A method and device for monitoring in real time the evolution of porosity during the dissolution of carbonates

Abstract

The application discloses a method and device for monitoring pore evolution in a carbonate rock corrosion process in real time, and relates to the technical field of carbonate rock pore evolution. The method comprises the following steps: selecting samples of different pore types and different physical property reservoirs; inputting a brine solution into the samples, and then performing NMR and SIP background value tests; inputting an acid solution into the samples after the NMR and SIP background value tests, and then performing NMR and SIP tests to obtain pore characteristic NMR and SIP test values of different batches of acid solution reactions; and based on the pore characteristic NMR and SIP test values, quantitatively characterizing carbonate rock pore characteristic evolution and determining main control factors of pore development. The application combines NMR and SIP, utilizes different response characteristics of reservoir rocks saturated with fluid under the action of a magnetic field and an electric field, and can quickly, non-destructively and in-situ measure the pore system of the whole sample. Different pore structure changes in the carbonate rock corrosion process are inversed and quantitatively characterized, so that the pore evolution law of the carbonate rock reservoir can be revealed.

Description

Technical Field

[0001] This invention relates to the field of carbonate rock pore evolution technology, and in particular to a method and apparatus for real-time monitoring of pore evolution during carbonate rock dissolution. Background Technology

[0002] Carbonate rocks are crucial oil and gas reservoirs. Their main rock-forming minerals, such as calcite and dolomite, are readily soluble and easily altered by various fluids during sedimentation and diagenesis, forming different reservoir spaces, such as intergranular dissolution pores, intergranular dissolution pores, and lattice pores. Therefore, directly revealing the porosity evolution of carbonate reservoirs through dissolution simulation experiments has become a powerful tool for studying carbonate reservoirs.

[0003] Previous studies by numerous scholars have yielded positive findings, ranging from single-mineral analysis of dolomite to analysis of different lithofacies assemblages, and from the influence of various environmental conditions (temperature, pressure, fluid, flow rate, etc.) on the dissolution effect to comparisons of dolomite morphology and porosity before and after dissolution. However, these studies have the following limitations: First, porosity observations only compare the two endpoints before and after dissolution, lacking research on porosity changes during the intermediate dissolution process; second, dissolution is primarily assessed through chemical analysis of the Ca in the dissolution solution. 2+ Mg 2+ Changes in ion concentration can be used to indirectly estimate the amount and rate of dissolution of dolomite, but there is a lack of direct means to monitor pore evolution. Third, due to limitations in sample size, field of view, and instrument resolution, only local and small areas of the sample can be observed, lacking a macroscopic understanding of the overall pore system of the sample.

[0004] Reservoir rock pores are filled with and adsorbed various charged fluids, such as brines and organic acids. Due to the influence of pore structure, the resonance amplitude, relaxation time, and conductivity of these charged fluids under magnetic and electric fields vary. Currently, Nuclear Magnetic Resonance (NMR) in petroleum geology mainly studies pore connectivity and pore size distribution by comparing the differences in fluid saturation and T2 (transverse relaxation time) distribution before and after centrifugation of cores (saturated brine). Spectral Induced Polarization (SIP) is less commonly used in petroleum geology, primarily reported for solid mineral exploration or as a geophysical method for studying electrical differences between aqueous media such as rocks and soils. No published literature combines both methods for studying pore evolution during acid dissolution of carbonate rocks (this invention mainly focuses on dolomite). Therefore, during the acid-karstification reaction of carbonate rocks, NMR and SIP can be used to monitor the electrical and magnetic changes of reservoir rocks to provide feedback on the porosity evolution characteristics of the reservoir rocks. Summary of the Invention

[0005] The purpose of this invention is to provide a method and apparatus for real-time monitoring of pore evolution during carbonate rock karstification. By combining NMR and SIP, and utilizing the different response characteristics of reservoir rocks saturated with fluids (such as brine and acid) under magnetic and electric fields, the pore system of the entire sample can be measured rapidly, non-destructively, and in situ. Inversion and quantitative characterization of different pore structure changes during carbonate rock karstification can reveal the pore evolution law of carbonate reservoirs and determine the main controlling factors for pore development in high-quality carbonate reservoirs. To achieve the above objective, this invention provides the following technical solution:

[0006] On the one hand, the present invention provides a method for real-time monitoring of pore evolution during carbonate karstification, the method comprising:

[0007] Select samples from reservoirs with different pore types and physical properties;

[0008] After the brine solution was introduced into the sample, NMR and SIP background values ​​were tested.

[0009] An acid solution was input into the sample after NMR and SIP background value testing, and NMR and SIP tests were performed to obtain the pore characteristics NMR and SIP test values ​​of different batches of acid dissolution reaction.

[0010] Based on the NMR and SIP test values ​​of the pore characteristics, the evolution of pore characteristics in carbonate rocks is quantitatively characterized and the main controlling factors of pore development are determined.

[0011] Furthermore, after obtaining the pore characteristic NMR and SIP test values ​​of different batches of acid dissolution reactions, the following steps are also included:

[0012] The dissolution experiment ends when the NMR and SIP test values ​​remain stable.

[0013] Furthermore, the specific steps for selecting reservoir samples with different pore types and physical properties are as follows:

[0014] Observe the lithology and pore development characteristics of the hand specimens, and initially select representative samples;

[0015] The representative sample was subjected to plunger sampling to obtain a plunger sample;

[0016] The representative sample was sliced ​​into thin rock sections and made into thin rock castings.

[0017] The porosity and permeability of the plunger sample were tested.

[0018] Based on the rock casting thin sections, the sample pore type was classified;

[0019] Based on the porosity, permeability tests and pore type classification, reservoir samples with different pore types and different physical properties were obtained.

