Conductive model and saturation evaluation method of lacustrine shale considering the influence of organic matter

Abstract

The present invention relates to a lacustrine shale conductive model and saturation evaluation method considering the influence of organic matter, belonging to the technical field of oil content evaluation of unconventional oil and gas reservoirs, including: 1) characterizing fluid information in shale samples based on pressure-maintained sealed samples and two-dimensional nuclear magnetic resonance technology; 2) classifying lacustrine shale lithology types according to shale organic carbon content and clay content, and analyzing the relationship between resistivity values ​​of different lithologies and free water and bound water porosity; 3) selecting siltstone interlayer samples, and inversely calculating the cementation index and saturation index of the inorganic pore conductive network; 4) establishing a lacustrine shale parallel conductive model, and calibrating rock electrical parameters by lithology; 5) establishing a lithology and lithology discrimination chart, a TOC prediction model, a bound water content prediction model and an effective porosity calculation model, and combining the lacustrine shale parallel conductive model to interpret oil saturation by different lithologies. The present invention provides accurate shale reservoir fluid information and provides a new idea for rock electrical parameter calibration.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil content evaluation of unconventional oil and gas reservoirs, and in particular relates to a lacustrine shale conductivity model and a saturation evaluation method considering the influence of organic matter. Background Art

[0002] Oil saturation is the ratio of the oil volume in the formation to the effective pore volume of the rock. It is an important parameter in reservoir geological evaluation. It is of great significance for determining the oil volume of the reservoir, estimating the recoverable oil reserves and predicting the recovery rate, and directly affects the exploration and development strategy of the reservoir. Oil saturation is also a key parameter for the evaluation of sweet spots in unconventional oil and gas resources, especially for lacustrine shale oil.

[0003] Well logging curves are often used to predict oil saturation. The basic steps are to establish a conductive model based on the rock conductivity mechanism, and then calibrate the parameters in the model through rock electrical experiments to obtain the water saturation calculation formula, and then calculate the oil saturation. Resistivity is sensitive to the response of fluids in rock pores, and resistivity curves are usually used to evaluate the oil saturation of formations. At present, two types of conductive models are mainly used for saturation calculation. One is to assume that the rock skeleton is pure sandstone, and ionic conduction in pore water is the main conductive mechanism. Water saturation can be calculated through reservoir porosity and resistivity curves, such as Archie formula. This type is mainly applicable to pure sandstone formations; the other type is to assume that the rock skeleton contains mud, and the matrix pore ion conduction and clay-bound water conduction are in parallel. The additional conductivity of clay needs to be considered in the conductive model, such as Indonesia equation, double water model and triple water model. This type of conduction is mainly applicable to muddy sandstone, mudstone, etc. In addition, according to the statistical relationship between oil content and conventional curves, the saturation interpretation model can also be established using optimization methods. This method is weak in theory and not universal.

[0004] Lacustrine shale is an important carrier for the development of shale oil. Shale has the characteristics of fine grain size, developed laminae, multiple mineral types, high clay and organic carbon content, and mainly nanoscale pores with poor pore connectivity. At the same time, the fluid occurrence forms are also diverse, including free oil, adsorbed oil, bound water, free water, etc. Due to the particularity of shale formations in terms of reservoir properties and occurrence, the above-mentioned conductive model and saturation formula have the following disadvantages when applied:

[0005] 1) The pore water in shale is stored in various forms, with high clay and organic carbon content. Organic matter and clay mostly exist in the form of a complex, which leads to a very complex conductive mechanism in shale formations. In addition to ionic conductivity in inorganic mineral pores, it also includes additional conductivity of clay, and organic matter affects the additional conductivity of clay. Therefore, the conductive model of pure sandstone or argillaceous sandstone is difficult to apply to lacustrine shale formations.

[0006] 2) Shale has small pores, poor connectivity, and various forms of fluid occurrence. It is difficult to conduct conventional rock electrical experiments on shale cores, and it is impossible to obtain relevant rock electrical parameters. The calculation accuracy of the shale saturation formula is low. Other means are needed to calibrate and obtain reasonable rock electrical parameters.

[0007] 3) Since shale core fluid is volatile, the oil content measured by traditional core placement can no longer reflect the actual situation of the formation. Establishing a saturation calculation model based on the correlation between oil content and logging curves will underestimate the actual oil saturation of the shale oil layer.

[0008] The difficulty of solving the above problems is as follows:

[0009] Inorganic minerals and organic matter coexist in shale, and there are various types of pores. In addition to free water and bound water, there are also various fluids such as adsorbed oil and free oil. How to obtain the content of different types of fluids is one of the key issues in accurately calibrating shale rock electrical parameters. At present, the combination of closed coring and two-dimensional nuclear magnetic resonance technology is expected to accurately characterize the in-situ fluid information of shale cores. Secondly, clay and organic matter in shale mostly exist in complexes. Oil molecules are usually adsorbed on the surface of organic matter. These oil molecules compete with the water adsorbed on the clay surface for adsorption, affecting the additional conductivity of the clay surface. The commonly used clay additional conductivity model needs to consider the influence of organic matter. At present, a clay additional conductivity model that considers the influence of organic matter has not yet been established, which reduces the accuracy of the lacustrine shale conductivity model and oil saturation calculation. Summary of the invention

[0010] In view of the problems existing in the prior art, the present invention provides a lacustrine shale conductivity model and a saturation evaluation method taking into account the influence of organic matter.

[0011] The present invention takes into account the influence of organic matter on the additional conductivity of clay, connects the additional conductivity of clay considering the influence of organic matter and the conductivity of free water ions in inorganic pores in parallel, constructs a conductivity model of lacustrine shale, and uses closed samples and two-dimensional nuclear magnetic resonance to finely characterize the in-situ fluid information of shale cores. Combined with conventional resistivity curves, the rock electrical parameters in the model are jointly calibrated, thereby forming an oil saturation evaluation method suitable for lacustrine shale.

