A method and system for obtaining shale pore and fracture volumes

Abstract

The present invention provides a method and system for obtaining shale pore and fracture volumes, pertaining to the field of unconventional oil and gas exploration and development. This method distinguishes pore volume from fracture volume based on the constant self-imbibition potential of fluids entering pores and fractures, thereby obtaining the pore and fracture volumes, respectively. While existing high-precision pore volume characterization methods are expensive and complex to operate, the present method is easy to operate and low-cost, meeting the requirements for field and laboratory calculations of core pore and fracture volumes. Furthermore, the present method is simple to operate, non-toxic and pollution-free, and the cores are reusable.

Description

Technical Field

[0001] The present invention belongs to the field of unconventional oil and gas exploration and development, and specifically relates to a method and system for obtaining shale pore and fracture volumes, which are used for core pore volume evaluation. Background Art

[0002] As oil and gas reservoir development gradually shifts from shallow layers to deep and ultra-deep layers, and from conventional reservoirs to unconventional reservoirs, shale oil and gas resources, as an important component of unconventional oil and gas resources, have become one of the most noteworthy unconventional oil and gas resources. Prior to shale oil and gas development, testing the porosity and permeability characteristics of shale reservoir rocks is extremely important in order to understand the basic physical properties of the reservoir and evaluate the economic and technical feasibility of oil and gas reservoir development.

[0003] Pores are the storage spaces for oil and gas resources, while fractures are the primary pathways for oil and gas to flow from the reservoir to the bottom of the well. Both play a crucial role in the development of shale oil and gas reservoirs. Accurately evaluating pore and fracture volumes provides strong support for formulating appropriate development strategies. Proper development measures can reduce development costs, avoid reservoir damage during development, and encourage more oil and gas to flow into the wellbore and be recovered to the surface, thereby increasing oil and gas production and achieving greater economic benefits.

[0004] Existing methods for measuring shale porosity include nuclear magnetic resonance (NMR), high-pressure mercury injection (HIP), and pressure pulse decay (PPE). Besides being expensive and complex, these methods also have other drawbacks. For example, the mercury used in HIP is a highly toxic fluid and can damage and contaminate the core after testing, rendering it unusable. Furthermore, because methane is a flammable gas, safety considerations must be taken into account when conducting experiments.

[0005] For an ideal circular capillary, the imbibition flow of the wetting phase fluid in the capillary is affected by the combined effects of capillary forces, viscous forces on the pore wall, gravity, and inertial forces. For dense porous media such as rock, the imbibition pores often differ significantly from the ideal circular capillary assumption. To study the influence of rock pore structure on the imbibition process, the relationship between imbibition volume and imbibition time was established by considering pore shape factor and pore tortuosity and assuming a uniform advance of the fluid imbibition front:

[0006]

[0007] Where M(t) is the mass of the self-priming fluid, g; A is the effective self-priming contact area, cm 2 ; φ is the porosity of the self-absorbing rock sample, τ is the pore tortuosity, and δ is the pore shape factor, all of which are dimensionless parameters.

[0008] Chinese patent publication CN110096669A discloses a method for determining fracture volume in carbonate reservoirs. The method comprises: establishing a well test analysis model that couples wellbore-cavity-formation flow, wherein the well test analysis model considers bedrock seepage, bedrock-to-cavity channeling, and pipe flow and fluctuation within the cave; establishing a flow model within the fractures based on the well test analysis model; and calculating the fracture volume based on the flow model within the fractures. This method allows for more accurate and reliable determination of fracture volume in fracture-cavity carbonate reservoirs, thereby providing a basis for determining geological reserves in fracture-cavity carbonate reservoirs and fundamental information for dynamic evaluation of such reservoirs. This method plays a significant role in ensuring the efficient development and improving economic benefits of fracture-cavity carbonate reservoirs. However, this patent is only applicable to carbonate reservoirs and is not applicable to shale gas reservoirs.

