9 It is a flow chart of the method for numerical simulation of digital core resistivity and construction of saturation model under deep overpressure and high temperature conditions of the present invention.

[0060] It should be noted that these drawings and text descriptions are not intended to limit the conceptual scope of the present invention in any way, but to illustrate the concept of the present invention for those skilled in the art by referring to specific embodiments. The elements in the drawings are schematic and not drawn to scale. DETAILED DESCRIPTION

[0061] In order to enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work should fall within the scope of protection of the present application.

[0062] The following embodiment of the present application takes the method for numerical simulation of digital core resistivity and construction of saturation model under deep overpressure and high temperature conditions as an example to explain the scheme of the present application in detail, but this embodiment cannot limit the scope of protection of the present application.

[0063] like Figures 1 to 9 As shown, the present invention provides a method for numerical simulation of digital core resistivity and construction of saturation model under deep overpressure and high temperature conditions, including:

[0064] Step 11, constructing a high-resolution digital core through core CT;

[0065] Step 12, based on the high-resolution digital core, the overpressure porosity experimental results are used for calibration to construct a digital core model under overpressure conditions;

[0066] Step 13, based on the digital core model under overpressure conditions, calculating the clay conductivity and formation water conductivity under high temperature conditions to obtain a digital core equivalent to overpressure and high temperature;

[0067] Step 14, numerical simulation is performed on the digital core equivalent to overpressure and high temperature, the resistivity and formation factor F of the saturated core with different porosities φ are calculated, and an F-φ cross-plot is constructed;

[0068] Step 15, constructing digital cores with different water saturations using a mathematical morphology algorithm, calculating the resistivity and resistivity increase coefficient RI of the digital cores with different water saturations Sw, and constructing a RI-Sw cross plot;

[0069] Step 16, based on the cross-plot, analyze the changing relationship between the core formation factor F and the rock porosity φ, the resistivity increase coefficient RI of the digital core with different saturations and the water saturation Sw, so as to construct a new conductivity equation and saturation model.

[0070] In the embodiment of the present invention, the construction of high-resolution digital core makes the analysis of rock microstructure more precise, which helps to improve the accuracy and reliability of geological modeling; by simulating the rock properties under overpressure and high temperature conditions, the actual state of oil and gas reservoirs underground can be better understood, thereby optimizing development strategies and improving oil and gas recovery rates; numerical simulation and the construction of cross plots help to build a more accurate saturation model and improve the accuracy and reliability of well logging interpretation; by analyzing the changing relationship between F and φ, RI and Sw, the conductivity mechanism of deep rocks can be more deeply understood, providing a new perspective for rock physics research; based on the analysis of cross plots, new conductivity equations and saturation models can be constructed, providing new theoretical tools for rock electrical property research and improving the efficiency and success rate of oil and gas exploration.

[0071] In a preferred embodiment of the present invention, the above step 11 includes:

[0072] Perform CT scanning on the core samples to obtain detailed structural information of the cores and obtain CT scanning images;

[0073] Preprocessing the CT scan image to obtain a preprocessed image;

[0074] According to the preprocessed image, the gradient information of the image is obtained, and the weak edges in the image are identified and segmented to obtain a segmented image;

[0075] Based on the segmented images, XRD experiments and porosity measurements are performed to obtain the mineral composition and porosity measurement data of the core;

[0076] The CT scan image segmentation images, the core mineral composition and porosity measurement data are combined to construct a high-resolution digital core.

[0077] In the embodiments of the present invention, the high-resolution digital core provides a detailed three-dimensional image of the internal structure of the rock, making the analysis of the porosity and permeability properties of the rock more accurate; through CT scanning and image processing technology, the weak edges and tiny pores in the rock can be clearly identified, which helps to gain a deep understanding of the internal structural characteristics of the rock; by scanning the core sample with an XRD diffractometer, the mineral composition information in the core can be determined; the high-resolution digital core provides a new data source and experimental platform for the study of rock physics and geology, which helps to promote the development of related disciplines; through simulation and analysis of the digital core, multiple experiments can be performed on the computer without consuming actual core samples, thereby reducing experimental costs and risks.