[0012] The technical solution of the present invention is:

[0013] The conductivity model and saturation evaluation method of lacustrine shale considering the influence of organic matter include:

[0014] 1) Based on pressure-retaining sealed samples and two-dimensional nuclear magnetic resonance technology, characterize the fluid information in shale samples to obtain effective porosity, effective oil porosity, free water porosity, bound water porosity, effective oil saturation and water saturation;

[0015] 2) According to the organic carbon content and clay content of shale, the lacustrine shale lithology types are divided, the relationship between the resistivity values ​​of different lithologies and the porosity of free water and bound water is analyzed, and abnormal data points are eliminated;

[0016] 3) Select siltstone interlayer samples and inversely calculate the cementation index and saturation index of the inorganic pore conductive network;

[0017] 4) Considering the clay additional conductive network affected by organic matter and the inorganic pore ion conductive network in parallel, a parallel conductive model of lacustrine shale is established, and the rock electrical parameters are calibrated according to lithology;

[0018] 5) Establish a lithology discrimination chart, a TOC prediction model, a bound water content prediction model, and an effective porosity calculation model, and combine the parallel conductivity model of lacustrine shale to interpret the oil saturation for different lithologies.

[0019] Preferably, according to the present invention, based on the pressure-maintained sealed sample and the two-dimensional nuclear magnetic resonance technology, the fluid information in the shale sample is characterized to obtain the effective porosity, effective oil porosity, free water porosity, bound water porosity, effective oil saturation and effective water saturation; including:

[0020] The lacustrine shale formation is subjected to pressure-maintaining and sealed coring. After the block sample is taken out, a one-dimensional nuclear magnetic resonance test is performed. The nuclear magnetic resonance signal gradually increases. When the difference between the two measured signal amounts is within 50 a.u., a two-dimensional nuclear magnetic resonance test is performed to measure the two-dimensional nuclear magnetic resonance signal. After the sample is taken out, it is weighed as m1, and the volume of the block sample is measured as V1.

[0021] According to the shale two-dimensional nuclear magnetic resonance fluid identification plate, the distribution ranges of free oil, adsorbed oil, bound water and free water are distinguished in the T1-T2 diagram, i.e., the result diagram obtained from the two-dimensional nuclear magnetic resonance test, and the signal quantity in each range is counted to obtain the signal quantity of different fluids;

[0022] According to the conversion relationship between the NMR signal and the fluid mass, the signal is converted into mass, and then combined with the density of different fluids, the volume of different fluids is converted. The sum of the volumes of free oil, adsorbed oil and free water is divided by the volume V1 to obtain the effective porosity φ of the sample. The sum of the volumes of free oil and adsorbed oil is divided by the volume V1 to obtain the effective oil-bearing porosity. The free water volume is divided by the core volume V1 to obtain the free water porosity φ. wf , the bound water volume is divided by the core volume V1 to obtain the bound water porosity φ cbw ; Effective oil porosity divided by effective porosity φ, to obtain effective oil saturation S o , 1-S o is the corresponding water saturation S w ;

[0023] Further preferably, after the lacustrine shale formation is pressurized and sealed for coring, block cores are selected and placed in a liquid nitrogen tank for cooling and storage.

[0024] Further preferably, in the two-dimensional nuclear magnetic resonance test, the echo interval of the two-dimensional nuclear magnetic resonance is less than 0.2 ms and the measurement time is less than 10 min.

[0025] Further preferably, when establishing a two-dimensional nuclear magnetic resonance fluid identification map for shale, any shale sample in the current layer is selected, and the two-dimensional nuclear magnetic resonance spectra of four states, namely, the original state, the state after oil washing and drying, the state saturated with oil, and the state saturated with water, are measured respectively, and the distribution ranges of different fluids are compared to establish a two-dimensional nuclear magnetic resonance fluid identification map for shale, and the identified fluids include free oil, adsorbed oil, free water, and bound water.

[0026] Further preferably, when establishing the conversion relationship between the nuclear magnetic resonance signal amount and the fluid mass, one-dimensional nuclear magnetic resonance tests are performed on water or oil of different masses, and the conversion relationship between the signal amount and mass of water or oil is established based on the T2 signal amounts corresponding to the different masses of water or oil; when performing the one-dimensional nuclear magnetic resonance test, the same measurement parameters as the two-dimensional nuclear magnetic resonance test are used.

[0027] According to the preferred embodiment of the present invention, the lacustrine shale lithology types are divided according to the shale organic carbon content and clay content, the relationship between the resistivity values ​​of different lithologies and the porosity of free water and bound water is analyzed, and abnormal data points are eliminated; including:

[0028] Measure the TOC and clay content of shale samples; according to TOC and clay content, divide the shale samples into four parts: siltstone interlayer, and the remaining shale samples are divided into three categories, including category C: low-clay shale, category B: felsic shale, and category A: clay shale;

[0029] According to the difference in logging response of different types of lithology, core depth is returned to obtain the logging curve value at the returned depth point, including natural gamma curve GR, resistivity curve RT, acoustic time difference curve DT, density curve DEN and neutron curve CNL. The resistivity curve RT and bound water porosity φ corresponding to the sample point are drawn according to four types of lithology. cbw , free water porosity φ wf The abnormal data points that deviate from the normal trend line are eliminated to obtain the data sets of bound water porosity, free water porosity and corresponding RT curves under different lithologies.

