A method and simulation device for quantitatively evaluating the sweep range and oil displacement efficiency of carbon dioxide and carbon dioxide assisted by heat in a tight reservoir

Abstract

The present application belongs to the technical field of oil and gas field development engineering, and particularly relates to a method and a simulation device for quantitatively evaluating the sweep range and oil washing efficiency of carbon dioxide and heat-assisted carbon dioxide in a tight reservoir. The quantitative evaluation method comprises the following steps: (1) constructing a long core simulation model; (2) collecting initial axial HSE signals and T2 maps of all cores in the long core simulation model; (3) simulating the injection of CO2 by using a device and calculating the volume of CO2 injected into the long core simulation model; (4) performing one round of huff and puff and collecting data; (5) if multiple rounds of huff and puff experiments are required, repeating steps (3) to (4); and (6) analyzing the sweep range and oil washing characteristics of CO2 in each huff and puff round. The quantitative evaluation method realizes the accurate characterization of the percolation behavior of CO2 and heat-mass enhanced CO2 in a tight reservoir, and provides important technical support for the efficient development of tight oil reservoirs.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of oil and gas field development engineering, and particularly relates to a method and a simulation device for quantitatively evaluating the sweep range and oil washing efficiency of carbon dioxide and heat-assisted carbon dioxide in a dense reservoir. BACKGROUND

[0002] Carbon dioxide enhanced oil recovery (CO2-EOR) is a technology for improving the efficiency of oil displacement from reservoir rocks and increasing the recovery ratio by injecting carbon dioxide into an oil reservoir and utilizing the physical and chemical effects of CO2 and crude oil to improve the flowability of crude oil. Due to its unique supercritical characteristics, it can have both gas diffusion ability and liquid solubility; at the same time, it also has environmental advantages and is recognized as the most potential development method for tight oil reservoirs.

[0003] In view of the percolation behavior of CO2 in a dense reservoir, current research mainly uses core displacement experiments combined with CT scanning or nuclear magnetic resonance technology for characterization. Although the existing method can obtain macroscopic recovery data, it generally has the following limitations:

[0004] (1) The experimental model mostly uses single matrix cores or simple fractured cores, which is difficult to truly reflect the complex fracture-matrix coupled percolation characteristics in the field.

[0005] (2) Most studies only focus on the production degree at different throughput cycles, lack systematic analysis of the extension of sweep range and the attenuation of oil washing efficiency in the multi-cycle throughput process, and cannot quantitatively characterize the longitudinal sweep range and oil washing efficiency of CO2, lacking the ability to predict the risk of channeling.

[0006] In addition, the existing technical system still has significant deficiencies in the understanding of the mechanism of heat-mass composite CO2 huff and puff, quantitative evaluation of development effect, etc., which seriously restricts the large-scale application of the technology in dense reservoirs. SUMMARY

[0007] Based on the fact that the current research on CO2 huff and puff in tight reservoirs mainly focuses on experimental research using short cores, and lacks quantitative characterization of the range of mobilized oil and oil washing efficiency of CO2 under the action of CO2 huff and puff and heat-mass synergy, the present application innovatively provides a method and a simulation device for quantitatively evaluating the sweep range and oil washing efficiency of carbon dioxide and heat-assisted carbon dioxide in tight reservoirs. The quantitative evaluation method fully considers the actual fracturing situation of the tight reservoir, constructs and characterizes a long core model of tight sandstone oil and gas seepage during development, evaluates the CO2 mobilization range and oil washing capacity under different development modes by simulating the actual CO2 huff and puff and heat-assisted CO2 huff and puff process, fills the gap in the prior art that lacks quantitative characterization of the range of mobilized oil and oil washing efficiency of CO2, and at the same time, the evaluation method can quantitatively study the heat-mass action enhanced CO2 diffusion coefficient and oil washing capacity, filling the gap in the current heat-assisted CO2 recovery technology for tight reservoirs that cannot provide experimental basis and data support.

[0008] The present application innovatively proposes an experimental method combining nuclear magnetic resonance experimental technology and fracture-matrix equivalent simulation, realizes precise characterization of the seepage behavior of CO2 and heat-mass enhanced CO2 in tight reservoirs by establishing quantitative evaluation indexes such as sweep efficiency, oil washing efficiency and sweep uniformity index, and provides important technical support for efficient development of tight oil reservoirs.

[0009] The specific technical solutions are as follows:

[0010] A method for quantitatively evaluating the sweep range and oil washing efficiency of carbon dioxide and heat-assisted carbon dioxide in tight reservoirs, comprising the following steps:

[0011] (1) Constructing a long core simulation model:

[0012] S1, first, select a plurality of geological cores of the tight reservoir according to the actual needs of the experiment, clean the cores with an organic solvent to remove residual oil and oil stains of the crude oil. The matrix cores described below are selected from the plurality of geological cores.

[0013] Then, measure and record the corresponding basic physical parameters of each selected geological core, including length l , diameter d , porosity φ 1 and gas permeability K 1.

[0014] S2, obtain the actual fracture data on site, including fracture length, fracture width, fracture conductivity and other data. The actual fracture data on site can be obtained by microseismic data inversion or fracturing simulation by Petrel numerical simulation software.

[0015] S3, due to the fracture with proppant conductivity is high, oil and gas seepage capacity is strong, the injection fluid in this part is mainly for horizontal spread, therefore, the present application focuses on the longitudinal spread and oil washing process of the injection fluid in the part without proppant fracture and microfracture matrix part. Among them, the microseismic data inversion or Petrel numerical simulation software fracture model can distinguish and obtain the part without proppant fracture and microfracture matrix part. And the matrix seepage length is equivalent to the drainage radius of the single well flow unit of the fracture, and its calculation method refers to the "fracture single well control reserve calculation method and process" disclosed in the patent CN113177322A.