[0020] Furthermore, the specific steps for performing NMR and SIP background value tests after introducing the brine solution into the sample are as follows:

[0021] The sample was pretreated to obtain a purified sample;

[0022] A brine solution is introduced into the purified sample to obtain a sample solution saturated with brine;

[0023] For the saturated halogen water The sample solution was subjected to NMR and SIP background value tests.

[0024] Furthermore, the halogen water The solution has the following characteristics:

[0025] The brine is one of CaCl2, NaCl, KCl or Na2SO4;

[0026] The brine solution has an input flow rate of 0.01–0.1 ml / min, a temperature of 25–40 °C, a salinity of 0.001–0.01 S / m, and an input volume of 50 ml.

[0027] Furthermore, the acid solution is one of acetic acid, dilute hydrochloric acid, dilute sulfuric acid, or oxalic acid.

[0028] Based on the above method, in another aspect, the present invention provides a device for real-time monitoring of pore evolution during carbonate karst erosion. The device includes: a sample solution input unit, a sample solution processing unit, and a solution output receiver; wherein...

[0029] The sample solution input unit is connected to the sample solution processing unit via a second valve;

[0030] The sample solution processing unit is connected to the solution output receiver via a third valve.

[0031] Furthermore, the sample solution input unit includes a solution input receiver, a solution input pump, a one-way valve, and an axial pressure pump; wherein,

[0032] The solution input receiver is configured as an open port and is connected to one end of the solution input pump via a pipe; the other end of the solution input pump is connected to a check valve via a first valve; one end of the check valve is connected to an axial pressure pump.

[0033] Furthermore, the sample solution processing unit includes a solution preheating chamber, a sample chamber, and a filter; wherein,

[0034] One end of the solution preheating chamber is connected to the sample solution processing unit via a second valve; the other end of the solution preheating chamber is connected to one end of the sample chamber, and the other end of the sample chamber is connected to one end of the filter; the other end of the filter is connected to the solution output receiver via a third valve.

[0035] Furthermore, the solution preheating chamber is equipped with a first temperature controller; the sample chamber is equipped with a second temperature controller and a confining pressure controller.

[0036] The technical effects and advantages of this invention are as follows:

[0037] First, this invention provides an experimental procedure and technical standard for combining NMR and SIP in the acid dissolution process of carbonate rocks.

[0038] Second, this invention uses the electrical and magnetic signals of NMR and SIP to interpret the pore evolution diagrams and corresponding theoretical models during the acid dissolution process of carbonate rocks, such as the DBL (Diffusion Boundary Layer) model.

[0039] Third, this invention explains the response characteristics of NMR and SIP to pore changes during the acid dissolution process of carbonate rocks with different pore sizes and lithologies, and identifies the controlling factors of different response characteristics.

[0040] Fourth, a set of hardware instruments based on NMR and SIP for monitoring the karstification process of carbonate rocks was invented.

[0041] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of a method for real-time monitoring of pore evolution during carbonate rock karstification according to the present invention;

[0043] Figure 2 Schematic diagrams showing different pore structures and the response characteristics of NMR and SIP under different pore structures in embodiments of the present invention;

[0044] Figure 3 This is a flowchart of a method for real-time monitoring of pore evolution during carbonate rock karstification according to an embodiment of the present invention;

[0045] Figure 4 This is a schematic diagram of a device for real-time monitoring of pore evolution during the karstification process of carbonate rocks, according to an embodiment of the present invention.

[0046] Figure 5 These are optical microscope images of samples 1-6 selected in Table 1 of this invention;

[0047] Figure 6 For the present invention Figure 5 NMR test results of the sample after etching with CaCl2 solution and acetic acid;

[0048] Figure 7 For the present invention Figure 5 SIP test results of samples after etching with CaCl2 solution and acetic acid;

[0049] Figure 8 The NMR background values ​​of samples 1-6 of this invention after passing through saturated CaCl2 solution are compared with the high-pressure mercury intrusion pore size distribution of sample 1.

[0050] Figure 9 These are plunger sample photographs of samples 1-3 of this invention;

[0051] In the diagram, 1-solution inlet receiver; 2-solution inlet pump; 3-first valve; 4-check valve; 5-axial pressure pump; 6-second valve; 7-first temperature controller; 8-solution preheating chamber; 9-second temperature controller; 10-sample chamber; 11-containing pressure controller; 12-filter; 13-third valve; 14-solution outlet receiver. Detailed Implementation

[0052] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0053] To address the shortcomings of existing technologies, this invention discloses a method for real-time monitoring of pore evolution during carbonate rock karstification. Figure 1 This is a schematic flowchart of a method for real-time monitoring of pore evolution during carbonate karst erosion according to the present invention. The method includes the following steps:

[0054] Select samples from reservoirs with different pore types and physical properties;

[0055] Introduce halogen into the sample water After solution preparation, NMR and SIP background values ​​were measured.

[0056] An acid solution was input into the sample after NMR and SIP background value testing, and NMR and SIP tests were performed to obtain the pore characteristics NMR and SIP test values ​​of different batches of acid dissolution reaction.

[0057] Based on the NMR and SIP test values ​​of the pore characteristics, the evolution of pore characteristics in carbonate rocks is quantitatively characterized and the main controlling factors of pore development are determined.

[0058] Preferably, after obtaining the pore characteristic NMR and SIP test values ​​of different batches of acid dissolution reactions, the method further includes the following steps:

[0059] The dissolution experiment ends when the NMR and SIP test values ​​remain stable.