[0030] Preferably, according to the present invention, a siltstone interlayer sample is selected, and the cementation index b and saturation index n of the inorganic porous conductive network are back-calculated using the Archie formula; comprising:

[0031] For the siltstone interlayer samples, the effective water saturation Sw , effective porosity f , resistivity curve RT, formation water resistivity R w The time satisfies Archie's formula:

[0032] (1);

[0033] in, RT is the resistivity curve value of the sample at the corresponding depth point, Ω.m; R w is the formation water resistivity, Ω.m, φ is the effective porosity, a decimal; S w is the effective water saturation, decimal; a , m is a constant;

[0034] Using the measured effective porosity f , effective water saturation S w The corresponding cementation index of the siltstone interlayer is calculated by back-calculating the resistivity curve RT at the corresponding depth point. b and saturation index n .

[0035] According to the preferred embodiment of the present invention, the clay additional conductive network and the inorganic pore ion conductive network considering the influence of organic matter are connected in parallel to establish a parallel conductive model of lacustrine shale, and the rock electrical parameters are calibrated according to lithology; including:

[0036] Assuming that the additional conductivity of clay and the free water ion conductivity of inorganic mineral pores are in parallel, the conductivity of shale is equivalent to the additional conductivity of clay. C qo and the free water ion conductivity in the pores of inorganic minerals C tw The specific formula is:

[0037] (2);

[0038] (3);

[0039] (4);

[0040] in, C t is the rock conductivity, s / m, which is the reciprocal of the resistivity curve RT; C tw is the free water conductivity of inorganic mineral pores, s / m; C qo is the additional conductivity of clay, s / m; Co is the formation water conductivity, s / m, is the formation water resistivity R w The reciprocal of C cm is the additional conductivity per unit volume of clay affected by organic matter, s / m, f is the effective porosity, a decimal; f cbw is the rock bound water porosity, decimal; S w is the formation water saturation, decimal; m is the cementation coefficient of the inorganic porous ion conductive network; n is the saturation index of the inorganic pore ion conductive network; m im is the cementation coefficient of the additional conductive network of organic matter-affected clay;

[0041] Additional conductivity per unit volume of clay affected by organic matter C cm , which is related to the TOC content. As the TOC content increases, C cw Gradually decrease, using the following formula:

[0042] (5);

[0043] Combining formulas (2)-(5), a parallel conductive model of lacustrine shale is established:

[0044] (6);

[0045] The effective porosity measured according to step 1) f , water saturation S w , irreducible water porosity f cbw The TOC content measured in step 2) is combined with the formation conductivity at the current depth. C t , calibrate rock electrical parameters according to the rock types A, B and C, including m im , k and l .

[0046] Preferably, according to the present invention, a lithology identification chart, a TOC prediction model, a bound water content prediction model and an effective porosity calculation model are established, and the oil saturation is interpreted according to different lithologies in combination with a parallel conductive model of lacustrine shale; including:

[0047] According to the resistivity curve RT, natural gamma curve GR and acoustic time difference curve DT corresponding to different lithologies, establish the discrimination chart of different lithologies;

[0048] According to resistivity RT and acoustic time difference DT, the prediction model of TOC was established by using ΔlgR method;

[0049] According to the relationship between clay content and bound water porosity, the f cbw prediction models;

[0050] Establish effective porosity based on density curve DEN and neutron curve CNL f Computational models;

[0051] According to the actual well logging curve, the different lithology distribution layers are identified, and the organic carbon content TOC, bound water porosity, and effective porosity change curves are calculated;

[0052] According to the parallel conductive model of lacustrine shale, namely, equation (6), the rock electrical parameters are selected according to the lithology and the corresponding water saturation S is calculated. w , 1-S w is the oil saturation S of the corresponding point o .

[0053] A computer device comprises a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, steps of a lacustrine shale conductivity model and a saturation evaluation method considering the influence of organic matter are implemented.

[0054] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of a lacustrine shale conductivity model and a saturation evaluation method that considers the influence of organic matter.

[0055] The beneficial effects of the present invention are:

[0056] The present invention provides a lacustrine shale conductivity model and saturation evaluation method considering the influence of organic matter. The traditional Archie equation and Indonesia equation are proposed in the context of pure sandstone or muddy sandstone formations, and are not suitable for shales with high mud content, especially for lacustrine shale reservoirs with relatively high clay content, complex pore structure, and developed organic matter. The calculation accuracy of the traditional model is limited. The present invention proposes the idea of ​​parallel conductivity of clay additional conductive network affected by organic matter and inorganic mineral pore free water conductive network in lacustrine shale, quantifies the influence of organic matter abundance on clay additional conductivity, distinguishes different lithologies to obtain model parameters, improves the prediction accuracy of oil saturation in lacustrine shale, and provides strong technical support for the exploration and development of shale oil. At the same time, in view of the difficulty that the fluid of lacustrine shale reservoir is complex and the pore connectivity is poor, and conventional rock electrical experiments cannot be carried out or it is difficult to restore the original fluid information, a closed coring and two-dimensional nuclear magnetic resonance combined method is adopted to provide accurate shale reservoir fluid information, providing a new idea for rock electrical parameter calibration. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 It is a flow chart of a lacustrine shale conductivity model and a saturation evaluation method considering the influence of organic matter provided in an embodiment of the present invention.

[0058] Figure 2 This is a two-dimensional nuclear magnetic resonance shale oil fluid identification plate provided by an embodiment of the present invention.

[0059] Figure 3 It is a schematic diagram of the relationship between fluid mass and nuclear magnetic resonance signal quantity provided by an embodiment of the present invention.

[0060] Figure 4 It is a schematic diagram of the relationship between the additional conductivity of clay affected by organic matter and TOC provided by an embodiment of the present invention.