[0016] Among them, the length conversion formula of each part in the long core simulation model is shown in formula (1):

[0017] (1);

[0018] In the formula, α Length ratio coefficient, m·cm -1 ;

[0019] L f Unpropped fracture length in the field, m;

[0020] L m Matrix seepage length, m;

[0021] L c Total length of long core simulation model, cm; select appropriate total length of long core simulation model according to actual needs of experiment;

[0022] L ef Total length of fracture core in long core simulation model, cm;

[0023] L em Total length of matrix core in long core simulation model, cm.

[0024] S4, first, according to the total length of fracture core and the total length of matrix core in the long core simulation model obtained by calculation, and combining the size requirement range of the sample by nuclear magnetic resonance test, the specified length of each geological core is determined; select appropriate geological core from the several geological cores obtained in S1 and cut into specified length. In order to facilitate subsequent nuclear magnetic resonance test, the length of each core is generally controlled in 5-7cm.

[0025] Then, fractures were created in the geological cores selected for the long core simulation model using wire cutting or Barcol splitting methods, ensuring that the permeability of each fractured core was consistent with the actual permeability of the fractures in the field. The permeability of the fractured cores was measured using nitrogen or helium gas after fracture creation, yielding the gas permeability of each fractured core after fracture creation. K cf The formula for calculating gas permeability is based on the "Experimental method and apparatus for evaluating the energy enhancement and permeability improvement effect of thermally assisted carbon dioxide huff and puff after fracturing in shale oil reservoirs" disclosed in patent CN119901879A.

[0026] The actual permeability of the cracks on site is calculated using the formula shown in equation (2):

[0027] (2);

[0028] In the formula, K f —Actual permeability of the actual cracks on site, mD;

[0029] C f —Crack conductivity, mD·m; this data is obtained through the aforementioned S2.

[0030] W f — Crack width, m; this data is obtained through the aforementioned S2.

[0031] S5. The fractured core and matrix core were combined and sorted using the harmonic averaging method, and the calculation formula is shown in equation (3):

[0032] (3);

[0033] In the formula, —The harmonic mean permeability of the corresponding core sample, in mD;

[0034] L —Total length of the corresponding core sample, in cm;

[0035] L i —No. i The length of the corresponding core sample, in cm;

[0036] K i —No. i The permeability of the corresponding core sample, in mD.

[0037] The corresponding core refers to the type of core used in the calculation (the fractured core or matrix core mentioned above). For example, when calculating the harmonic average permeability of the fractured core in the long core simulation model, then...L = L ef , cm; L i is the designated length of the first i block of fractured core, cm; K i is the permeability of the first i block of fractured core, obtained from S4 above.

[0038] When calculating the harmonic average permeability of matrix core in a long core simulation model, then L = L em , cm; L i is the designated length of the first i block of matrix core, cm; K i is the permeability of the first i block of matrix core, obtained from S1 above, i.e. the gas measured permeability corresponding to the first i block of matrix core K 1.

[0039] The value of the fractured core calculated from equation (3) is compared with the permeability of all fractured cores, and the fractured core with the smallest absolute difference between the permeability and the value of is placed at the end of all fractured cores. Then, the remaining all fractured cores are recalculated according to equation (3) to obtain a new value of, and the newly obtained value of is compared with the remaining fractured cores, and the fractured core with the smallest absolute difference between the permeability and the newly obtained value of is placed at the second end of all fractured cores, and so on, to arrange all the fractured cores.

[0040] The value of the matrix core calculated from equation (3) is compared with the permeability of all matrix cores, and the matrix core with the smallest absolute difference between the permeability and the value of is placed at the end of all matrix cores. Then, the remaining all matrix cores are recalculated according to equation (3) to obtain a new value of, and the newly obtained value of is compared with the remaining matrix cores, and the matrix core with the smallest absolute difference between the permeability and the newly obtained value of is placed at the second end of all matrix cores, and so on, to arrange all the matrix cores.

[0041] The value of the fractured core calculated from equation (3) is compared with the permeability of all fractured cores, and the fractured core with the smallest absolute difference between the permeability and the value of is placed at the end of all fractured cores. Then, the remaining all fractured cores are recalculated according to equation (3) to obtain a new value of, and the newly obtained value of is compared with the remaining fractured cores, and the fractured core with the smallest absolute difference between the permeability and the newly obtained value of is placed at the second end of all fractured cores, and so on, to arrange all the fractured cores.

[0042] The value of the matrix core calculated from equation (3) is compared with the permeability of all matrix cores, and the matrix core with the smallest absolute difference between the permeability and the value of is placed at the end of all matrix cores. Then, the remaining all matrix cores are recalculated according to equation (3) to obtain a new value of, and the newly obtained value of is compared with the remaining matrix cores, and the matrix core with the smallest absolute difference between the permeability and the newly obtained value of is placed at the second end of all matrix cores, and so on, to arrange all the matrix cores. ​​​​​​

[0043] Finally, all the fracture cores are placed in the front end of the arranged matrix cores according to the principle of fracture core placement in the front end of matrix core, and the required long core simulation model is constructed.

[0044] (2) Collect the initial axial HSE signal and T2 spectrum of all cores in the long core simulation model:

[0045] First, all the cores in the long core simulation model are vacuumed and saturated with experimental simulation oil.

[0046] Then, using the GR-HSE pulse sequence and CPMG pulse sequence of the nuclear magnetic resonance device, the initial axial HSE signal and T2 spectrum of all cores are collected in the order arranged in step (1) S5.