[0060] Preferably, the specific steps for selecting reservoir samples with different pore types and physical properties are as follows:

[0061] Observe the lithology and pore development characteristics of the hand specimens, and initially select representative samples;

[0062] The representative sample was subjected to plunger sampling to obtain a plunger sample;

[0063] The representative sample was sliced ​​into thin rock sections and made into thin rock castings.

[0064] The porosity and permeability of the plunger sample were tested.

[0065] Based on the rock casting thin sections, the sample pore type was classified;

[0066] Based on the porosity, permeability tests and pore type classification, reservoir samples with different pore types and different physical properties were obtained.

[0067] Preferably, the step of introducing halogen into the sample water After solution preparation, the specific steps for NMR and SIP background value testing are as follows:

[0068] The sample was pretreated to obtain a purified sample;

[0069] A brine solution is introduced into the purified sample to obtain a sample solution saturated with brine;

[0070] For the saturated halogen water The sample solution was subjected to NMR and SIP background value tests.

[0071] Preferably, the halogen water The solution has the following characteristics:

[0072] The brine is one of CaCl2, NaCl, KCl or Na2SO4;

[0073] The brine solution has an input flow rate of 0.01–0.1 ml / min, a temperature of 25–40 °C, a salinity of 0.001–0.01 S / m, and an input volume of 50 ml.

[0074] Preferably, the acid solution is one of acetic acid, dilute hydrochloric acid, dilute sulfuric acid, or oxalic acid.

[0075] Various charged fluids, such as brine and acid solutions, fill and adsorb into the pores of reservoir rocks. Due to the influence of pore structure, the resonance amplitude, relaxation time, conductivity, and other electromagnetic response characteristics of charged fluids under the action of magnetic and electric fields are not entirely the same.

[0076] Natural reservoir rocks have complex pore structures. Figure 2 This is a schematic diagram illustrating different pore structures and the response characteristics of NMR and SIP under different pore structures according to embodiments of the present invention. Now, in conjunction with... Figure 2 The response characteristics of NMR and SIP under different pore structures are illustrated by example. Figure 2 The 'a' represents the actual complex pore structure, showing isolated and interconnected pores, as well as small and large pores. Taking salt water as an example... Figure 2 b shows that the nuclear magnetic resonance amplitude of hydrogen nuclei is the smallest and the relaxation time is the shortest in isolated pores saturated with salt water under the action of an electromagnetic field. Figure 2 The d-values ​​show that the macropores saturated with salt water under the influence of an electromagnetic field exhibit the largest NMR amplitude and the longest relaxation time. Figure 2 The value of c indicates that the nuclear magnetic resonance amplitude and relaxation time of small pores saturated with brine under the influence of an electromagnetic field are moderate. Similarly, the conductivity of rock pores saturated with brine varies under the influence of currents of different frequencies. This difference can be explained by empirical and semi-empirical models, such as the Equivalent Double Layer (EDL) model, which can be used to calculate the pore size distribution. Figure 2 The figure shows the pore structure and electron adsorption diagram of large and small pores under the EDL model. The EDL model of pore structure indicates that isolated pores do not carry current; small pores, such as those at bends and narrow points in connected pores, have a larger specific surface area and adsorb more charge than large pore cavities, thus causing changes in conductivity. In actual measurements, the conductivity σ of SIP... * It consists of a real part conductivity σ′ and an imaginary part conductivity σ″, which correspond to the structure of large and small pores, respectively.

[0077] Specifically, when fluid-saturated reservoir rocks undergo spectral excited polarization (also called polarization), the response signal of the porous medium will exhibit phase amplitude and phase difference, according to Archie's formula:

[0078]

[0079] σ"∝S por ∑ s (2),

[0080] In the formula, σ' is the real part, representing the excitation response signal of large pores, reflecting the pore size of large pores; σ” is the imaginary part, representing the excitation response signal of small pores, reflecting the pore size of small pores; F is the formation factor; σ′ s σ is the real part of the electrical conductivity of solid rock; f S is the fluid conductivity; por ∑ represents the area of ​​the pores; s "is the sum of the imaginary parts of the conductivity of all solid rocks; σ' and σ" can be derived from the amplitude |σ| and phase difference of the conductivity at different current frequencies. The results are shown in equations (3) and (4):

[0081]

[0082]

[0083] In the formula, |σ| and The results are directly output from the experimental instruments, thus obtaining σ′(ω) and σ"i(ω), and then analyzing the pore structure modification and seepage characteristics of the rock.

[0084] Simulation and pore evolution studies of water (acid) karst corrosion processes in various carbonate rocks. Experimental temperatures range from 10 to 90℃, experimental pressures from 5 to 30 MPa, and experimental fluids include (but are not limited to) pure water, brine, acetic acid, and other different reaction fluids.

[0085] Figure 3 This is a flowchart illustrating a method for real-time monitoring of pore evolution during carbonate rock karstification according to an embodiment of the present invention. It mainly consists of four steps: sample identification and selection, NMR and SIP determination of sample pore characteristic background values, NMR and SIP testing of pore characteristics in different batches of acid dissolution reactions, and determination of pore evolution and main controlling factors of pore development in carbonate rocks. The following explanation uses CaCl2 and acetic acid solution as an example; the specific steps are as follows:

[0086] Step 1: Sample Identification and Selection

[0087] The main purpose of this step is to select typical samples of reservoirs with different pore types and physical properties. To this end, it is necessary to first observe the lithology and pore development characteristics of the hand specimens and preliminarily select representative samples. Then, a plunger sample is drilled using a 1-inch (2.54 cm) diameter drill and sliced. Rock casting thin sections are made using a high-pressure casting instrument. The porosity and permeability of the plunger sample are tested according to the national standard (GB / T29172-2012, Core Analysis Methods). Correspondingly, the microstructure and pore development characteristics of the sample are accurately observed under an optical microscope, thereby selecting typical samples of reservoirs with different pore types and physical properties.