[0061] Figure 5 It is a comparison chart of the shale oil saturation prediction results of Well A provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0062] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Example 1

[0063] like Figure 1 As shown in the figure, the conductivity model and saturation evaluation method of lacustrine shale considering the influence of organic matter include:

[0064] S101: Based on pressure-retaining sealed samples and two-dimensional nuclear magnetic resonance technology, characterize the fluid information in shale samples to obtain effective porosity, effective oil porosity, free water porosity, bound water porosity, effective oil saturation and water saturation;

[0065] S102: Classify the lacustrine shale lithology types according to the shale organic carbon content and clay content, analyze the relationship between the resistivity values ​​of different lithologies and the porosity of free water and bound water, and eliminate abnormal data points;

[0066] S103: Select siltstone interlayer samples and inversely calculate the cementation index and saturation index of the inorganic pore conductive network;

[0067] S104: Considering the clay additional conductive network affected by organic matter and the inorganic pore ion conductive network in parallel, a parallel conductive model of lacustrine shale is established, and the rock electrical parameters are calibrated according to lithology;

[0068] S105: Establish a lithology discrimination chart, a TOC prediction model, a bound water content prediction model, and an effective porosity calculation model, and combine the parallel conductivity model of lacustrine shale to interpret the oil saturation according to different lithologies. Example

[0069] The difference between the lacustrine shale conductivity model and saturation evaluation method considering the influence of organic matter described in Example 1 is that:

[0070] Based on pressure-retaining sealed samples and two-dimensional nuclear magnetic resonance technology, the fluid information in shale samples is characterized to obtain effective porosity, effective oil porosity, free water porosity, bound water porosity, effective oil saturation and effective water saturation; including:

[0071] The lacustrine shale formation is subjected to pressure maintenance and closed coring. The sample selection should cover the main lithology types as much as possible, and the number of the same lithology should be no less than 5. In the laboratory, after the block sample is taken out, it is quickly loaded into the nuclear magnetic resonance measuring tube, and a one-dimensional nuclear magnetic resonance test (T2) is performed at a certain time interval (1min). The nuclear magnetic resonance signal gradually increases. When the difference between the two measured signal amounts is within 50a.u., a two-dimensional nuclear magnetic resonance test is performed to measure the two-dimensional nuclear magnetic resonance signal (T1-T2). After the sample is taken out, it is weighed as m1, and the volume of the block sample is measured by the buoyancy method as V1.

[0072] One-dimensional nuclear magnetic resonance test: The hydrogen nuclei in the fluid inside the rock in a uniformly distributed static magnetic field are magnetized and present a magnetization vector. At this time, the nuclear magnetic resonance phenomenon will occur when the radio frequency field is given to the rock sample. After the radio frequency field is removed, a signal with an exponential function trend decay can be obtained. The decay rate can be measured by the longitudinal relaxation time and the transverse relaxation time (T1, T2); the transverse relaxation time T2 is faster than the longitudinal relaxation time T1, so T2 is usually used to measure signal decay. The smaller the pore size of the rock, the faster the hydrogen nucleus energy will be lost as the collision between the hydrogen nucleus and the pore wall becomes more frequent, and the shorter T2 is. Recording this decay process through technical software is a one-dimensional nuclear magnetic resonance test.

[0073] Two-dimensional nuclear magnetic resonance test: When there are multiple components in the rock, the proton T2 relaxation time of each component basically overlaps, and a single T2 spectrum distribution is difficult to reveal all the hydrogen nuclear relaxation characteristics of the shale. It is necessary to use longitudinal-transverse relaxation (T1-T2) technology to obtain different hydrogen nuclear relaxation information of the shale. T1 and T2 are affected by the fluid viscosity and the fluid molecular radius. The characteristics of T2 and T1 / T2 values ​​of different fluid components are different. Usually, oil has a higher T1 / T2 value, while water has a lower T1 / T2 value. Based on this understanding, two-dimensional nuclear magnetic resonance technology can be used to distinguish oil, water and solid organic matter signals in rock pores. Recording this process through technical software is called two-dimensional nuclear magnetic resonance testing.

[0074] According to the shale two-dimensional nuclear magnetic resonance fluid identification plate, in the T1-T2 diagram, i.e., the result diagram obtained from the two-dimensional nuclear magnetic resonance test, the distribution ranges of free oil, adsorbed oil, bound water and free water are distinguished, and the signal amounts in each range are counted to obtain the signal amounts of different fluids; Figure 2 As shown in the figure, according to the two-dimensional NMR fluid identification chart, the signal amount of different types of fluids in shale can be identified, such as area A is kerogen, area B is adsorbed oil, area C is free oil, area D is bound water, and area E is free water. This chart can measure the two-dimensional NMR spectra of shale in the original state, after oil washing and drying, saturated water and saturated oil states, and obtain the distribution areas of different fluids by comparison.

[0075] Shale 2D NMR fluid identification chart: Use dichloromethane and toluene in a ratio of 3:1 to wash the shale core for 10-15 days. After washing, conduct pyrolysis experiments on the samples to ensure that most of the residual oil in the samples is washed out. After washing, the samples are dried, and the 2D NMR signals of the dry samples are measured to obtain the positions of kerogen and bound water in the 2D NMR spectrum; then, the rock samples are saturated with water, and their NMR signals are measured to obtain the positions of free water. After drying, the rock samples are saturated with oil, and the NMR signals are measured to obtain the positions of free oil and adsorbed oil. At the same time, the pyrolysis S of the saturated oil rock samples is measured. 2-1(Adsorbed oil) parameters accurately determine the boundary between adsorbed oil and free oil. The plate that divides the positions of each fluid component on the two-dimensional nuclear magnetic resonance spectrum according to the T1, T2, and T1 / T2 values ​​is the two-dimensional nuclear magnetic resonance fluid identification plate.