[0078] In the specific implementation process of the present invention, a core sample is determined, cut and ground, and a high-resolution CT scanning device is used to scan the core sample to obtain a high-quality CT scanning image; detailed structural information of the core sample is obtained from the CT scanning device to form a CT scanning image; a denoising algorithm, a contrast enhancement algorithm and a smoothing algorithm are used to process the CT scanning image to obtain a pre-processed image, and a gradient calculation is performed on the pre-processed image to obtain the gradient value of each pixel in the image; based on the gradient information of the image, weak edges in the image are identified and segmented, and small changes in the image are responded to. , segment the image into different components to obtain a segmented image, in which different components can be clearly separated; perform XRD experiments on different components in the segmented image, use an XRD diffractometer to scan the core sample, obtain the diffraction spectrum, and by analyzing the diffraction spectrum, the mineral composition information in the core can be determined; use image processing technology and physical measurement methods to measure the porosity of the core sample to obtain porosity data; finally, the CT scan image, segmented image, mineral composition data obtained from the XRD experiment, and porosity measurement data are integrated to construct a high-resolution digital core.

[0079] In a preferred embodiment of the present invention, the above step 12 includes:

[0080] According to the high-resolution digital core, a three-dimensional image of any shape and size is determined, and the pore space of the digital core is eroded and expanded to obtain the calculation result;

[0081] According to the calculation results, the porosity after overburden pressure is obtained;

[0082] The porosity of the digital core after overpressure is calibrated with the porosity of the core overpressure experiment to construct the digital core under overpressure conditions.

[0083] In an embodiment of the present invention, the pore structure inside the rock can be characterized in detail through high-resolution digital cores, including the shape, size, and distribution characteristics of the pores. Corrosion and expansion operations are performed on this basis, which can more accurately simulate the changes in the pore structure under different pressure conditions; the calculation results provide specific values ​​of the porosity after overburdening, making the evaluation of the pore structure changes more quantitative and accurate; the calculated porosity after overburdening is compared with the porosity of the core overburdening experiment to verify the reliability of the digital core model and the simulation method; combining the results of digital core simulation and physical experiments, a comprehensive and reliable data set can be formed.

[0084] In the specific implementation process of the present invention, the structural element is determined according to the size and shape of the pores, and the selected structural element is used to perform an erosion operation on the pore space in the three-dimensional image, and the origin of the structural element is aligned with the pixel point currently being processed. Only when all pixel values ​​covered by the structural element are target objects and the pixel values ​​at the corresponding positions in the structural element are also target objects, the pixel point of the result image is assigned to the target object; otherwise, the pixel point of the result image is assigned to a non-target object; the operation steps are repeated for each pixel point in the original image until all pixel points are processed, and the obtained image is the eroded image.

[0085] On the basis of the erosion operation, the expansion operation is performed on the pore space. The origin of the structure element is aligned with the pixel currently being processed. The original image area covered by the structure element is checked to determine whether there is a target pixel in the area. If there is at least one target pixel in the area covered by the structure element, the pixel value of the corresponding position in the result image is set to the target object. If the area covered by the structure element is all background pixels, the pixel value of the corresponding position in the result image may remain unchanged. The operation steps are repeated for each pixel in the original image until all pixels are processed. The obtained image is the expanded image.

[0086] According to the three-dimensional image after corrosion and expansion operation, the porosity after overburden pressure is calculated by the ratio of pore volume to total volume; the porosity data under corresponding pressure conditions are obtained from the core overburden pressure experiment; the calculated porosity after overburden pressure is compared with the experimental porosity, and if the two are basically close, the digital core of formation conditions is output; if the two are greatly different, the structural elements are readjusted to corrode and expand the pores until the porosity is consistent with the overburden pressure porosity experimental results.

[0087] In a preferred embodiment of the present invention, the above step 13 includes:

[0088] Based on digital core under overpressure conditions, clay mineral types and volume content are determined. To obtain the equivalent cation exchange capacity of clay minerals, CEC eq is the equivalent cation exchange concentration of clay minerals, V i is the volume content of the i-th mineral, i is the index, and n is the number of mineral types;

[0089] According to the equivalent cation exchange capacity of clay minerals, To obtain the cation solubility per unit volume Q v and core experimental porosity φ t , where ρ cl is the density of clay particles, Q v is the cation solubility per unit volume Q v ;

[0090] According to the cation solubility per unit volume, C cl =B T Q v The conductivity of clay under high temperature conditions is obtained, where C cl is the conductivity of clay minerals, B T It is the equivalent conductivity of exchange cations on the surface of clay particles at temperature T.