[0088] Step 2: NMR and SIP determination of sample pore background values

[0089] Figure 4 This is a schematic diagram of a device for real-time monitoring of pore evolution during carbonate karst erosion, as described in an embodiment of the present invention. Figure 4 The device is sequentially connected to a solution input receiver 1, a solution input pump 2, a one-way valve 4, an axial pressure pump 5, a solution preheating chamber 8, a sample chamber 10, a filter 12, and a solution output receiver 14. A first valve 3 connects the solution input pump 2 and the one-way valve 4; a second valve 6 connects the axial pressure pump 5 and the solution preheating chamber 8; and a third valve 13 connects the filter 12 and the solution output receiver 14. The solution preheating chamber 8 is equipped with a first temperature controller 7, and the sample chamber 10 is equipped with a second temperature controller 9 and a confining pressure controller 11.

[0090] Before the experiment, the cleaned sample was dried in a 120℃ oven for 24 hours, and then placed in... Figure 4 In the sample chamber 10 of the high-temperature, high-pressure water-rock reaction apparatus, the sample temperature is adjusted to 40°C by the second temperature controller 9, and the confining pressure in the sample chamber 10 is maintained at 1200-1600 psi (8.27-11.03 MPa) by the confining pressure controller 11. A CaCl2 solution with a salinity of 0.001 S / m is prepared and placed in the solution input receiver 1. The CaCl2 solution is input into the sample chamber 10 by the solution input pump 2. The CaCl2 solution flows in one direction only through the action of the one-way valve 4 to prevent backflow. The axial pressure is controlled at 750 psi (5.17 MPa) by the axial pressure pump 5, and the solution is input into the solution preheating chamber 8 at a flow rate of 0.05 ml / min. The temperature of the CaCl2 solution is adjusted to 40°C by the first temperature controller 7. Then, 50 ml of CaCl2 solution is injected into the sample chamber 10. Afterward, the sample is taken out for NMR and SIP measurements as background values ​​for the original porosity characteristics of the sample.

[0091] Step 3: Pore characteristics NMR and SIP tests of different batches of acid dissolution reaction

[0092] After NMR and SIP background measurements of the sample, the input solution CaCl2 was discharged through filter 12 into the solution output receiver 14 and replaced with a prepared acetic acid solution (prepared from analytical grade acetic acid reagent and distilled water, with a volume fraction of 0.2% and a pH of 3). Maintaining constant ambient temperature and pressure, 50 ml of acetic acid solution was introduced into the sample chamber at a flow rate of 0.03 ml / min to dissolve the dolomite sample. After each acid dissolution experiment using acetic acid, the sample was removed for NMR and SIP measurements. The dissolution experiment was terminated when the NMR and SIP values ​​remained stable.

[0093] Step 4: Determining the Main Controlling Factors of Pore Evolution and Pore Development in Carbonate Rocks

[0094] The pores in carbonate rocks are mainly formed by the dissolution of rock-forming minerals calcite and dolomite by different fluids during different geological periods, such as seawater and freshwater during the quasi-syngenetic period, hot brine during the burial period, organic acids during the reservoir formation period, and freshwater during the surface period. Different fluids have different effects on pores, resulting in different pore effects. By analyzing the pores formed by the dissolution of samples with different lithologies, pore sizes, and physical properties by different fluids, we can infer the main influencing factors and the main geological periods of pore formation, thus providing a basis for the formation of carbonate reservoirs and the prediction of oil and gas exploration.

[0095] Based on the above method, this invention also discloses a device for real-time monitoring of pore evolution during carbonate karst erosion. The device includes: a sample solution input unit, a sample solution processing unit, and a solution output receiver 14; wherein...

[0096] The sample solution input unit is connected to the sample solution processing unit via the second valve 6;

[0097] The sample solution processing unit is connected to the solution output receiver 14 via the third valve 13.

[0098] Furthermore, the sample solution input unit includes a solution input receiver 1, a solution input pump 2, a one-way valve 4, and an axial pressure pump 5; wherein,

[0099] The solution input receiver 1 is configured as an open port and is connected to one end of the solution input pump 2 via a pipe; the other end of the solution input pump 2 is connected to the check valve 4 via the first valve 3; one end of the check valve 4 is connected to the axial pressure pump 5.

[0100] Furthermore, the sample solution processing unit includes a solution preheating chamber 8, a sample chamber 10, and a filter 12; wherein,

[0101] One end of the solution preheating chamber 8 is connected to the sample solution processing unit via the second valve 6; the other end of the solution preheating chamber 8 is connected to one end of the sample chamber 10, and the other end of the sample chamber 10 is connected to one end of the filter 12; the other end of the filter 12 is connected to the solution output receiver 14 via the third valve 13.

[0102] Furthermore, the solution preheating chamber 8 is equipped with a first temperature controller 7; the sample chamber 10 is equipped with a second temperature controller 9 and a confining pressure controller 11.