[0076] According to the conversion relationship between the nuclear magnetic signal and the fluid mass, the signal is converted into mass, and then combined with the density of different fluids (0.75 cm for n-dodecane 3 / g, water is 1cm 3 / g), and convert it into the volume of different fluids (fluid mass / density), such as free oil V of , adsorption oil V oa , bound water V cbw , Free Water V wf The sum of the volumes of free oil, adsorbed oil and free water divided by the volume V1 gives the effective porosity φ of the sample. The sum of the volumes of free oil and adsorbed oil divided by the volume V1 gives the effective oil-bearing porosity. The free water volume divided by the core volume V1 gives the free water porosity φ. wf , the bound water volume is divided by the core volume V1 to obtain the bound water porosity φ cbw ; Effective oil porosity divided by effective porosity φ, to obtain effective oil saturation S o , 1-S o is the corresponding water saturation S w ;

[0077] like Figure 3 As shown in the figure, by statistically analyzing the relationship between crude oil or formation water of different qualities and one-dimensional NMR signal, the conversion relationship between the NMR signal of oil or water and the fluid mass can be determined, thereby realizing the conversion of fluid signal to mass. In this example, crude oil from a nearby shale oil production well is selected, with a conversion coefficient of 0.1844 mg / au, and the conversion coefficient of water is 0.2102 mg / au.

[0078] After pressure-maintaining and airtight coring of the lacustrine shale formation, the block cores are quickly selected and placed in a liquid nitrogen tank for cooling and preservation, minimizing the volatilization of fluid in the cores.

[0079] In the two-dimensional nuclear magnetic resonance test, the echo interval of the two-dimensional nuclear magnetic resonance is less than 0.2ms and the measurement time is less than 10min.

[0080] When establishing the shale two-dimensional nuclear magnetic resonance fluid identification plate, select any shale sample in the current layer, measure the two-dimensional nuclear magnetic resonance spectra of the original state, the state after washing and drying, the state saturated with oil and the state saturated with water, compare the distribution range of different fluids, and establish the shale two-dimensional nuclear magnetic resonance fluid identification plate. The identified fluids include free oil (T2>2ms, T1 / T2>1), adsorbed oil (0.2ms <T2<2ms, T1> 10ms), free water (0.2ms) <T2<2ms, T1<10ms, T1 / T2> 1) and bound water (0.2ms <T2<2ms, T1<10ms, T1 / T2> 1). In nuclear magnetic resonance, the process of atomic nuclei recovering from high energy to low energy is called relaxation. T2 and T1 are the transverse and longitudinal relaxation times.

[0081] When establishing the conversion relationship between the nuclear magnetic resonance signal and the fluid quality, one-dimensional nuclear magnetic resonance tests are performed on water or oil of different qualities (shale oil production wells or n-dodecane can be selected as a substitute), and the conversion relationship between the signal and quality of water or oil is established based on the T2 signal corresponding to the different qualities of water or oil; when performing one-dimensional nuclear magnetic resonance testing, the same measurement parameters as those of two-dimensional nuclear magnetic resonance testing are used.

[0082] According to the organic carbon content and clay content of shale, the lacustrine shale lithology types are divided, the relationship between the resistivity values ​​of different lithologies and the porosity of free water and bound water is analyzed, and abnormal data points are eliminated; including:

[0083] According to the industry standards "GB / T 19145-2022 Determination of Total Organic Carbon in Sedimentary Rocks" and "SY / T 5163-2018 X-ray Diffraction Analysis Method for Clay Minerals and Common Non-Clay Minerals in Sedimentary Rocks", the organic carbon content TOC and clay content of shale samples were measured; according to TOC and clay content, the shale samples were divided into four parts: siltstone interlayers (siltstone particles accounted for more than 50%, siltstone particles refer to particles with a particle size greater than 30μm, and the proportion of rock siltstone particles was obtained by thin section identification statistics), and the remaining shale samples were divided into three categories, including Class C: low-clay shale (clay content <40%), Class B: felsic shale (40% < clay content <45%), and Class A: clay shale (clay content >45%);

[0084] According to the difference in logging response of different types of lithology, such as the low acoustic time difference DT and higher resistivity RT characteristics corresponding to the siltstone interlayer, the core depth is returned to obtain the logging curve value at the returned depth point, including the natural gamma curve GR, resistivity curve RT, acoustic time difference curve DT, density curve DEN and neutron curve CNL. The natural gamma curve GR, resistivity curve RT, acoustic time difference curve DT, density curve DEN and neutron curve CNL can be directly read in the logging software; divided into four types of lithology (including siltstone interlayer, type A, type B, type C) to draw the resistivity curve RT and bound water porosity φ corresponding to the sample point cbw , free water porosity φ wf The abnormal data points that deviate from the normal trend line are eliminated to obtain the data sets of bound water porosity, free water porosity and corresponding RT curves under different lithologies.

[0085] The siltstone interlayer samples were selected and the cementation index b and saturation index n of the inorganic pore conductive network were calculated using the Archie formula; including:

[0086] For the siltstone interlayer samples, the effective water saturation S w , effective porosity f , resistivity curve RT, formation water resistivity R w The time satisfies Archie's formula:

[0087] (1);

[0088] in, RT is the resistivity curve value of the sample at the corresponding depth point, Ω.m; R w is the formation water resistivity, Ω.m, which is converted from the mineralization of oilfield production water; φ is the effective porosity, a decimal; S w is the effective water saturation, decimal; a , m is a constant; all are equal to 1.

[0089] Using the measured effective porosity f , effective water saturation S w The corresponding cementation index of the siltstone interlayer is calculated by back-calculating the resistivity curve RT at the corresponding depth point. b and saturation index n The resistivity of formation water can be obtained by querying the resistivity-mineralization chart based on the mineralization of formation water and formation temperature information. b and n It can be equivalent to the rock electrical parameters of the free water ion conductive network in the pores of inorganic minerals.