[0091] In the embodiment of the present invention, the digital core equivalent to overpressure and high temperature can more accurately predict the conductivity distribution and fluid flow behavior in the actual formation. Based on the more accurate prediction, the recovery rate can be improved. Through digital core and simulation technology, the dependence on actual core samples can be reduced and the experimental cost can be reduced.

[0092] In a preferred embodiment of the present invention, in the above step 13, the calculation formula of the formation water conductivity under high temperature conditions is:

[0093]

[0094] Among them, C w is the formation water conductivity, and are the formation water conductivity at temperatures T2 and T1 respectively, and α is the temperature coefficient of conductivity, where α is approximately 0.005 at 140°C.

[0095] In the embodiments of the present invention, the conductivity of formation water at high temperature can be accurately predicted based on known formation water conductivity and temperature conditions, which is of great significance for understanding fluid behavior in the formation, optimizing development strategies, and improving recovery rates; it reduces dependence on traditional experimental methods, thereby reducing experimental costs and shortening research cycles, and also improves accuracy and reliability.

[0096] In the specific implementation process of the present invention, XRD is used to determine the type and volume content of clay minerals, and the equivalent cation exchange capacity of clay minerals is calculated; then, the equivalent cation exchange capacity is used to calculate the cation solubility per unit volume and the core experimental porosity; finally, the conductivity of high-temperature clay minerals is calculated using the cation solubility per unit volume and the core experimental porosity, and the effect of temperature on the conductivity of formation water is calculated, wherein α is the conductivity temperature coefficient, which indicates the rate at which conductivity increases with increasing temperature. Waxman and Smits gave the relationship between α and temperature in their research, and α is about 0.005 at 140°C.

[0097] In a preferred embodiment of the present invention, the above step 14 includes:

[0098] According to the digital core equivalent to overpressure and high temperature, the three-dimensional digital core finite element nodes are established and Get the energy of a pixel unit of the digital core, where σ pq is the conductivity tensor of the pixel unit, D rs is the stiffness matrix, e p and e q is the component of the electric field, u r and u s is the voltage component, E n is the energy of the pixel unit;

[0099] The energy of a pixel unit in the digital core is calculated to find the extreme value of the total energy, and the Calculate the voltage distribution of each pixel unit to realize numerical simulation of digital core, The partial derivative of energy with respect to the electric field component is 0, u m is the voltage component;

[0100] According to the numerical simulation of the digital core, the formation factor F of the core is obtained, and the Construct F-φ cross-plot to realize numerical simulation, where F is the formation factor of the core, R0 and R w is the intrinsic resistivity of rock and is the resistivity of water, and φ represents the porosity of rock.

[0101] In the embodiments of the present invention, the rock physical properties, especially the resistivity, under actual formation conditions can be accurately simulated by numerical simulation methods; the distribution and movement of fluids in the formation can be understood by simulating the rock resistivity under different overpressure and high temperature conditions; the numerical simulation method can reduce the demand for actual core samples, thereby reducing experimental costs and shortening the research cycle; by combining the numerical simulation results with the F-φ cross-plot, the geological model can be verified and improved to more accurately reflect the actual formation conditions; accurate numerical simulation and F-φ cross-plot can monitor fluid dynamics, predict production trends and formulate effective production-increasing measures, and combine digital core technology, numerical simulation and cross-plot analysis to promote technological innovation in related fields.

[0102] In the specific implementation process of the present invention, a three-dimensional digital core is constructed based on the digital core data equivalent to overpressure and high temperature, and the digital core is divided into a finite number of units, each unit contains multiple nodes, and the coordinates of each node and the information of the adjacent units are determined; for each pixel unit in the digital core, according to the conductivity tensor σ pq and the stiffness matrix D rsCalculate its energy. The energy expression involves the electric field component and the voltage component. Use the variational principle to solve the extreme value of the total energy, that is, solve the equation group whose partial derivative of energy with respect to the electric field component is 0. By solving the equation group, the voltage distribution of each pixel unit is obtained. Special treatment is performed on the nodes on the boundary to make them meet the periodic boundary conditions. Set the stop condition C = 1×10 -7 When the square sum of the norm of the gradient vector is less than this threshold, the simulation process will stop automatically. After the simulation stops, the conductivity of the digital core is calculated based on the voltage distribution and other physical parameters. The constructed digital cores with different porosities are completely saturated with water, and the finite element method is used to carry out numerical simulation. The formation factors of these cores are related to the inherent resistivity of the rock, the resistivity of water, and the porosity of the rock. According to the calculated F value and the corresponding porosity φ value, the F-φ cross-plot is constructed, and the F-φ cross-plot is analyzed to deduce the relationship between F and φ.