[0103] Example

[0104] Using the method and apparatus of this invention, pore evolution simulation analysis of typical Cambrian (dolomite) carbonate rock samples from the Cambrian and Ordovician systems in the Tarim Basin and the Ordos Basin revealed that dissolution simulation based on joint NMR and SIP inversion can effectively distinguish and characterize the pore development characteristics of different pore types, physical properties, and samples. Furthermore, it can infer the main controlling factors of pore development based on different pore evolution patterns. Case studies are as follows:

[0105] Dissolution simulation experiments were conducted using plunger samples from Cambrian and Ordovician dolomite reservoirs in the Tarim Basin and the Ordovician reservoirs, respectively. Before the experiments, the porosity and permeability of the samples were measured, and the samples were lithologically identified and classified using an optical microscope. Table 1 shows the information of the selected samples. Figure 5 The images shown in Table 1 are optical microscope images of samples 1-6 selected in this invention. As shown in Table 1, samples 1-3 are tuffaceous dolomite, collected from the porous reservoir of the Lower Cambrian Xiaoerbulak Formation in the Tarim Basin. Figure 5 In portions a to c, the pores of the corresponding samples are mainly dissolution pores and intergranular dissolution pores, with visible development of solution cracks. Specifically, Figure 5 Sample a is No. 1, which is strongly eroded, mainly by dissolution pores and intergranular dissolution pores. The dissolution pores are connected by dissolution fractures. Hotan 2 well, 6495.2m; Figure 5 b is sample number 2, which is mainly composed of dissolution pores, with a small number of intergranular dissolution pores and dissolution cracks, as shown in the Shierike section; Figure 5 Sample c is sample 3, mainly composed of dissolution cavities, from the Xigou section; samples 4-6 are siliceous dolomite, collected from the Middle Ordovician Majiagou Formation porous reservoir in the Ordos Basin, such as... Figure 5 As shown in d~f, the pores of the corresponding samples are mainly intergranular dissolution pores, with a small number of dissolution cracks. Figure 5 The d value is for sample No. 4, which is mainly composed of intercrystalline dissolution pores, Tao 112 well, 3619.32m; Figure 5 Sample e is No. 5, which is mainly composed of intercrystalline and intragranular dissolution pores. The particles are bioclastic, and some pores are filled with dolomite and calcite. The red crystals in the figure are calcite stained with alizarin red. Tao 112 well, 3386.44m. Figure 5 Sample f is No. 6, with poorly developed pores and a layered structure. Calcite (red crystals in the figure) is evenly distributed among the dolomite. It is from Well Tao 112, at a depth of 3316.77 m. The helium porosity of these samples ranges from 1.82% to 11.52%, and the permeability ranges from 0.001% to 19.8 mD, classifying them as ultra-low porosity to ultra-low permeability to low porosity to low permeability samples.

[0106] Table 1 shows the sample information selected.

[0107]

[0108] Based on the steps described above, basic porosity and permeability measurements, lithological identification, and pore type identification were performed on the samples in Table 1 under a microscope. Then, according to step two, background value tests of pore characteristics were conducted on the samples. The testing instruments were:

[0109] NMR: Magritek Rock Core Analzyer nuclear magnetic resonance core analyzer, operating frequency 2MHz, test temperature 27℃; NMR test values ​​mainly include nuclear magnetic porosity, nuclear magnetic permeability, relaxation time, etc.

[0110] SIP: Ontash's SIP instrument, with a testing frequency of 0.01Hz-10000Hz and a testing temperature of 20℃; SIP test values ​​mainly include real part conductivity (σ') and imaginary part conductivity (σ”) and specific surface area at different frequencies.

[0111] In the experiment, the NMR and SIP test values ​​after passing through CaCl2 solution were recorded as "0CaCl2", and the values ​​after different numbers of acetic acid etching were recorded as "i-acid" (i = 1 to 6).

[0112] like Figure 6 and Figure 7 Under conditions of 40℃ and 5.17 MPa, respectively, the present invention Figure 5 The NMR and SIP test results of the samples after etching with CaCl2 solution and acetic acid are shown. Figure 6 In the diagrams, a to f represent the NMR transverse relaxation time distributions of samples 1-6, respectively. Figure 7 In the figure, a to f are the trends of real and imaginary conductivity of samples 1-6 as a function of different current frequencies, measured by the spectral polarization method.

[0113] Figure 6 and Figure 7 This indicates that the NMR transverse relaxation time and SIP conductivity of samples with different physical properties differ significantly. For example, samples with high porosity and high permeability have long transverse relaxation times and T2 spectra with mostly single-peak distributions; conversely, samples with low porosity and low permeability have short transverse relaxation times and T2 spectra with double-peak or triple-peak distributions. This also corresponds to different pore structure types. For pore type samples (1-3), the T2 spectra have single-peak distributions (e.g., ...). Figure 6 (a~c), 4~6 are porous type, multi-peak distribution (e.g. Figure 6 (d~f).

[0114] SIP conductivity is more sensitive to changes in porosity, permeability, pore structure and size, exhibiting more complex phenomena (such as...). Figure 7For example, sample 1, which has the best physical properties, has the highest real conductivity but a moderate imaginary conductivity. Samples 5 and 6, with lower porosity, have the highest imaginary conductivity, indicating that sample 1 has large pores and underdeveloped micropores, while samples 5 and 6 are predominantly micropores. Samples 2 and 4 have similar porosity, but sample 4 has a slightly higher real conductivity than sample 2, while sample 4 has a slightly higher imaginary conductivity. This indicates that sample 4 has more macropores than sample 2, and sample 2 has more micropores than sample 4. Therefore, although their porosity is similar, their permeability differs by an order of magnitude (e.g., ...). Figure 7 (b and e).