[0047] (3) Use the device to simulate the injection of CO2 and calculate the volume of CO2 injected into the long core simulation model:

[0048] First, add filter paper in the middle of each core in the long core simulation model to eliminate end effect, and then place them in the core holder in turn, and the end of the core holder is filled with experimental simulation oil.

[0049] Then, according to the actual needs of the experiment, stop after injecting CO2 gas for a period of time, record the initial pressure of CO2 gas P o , the initial volume of CO2 gas V o , the end pressure of CO2 gas injection P a and the displacement pump injection volume V i .

[0050] The amount of CO2 injected into the long core simulation model is calculated by the following formula (4):

[0051] (4);

[0052] In the formula, n o — CO2 original total amount, mol;

[0053] P o — CO2 gas initial pressure, MPa;

[0054] V o — CO2 gas initial volume, mL;

[0055] Z o—Compressibility factor of CO2 gas at initial temperature and pressure, dimensionless;

[0056] R —Molar gas constant, J / (mol·K);

[0057] T o —Initial temperature of CO2 gas, K;

[0058] n a —Amount of CO2 substance remaining at the end of injection, mol;

[0059] P a —End pressure of CO2 gas injection, MPa;

[0060] V a —Volume of CO2 gas remaining at the end of injection, mL;

[0061] Z a —Compressibility factor of CO2 gas at end temperature and pressure of injection, dimensionless;

[0062] T a —End temperature of CO2 gas injection, K;

[0063] n d —Amount of CO2 substance in the volume of the front-end pipeline of the long core holder, mol;

[0064] V d —Volume of the front-end pipeline of the long core holder, mL;

[0065] V i —Pumping volume of the displacement pump, mL;

[0066] n i —Amount of CO2 substance injected into the long core simulation model, mol.

[0067] wherein the volume of the front-end pipeline of the long core holder is V d The measurement is performed in the following manner:

[0068] A columnar iron block with no permeability is placed in the long core holder, and CO2 gas is injected into the long core holder at constant pressure. When the overall pressure is stable, the pumping volume of the displacement pump is the volume of the front-end pipeline of the long core holder V d .

[0069] Finally, the volume of CO2 injected into the long core simulation model under any temperature and pressure conditions can be solved, and the calculation formula is shown in equation (5): n i The volume of CO2 injected into the long core simulation model under any temperature and pressure conditions can be solved, and the calculation formula is shown in equation (5):

[0070] (5);

[0071] In the formula, V s — CO2 gas volume under simulated temperature and pressure conditions, mL;

[0072] n i — CO2 material injected into the long core simulation model, mol;

[0073] Z s — CO2 gas compression factor under simulated temperature and pressure conditions, dimensionless;

[0074] R — molar gas constant, J / (mol·K);

[0075] T s — simulated temperature, K;

[0076] P s — simulated pressure, MPa.

[0077] (4) Perform a round of huff and puff and collect data:

[0078] First, soak the well; if the simulation is hot assisted CO2 huff and puff, heat the device to the specified temperature and then soak the well;

[0079] Then, after soaking is completed, return the fluid to atmospheric pressure, and sequentially remove the cores in the order arranged in step (1) S5, and mark the inlet and outlet end faces of the cores;

[0080] Finally, use the GR-HSE pulse sequence and CPMG pulse sequence of the nuclear magnetic resonance device to sequentially collect the axial HSE signals and T2 maps corresponding to all cores after a round of huff and puff.

[0081] (5) If multiple rounds of huff and puff experiments are required, repeat steps (3)-(4) above.

[0082] (6) Analyze the sweep range and oil washing characteristics of CO2 in each huff and puff round:

[0083] a. Calculate the CO2 sweep efficiency in each huff and puff round, and the calculation formula is shown in equation (6):

[0084] (6);

[0085] wherein, η s — CO2 sweep efficiency of each huff and puff cycle, %;

[0086] L Hi — sum of initial T2 map signal values of all cores in the long core simulation model, dimensionless. i — length of HSE signal attenuation of the block core, cm.

[0087] d i — diameter of the block core in the long core simulation model, cm. i

[0088] φ i — porosity of the block core in the long core simulation model, %. i

[0089] i — length of the corresponding core, cm. L i

[0090] wherein, the core diameter and core porosity of formula (6) are the basic physical parameters of the selected geological core measured by S1 in step (1).

[0091] b. calculate the CO2 oil washing efficiency of each huff and puff cycle, which is calculated according to formula (7):

[0092] (7);

[0093] wherein, η w — CO2 oil washing efficiency of each huff and puff cycle, %.

[0094] T 2o — sum of initial T2 map signal values of all cores in the long core simulation model, dimensionless.

[0095] T 2a — sum of T2 map signal values of all cores after huff and puff in the long core simulation model, dimensionless.

[0096] η s — CO2 sweep efficiency of each huff and puff cycle, %.

[0097] ​​​c. The sweep efficiency spread rate is used to evaluate the spread capability of CO2 in each throughput round. Its calculation formula is shown in equation (8):

[0098] (8);

[0099] In the formula, D s —Sweep efficiency expansion rate, %

[0100] η sn —No. n CO2 spillover efficiency per round, %

[0101] η s(n+1) —No. n +1 round CO2 spillover efficiency, %.

[0102] d. The washing efficiency decay rate is used to evaluate the decreasing trend of CO2 washing capacity in each throughput cycle. Its calculation formula is shown in equation (9):

[0103] (9);

[0104] In the formula, D w —Energy washing efficiency reduction rate, %

[0105] η wn —No. n CO2 washing efficiency per cycle, %

[0106] η w(n+1) —No. n +1 round of CO2 oil washing efficiency, %.