[0009] Chinese patent publication CN106644873A discloses a method for characterizing the organic pore volume of shale, comprising the following steps: 1) obtaining a first organic pore size coefficient a1 of the shale according to a first calculation model formula 1; obtaining a second organic pore size coefficient a2 of the shale according to a second calculation model formula 2; and obtaining a third organic pore size coefficient a3 of the shale according to a third calculation model formula 3; and 2) characterizing the organic pore volume of the shale using the first organic pore volume ratio ω1, the second organic pore volume ratio ω2, and the third organic pore volume ratio ω3. This patent overcomes the drawback of existing technologies that cannot quantitatively characterize the organic pore volume of shale, but the model parameters are difficult to obtain.

[0010] Chinese patent publication CN112129802A discloses a method for quantitatively analyzing the pore volume increments at different scales in hydrated shale. This method first saturates a standard rock sample with a first solvent that does not hydrate the shale, obtaining data on the original effective pore volume. The sample is then saturated with water to obtain data on the changes in pore volume at different scales after hydration. This patent quantitatively evaluates the absolute increase in effective pore volume at different scales within the shale under hydration, providing practical guidance for field screening of shale reservoirs suitable for post-hydration "well soaking" to increase production, but is less applicable to lacustrine shales.

[0011] The Chinese open-access paper, "Full-pore-size characterization of the pore structure of the Longmaxi Formation shale in southeastern Sichuan and its control on gas content" (Earth Science Frontiers, March 2016), conducted full-pore-size characterization of the pore structure of the Longmaxi Formation shale in southeastern Sichuan through CO2 adsorption, N2 adsorption, CH4 isothermal adsorption, and high-pressure mercury injection experiments, and demonstrated the control of pore structure on shale gas content. Multiple high-end and precise characterization methods were combined to quantitatively characterize the pore structure, providing an important basis for understanding the microscopic characteristics of reservoir pore structure and providing strong support for the formulation of development plans and the implementation of growth measures. However, this method is expensive, time-consuming, and complex to operate, making it unsuitable for field work.

[0012] The Chinese open-access paper, "Analysis of Shale Structure, Fractal Characteristics, and Influencing Factors Using Nitrogen Adsorption and Mercury Intrusion," (Petroleum Geology and Recovery, December 2015), combined nitrogen adsorption and mercury intrusion to characterize the pore distribution, porosity, and fractal characteristics of Permian shales in the southern Anhui region of the Lower Yangtze. This combination of multiple high-end, sophisticated characterization methods quantitatively characterized the pore structure, providing an important basis for understanding the microscopic characteristics of reservoir pore structure and supporting the formulation of development plans and the implementation of growth measures. However, this method is expensive and time-consuming, and the experimental methods, data processing, and operations are complex, making it unsuitable for field work.

[0013] The Chinese open paper "Establishment of a 'Four-Porosity' Model for Shale Reservoirs and a Method for Quantitative Characterization Using Well Logging" (Petroleum & Natural Gas Geology, April 2014) proposes a method for quantitatively evaluating the total pore volume and microscopic pore components of shale reservoirs using well logging data, based on an analysis of core and well logging response characteristics: ① Based on a volume model, the total porosity of shale reservoirs is determined using density logging data or sonic logging data; ② The volume content of organic matter is determined by combining conventional well logging data with natural gamma ray spectroscopy logging data, and the calibration coefficient is determined using scanning electron microscopy (SEM) technology to obtain a method for calculating organic porosity; ③ Clay pores are the primary storage space for irreducible water, and the clay content is determined point by point using well logging data and correlated with adjacent mudstone to obtain a method for calculating clay porosity; ④ Based on the dual laterolog response characteristics of microfractures, a method for calculating microfractures is obtained through forward and inverse numerical simulation; ⑤ The difference between total porosity and organic pores, clay pores, and microfractures is the detrital porosity. Core results show that the microscopic pore composition calculated using this method agrees well with core testing results, demonstrating the validity of the method. This method, using field data, established a relationship between clay mineral pores, organic pores, and total porosity. However, this method is time-consuming and expensive to implement, and requires a significant amount of field data.