[0115] The trends of the real and imaginary conductivity of the SIP vary with the change of current frequency. The real conductivity of samples 1, 3, and 5 remains essentially unchanged with increasing frequency, exhibiting a stable trend. Figure 7 The values ​​of a, c, and e indicate that the macropore size distribution is uniform across the three components. Figure 5 Among samples a, c, and e, the macropore structure is simple and "rounded." The real conductivity of samples 2 and 6 decreases with increasing frequency, while the real conductivity of sample 4 increases with increasing frequency. The change in imaginary conductivity with frequency is mainly divided into two categories: sample 1 and samples 2-6. For sample 1, the imaginary conductivity decreases with increasing frequency in the 0.01–50 Hz range; in the 50–1000 Hz range, it gradually increases with increasing frequency, and the imaginary conductivity value remains relatively stable throughout the entire 0.01–1000 Hz frequency range. The imaginary conductivity values ​​of the other five samples are very small in the low-frequency range, much smaller than that of sample 1, but the conductivity values ​​increase exponentially with increasing frequency, and at high frequencies, they are all greater than those of sample 1. Figure 7 b to f. This phenomenon indicates that sample 1 is dominated by large pores, with underdeveloped small pores, and the small pores have a uniform pore size distribution. Figure 8 The graph shows the NMR background values ​​of samples 1-6 after passing through a saturated CaCl2 solution and the pore size distribution of high-pressure mercury intrusion in sample 1. Figure 8 The results show that the pores in sample 1 are mainly micron-sized, with pores having a throat radius of 1–25 μm accounting for 72.10% of the distribution and contributing 99.98% to the permeability. Although there are a small number of nano-sized pores, they are isolated and do not contribute to the storage performance.

[0116] NMR relaxation time and SIP conductivity can well reflect the pore characteristics of reservoir rocks. Table 2 shows the comparison of NMR porosity, permeability and logarithmic mean of T2 of the samples before and after the dissolution experiment. The response of the two to the pore evolution characteristics of the samples during the dissolution process is analyzed in conjunction with Table 2 as follows.

[0117] Table 2: Comparison of NMR porosity, permeability, and logarithmic mean of T2 values ​​of samples before and after the dissolution experiment

[0118]

[0119] Note: " / " indicates items that were not tested (calculated).

[0120] Dolomite

[0121] Pore ​​size distribution of sample 1 before and after etching (e.g.) Figure 6 a) All samples exhibit a unimodal distribution, but the changes differ between large and small pores. Large pores decrease in diameter after etching; small pores show a slight decrease in diameter after one acid dissolution compared to the original diameter, but an increase after 2-5 acid dissolutions; the real conductivity after etching is approximately three times that before etching (e.g., ...). Figure 7 (a and Table 2) shows that the imaginary conductivity initially decreases and then increases with increasing current frequency before etching, and then shows a continuous increasing trend after etching (e.g., ...). Figure 7 (a) From Table 2, it can be seen that the porosity of sample 1 before and after etching and the logarithmic mean of T2 are not significantly different. Except for a slight decrease in porosity after the second etching, the porosity of the other samples slightly increases after acid etching, with the increase being less than 5%. The logarithmic mean of T2 increases first after the first acid etching and then decreases continuously.

[0122] Sample No. 2 exhibited a bimodal pore size distribution before etching and a unimodal distribution after etching (e.g., ...). Figure 6 (b) Compared to the original pore size, the content of large pores decreased significantly after dissolution, while the content of small pores increased; the real conductivity after dissolution was approximately 2 to 3 times that before dissolution (e.g., Figure 7 (as shown in b and Table 2), the imaginary conductivity increases with increasing current frequency, and except after the third acid dissolution, the imaginary conductivity values ​​are all smaller than the original values ​​of the samples (e.g., ...). Figure 7 (b) The porosity of the samples did not change significantly before and after etching, but the logarithmic mean of T2 after etching was smaller than that before etching, indicating that the average pore radius of the samples showed a decreasing trend (as shown in Table 2).

[0123] Sample 3 exhibits a similar pore size evolution pattern to the first two samples before and after etching, with both showing a unimodal pore size distribution. After etching, the content of macropores significantly decreases, while the content of micropores slightly increases. The real conductivity is higher than before etching, while the imaginary conductivity, except for the first and second acid dissolutions, is lower than before etching. Unlike samples 2 and 14, in sample 3, both porosity and the logarithmic mean of T2 decrease simultaneously as etching progresses.

[0124] Rose quartz dolomite

[0125] Before and after dissolution, the pore size distribution of the powder crystal dolomite sample was multi-peaked (e.g. Figure 6(c) The evolution patterns of large and small pore sizes are basically consistent: after dissolution, the content of large pores increases, while the content of small pores decreases. The evolution of electrical conductivity, however, shows a more significant difference: after dissolution of sample 4, the real conductivity actually decreases, approximately half the value of the real conductivity before dissolution (e.g., ...). Figure 7 (d); The real conductivity of samples 5 and 6 after etching was 4-7 times that before etching (e.g., Figure 7 e Figure 7 (f and Table 2). The imaginary conductivity after dissolution shows a similar trend to that of the tuff dolomite sample No. 4, increasing with increasing current frequency. Figure 7 (d); The imaginary conductivity of samples 5 and 6 follows the opposite pattern to the first four samples, initially increasing with increasing current frequency, then rapidly decreasing when the current frequency exceeds 1000Hz (e.g., ...). Figure 7 e and Figure 7 f).

[0126] The porosity of the three samples increased significantly after etching compared to before etching. The porosity after the final acid etching increased by 33%, 22%, and 23% respectively compared to the original porosity. As etching continued, the logarithmic mean of T2 for sample 4 decreased continuously, while the logarithmic mean of T2 for samples 5 and 6 increased continuously.

[0127] Comparison of six samples from the two lithologies reveals that the pore size distribution of the tuffaceous dolomite before and after dissolution is unimodal, while that of the microcrystalline dolomite is multimodal. Except for sample 3, whose porosity after dissolution is lower than before, the porosity of the other five samples is higher after dissolution, particularly samples 4-6, where the increase in porosity is significant. Except for sample 4, the real electrical conductivity after dissolution is higher than before, increasing by approximately 2-7 times. The conductivity changes of samples 1-4 before and after dissolution show a generally consistent trend, while samples 5 and 6 show the opposite trend. These different phenomena may be controlled by the lithology, pore type, and physical properties of the samples.