[0107] e. The sweep uniformity index is used to evaluate the sweep uniformity of CO2 in shale reservoirs and the uniformity of oil washing, and can be used to determine the occurrence of gas channeling and other behaviors. The higher the sweep uniformity index, the more uniform the CO2 sweep uniformity; if the sweep uniformity index is significantly less than 1, it indicates that channeling has occurred in some areas. Its calculation formula is shown in equation (10):

[0108] (10);

[0109] In the formula, I u —The uniformity of the wave is dimensionless;

[0110] η w —CO2 wash efficiency per churn, %

[0111] I i The sweep efficiency evaluation index is %.

[0112] The sweep efficiency evaluation index is %. I i The oil displacement efficiency is defined as the oil displacement efficiency under the condition of complete uniform sweep and no gas channeling. Generally, the average oil displacement efficiency measured by the CO2 huff and puff experiment of each core is taken, and the definition can be considered as directly representing the oil displacement effect under the ideal uniform sweep state.

[0113] A simulation device for the quantitative evaluation method of the sweep range and oil displacement efficiency of carbon dioxide and heat-assisted carbon dioxide in a tight reservoir, comprising a CO2 gas cylinder, a CO2 gas container, an oil container, a low-field nuclear magnetic resonance device and a long core holder placed in a thermostat.

[0114] The CO2 gas cylinder is connected with the gas pressurizing pump through a pipeline and a two-way valve No. 1; the gas pressurizing pump is connected with the left port of a three-way valve No. 1 through a pipeline and a two-way valve No. 2; the lower port of the three-way valve No. 1 is connected with the top end of the CO2 gas container through a pipeline; the bottom end of the CO2 gas container is connected with a displacement pump No. 1 through a pipeline and a two-way valve No. 3; the upper port of the three-way valve No. 1 is connected with the left port of a three-way valve No. 2 through a pipeline and a two-way valve No. 4, and a pressure gauge No. 1 is arranged on the pipeline segment between the upper port of the three-way valve No. 1 and the two-way valve No. 4; the lower port of the three-way valve No. 2 is connected with a vent valve; the right port of the three-way valve No. 2 is connected with the left end of the long core holder; the fracture core and the matrix core are placed in the long core holder; the top of the long core holder is connected with a hand pump through a pipeline and a two-way valve No. 5, and a pressure gauge No. 3 is arranged on the pipeline segment between the top of the long core holder and the two-way valve No. 5; the right end of the long core holder is connected with the top of the oil container through a pipeline and a two-way valve No. 6, and a pressure gauge No. 4 is arranged on the pipeline segment between the right end of the long core holder and the two-way valve No. 6; the bottom of the oil container is connected with a displacement pump No. 2 through a pipeline and a two-way valve No. 7.

[0115] The method for quantitatively evaluating the sweep range and oil displacement efficiency of carbon dioxide and heat-assisted carbon dioxide in a tight reservoir solves the problem of the lack of quantitative characterization of the CO2 sweep range and oil displacement efficiency in the prior art. Based on the dynamic acquisition of the core axial HSE signal and T2 spectrum by the nuclear magnetic resonance technology, a multi-dimensional quantitative evaluation system of the sweep efficiency, the oil displacement efficiency, the sweep efficiency expansion rate, the oil displacement efficiency attenuation rate and the sweep uniformity index is first established by combining the corresponding calculation formula, and the dynamic behavior of CO2 in the unpropped fracture and the matrix is accurately quantified.

[0116] Meanwhile, through multiple rounds of throughput experiments (dynamically tracking sweepout rate, oil displacement rate and sweepout uniformity index), the CO2 channeling law and oil displacement capacity reduction characteristics are revealed, the limitation of traditional single displacement experiment is broken through, standardized experiment support is provided for CO2 throughput scheme design in the field, and theoretical innovation and engineering application value are combined. BRIEF DESCRIPTION OF DRAWINGS

[0117] Figure 1 The schematic diagram of the simulation device used in the quantitative evaluation method of the present application.

[0118] Among them, 1 is a CO2 cylinder, 2 is a two-way valve No. 1, 3 is a gas pressure pump, 4 is a two-way valve No. 2, 5 is a three-way No. 1, 6 is a CO2 gas container, 7 is a two-way valve No. 3, 8 is a displacement pump No. 1, 9 is a pressure gauge No. 1, 10 is a two-way valve No. 4, 11 is a three-way No. 2, 12 is a vent valve, 13 is a pressure gauge No. 2, 14 is a thermostat, 15 is a long core holder, 16 is a fracture core, 17 is a matrix core, 18 is a low-field nuclear magnetic resonance device, 19 is a pressure gauge No. 3, 20 is a two-way valve No. 5, 21 is a hand pump, 22 is a pressure gauge No. 4, 23 is a two-way valve No. 6, 24 is an oil container, 25 is a two-way valve No. 7, and 26 is a displacement pump No. 2.

[0119] Figure 2 The initial HSE signal curve of the No. 1-4 core collected in step (2) of the quantitative evaluation method of Example 2.

[0120] Figure 3 The initial T2 spectrum of the No. 1-4 core collected in step (2) of the quantitative evaluation method of Example 2.

[0121] Figure 4 The HSE signal curve of the No. 1-4 core measured in steps (4) and (5) of the quantitative evaluation method of Example 2 for different throughput rounds (first round, second round, third round) of thermal-assisted CO2 throughput.

[0122] Figure 5 The T2 spectrum of the No. 1-4 core measured in step (4) of the quantitative evaluation method of Example 2 for the first throughput round of thermal-assisted CO2 throughput.