[0103] In a preferred embodiment of the present invention, the above step 15 includes:

[0104] Numerical simulations were performed on digital cores with different saturations to obtain the core resistivity and resistivity increase coefficient RI. Construct the RI-Sw intersection diagram, where R t is the rock resistivity, R w is the resistivity of water, RI is the digital core resistivity increase coefficient of different saturations, S w is the water saturation;

[0105] In an embodiment of the present invention, the digital core is used to accurately describe the fluid distribution and rock physical properties, and the development effect of the oil and gas reservoir is accurately predicted based on the numerical simulation results of the digital core, thereby optimizing the development plan and improving the recovery rate of the oil and gas reservoir; through the analysis of the digital core, the uncertainty factors of the fluid distribution and pore structure in the oil and gas reservoir are understood, thereby reducing the risks in the development process. As an important part of the digitization of oil and gas fields, the digital core can provide basic data support for the construction of intelligent oil and gas fields, and promote the development of oil and gas fields in a more intelligent and efficient direction.

[0106] In a preferred embodiment of the present invention, the above step 16 includes:

[0107] According to the cross plot, the relationship between resistivity and porosity, water saturation and formation water resistivity under overpressure and high temperature conditions is deduced. t =f(φ)g(S w )R w , to obtain a new conductivity equation, and transform the new conductivity equation to obtain the saturation model.

[0108] In an embodiment of the present invention, under conditions of overpressure and high temperature in the formation, the traditional saturation model may no longer be applicable, and the new model will provide more accurate predictions. Accurate water saturation predictions are crucial to the development of oil and gas fields and optimize development strategies. By more accurately predicting water saturation, explorers can more effectively identify potential oil and gas reservoirs, thereby improving exploration efficiency.

[0109] like Figure 2 As shown, a digital core resistivity numerical simulation and saturation model construction system 20 under deep overpressure and high temperature conditions includes:

[0110] The acquisition module 21 is used to construct a high-resolution digital core through core CT; calibrate the high-resolution digital core with the overburden porosity test results to construct a digital core model under overpressure conditions; based on the digital core model under overpressure conditions, calculate the clay conductivity and formation water conductivity under high temperature conditions to obtain a digital core equivalent to overpressure and high temperature.

[0111] The processing module 22 is used to perform numerical simulation on the digital core equivalent to overpressure and high temperature, calculate the resistivity and formation factor F of saturated cores with different porosities (φ), and construct an F-φ intersection diagram; use a mathematical morphology algorithm to construct digital cores with different water saturations, calculate the resistivity and resistivity increase coefficient RI of digital cores with different water saturations Sw, and construct an RI-Sw intersection diagram; according to the intersection diagram, analyze the changing relationship between the formation factor F of the core and the porosity φ of the rock, and the resistivity increase coefficient RI of the digital cores with different saturations and the water saturation Sw, so as to construct a new conductivity equation and saturation model.

[0112] The embodiment of the present invention further provides a computing device, comprising: a processor, a memory storing a computer program, wherein when the computer program is executed by the processor, the method described above is executed. All implementations in the above method embodiment are applicable to this embodiment and can achieve the same technical effect.

[0113] like Figures 5 to 7 As shown, when specifically applied, the present invention specifically includes the following steps:

[0114] Core preparation and overpressure and high temperature condition setting: The core samples come from a deep tight sandstone reservoir in a depression in Area A. Representative cores were selected for X-CT scanning with a scanning resolution of 1.96μm; XRD whole rock and clay analysis experiments were carried out;

[0115] according to Figure 5 The process shown in the figure successively constructs the digital core under the formation overburden condition, with the target layer temperature of 140°C and the pressure of 40 MPa. Figure 6This is a digital core model after pressure equivalence. In the figure, the black component represents pores, the green component represents clay minerals, the white component represents quartz minerals, the light blue component represents calcareous minerals, and the yellow component represents conductive minerals. The large pores are reduced and some small pores are closed. According to the above method, a total of 5 digital cores after overburden pressure were established.