[0014] Therefore, it is necessary to propose a safe, scientific and efficient calculation method for shale pore and fracture volumes, and effectively distinguish pore volume from fracture volume, which is of great significance for accurately evaluating shale reservoir properties. Summary of the Invention

[0015] The purpose of the present invention is to solve the difficulties existing in the above-mentioned prior art and provide a method and system for obtaining the pore and fracture volumes of shale, calculate the pore and fracture volumes of shale cores through the permeability curve, evaluate the porosity and permeability characteristics of the reservoir, and lay the foundation for subsequent work.

[0016] The present invention is achieved through the following technical solutions:

[0017] The first aspect of the present invention provides a method for obtaining the pore and fracture volumes of shale. The method distinguishes the pore volume and fracture volume based on the constant self-imbibition potential of fluids entering the pores and fractures, respectively, and then obtains the pore volume and fracture volume respectively.

[0018] A further improvement of the present invention is:

[0019] The method comprises:

[0020] Step 1: Select a standard shale core and dry it;

[0021] Step 2: Prepare the solution and test the density of the solution, i.e. the fluid density ρ;

[0022] Step 3: Immerse the core completely in the solution to conduct a self-imbibition experiment;

[0023] Step 4: Monitor and record the self-imbibition rate of the core during the self-imbibition experiment;

[0024] Step 5: Draw a scatter plot of the self-priming amount with respect to the square root of the self-priming time;

[0025] Step 6: Fit the self-priming amount scatter plot to obtain the self-priming curve;

[0026] Step 7: Obtain the fracture volume and pore volume of the core.

[0027] A further improvement of the present invention is:

[0028] In step 1, a vacuum drying oven is used to vacuum and dry the core.

[0029] A further improvement of the present invention is:

[0030] The solution configured in step 2 is a KCl solution.

[0031] A further improvement of the present invention is:

[0032] The operation of step 4 includes:

[0033] An electronic balance and a computer are used to monitor and record the self-imbibition amount of the core in real time;

[0034] When the difference between the two self-priming amounts separated by 8 hours is less than 3% of the last self-priming amount, the self-priming experiment ends.

[0035] A further improvement of the present invention is:

[0036] The operation of step 5 includes:

[0037] With the square root of the self-priming time as the horizontal coordinate and the self-priming amount as the vertical coordinate, the self-priming amount corresponding to each sampling time point is plotted on the coordinate graph to form a scatter plot of self-priming amount.

[0038] A further improvement of the present invention is:

[0039] The operation of step 6 includes:

[0040] Find the turning point of the self-priming volume on the self-priming volume scatter plot;

[0041] The discrete points on both sides of the turning point are fitted to obtain two fitted self-imbibition curves. The self-imbibition curve on the left side of the turning point is the first stage, and the self-imbibition curve on the right side of the turning point is the second stage.

[0042] Read the slope k1 of the linear regression equation of the first stage, the slope k2 of the linear regression equation of the second stage, the square root t1 of the end time point of the first stage, and the square root t2 of the end time point of self-priming.

[0043] A further improvement of the present invention is:

[0044] The operation of step 7 includes:

[0045] The fracture volume of the core is calculated using the following formula (1), and the pore volume of the core is calculated using formula (2):

[0046]

[0047]

[0048] Among them, V f 、V p are the fracture volume and pore volume of the core, respectively.

[0049] A second aspect of the present invention provides a system for obtaining shale pore and fracture volumes, the system comprising:

[0050] Acquisition unit: used to collect the self-imbibition of the core at each sampling time point;

[0051] Self-priming amount scatter plot drawing unit: connected to the acquisition unit, used for drawing a self-priming amount scatter plot of the self-priming amount with respect to the square root of the self-priming time;

[0052] Curve fitting unit: connected to the self-priming amount scatter plot drawing unit, used to fit the self-priming amount scatter plot to obtain the self-priming curve;

[0053] The calculation unit is connected to the curve fitting unit and is used to obtain the fracture volume and pore volume of the core.