[0123] Figure 6 The T2 spectrum of the No. 1-4 core measured in step (5) of the quantitative evaluation method of Example 2 for the second throughput round of thermal-assisted CO2 throughput.

[0124] Figure 7 The T2 spectrum of the No. 1-4 core measured in step (5) of the quantitative evaluation method of Example 2 for the third throughput round of thermal-assisted CO2 throughput. DETAILED DESCRIPTION

[0125] The technical solutions of the present application will be described in detail below with reference to the accompanying drawings.

[0126] Embodiment 1

[0127] The simulation device for the method for quantitatively evaluating the sweep range and oil displacement efficiency of carbon dioxide and heat-assisted carbon dioxide in a dense reservoir comprises a CO2 gas cylinder 1, a CO2 gas container 6, an oil container 24, a low-field nuclear magnetic resonance device 18 and a long core holder 15 placed in a thermostat 14.

[0128] The CO2 gas cylinder 1 is connected with a gas pressurizing pump 3 through a pipeline and a two-way valve No. 1 2. The gas pressurizing pump 3 is connected with a left port of a three-way valve No. 1 5 through a pipeline and a two-way valve No. 2 4. A lower port of the three-way valve No. 1 5 is connected with a top end of the CO2 gas container 6 through a pipeline. A bottom end of the CO2 gas container 6 is connected with a displacement pump No. 1 8 through a pipeline and a two-way valve No. 3 7. An upper port of the three-way valve No. 1 5 is connected with a left port of a three-way valve No. 2 1 1 through a pipeline and a two-way valve No. 4 1 0. A pressure gauge No. 1 9 is arranged on a pipeline segment between the upper port of the three-way valve No. 1 5 and the two-way valve No. 4 1 0. A lower port of the three-way valve No. 2 1 1 is connected with a vent valve 1 2. A right port of the three-way valve No. 2 1 1 is connected with a left end of the long core holder 1 5. The long core holder 1 5 is placed with a fracture core 1 6 and a matrix core 1 7. A top part of the long core holder 1 5 is connected with a hand pump 2 1 through a pipeline and a two-way valve No. 5 2 0. A pressure gauge No. 3 1 9 is arranged on a pipeline segment between the top part of the long core holder 1 5 and the two-way valve No. 5 2 0. A right end of the long core holder 1 5 is connected with a top part of the oil container 2 4 through a pipeline and a two-way valve No. 6 2 3. A pressure gauge No. 4 2 2 is arranged on a pipeline segment between the right end of the long core holder 1 5 and the two-way valve No. 6 2 3. A bottom part of the oil container 2 4 is connected with a displacement pump No. 2 2 6 through a pipeline and a two-way valve No. 7 2 5.

[0129] In use, the fracture core 1 6 and the matrix core 1 7 saturated with the experimental simulation oil are tested by the low-field nuclear magnetic resonance device 1 8 for GR-HSE pulse sequence and CPMG pulse sequence to obtain the initial HSE signal and T2 spectrum of the cores, and then are placed in the long core holder 1 5 in the order, wherein filter paper is placed between each core to eliminate end effect.

[0130] The two-way valve No. 6 2 3 and the two-way valve No. 7 2 5 are opened, and the experimental simulation oil in the oil container 2 4 is displaced into the pipeline at the end of the long core holder 1 5 by the displacement pump No. 2 2 6, and then the two-way valve No. 6 2 3 and the two-way valve No. 7 2 5 are closed.

[0131] The two-way valve No. 5 2 0 is opened, and the confining pressure of the long core holder 1 5 is applied by the hand pump 2 1, and the pressure value can be read by the pressure gauge No. 3 1 9.

[0132] Open two-way valve 1 No. 2 and two-way valve 2 No. 4, use gas pressurizing pump 3 to pressurize the gas in CO2 cylinder 1 into CO2 gas container 6, then close two-way valve 1 No. 2 and two-way valve 2 No. 4.

[0133] Open two-way valve 3 No. 7, use displacement pump 1 No. 8 to keep the gas pressure in CO2 gas container 6 constant to the experimental pressure, the pressure value can be read by pressure gauge 1 No. 9, then open two-way valve 4 No. 10 to inject CO2 gas for a period of time, and then close two-way valve 4 No. 10 to carry out huff and puff. Open thermostat 14 to heat the long core system to the specified temperature during the huff and puff.

[0134] After the huff and puff, use vent valve 12 to flow back the fluid to atmospheric pressure, use hand pump 21 to unload the confining pressure of long core holder 15, then take out fracture core 16 and matrix core 17 in turn and mark the inlet and outlet end faces, use low-field nuclear magnetic resonance equipment 18 to carry out GR-HSE pulse sequence and CPMG pulse sequence test, obtain the HSE signal and T2 map of the core after one round of thermal assisted CO2 huff and puff.

[0135] If multiple rounds of huff and puff are required, place the cores in the long core holder 15 in turn again according to the sequence, apply confining pressure, then carry out injection, huff and puff and flow back, which is consistent with the above description and will not be repeated here.

[0136] Place a columnar iron block with no permeability capacity in long core holder 15, use hand pump 21 to apply confining pressure to long core holder 15, the pressure value can be read by pressure gauge 3 No. 19, then use displacement pump 1 No. 8 to displace CO2 in CO2 gas container 6 into the front pipeline of long core holder 15, when the overall pressure is stable, record the injection amount of displacement pump 1 No. 8 for subsequent CO2 injection amount calculation.