[0116] Assuming the formation temperature is 140℃, the conductivity of the skeleton minerals. cl =B T Q v Calculate the conductivity of clay minerals in 5 digital cores using Eq. The conductivity of the formation water is calculated by overpressure and high temperature equivalence. The resistivity can be calculated by numerical simulation of each constructed digital core using the finite element method.

[0117] Relationship between F and φ: The five digital cores constructed were fully saturated with water, and numerical simulation was carried out using the finite element method to calculate the resistivity R0 and formation factor F of the five cores, and to construct the F-φ cross-plot; Figure 6 Under overpressure and high temperature conditions In the cross-plot, the red and black data points are the numerical simulation results and the high-temperature and high-pressure rock electrical experimental results respectively; the resistivity numerical simulation results under deep overpressure and high-temperature conditions are basically close to the rock electrical experimental results, and the relationship between F and φ still conforms to the first formula of Archie's law:

[0118] The relationship between F and φ under the conditions of overpressure and high temperature is fitted as follows:

[0119]

[0120] According to the rock electrical experimental results, the relationship between F and φ under ground conditions is fitted as follows:

[0121]

[0122] Relationship between RI and Sw: Mathematical morphology calculation method is used to simulate the distribution of oil and water in rock pores under formation overpressure and high temperature conditions, and digital cores with different water saturations are constructed. Finite element method is used to carry out numerical simulation, calculate the resistivity increase coefficient RI of 5 cores at multiple saturations, construct RI-Sw cross plot, and analyze the relationship between resistivity and oil content under formation overpressure and high temperature conditions. Figure 7 Shown is the RI-Sw crossplot of formation conditions;

[0123] From the simulation results, as the displacement progresses, the water saturation gradually decreases, and the RI-Sw curves of the five samples bend downward to varying degrees. This shows that when the water saturation is constant, the resistivity of the formation under overpressure and high temperature is slightly lower than the resistivity of the ground experiment. This is mainly caused by the decrease in the resistivity of the bound water in the formation under overpressure and high temperature. In the double logarithmic coordinates, the RI and Sw of the overpressure and high temperature simulation are in an exponential function relationship, reflecting the new conductive properties of the low-permeability reservoir, which is different from the power function relationship of the traditional rock physics experiment. When the resistivity is constant, the water saturation calculated by the new model is less than the result calculated by the Archie model, that is, the oil saturation calculated by the new model is higher. Therefore, the oil saturation evaluated by the new model is higher, which is of great significance for reserve evaluation:

[0124] The relationship between RI and Sw under the conditions of overpressure and high temperature is fitted as follows:

[0125]

[0126] According to the rock electrical experimental results, the relationship between RI and Sw under ground conditions is fitted as follows:

[0127]

[0128] Derivation of saturation model: Based on the relationship between F and φ and the relationship between RI and Sw, the new conductivity equation is derived as follows: By taking the logarithm of both sides of the formula, we can get: This equation is a tight sandstone reservoir saturation model under formation overpressure and high temperature conditions obtained by digital core technology;

[0129] Similarly, the related equations under ground conditions are: Japanese style The Archie saturation model obtained from rock physics experiments under ground conditions is:

[0130] like Figure 8 As shown, when it is applied specifically, the specific example analysis is:

[0131] The target area is a deep low-permeability clastic oil and gas reservoir in a depression in Area A. The lithology is mainly feldspar lithic quartz sandstone and lithic sandstone, followed by lithic feldspar sandstone and feldspar lithic sandstone. The reservoir porosity is 2%-15%, the average porosity is about 8.4%, and the permeability is 0.001~10×10 -3 μm 2 The average permeability is about 3.8×10 -3 μm 2, the porosity-permeability relationship is complex. Well H is an exploration well in the area. The target layer is buried more than 3500m deep, with an average porosity of about 9.5% and a permeability of about 2.8mD. The resistivity is obtained by deep detection resistivity, the porosity is obtained by neutron-density logging intersection, and the formation water resistivity is 0.16Ω.m. The saturation of the well is calculated using the new model and the Archie model, respectively. The parameters of the Archie model are taken from the results of rock electrical experiments.