[0054] A further improvement of the present invention is:

[0055] The collection unit includes: a computer and an electronic balance connected thereto.

[0056] A further improvement of the present invention is:

[0057] The self-priming amount scatter plot drawing unit uses the square root of the self-priming time as the abscissa and the self-priming amount as the ordinate, and draws the self-priming amount corresponding to each sampling time point on a coordinate graph to form a self-priming amount scatter plot.

[0058] A further improvement of the present invention is:

[0059] The curve fitting unit finds the turning point where the self-priming amount turns on the scatter plot of the self-priming amount, and fits the discrete points on both sides of the turning point to obtain two fitted self-priming curves, the self-priming curve on the left side of the turning point is the first stage, and the self-priming curve on the right side of the turning point is the second stage; then reads the slope k1 of the linear regression equation of the first stage, the slope k2 of the linear regression equation of the second stage, the square root t1 of the end time point of the first stage, and the square root t2 of the self-priming end time point.

[0060] A further improvement of the present invention is:

[0061] The calculation unit calculates the fracture volume of the core using the following formula (1) and calculates the pore volume of the core using formula (2):

[0062]

[0063]

[0064] Among them, V f 、V p are the fracture volume and pore volume of the core respectively; ρ is the fluid density.

[0065] Compared with the prior art, the present invention has the following beneficial effects:

[0066] (1) Simple operation and low cost. While existing high-precision pore volume characterization methods are expensive and complex to operate, the method proposed in the present invention is easy to operate and low-cost, and can meet the needs of field and laboratory calculations of core pore and fracture volumes. Furthermore, the method of the present invention is simple to operate, non-toxic and pollution-free, and the cores can be reused.

[0067] (2) Accurate results. Shale has a high clay mineral content, well-developed bedding fractures, and small pore throats, which give it strong hydrophilicity and capillary forces. After a certain period of self-imbibition, water molecules enter the crystal layers and mineral pores under the action of capillary forces, fully occupying the space therein, making the test results accurate.

[0068] (3) Ability to distinguish between core pore volume and fracture volume: The present invention distinguishes between pore volume and fracture volume based on the constant self-imbibition potential of fluids entering pores and fractures, respectively. Existing porosity measurement methods, however, obtain the porosity by dividing the sum of the pore volume and fracture volume by the total core volume, which cannot effectively distinguish between fracture volume and pore volume. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 A flowchart of the steps of the method of the present invention;

[0070] Figure 2 It is a schematic diagram of the self-priming curve stage division;

[0071] Figure 3 1 is the core self-imbibition curve and its division in the embodiment. DETAILED DESCRIPTION

[0072] The present invention is further described in detail below with reference to the accompanying drawings:

[0073] The present invention provides a method for obtaining shale pore volume and fracture volume through an imbibition curve, which is applicable to unconventional tight gas reservoirs.

[0074] The method of the present invention comprises:

[0075] Step 1: Select a standard shale core and dry it for later use: Use existing technology to obtain a standard shale core and dry it. Specifically, place the core in a vacuum drying oven for vacuuming and drying. Vacuuming is used to cooperate with the drying process to achieve a better drying effect.

[0076] Step 2: preparing a KCl solution of a certain concentration and testing the density of the solution;

[0077] Step 3: The core prepared in step 1 is completely immersed in the solution prepared in step 2 to conduct a self-imbibition experiment;

[0078] Step 4: During the self-imbibition experiment, an electronic balance and a computer are used to monitor and record the mass change of the core (i.e., the self-imbibition amount) in real time. When the difference between the two self-imbibition amounts at an interval of 8 hours is less than 3% of the last self-imbibition amount, the self-imbibition experiment ends;

[0079] Specifically, connect the electronic balance to the computer, turn on the computer and the electronic balance, and tie the core with a thin wire. At this time, the reading of the electronic balance is the weight of the thin wire and the dry core. Click the "Tare" button on the electronic balance to return the reading of the electronic balance to zero. Then immerse the core completely in the KCl solution. The core begins to self-absorb the water phase. At this time, the reading of the electronic balance is the self-absorption amount of the core. The software can be used to record the reading of the electronic balance at each sampling time point.