[0137] Example 2

[0138] The application will be further described below through specific application examples:

[0139] The device used to carry out the experiment is shown in Figure 1 . The specific experimental steps are as follows:

[0140] (1) Construct a long core simulation model:

[0141] The core samples in this example are taken from M block of Xinjiang Oilfield, which is a typical tight conglomerate reservoir. Mix petroleum ether and ethanol at a volume ratio of 1:1 to form a machine solvent to clean the geological cores, remove residual oil and oil stains inside the cores. Then measure the length l , diameter d , porosity φ 1 and gas permeability KThe basic physical property parameters of 1 are shown in Table 1.

[0142] Table 1: Core basic physical property table

[0143]

[0144] According to the seismic inversion and actual geological data of the M block of Xinjiang Oilfield, the average length of the unsupported fracture of the M1 well in the block is about 25 m, the average width of the unsupported fracture is about 0.4 m, and the flow conductivity of the unsupported fracture is about 4-6 mD·m. The matrix seepage radius is about 25.5 m. Therefore, it is considered that the length of the unsupported fracture of the well is L f approximately equal to the matrix seepage length L m , both of which are 25 m.

[0145] The total length of the long core simulation model in this embodiment is L c 26 cm, and the length ratio coefficient α can be calculated according to formula (1) .

[0146] The total length of the fracture core in the long core simulation model is L ef 13 cm, and the total length of the matrix core in the long core simulation model is L em 13 cm.

[0147] According to formula (2) , the actual permeability of the actual unsupported fracture in the field can be calculated to be about 10-15 mD.

[0148] Since the lengths of the fracture core and the matrix core exceed the size range of the nuclear magnetic resonance test, the fracture core part and the matrix core part are each divided into two cores with lengths of 5 cm and 8 cm, as shown in Table 1.

[0149] The samples of core numbers 1 and 2 are selected to form fractures by the Brazilian splitting method. The cores after fracture formation are measured for permeability using nitrogen or helium gas, and the gas measurement permeability of each fracture core after fracture formation is K cf , which is approximately the same as the actual unsupported fracture permeability.

[0150] The final basic physical property parameters of each core in the long core simulation model of this embodiment are shown in Table 2.

[0151] Table 2: Division of fracture core and matrix core and basic physical property table

[0152]

[0153] S5, according to the permeability data of the fractured core and matrix core shown in Table 2, the harmonic average permeability of the fractured core and the harmonic average permeability of the matrix core are calculated respectively by using formula (3).

[0154] (3);

[0155] Through calculation, the harmonic average permeability of the fractured core is 12.481 mD, and the harmonic average permeability of the matrix core is 0.9478 mD.

[0156] Comparing the calculated harmonic average permeability of the fractured core with the permeability of the fractured core No. 1 and the permeability of the fractured core No. 2 respectively, it can be seen that the fractured core No. 2 is closest to the calculated harmonic average permeability of the fractured core, so the fractured core No. 2 is arranged at the end of the fractured core No. 1.

[0157] Comparing the calculated harmonic average permeability of the matrix core with the permeability of the matrix core No. 3 and the permeability of the matrix core No. 4 respectively, it can be seen that the matrix core No. 4 is closest to the calculated harmonic average permeability of the matrix core, so the matrix core No. 4 is arranged at the end of the matrix core No. 3.

[0158] According to the principle that the fractured core is placed at the front end of the matrix core, the arrangement order of the long core simulation model of the embodiment is in turn core No. 1, core No. 2, core No. 3 and core No. 4.

[0159] (2) Collect the initial axial HSE signal and T2 spectrum of all cores in the long core simulation model:

[0160] First, after vacuumizing the cores No. 1-4 for 4h, saturate them with experimental simulation oil at a pressure of 30MPa for 4 days.

[0161] Then, use the low-field nuclear magnetic resonance device 18 to test the GR-HSE pulse sequence and the CPMG pulse sequence, and according to the arrangement order core No. 1→core No. 2→core No. 3→core No. 4, collect and obtain the initial HSE signal (as shown in Figure 2 ) and T2 spectrum (as shown in Figure 3 ) of cores No. 1-4 in turn.

[0162] (3) Simulate the injection of CO2 by using the device and calculate the volume of CO2 injected into the long core simulation model:

[0163] First, the impermeable iron block is placed in the long core holder 15, the hand pump 21 is used to apply 20 MPa confining pressure to the long core holder 15, and then the displacement pump No. 1 8 is used to keep the CO2 in the CO2 gas container 6 at a constant pressure of 15 MPa, and then the displacement pump No. 1 8 is used to displace the CO2 into the front-end pipeline of the long core holder 15. When the overall pressure is stabilized at 15 MPa, the injection volume of the displacement pump No. 1 8 is 2.8 mL, and thus the volume of the front-end pipeline of the long core holder 15 is V d 2.8 mL.

[0164] Then, the cores No. 1-4 are placed in the long core holder 15 in the order of core No. 1, core No. 2, core No. 3 and core No. 4 from the inlet end to the outlet end, and filter paper is added in the middle of each core to eliminate the end effect.

[0165] The two-way valve No. 6 23 and the two-way valve No. 7 25 are opened, and the experimental simulation oil in the oil container 24 is displaced into the end pipeline of the long core holder 15 by using the displacement pump No. 2 26, and then the valves are closed.

[0166] The hand pump 21 is used to apply 20 MPa confining pressure to the long core holder 15.

[0167] The gas pressurizing pump 3 and the displacement pump No. 1 8 are used to keep the CO2 in the CO2 gas container 6 at a constant pressure of 15 MPa, and then the two-way valve No. 4 10 is opened to inject the CO2 for 30 min, and then the injection is stopped.

[0168] The initial pressure of the CO2 gas is recorded P o 15.5 MPa, the initial volume of the CO2 gas is V o 100 mL, the end pressure of the CO2 gas injection is P a 15.1 MPa, and the injection volume of the displacement pump is V i 2.824 mL.