[0132] In the figure, the first track is depth, the second track is gamma, natural potential and caliper logging while drilling, the third track is density, neutron and acoustic time difference logging while drilling, the fourth track is resistivity logging, and the fifth track is a comparison of saturation calculation results, where the black dots are the true saturation of the formation obtained using mercury injection data. The sixth track is the mineral profile. It can be seen that compared with the Archie model, the oil saturation calculated by the new model established under overpressure and high temperature formation conditions is significantly higher and more consistent with the core saturation, indicating that the relationship between RI and Sw index in the model is more consistent with the conductivity mechanism of low permeability reservoirs, and therefore, the calculation accuracy is higher.

[0133] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for numerical simulation of digital core resistivity and construction of saturation model under deep overpressure and high temperature conditions, characterized in that: include: Through core CT, high-resolution digital cores can be constructed; Based on the high-resolution digital core, the overpressure porosity experimental results are used for calibration to construct a digital core model under overpressure conditions; Based on the digital core model under overpressure conditions, the conductivity of clay and formation water under high temperature conditions are calculated to obtain digital cores equivalent to overpressure and high temperature; Numerical simulations were performed on digital cores with equivalent overpressure and high temperature, the resistivity and formation factor F of saturated cores with different porosities φ were calculated, and F-φ crossplots were constructed; The digital cores with different water saturation were constructed by using mathematical morphology algorithm, the resistivity and resistivity increase coefficient RI of the digital cores with different water saturation Sw were calculated, and the RI-Sw cross plot was constructed. According to the cross-plot, the relationship between the core formation factor F and the rock porosity φ, the resistivity increase coefficient RI of the digital core with different saturations and the water saturation Sw is analyzed, so as to construct a new conductivity equation and saturation model.

2. The method for numerical simulation of digital core resistivity and construction of saturation model under deep overpressure and high temperature conditions according to claim 1, characterized in that: Core CT is used to construct high-resolution digital cores, including: Perform CT scanning on the core samples to obtain detailed structural information of the cores and obtain CT scanning images; Preprocessing the CT scan image to obtain a preprocessed image; According to the preprocessed image, the gradient information of the image is obtained, and the weak edges in the image are identified and segmented to obtain a segmented image; Based on the segmented images, XRD experiments and porosity measurements are performed to obtain the mineral composition and porosity data of the core; The CT scan image segmentation images, the core mineral composition and porosity measurement data are combined to construct a high-resolution digital core.

3. The method for numerical simulation of digital core resistivity and construction of saturation model under deep overpressure and high temperature conditions according to claim 2, characterized in that: Based on the high-resolution digital core, the overpressure porosity experimental results are used for calibration to construct the digital core under overpressure conditions, including: According to the high-resolution digital core, a three-dimensional image of any shape and size is determined, and the pore space of the digital core is eroded and expanded to obtain the calculation result; According to the calculation results, the porosity after overburden pressure is obtained; The porosity of the digital core after overpressure is calibrated with the porosity of the core overpressure experiment to construct the digital core under overpressure conditions.

4. The method for numerical simulation of digital core resistivity and construction of saturation model under deep overpressure and high temperature conditions according to claim 3 is characterized in that: Based on the digital core under overpressure conditions, the clay conductivity and formation water conductivity under high temperature conditions are calculated to obtain the digital core equivalent to overpressure and high temperature, including: Based on digital core under overpressure conditions, clay mineral types and volume content are determined. To obtain the equivalent cation exchange capacity of clay minerals, CEC eq is the equivalent cation exchange concentration of clay minerals, V i is the volume content of the i-th mineral, i is the index, and n is the number of mineral types; According to the equivalent cation exchange capacity of clay minerals, To obtain the cation solubility per unit volume Q v and core experimental porosity φ t , where ρ cl is the density of clay particles, Q v is the cation solubility per unit volume Q v ; According to the cation solubility per unit volume, C cl =B T Q v The conductivity of clay under high temperature conditions is obtained, where C cl is the conductivity of clay minerals, B T It is the equivalent conductivity of exchange cations on the surface of clay particles at temperature T.