[0080] Step 5: Draw a scatter plot of the self-priming amount with respect to the square root of the self-priming time;

[0081] With the square root of the self-priming time as the horizontal coordinate and the self-priming amount as the vertical coordinate, the self-priming amount corresponding to each sampling time point is plotted on the coordinate graph to form a self-priming amount scatter plot. At this time, the points corresponding to each self-priming amount are discrete points.

[0082] According to the relationship between the core self-imbibition volume and self-imbibition time established in existing literature, as shown in the following formula, the self-imbibition mass is positively correlated with the square root of time. Therefore, the abscissa of the self-imbibition volume scatter plot uses the square root of the self-imbibition time.

[0083]

[0084] Step 6: Use the linear regression equation to fit the self-priming scatter plot to obtain the self-priming curve:

[0085] like Figure 2 As shown, the turning point where the self-priming amount turns is found on the self-priming amount scatter plot, the turning point divides the self-priming scatter plot into two stages, and then the discrete points on both sides of the turning point are fitted to obtain two fitted self-priming curves, the self-priming curve on the left side of the turning point is the first stage, and the self-priming curve on the right side of the turning point is the second stage, the slope k1 of the linear regression equation of the first stage, the slope k2 of the linear regression equation of the second stage, the square root t1 of the end time point of the first stage, and the square root t2 of the self-priming end time point are read;

[0086] Step 7: Calculate the fracture volume of the core using the following formula (1), and calculate the pore volume of the core using formula (2):

[0087]

[0088]

[0089] Where Vf 、V p are the fracture volume and pore volume of the core, cm 3 ; t1 is the square root of the end time of the first stage, h 0.5 ; t2 is the square root of the end time of self-priming, h 0.5 ; ρ is the fluid density, g / cm 3 ; k1 is the slope of the first stage curve, k2 is the slope of the second stage curve, both are dimensionless parameters.

[0090] The embodiments of the inventive method are as follows:

[0091] [Example 1]

[0092] like Figure 1 As shown, the method includes:

[0093] S1, prepare standard shale core, vacuum and dry it for use;

[0094] S2, measuring the porosity of the core;

[0095] S3, prepare a 7% KCl solution and test the fluid density ρ;

[0096] S4, fully immerse the saturated core with KCl solution;

[0097] S5, conduct a self-imbibition experiment, monitor the core mass change using an electronic balance and a data acquisition system (i.e., a computer), and vacuum and dry the core after the self-imbibition experiment.

[0098] S6, draw a scatter plot of the self-imbibition amount of the core versus the square root of the self-imbibition time;

[0099] S7, divide the two stages according to the turning point on the scatter plot of the self-imbibition amount, and fit the self-imbibition curves of the two stages respectively: use existing computer software to fit the two stages respectively to obtain two linear regression equations, read out the slopes k1 and k2 of the two linear regression equations, the square root t1 of the end time point of the first stage, and the square root t2 of the end time point of the self-imbibition.

[0100] S8, calculate the fracture volume V of the core according to the above formulas (1) and (2) f and pore volume V p .

[0101] The porosity measured in step S2 was used to verify the method of the present invention, and the verification results showed that the calculation results of the method of the present invention were highly accurate.

[0102] The method provided by the present invention can distinguish the pore volume and fracture volume of shale cores, providing an important basis for accurately evaluating reservoir physical properties and having important significance for the formulation of subsequent gas well production systems.