[0169] According to formula (4), the residual volume of the CO2 gas at the end of the injection is V a = V o - V i = 100 - 2.824 = 97.176 mL.

[0170] The compressibility factor of the CO2 gas under the initial temperature and pressure condition is Z o 0.3038, the initial temperature of the CO2 gas is T o 293.15 K, and the compressibility factor of the CO2 gas under the temperature and pressure condition at the end of the injection isZ a 0.3038, the CO2 gas injection end temperature T a 293.15 K.

[0171] The simulation temperature is calculated by formula (4) and formula (5) T s T a 293.15 K, Z s Z a 0.3038, the simulation pressure P s P a The CO2 gas volume injected into the long core simulation model under 15.1 MPa V s 2.673 mL, about 0.2 times the core pore volume.

[0172] (4) One round of huff and puff is performed and data is collected:

[0173] First, the long core system pressure is heated to 110°C in the thermostat 14, and the well is soaked for 3 hours.

[0174] Then, after the soaking is completed, the fluid is returned to atmospheric pressure by the vent valve 12, the confining pressure of the long core holder 15 is unloaded, and then the fractured core 16 and the matrix core 17 are taken out in turn and the inlet and outlet end faces are marked.

[0175] Finally, after the core sample is naturally cooled to room temperature, the GR-HSE pulse sequence and CPMG pulse sequence test are performed by the low-field nuclear magnetic resonance device 18, and the HSE signal and T2 map of the first round of thermal assisted CO2 huff and puff of the cores 1-4 are collected in the order of core 1→core 2→core 3→core 4, as shown in Figure 4 and Figure 5 .

[0176] (5) The repeated experiments according to steps (3)-(4) of the embodiment are performed to test the data of the second and third rounds of thermal assisted CO2 huff and puff, wherein the HSE signals of the second and third rounds of thermal assisted CO2 huff and puff of the cores are as shown in Figure 4 , and the T2 maps are as shown in Figure 6 and Figure 7 .

[0177] (6) The sweep range and oil washing characteristics of CO2 in each huff and puff round are analyzed:

[0178] a, the CO2 sweep efficiency in each huff and puff round is calculated:​​​

[0179] Firstly, by Figure 4 It can be concluded that the length of HSE signal attenuation of No. 1 core under the first throughput round is 5 cm, the length of HSE signal attenuation of No. 2 core is 2.93 cm, the length of HSE signal attenuation of No. 3 core is 0 cm, and the length of HSE signal attenuation of No. 4 core is 0 cm.

[0180] The length of HSE signal attenuation of No. 1 core under the second throughput round is 5 cm, the length of HSE signal attenuation of No. 2 core is 8 cm, the length of HSE signal attenuation of No. 3 core is 0 cm, and the length of HSE signal attenuation of No. 4 core is 0 cm.

[0181] The length of HSE signal attenuation of No. 1 core under the third throughput round is 5 cm, the length of HSE signal attenuation of No. 2 core is 8 cm, the length of HSE signal attenuation of No. 3 core is 2.70 cm, and the length of HSE signal attenuation of No. 4 core is 0 cm.

[0182] According to the data in Table 1, the formula (6) is combined:

[0183] ;

[0184] It can be calculated that the CO2 sweep efficiency under the first, second and third throughput rounds is 33.36%, 55.50% and 64.20% respectively.

[0185] b, calculate the sweep efficiency expansion rate:

[0186] According to the formula (8) ; it can be calculated that the sweep efficiency expansion rate under the second throughput round is 66.37%, and the sweep efficiency expansion rate under the third throughput round is 15.68%.

[0187] c, calculate the CO2 oil washing efficiency of each throughput round:

[0188] It can be known from Figure 3 that the sum of the initial T2 spectrum signal values of all cores in the long core simulation model in the embodiment is 140274.64.

[0189] It can be known from Figure 5 , 6 , 7 that the sum of the T2 spectrum signal values of all cores in the long core simulation model after the first throughput round is 122577.64, the sum of the T2 spectrum signal values of all cores in the long core simulation model after the second throughput round is 117141.28, and the sum of the T2 spectrum signal values of all cores in the long core simulation model after the third throughput round is 103733.10.

[0190] According to the formula (7) The first, second and third throughputs oil displacement efficiency can be calculated as 37.82%, 29.71% and 40.57% respectively.

[0191] d. Calculate oil displacement efficiency decay rate:

[0192] According to formula (9) The second and third throughputs oil displacement efficiency decay rate can be calculated as 27.30% and -36.55% respectively.

[0193] It can be seen that when the CO2 cracks the core, the oil displacement efficiency decreases with the throughputs. When the CO2 reaches the matrix core, the oil displacement efficiency increases to some extent and the decay trend decreases due to the poor core permeability and good CO2 diffusion.

[0194] e. Calculate the sweep uniformity index:

[0195] First, the average oil displacement efficiency of each core measured by the CO2 throughputs experiment is taken as the sweep uniformity evaluation index of the long core simulation model throughputs I i This definition can be considered as directly representing the oil displacement effect under the ideal uniform sweep state.

[0196] Therefore, the sweep uniformity evaluation index of the first, second and third throughputs is 26.23%, 35.08% and 40.71% respectively.

[0197] According to formula (10) The sweep uniformity index of the first, second and third throughputs of the long core simulation model can be calculated as 1.44, 0.85 and 1.00 respectively. It can be seen that the CO2 sweep is relatively uniform under the conditions of the present embodiment and no channeling phenomenon occurs.