5. The method for numerical simulation of digital core resistivity and construction of saturation model under deep overpressure and high temperature conditions according to claim 4, characterized in that: The calculation formula of formation water conductivity under high temperature conditions is: Among them, C w is the formation water conductivity, and are the formation water conductivity at temperatures T2 and T1 respectively, and α is the temperature coefficient of conductivity, where α is approximately 0.005 at 140°C.

6. The method for numerical simulation of digital core resistivity and construction of saturation model under deep overpressure and high temperature conditions according to claim 5, characterized in that: The resistivity of the digital core equivalent to overpressure and high temperature is numerically simulated, the resistivity of the saturated core with different porosity φ is calculated, and the resistivity of the core with different porosity φ is constructed. Crossplot, including: According to the digital core equivalent to overpressure and high temperature, the three-dimensional digital core finite element nodes are established and Get the energy of a pixel unit of the digital core, where σ pq is the conductivity tensor of the pixel unit, D rs is the stiffness matrix, e p and e q is the component of the electric field, u r and u s is the voltage component, E n is the energy of the pixel unit; The energy of a pixel unit in the digital core is calculated to find the extreme value of the total energy, and the Calculate the voltage distribution of each pixel unit to realize numerical simulation of digital core, The partial derivative of energy with respect to the electric field component is 0, u m is the voltage component; According to the numerical simulation of the digital core, the formation factor F of the core is obtained, and the Build Crossplot to achieve numerical simulation, where F is the formation factor of the core, R0 is the resistivity of the saturated core with completely different porosity φ, and R w is the resistivity of formation water, and φ represents the porosity of rock.

7. The method for numerical simulation of digital core resistivity and construction of saturation model under deep overpressure and high temperature conditions according to claim 6, characterized in that: The digital cores with different water saturations are constructed by using mathematical morphology algorithm, the resistivity and resistivity increase coefficient RI of the digital cores with different water saturations Sw are calculated, and the RI-Sw cross-plot is constructed, including: Numerical simulations were performed on digital cores with different saturations to obtain the core resistivity and resistivity increase coefficient RI. Construct the RI-Sw intersection diagram, where R t is the rock resistivity, R w is the resistivity of water, RI is the digital core resistivity increase coefficient of different saturation, S w is the water saturation.

8. The method for numerical simulation of digital core resistivity and construction of saturation model under deep overpressure and high temperature conditions according to claim 7, characterized in that: According to the cross-plot, the relationship between the formation factor F of the core and the porosity φ of the rock, the resistivity increase coefficient RI of the digital core with different saturations and the water saturation Sw is analyzed, so as to construct a new conductivity equation and saturation model, including: According to the cross-plot, the relationship between resistivity and porosity, water saturation and formation water resistivity under overpressure and high temperature conditions is deduced. t =f(φ)g(S w )R w , to obtain a new conductivity equation, and transform the new conductivity equation to obtain the saturation model.

9. A digital core resistivity numerical simulation and saturation model construction system under deep overpressure and high temperature conditions, characterized by: include: Acquisition module, used to construct high-resolution digital cores through core CT; Based on the high-resolution digital core, the overpressure porosity experiment results are used for calibration to construct a digital core model under overpressure conditions. Based on the digital core model under overpressure conditions, the clay conductivity and formation water conductivity under high temperature conditions are calculated to obtain a digital core equivalent to overpressure and high temperature. The processing module is used to perform numerical simulation on digital cores equivalent to overpressure and high temperature, calculate the resistivity and formation factor F of water-saturated cores with different porosities φ, and construct an F-φ cross-plot; use mathematical morphology algorithms to construct digital cores with different water saturations, calculate the resistivity and resistivity increase coefficient RI of digital cores with different water saturations Sw, and construct an RI-Sw cross-plot; based on the cross-plot, analyze the changing relationship between the formation factor F of the core and the porosity φ of the rock, and the resistivity increase coefficient RI of the digital cores with different saturations and the water saturation Sw, so as to construct a new conductivity equation and saturation model.

10. A computing device, characterized in that include: one or more processors; A storage device, used for storing one or more programs, when the one or more programs are executed by the one or more processors, the one or more processors implement the method according to any one of claims 1-8.

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