[0103] The application examples of the method of the present invention are as follows:

[0104] [Example 2]

[0105] In order to explain the technical features, objectives and beneficial effects of the present invention more clearly, the content and features of the present invention are further described in detail with reference to specific parameters and embodiments. The specific steps are as follows:

[0106] Step 1: Select two standard shale cores, Core A and Core B, and place all cores in a vacuum drying oven at 65°C for 48 hours;

[0107] Step 2: According to SY / T 5336-2006 Core Analysis Method, the core's basic physical properties, such as porosity, length, diameter, mass, and permeability, are tested as described in Step 1. The basic physical properties of the core are shown in Table 1.

[0108]

[0109]

[0110] Table 1

[0111] Step 3: Take 14g KCl solid medicine and 200ml distilled water, slowly add KCl solid powder into the distilled water and stir with a glass rod until the medicine is completely added and dissolved. Measure the density of the fluid. The density of 7% KCl solution at room temperature and pressure is 1g / cm 3 ;

[0112] Step 4: Immerse the core completely in the 7% KCl solution for saturation;

[0113] Step 5: During the imbibition process, an electronic balance and a computer are used to monitor and record the mass change of the core in real time. Since computer software is used to record the core self-imbibition, the sampling time interval can be set on the software, such as 1 min, 5 min, 10 min, 30 min, 60 min, etc. In this embodiment, within 4 hours after the start of imbibition, the sampling interval is 10 min, and after 4 hours, the sampling interval is 60 min. After 41 hours of self-imbibition, the self-imbibition of core A is 0.9518 g (obtained directly from the reading of the electronic balance), and the self-imbibition of core A is 0.9802 g after 49 hours. The change in the self-imbibition of the two cores with an interval of 8 hours is 0.0284 g, which is less than 3% (0.0294 g) of the self-imbibition of 0.9802 g at this time. Therefore, the self-imbibition of core A ends.

[0114] Using the same method, an imbibition experiment was carried out on Core B. The imbibition amount of Core B was 0.7463 g at 41 hours and 0.7466 g at 49 hours. The change in the imbibition amount of the core between two measurements with an interval of 8 h was less than 3% (0.0224 g) of the imbibition amount of 0.7466 g at this time, and the imbibition of Core B ended;

[0115] Step 6: Make a scatter plot of the imbibition amount of the core described in Step 5 against the square root of the imbibition time;

[0116] Step 7: After the imbibition experiment ends, in the coordinate graph plotted according to the imbibition amount corresponding to each sampling time point, the shape formed by connecting each discrete point in sequence is similar to the Chinese character "厂". There will be a relatively obvious turning point, which is the dividing point for dividing the two stages. Two imbibition curves are obtained by fitting the discrete points on both sides of the turning point using a linear regression equation. The turning point is the demarcation point of the two imbibition curves, that is, the imbibition curve is divided into two stages. Read the slope k of the linear regression equation of the first stage of Core A 1A which is 0.2665, and the slope k of the linear regression equation of the second stage 2A is 0.0887. The slope k of the linear regression equation of the first stage of Core B 1B is 0.3069, and the slope k of the linear regression equation of the second stage 2B is 0.035. The square root t of the end time point of the first stage of Core A 1A is 2.4 h 0.5 and the square root t of the end time point of the first stage of Core B 1B is 1.8 h 0.5 The square roots t and t of the final imbibition time points of Core A and Core B 2A and 2B are both 7 h 0.5 as shown in Figure 3 shown.

[0117] It should be noted that the first stage is the imbibition stage dominated by fractures. In this stage, both fractures and pores imbibe, but fractures are the main part, and the slope k1 of the curve is larger. In the second stage, the fractures are already filled with fluid, and the presence of the fracture surface expands the contact area between the fluid and the shale matrix. Pore imbibition dominates, but due to the matrix being dense, the pore throat being small, and the aqueous phase dispersing slowly, the slope k2 of the curve in the second stage is smaller.

[0118] Step 8: Calculate the fracture volume of the core using Equation (1) and calculate the pore volume of the core using Equation (2).