[0128] As a microbial dolomite, tuffaceous dolomite's structure is controlled by microbial fabrication. Its pores are primarily framework pores and dissolution cavities formed after the organic-rich components are dissolved. These pores have large diameters, such as... Figure 5 The values ​​of a and c in 5 show a unimodal distribution; the microcrystalline dolomite is mainly composed of fine dolomite crystals, with pores consisting primarily of intercrystalline pores and intercrystalline dissolution pores. These pores are small in diameter, but after being altered by dissolution, larger dissolution pores are formed, such as... Figure 5 Therefore, the aperture is mainly distributed in a multi-peak pattern, such as d. Figure 6 Samples b, e, and f. After multiple etching processes, all six samples retained their original pore size distribution characteristics, indicating that the pore size distribution after etching was inherited.

[0129] Of the three clotted stone samples, samples 1 and 2 showed virtually no change in porosity before and after dissolution, while sample 3 exhibited a significant decrease in porosity after dissolution. The logarithmic mean of T2 for all three samples decreased after dissolution compared to before, while the real conductivity increased significantly after dissolution. Samples 1 and 3, which had high original permeability, showed a significant decrease in imaginary conductivity. This phenomenon suggests that the dissolution process may be controlled by the original pore structure: fluid flows along macropores, throats, etc.

[0130] The dominant flow channels dissolve the pore walls of macropores, making the simple and "rounded" macropores more complex by "branching," thereby adsorbing more current-carrying fluids and increasing conductivity. Figure 9 These are plunger sample photographs of samples 1-3 of this invention, combined with... Figure 2 and Figure 9 In samples 1 and 3, large-pore dissolution cavities are well-developed, with preferential dissolution occurring on the pore walls of the large pores. Subsequently, the dissolved material may precipitate in the smaller pore areas, leading to a significant decrease in the imaginary conductivity. Zhang Tianfu et al. (2009), Noiriel et al. (2009), and Fang Yang et al. (2016) used scanning electron microscopy and CT to observe the evolution characteristics of pores, cavities, and fissures before and after dissolution in carbonate rocks. They found that under the action of acidic fluids such as hydrochloric acid and acetic acid, dissolution preferentially occurs in the structural and compositional differences and energy-weak zones such as the original pores, fissures, and grain edges. Further observation revealed that the originally smooth pore walls, fissure walls, and grain surfaces become uneven under dissolution, forming secondary micropores in three-dimensional space (Noiriel et al., 2007).

[0131] Calcite and dolomite, the rock-forming minerals of carbonate rocks, exhibit different dissolution effects, but other components such as gypsum and clay minerals may also influence the formation of dissolution pores. Sample No. 1 is a gypsum-containing sample (e.g., Figure 5 a and Figure 9 (a) As the acid dissolves the sample, the internal pore volume continuously increases, but the average transverse relaxation time decreases and the conductivity increases. This suggests that the presence of gypsum on the pore wall may cause the pore size to decrease and the conductivity to increase after absorbing charged liquid. Samples 2 and 3 are field outcrops containing impurities such as clay (e.g., ... Figure 9 (b) and (c) When the acetic acid solution enters the sample, sample 2, due to its extremely low permeability, experiences a significant increase in pore volume due to the dissolution effect of acid on the clay as it expands. Under the combined influence of these two factors, both pore volume and pore size exhibit a back-and-forth increase and decrease phenomenon. In sample 3, due to the expansion of the clay component by absorbing the liquid, both pore volume and pore size decrease after acid is introduced.

[0132] The original pores in the experimental samples mainly fall into two categories: dissolution pores and intergranular dissolution pores (such as...). Figure 5 and Figure 9Table 2 shows that the logarithmic mean of T2 indicates a significant decrease in the average pore size after etching of porous samples. The maximum reduction rates for samples 1-3 after etching are 8%, 30%, and 49%, respectively. Among the porous samples, samples 5 and 6 show a significant increase in average pore size after etching, with maximum increases of 88% and 97%, respectively. Sample 4 shows a decrease in average pore size after etching, with a maximum reduction rate of 14%. As mentioned above, in the etching process, pores dominated by large pores preferentially undergo pore wall etching, while the pore body itself is not altered, but secondary small pores are formed, thus reducing the pore size and increasing conductivity. In the etching process of intergranular dissolution pores dominated by small pores, acetic acid flows mainly to the small pores under high pressure, at which point the pore body is etched, and the pore size expands. Although sample 4 is dominated by intergranular dissolution pores, its pore size is relatively large, comparable to that of porous samples (e.g., Figure 6 (a to d) Under the controlled volume of acetic acid solution in this experiment, the dissolution pattern is similar to that of the porous sample, and the overall pore size decreases.

[0133] Except for sample No. 3, the porosity of all other samples increased to varying degrees after etching, with an increase rate ranging from 0% to 33%. Samples with good original properties did not show significant improvement in properties after etching; for example, the porosity increase of sample No. 1, which had the best properties, was [missing value].

[0134] Within 5%. For samples with poor physical properties, porosity improved significantly after etching; for example, samples 5 and 6 showed a maximum increase in porosity of 23% after etching. This is because the experiment controlled the acid flow volume to -50 ml per pass. With a fixed volume, the amount of acid dissolved is constant, and for samples with high porosity, the proportion of newly dissolved volume is relatively low. Compared to porosity, the improvement in permeability after etching increases by orders of magnitude; for example, the permeability of sample 5 increased by one order of magnitude after etching, and that of sample 6 increased by three orders of magnitude. This may be because acetic acid under high pressure etches dominant channels, connecting the pore network and improving permeability. The porosity of sample 3 actually decreased after etching, possibly due to impurities such as clay in the sample swelling upon contact with water and clogging the pores.