[0090] Considering the clay additional conductive network affected by organic matter and the inorganic pore ion conductive network in parallel, a parallel conductive model of lacustrine shale is established, and the rock electrical parameters are calibrated according to lithology; including:

[0091] Assuming that the additional conductivity of clay and the free water ion conductivity of inorganic mineral pores are in parallel, the conductivity of shale is equivalent to the additional conductivity of clay. C qo and the free water ion conductivity in the pores of inorganic minerals C tw The specific formula is:

[0092] (2);

[0093] (3);

[0094] (4);

[0095] in, C t is the rock conductivity, s / m, which is the reciprocal of the resistivity curve RT; C tw is the free water conductivity of inorganic mineral pores, s / m; C qo is the additional conductivity of clay, s / m; C o is the formation water conductivity, s / m, is the formation water resistivity R w The reciprocal of C cm is the additional conductivity of clay per unit volume after being affected by organic matter, s / m. When TOC is 0, the additional conductivity of clay is not affected by organic matter. C cm The value should be the theoretical value (6.8 s / m); f is the effective porosity, a decimal; f cbw is the rock bound water porosity, decimal; S w is the formation water saturation, decimal; m is the cementation coefficient of the inorganic porous ion conductive network; n is the saturation index of the inorganic pore ion conductive network; m im is the cementation coefficient of the additional conductive network of organic matter-affected clay;

[0096] Clay-added conductive network affected by organic matter; the surface of clay minerals in rocks carries negative charge, and needs to absorb cations from nearby aqueous solution to achieve electrical balance. The movement of cations causes conductivity. Organic compounds in shale are usually adsorbed on the surface or interlayer of clay minerals under the influence of ionic bonds or molecular bonds (van der Waals attraction), forming an organic-clay complex. The content of organic matter affects the cation exchange capacity and thus the conductivity of the complex. This is the clay-added conductive network under the influence of organic matter.

[0097] Inorganic pore ion conductive network: There are many interconnected pores inside and around the inorganic minerals in the rock, and the fluid in the pores can conduct electricity, forming an inorganic pore ion conductive network.

[0098] Additional conductivity per unit volume of clay affected by organic matter C cm , which is related to the TOC content. As the TOC content increases, C cw Gradually decrease, using the following formula:

[0099] (5);

[0100] Combining formulas (2)-(5), a parallel conductive model of lacustrine shale is established:

[0101] (6)

[0102] According to the effective porosity measured in step S101 f , water saturation S w , irreducible water porosity f cbw and the organic carbon content TOC measured in step S102, combined with the formation conductivity at the current depth C t (1 / RT), and calibrate the rock electrical parameters of Class A, Class B and Class C lithologies, including m im , k and l The specific steps are: first, according to f , S w , n and b The conductivity of the inorganic mineral pore ion conductive part of the sample is calculated C tw ,pass C t - C tw Get the additional conductivity of clay affected by organic matter Cqo , and then the additional conductivity of clay per unit volume is obtained as 1 / C cw By adjusting m im value, get TOC and 1 / C cw The scatter point relationship is ensured to ensure that the linear fitting line of the scatter point relationship passes through the coordinate point (0,1 / 6.8). At this time, the corresponding lithology of this type is obtained. m im Value, linear fitting is performed on the scattered point relationship, and we get k and l According to the above steps, the rock electrical parameters of different rock types are obtained. Figure 4 As shown, the TOC content of type A, B and C lithologies and the inverse of the additional conductivity per unit volume of clay affected by organic matter are 1 / C cm By adjusting m im Parameters can make the fitting lines of data points of different lithologies approximately pass through the coordinate point (0, 1 / 6.8), that is, when TOC is 0, the additional conductivity of clay per unit volume is close to 6.8 s / m. m im After the parameters are obtained, the parameters can be obtained through linear fitting. k and l For type C lithology, m im The value is 1.54, k The value is 0.1335, l The value is 0.132; for type B lithology, m im The value is 1.56, k The value is 0.0434, l The value is 0.1383; for type A lithology, m im The value is 1.84, k The value is 0.0094, l The value is 0.1496. From C to A lithology, k The value gradually decreases, indicating that the effect of organic matter on the additional conductivity of clay is weakened.

[0103] Based on conventional logging curves, we established the lithology identification chart, TOC prediction model, bound water content prediction model and effective porosity calculation model, combined with the parallel conductivity model of lacustrine shale, to interpret the oil saturation according to different lithologies; including:

[0104] According to the resistivity curve RT, natural gamma curve GR and acoustic time difference curve DT corresponding to different lithologies, establish the discrimination chart of different lithologies; specifically including:

[0105] The idea of ​​establishing lithofacies identification standards by classification is adopted, and the steps of "first distinguishing the main lithologies (siltstone, transitional lithology, mudstone), and then subdividing the specific lithofacies" are followed to establish the logging identification standards for the main lithofacies. The logging identification standards for the Qing 1 shale lithofacies are shown in Table 1.