[0119]

[0120]

[0121] Where t1 is the square root of the end time of the first stage, h 0.5 ; t2 is the square root of the end time of self-priming, h 0.5 ; V f 、V p are the core fracture and pore volumes, cm 3 ; ρ is the fluid density, g / cm 3 ; k1 is the slope of the first stage curve, k2 is the slope of the second stage curve, both are dimensionless parameters.

[0122] According to the fitting line of the core self-imbibition curve, the slopes k1 and k2 and t1 and t2 of the two self-imbibition stages are read out, and then V is calculated. f 、V p The porosity of the core is calculated using formula (4) and compared with the porosity of the core measured experimentally. The deviation between the porosity obtained by the method of the present invention and the porosity measured experimentally is calculated according to formula (5). The calculation results show that the deviation is less than 5%, and the accuracy is very high.

[0123] This example demonstrates the high accuracy of the method of the present invention using two cores, and shows that the turning points and the slopes of the first and second stages are different for different cores. In actual use of the method of the present invention, only one core is required.

[0124]

[0125]

[0126] V 岩心 It is the apparent volume of the core, which can be calculated using the diameter and length of the core.

[0127] φ 实测值 is the actual measured core porosity, φ 计算值 is the calculated porosity of the core.

[0128] The calculation results are shown in Table 2.

[0129]

[0130] Table 2

[0131] The method provided by the present invention can distinguish the pore volume and fracture volume of shale cores, providing an important basis for accurately evaluating reservoir physical properties and having important significance for the formulation of subsequent gas well production systems.

[0132] The present invention also provides a system for obtaining shale pore and fracture volumes, and an embodiment of the system is as follows:

[0133] [Example 3]

[0134] The system comprises:

[0135] Acquisition unit: used to collect the self-imbibition of the core at each sampling time point;

[0136] Self-priming amount scatter plot drawing unit: connected to the acquisition unit, used for drawing a self-priming amount scatter plot of the self-priming amount with respect to the square root of the self-priming time;

[0137] Curve fitting unit: connected to the self-priming amount scatter plot drawing unit, used to fit the self-priming amount scatter plot to obtain the self-priming curve;

[0138] The calculation unit is connected to the curve fitting unit and is used to obtain the fracture volume and pore volume of the core.

[0139] Specifically, the acquisition unit includes: a computer and an electronic balance connected thereto.

[0140] Specifically, the self-priming amount scatter plotting unit uses the square root of the self-priming time as the abscissa and the self-priming amount as the ordinate, and plots the self-priming amount corresponding to each sampling time point on a coordinate graph to form a self-priming amount scatter plot.

[0141] Specifically, the curve fitting unit finds the turning point where the self-priming amount turns on the self-priming amount scatter plot, and fits the discrete points on both sides of the turning point to obtain two fitted self-priming curves, the self-priming curve on the left side of the turning point is the first stage, and the self-priming curve on the right side of the turning point is the second stage; then reads the slope k1 of the linear regression equation of the first stage, the slope k2 of the linear regression equation of the second stage, the square root t1 of the end time point of the first stage, and the square root t2 of the self-priming end time point.

[0142] Specifically, the calculation unit calculates the fracture volume of the core using the following formula (1) and calculates the pore volume of the core using formula (2):

[0143]

[0144]

[0145] Among them, V f 、V p are the fracture volume and pore volume of the core respectively; ρ is the fluid density.

[0146] Finally, it should be noted that the above technical solution is only one embodiment of the present invention. For those skilled in the art, it is easy to make various types of improvements or modifications based on the application methods and principles disclosed in the present invention, and it is not limited to the method described in the above specific embodiment of the present invention. Therefore, the method described above is only preferred and does not have a restrictive meaning.