[0135] Through case study analysis of dissolution simulations of dolomite reservoirs in the Tarim Basin and Ordos Basin, it can be concluded that:

[0136] (1) The relaxation time of nuclear magnetic resonance and the combination of the real and imaginary parts of the spectrum polarization can effectively reflect the characteristics of reservoir porosity. For example, the characterization of the porosity of clump dolomite and grain dolomite indicates that the reservoir space type of clump dolomite is pore-cavity type, and the pore structure is distributed in a single peak; the reservoir space type of grain dolomite is pore type or pore-cavity type, and the pore structure is distributed in a plateau type with multiple peaks.

[0137] (2) The simulation of carbonate karstification based on the joint inversion of nuclear magnetic resonance and spectral polarization method can effectively characterize and reveal the pore evolution law in the carbonate karstification process.

[0138] The joint inversion study based on both factors indicates that rock composition, physical properties, and reservoir space type influence pore evolution during the dissolution process. Experiments comparing different lithologies (clustered dolomite and fine-grained dolomite), different physical property differences (porosity and permeability), and different reservoir space types (pore-type, pore-fracture type, pore-cavity type) revealed that rock mineral composition has a significant controlling effect on the dissolution effect; gypsum and clay minerals are unfavorable for pore size increase during dissolution. The original physical properties of the rock also have some controlling effect on the dissolution effect, but this is weaker than the influence of rock mineral composition.

[0139] The pore size distribution of rocks has a certain controlling effect on the development of dissolution, and rock samples with a high content of large pores are conducive to the development of dissolution.

[0140] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for real-time monitoring of pore evolution during carbonate rock karstification, characterized in that, The method includes: Select samples from reservoirs with different pore types and physical properties; Introduce halogen into the sample water After solution preparation, NMR and SIP background values ​​were measured. The halogen water The solution has the following characteristics: the brine is one of CaCl2, NaCl, KCl or Na2SO4; An acid solution was input into the sample after NMR and spectral excitation polarization SIP background value tests, and NMR and SIP tests were performed to obtain the pore characteristics NMR and SIP test values ​​of different batches of acid dissolution reactions. Based on the NMR and SIP test values ​​of the pore characteristics, the evolution of pore characteristics in carbonate rocks is quantitatively characterized and the main controlling factors of pore development are determined.

2. The method according to claim 1, characterized in that, After obtaining the pore characteristic NMR and SIP test values ​​of different batches of acid dissolution reactions, the following steps are also included: The dissolution experiment ends when the NMR and SIP test values ​​remain stable.

3. The method according to claim 1, characterized in that, The specific steps for selecting reservoir samples with different pore types and physical properties are as follows: Observe the lithology and pore development characteristics of the hand specimens, and initially select representative samples; The representative sample was subjected to plunger sampling to obtain a plunger sample; The representative sample was sliced ​​into thin rock sections and made into thin rock castings. The porosity and permeability of the plunger sample were tested. Based on the rock casting thin sections, the sample pore type was classified; Based on the porosity, permeability tests and pore type classification, reservoir samples with different pore types and different physical properties were obtained.

4. The method according to claim 1, characterized in that, The input of halogen into the sample water After solution preparation, the specific steps for NMR and SIP background value testing are as follows: The sample was pretreated to obtain a purified sample; Introduce halogen into the purified sample water The solution was obtained by saturating with halogen. water The sample solution; For the saturated halogen water The sample solution was subjected to NMR and SIP background value tests.

5. The method according to claim 4, characterized in that, The halogen water The inlet flow rate of the solution is 0.01~0.1 ml / min, and the temperature is 25~40°C. C, salinity 0.001~0.01 S / m, input volume 50ml.

6. The method according to claim 1, characterized in that, The acid solution is one of acetic acid, dilute hydrochloric acid, dilute sulfuric acid, or oxalic acid.

7. A device for real-time monitoring of pore evolution during carbonate karst erosion, used to implement the method described in any one of claims 1-6, characterized in that, The device includes: a sample solution input unit, a sample solution processing unit, and a solution output receiver (14); wherein... The sample solution input unit is connected to the sample solution processing unit via the second valve (6); The sample solution processing unit is connected to the solution output receiver (14) via a third valve (13).

8. The apparatus according to claim 7, characterized in that, The sample solution input unit includes a solution input receiver (1), a solution input pump (2), a one-way valve (4), and an axial pressure pump (5); wherein, The solution input receiver (1) is set to be open and connected to one end of the solution input pump (2) through a pipe; the other end of the solution input pump (2) is connected to the check valve (4) through the first valve (3); one end of the check valve (4) is connected to the axial pressure pump (5).

9. The apparatus according to claim 7, characterized in that, The sample solution processing unit includes a solution preheating chamber (8), a sample chamber (10), and a filter (12); wherein, One end of the solution preheating chamber 8 is connected to the sample solution processing unit via a second valve (6); the other end of the solution preheating chamber (8) is connected to one end of the sample chamber (10), and the other end of the sample chamber (10) is connected to one end of the filter (12); the other end of the filter (12) is connected to the solution output receiver (14) via a third valve (13).

10. The apparatus according to claim 9, characterized in that, The solution preheating chamber (8) is equipped with a first temperature controller (7); the sample chamber (10) is equipped with a second temperature controller (9) and a confining pressure controller (11).

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