[0106] Table 1. Standard table for well logging identification of Qing 1 shale lithofacies;

[0107] According to the resistivity RT and the acoustic time difference DT, the ΔlgR method is used to establish the TOC prediction model; as shown below:

[0108] TOC=f1(RT,DT)=a1*RT+b1*DT+c1;

[0109] Among them, parameters a1, b1, and c1 are obtained through core test TOC and RT and DT curves at corresponding depth points through multiple linear regression;

[0110] According to the relationship between clay content and bound water porosity, the f cbw The prediction model is as follows:

[0111] f cbw =f2(Vsh)=a2*Vsh+b2;

[0112] Among them, parameters a2 and b2 are based on the clay content Vsh and bound water porosity of the core test. f cbw Data,obtained through linear regression;

[0113] The clay content Vsh is related to the neutron curve CNL and the density curve DEN as follows: Vsh=f3(CNL,DEN)=a3*CNL+b3*DEN+c3;

[0114] Among them, parameters a3, b3 and c3 are obtained by multiple linear regression based on the clay content of core tests and the CNL and DEN curves at the corresponding depth points;

[0115] Then, the clay content Vsh is calculated based on the well logging, and the irreducible water porosity is calculated based on f2 (Vsh);

[0116] Establish effective porosity based on density curve DEN and neutron curve CNL f The calculation model is as follows:

[0117] f=f4(DEN,CNL)=a4*DEN+b4*CNL+c4;

[0118] Among them, parameters a4, b4, and c4 are obtained through multiple linear regression using core test effective porosity and DEN and CNL curves at corresponding depth points;

[0119] According to the actual well logging curve, the different lithology distribution layers are identified, and the organic carbon content TOC, bound water porosity, and effective porosity change curves are calculated;

[0120] According to the parallel conductive model of lacustrine shale, namely, equation (6), the rock electrical parameters are selected according to the lithology and the corresponding water saturation S is calculated. w , 1-S w is the oil saturation S of the corresponding point o .

[0121] like Figure 5 As shown in the figure, Well A is an exploration well in the Qing 1st shale oil formation in the southern Songliao Basin. Closed coring and two-dimensional nuclear magnetic resonance testing were carried out. Based on the TOC, clay content, effective porosity, irreducible water porosity and other data of the core test, a logging evaluation model was established to accurately predict the vertical changes of TOC, effective porosity and irreducible water porosity; combined with the lithology identification results, rock electrical parameters were selected by lithology to interpret the oil saturation. The accuracy of the oil saturation calculated this time is significantly higher than that of the traditional Archie formula and Indonesian formula, and can accurately reveal the vertical changes in the oil content of shale. Example 2

[0122] A computer device includes a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the steps of the lacustrine shale conductivity model and saturation evaluation method considering the influence of organic matter described in Example 1 or 2 are implemented. Example 3

[0123] A computer-readable storage medium having a computer program stored thereon, wherein when the computer program is executed by a processor, the steps of the lacustrine shale conductivity model and saturation evaluation method considering the influence of organic matter described in Example 1 or 2 are implemented.

Claims

1. A conductivity model and saturation evaluation method for lacustrine shale considering the influence of organic matter, characterized in that: include: 1) Based on pressure-retaining sealed samples and two-dimensional nuclear magnetic resonance technology, characterize the fluid information in shale samples to obtain effective porosity, effective oil porosity, free water porosity, bound water porosity, effective oil saturation and water saturation; 2) According to the organic carbon content and clay content of shale, the lacustrine shale lithology types are divided, the relationship between the resistivity values ​​of different lithologies and the porosity of free water and bound water is analyzed, and abnormal data points are eliminated; 3) Select siltstone interlayer samples and back-calculate the cementation index and saturation index of the inorganic pore conductive network; 4) Considering the clay additional conductive network affected by organic matter and the inorganic pore ion conductive network in parallel, a parallel conductive model of lacustrine shale is established, and the rock electrical parameters are calibrated according to lithology; 5) Establish the lithology identification chart, TOC prediction model, bound water content prediction model and effective porosity calculation model, and interpret the oil saturation according to different lithologies by combining the parallel conductive model of lacustrine shale; Considering the clay additional conductive network affected by organic matter and the inorganic pore ion conductive network in parallel, a parallel conductive model of lacustrine shale is established, and the rock electrical parameters are calibrated according to lithology; including: Assuming that the additional conductivity of clay and the free water ion conductivity of inorganic mineral pores are in parallel, the shale conductivity is equivalent to the additional conductivity of clay C. qo and the free water ion conductivity C in the pores of inorganic minerals tw The specific formula is: C t =C tw +C qo #(2) Among them, C t is the rock conductivity, s / m, which is the reciprocal of the resistivity curve RT; C tw is the free water conductivity of inorganic mineral pores, s / m; C qo is the additional conductivity of clay, s / m; C o is the formation water conductivity, s / m, is the formation water resistivity R w The reciprocal of cm is the additional conductivity of clay per unit volume after being affected by organic matter, s / m, φ is the effective porosity, a decimal; φ cbw is the rock bound water porosity, decimal; S w is the formation water saturation, a decimal; m is the cementation coefficient of the inorganic pore ion conductive network; n is the saturation index of the inorganic pore ion conductive network; m im is the cementation coefficient of the additional conductive network of clay affected by organic matter; Additional conductivity C per unit volume of clay affected by organic matter cm , which is related to the TOC content. As the TOC content increases, C cw Gradually decrease, using the following formula: Combining formulas (2)-(5), a parallel conductive model of lacustrine shale is established: According to the effective porosity φ and water saturation S measured in step 1), w , bound water porosity φ cbw The organic carbon content TOC measured in step 2) is combined with the formation conductivity C at the current depth. t , calibrate rock electrical parameters according to the rock types A, B and C, including m im , k and l.