Claims

1. A method for obtaining shale pore and fracture volumes, characterized by: The method distinguishes the pore volume from the fracture volume based on the constant self-imbibition potential of fluids entering pores and fractures, thereby obtaining the pore volume and fracture volume respectively. The method comprises: Step 1: Select a standard shale core and dry it; Step 2: Prepare the solution and test the density of the solution, i.e. the fluid density ρ; Step 3: Immerse the core completely in the solution to conduct a self-imbibition experiment; Step 4: Monitor and record the self-imbibition rate of the core during the self-imbibition experiment; Step 5: Draw a scatter plot of the self-priming amount with respect to the square root of the self-priming time; Step 6: Fit the self-priming amount scatter plot to obtain the self-priming curve; Step 7: Obtain the fracture volume and pore volume of the core; The operation of step 6 includes: Find the turning point of the self-priming volume on the self-priming volume scatter plot; The discrete points on both sides of the turning point are fitted to obtain two fitted self-imbibition curves. The self-imbibition curve on the left side of the turning point is the first stage, and the self-imbibition curve on the right side of the turning point is the second stage. Read the slope k1 of the linear regression equation of the first stage, the slope k2 of the linear regression equation of the second stage, the square root t1 of the end time point of the first stage, and the square root t2 of the end time point of self-priming; The operation of step 7 includes: The fracture volume of the core is calculated using the following formula (1), and the pore volume of the core is calculated using formula (2): Among them, V f 、V p are the fracture volume and pore volume of the core, respectively.

2. The method for obtaining shale pore and fracture volumes according to claim 1, characterized in that: In step 1, a vacuum drying oven is used to vacuum and dry the core.

3. The method for obtaining shale pore and fracture volumes according to claim 1, characterized in that: The solution configured in step 2 is a KCl solution.

4. The method for obtaining shale pore and fracture volumes according to claim 1, characterized in that: The operation of step 4 includes: An electronic balance and a computer are used to monitor and record the self-imbibition amount of the core in real time; When the difference between the two self-priming amounts separated by 8 hours is less than 3% of the last self-priming amount, the self-priming experiment ends.

5. The method for obtaining shale pore and fracture volumes according to claim 1, wherein: The operation of step 5 includes: With the square root of the self-priming time as the horizontal coordinate and the self-priming amount as the vertical coordinate, the self-priming amount corresponding to each sampling time point is plotted on the coordinate graph to form a scatter plot of self-priming amount.

6. A system for obtaining shale pore and fracture volumes, characterized by: The system comprises: Acquisition unit: used to collect the self-imbibition of the core at each sampling time point; Self-priming amount scatter plot drawing unit: connected to the acquisition unit, used for drawing a self-priming amount scatter plot of the self-priming amount with respect to the square root of the self-priming time; Curve fitting unit: connected to the self-priming amount scatter plot drawing unit, used to fit the self-priming amount scatter plot to obtain the self-priming curve; The calculation unit is connected to the curve fitting unit and is used to obtain the fracture volume and pore volume of the core; The curve fitting unit finds the turning point where the self-priming amount turns on the self-priming amount scatter plot, and fits the discrete points on both sides of the turning point to obtain two fitted self-priming curves, the self-priming curve on the left side of the turning point is the first stage, and the self-priming curve on the right side of the turning point is the second stage; then reads the slope k1 of the linear regression equation of the first stage, the slope k2 of the linear regression equation of the second stage, the square root t1 of the end time point of the first stage, and the square root t2 of the self-priming end time point; The calculation unit calculates the fracture volume of the core using the following formula (1) and calculates the pore volume of the core using formula (2): Among them, V f 、V p are the fracture volume and pore volume of the core respectively; ρ is the fluid density.

7. The system for obtaining shale pore and fracture volumes according to claim 6, characterized in that: The collection unit includes: a computer and an electronic balance connected thereto.

8. The system for obtaining shale pore and fracture volumes according to claim 6, characterized in that: The self-priming amount scatter plot drawing unit uses the square root of the self-priming time as the abscissa and the self-priming amount as the ordinate, and draws the self-priming amount corresponding to each sampling time point on a coordinate graph to form a self-priming amount scatter plot.

Images