2. The lacustrine shale conductivity model and saturation evaluation method considering the influence of organic matter according to claim 1, characterized in that: Based on pressure-retaining sealed samples and two-dimensional nuclear magnetic resonance technology, the fluid information in shale samples is characterized to obtain effective porosity, effective oil porosity, free water porosity, bound water porosity, effective oil saturation and effective water saturation; including: The lacustrine shale formation is subjected to pressure-maintaining and sealed coring. After the block sample is taken out, a one-dimensional nuclear magnetic resonance test is performed. The nuclear magnetic resonance signal gradually increases. When the difference between the two measured signal amounts is within 50 a.u., a two-dimensional nuclear magnetic resonance test is performed to measure the two-dimensional nuclear magnetic resonance signal. After the sample is taken out, it is weighed as m1, and the volume of the block sample is measured as V1. According to the shale two-dimensional nuclear magnetic resonance fluid identification plate, the distribution ranges of free oil, adsorbed oil, bound water and free water are distinguished in the T1-T2 diagram, i.e., the result diagram obtained from the two-dimensional nuclear magnetic resonance test, and the signal quantity in each range is counted to obtain the signal quantity of different fluids; According to the conversion relationship between the NMR signal and the fluid mass, the signal is converted into mass, and then combined with the density of different fluids, the volume of different fluids is converted. The sum of the volumes of free oil, adsorbed oil and free water is divided by the volume V1 to obtain the effective porosity φ of the sample. The sum of the volumes of free oil and adsorbed oil is divided by the volume V1 to obtain the effective oil-bearing porosity. The free water volume is divided by the core volume V1 to obtain the free water porosity φ. wf , the bound water volume is divided by the core volume V1 to obtain the bound water porosity φ cbw ; Effective oil porosity divided by effective porosity φ, to obtain effective oil saturation S o , 1-S o is the corresponding water saturation S w .

3. The lacustrine shale conductivity model and saturation evaluation method considering the influence of organic matter according to claim 2, characterized in that: After pressure-maintaining and sealed coring of the lacustrine shale formation, block cores are selected and placed in a liquid nitrogen tank for cooling and preservation.

4. The lacustrine shale conductivity model and saturation evaluation method considering the influence of organic matter according to claim 2, characterized in that: In the two-dimensional nuclear magnetic resonance test, the echo interval of the two-dimensional nuclear magnetic resonance is less than 0.2ms and the measurement time is less than 10min.

5. The lacustrine shale conductivity model and saturation evaluation method considering the influence of organic matter according to claim 2, characterized in that: When establishing a shale two-dimensional nuclear magnetic resonance fluid identification map, select any shale sample in the current layer, measure the two-dimensional nuclear magnetic resonance spectra of the original state, the state after oil washing and drying, the state saturated with oil and the state saturated with water, compare the distribution ranges of different fluids, and establish a shale two-dimensional nuclear magnetic resonance fluid identification map. The identified fluids include free oil, adsorbed oil, free water and bound water.

6. The lacustrine shale conductivity model and saturation evaluation method considering the influence of organic matter according to claim 2, characterized in that: When establishing the conversion relationship between the nuclear magnetic resonance signal and the fluid quality, one-dimensional nuclear magnetic resonance tests are performed on water or oil of different qualities, and the conversion relationship between the signal and quality of water or oil is established based on the T2 signal corresponding to the different qualities of water or oil; when performing one-dimensional nuclear magnetic resonance testing, the same measurement parameters as those of two-dimensional nuclear magnetic resonance testing are used.

7. The lacustrine shale conductivity model and saturation evaluation method considering the influence of organic matter according to claim 1, characterized in that: According to the organic carbon content and clay content of shale, the lithology types of lacustrine shale are divided, the relationship between the resistivity values ​​of different lithologies and the porosity of free water and bound water is analyzed, and abnormal data points are eliminated; include: Measure the TOC and clay content of shale samples; according to TOC and clay content, divide the shale samples into four parts: siltstone interlayer, and the remaining shale samples are divided into three categories, including category C: low-clay shale, category B: felsic shale, and category A: clay shale; According to the difference in logging response of different types of lithology, core depth is returned to obtain the logging curve value at the returned depth point, including natural gamma curve GR, resistivity curve RT, acoustic time difference curve DT, density curve DEN and neutron curve CNL. The resistivity curve RT and bound water porosity φ corresponding to the sample point are drawn according to four types of lithology. cbw , free water porosity φ wf The abnormal data points that deviate from the normal trend line are eliminated to obtain the data sets of bound water porosity, free water porosity and corresponding RT curves under different lithologies.

8. The lacustrine shale conductivity model and saturation evaluation method considering the influence of organic matter according to claim 1, characterized in that: Select siltstone interlayer samples and use Archie's formula to back-calculate the cementation index b and saturation index n of the inorganic pore conductive network; including: For the siltstone interlayer sample, the effective water saturation S w , effective porosity φ, resistivity curve RT, formation water resistivity R w The time satisfies Archie's formula: Among them, RT is the resistivity curve value of the sample at the corresponding depth point, Ω.m; R w is the formation water resistivity, Ω.m, φ is the effective porosity, decimal; S w is the effective water saturation, a decimal; a and m are constants; Using the measured effective porosity φ, effective water saturation S w The cementation index b and saturation index n corresponding to the siltstone interlayer are calculated by back-calculating the resistivity curve RT at the corresponding depth point.

9. The lacustrine shale conductivity model and saturation evaluation method considering the influence of organic matter according to any one of claims 1 to 8, characterized in that: Establish lithology identification chart, TOC prediction model, bound water content prediction model and effective porosity calculation model, combine with lacustrine shale parallel conductivity model, and interpret oil saturation according to different lithologies; including: According to the resistivity curve RT, natural gamma curve GR and acoustic time difference curve DT corresponding to different lithologies, establish the discrimination chart of different lithologies; According to resistivity RT and acoustic time difference DT, the prediction model of TOC was established by using ΔlgR method. According to the relationship between clay content and bound water porosity, φ cbw prediction models; The calculation model of effective porosity φ is established based on the density curve DEN and the neutron curve CNL; According to the actual well logging curve, the different lithology distribution layers are identified, and the organic carbon content TOC, bound water porosity, and effective porosity change curves are calculated; According to the parallel conductive model of lacustrine shale, namely, formula (6), the rock electrical parameters are selected according to the lithology, and the corresponding water saturation S is calculated. w , 1-S w is the oil saturation S of the corresponding point o .

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