Claims

1. A method for quantitatively evaluating the sweep volume and oil displacement efficiency of carbon dioxide and heat-assisted carbon dioxide in a tight reservoir, characterized by, Comprise the following steps: (1) Construct long core simulation model: S1, first, according to the actual need of the experiment selects several pieces of dense reservoir geological core, using organic solvent to clean the core, remove the residual oil and oil stains of crude oil; Then, the corresponding basic physical parameters of each selected geological core are measured and recorded, including length l , diameter d , porosity φ 1 and gas measured permeability K 1; S2, obtain the actual fracture data, including fracture length, fracture width, fracture conductivity; S3, the length conversion formula of each part of the long core simulation model constructed is shown in formula (1): （1）； In the formula, α — length proportionality coefficient, m-cm -1 ; L f — unsupported fracture length in the mine, m; L m - matrix percolation length, m; L c — Total length of long core analog model, cm; L ef — Total length of fractured cores in long core analog model, cm; L em — total length of matrix core in long core analog model, cm; S4, first, according to the total length of the fracture core and the total length of the matrix core calculated in the long core simulation model, and combining the size range of the sample required by the nuclear magnetic resonance test, the specified length of each geological core is determined; Select the geological core from the several pieces of geological core obtained in S1 and cut it into the specified length; Then, fracture is made to the geological core selected as the fracture core in the long core simulation model, so that the permeability of each fracture core is consistent with the actual permeability of the actual fracture; The actual permeability calculation formula of the actual fracture is shown in formula (2): （2）； wherein K f - Actual permeability of the actual fracture in the field, mD; C f - fracture conductivity, mD-m; W f — crack width, m; S5, use harmonic average method to arrange the fracture core and matrix core respectively, and the calculation formula is shown in formula (3): （3）； wherein - the harmonic average permeability of the respective core, mD; L - total length of the respective core, cm; L i — first i Length of core corresponding block, cm; K i — first i Block permeability of the corresponding core, mD; The value of the fractured core calculated from formula (3) is compared with the permeability of all the fractured cores, and the fractured core with the smallest absolute value difference between the permeability and the value of formula (3) is placed at the end of all the fractured cores. The value of the fractured core calculated from formula (3) is compared with the permeability of all the fractured cores, and the fractured core with the smallest absolute value difference between the permeability and the value of formula (3) is placed at the end of all the fractured cores. The value of the fractured core calculated from formula (3) is compared with the permeability of all the fractured cores, and the fractured core with the Then, all the remaining fracture cores are recalculated according to formula (3) to obtain new values, the newly obtained values are compared with the remaining fracture cores, and the fracture core with the minimum absolute difference between the permeability and the newly obtained value is placed at the second last end of all the fracture cores, and the same is done for all the fracture cores. The value of the matrix core calculated from formula (3) is compared with the permeability of all the matrix cores, and the matrix core with the smallest absolute value difference between the permeability and the value of formula (3) is placed at the end of all the matrix cores. The value of the matrix core calculated from formula (3) is compared with the permeability of all the matrix cores, and the matrix core with the smallest absolute value difference between the permeability and the value of formula (3) is placed at the end of all the matrix cores. The value of the matrix core calculated from formula (3) is compared with the permeability of all the matrix Then, all the remaining matrix cores are recalculated according to formula (3) to obtain new values, the newly obtained values are compared with the remaining matrix cores, and the matrix core with the minimum absolute difference between the permeability and the newly obtained value is placed at the second last end of all the matrix cores, and the same is done to arrange all the matrix cores. Finally, according to the principle that the fracture core is placed at the front end of the matrix core, all the fracture cores are placed at the front end of the arranged matrix core in the order of arrangement, and the required long core simulation model is constructed; (2) Collect the initial axial HSE signal and T2 spectrum of all cores in the long core simulation model: First, vacuumize and saturate all cores in the long core simulation model with experimental simulation oil; Then, use the GR-HSE pulse sequence and CPMG pulse sequence of nuclear magnetic resonance equipment to collect the initial axial HSE signal and T2 spectrum of all cores in the order arranged in S5 of step (1); (3) Use the device to simulate the injection of CO2 and calculate the amount of CO2 injected into the long core simulation model: First, put filter paper in the middle of each core in the long core simulation model to eliminate the end effect, and then put it in the core holder, and the end of the core holder is filled with experimental simulation oil; Then, according to the actual needs of the experiment, constant pressure injection of CO2 gas for a period of time, then stop, record the initial pressure of CO2 gas P o , CO2 gas initial volume V o , CO2 gas injection end pressure P a and displacement pump injection volume V i ; Use the following formula (4) to calculate the amount of CO2 injected into the long core simulation model: （4）； wherein n o — CO2original total amount of substance, mol; P o -CO2 gas initial pressure, MPa; V o - CO2 gas initial volume, mL; Z o Compressibility factor, dimensionless, at initial temperature and pressure conditions of CO2 gas R — molar gas constant, J / (mol-K); T o - initial temperature of the CO2 gas, K; n a — amount of CO2 substance remaining at the end of injection, mol; P a — CO2 gas injection end pressure, MPa; V a - volume of CO2 gas remaining at the end of the injection, mL; Z a Compressibility factor, dimensionless, at the end-of-injection temperature and pressure conditions for CO2 gas T a — CO2 gas injection end temperature, K; n d — long core holder front-end line volume CO2 amount of substance, mol; V d — Long core holder front-end tubing volume, mL; V i Displacement pump injection volume, mL; n i — amount of CO2 substance injected into the long core analog model, mol; Finally, the amount of CO2 material injected into the long core simulation model is calculated according to the volume of CO2 material injected into the long core simulation model under the simulated temperature and pressure conditions n i The volume of CO2 injected into the long core simulation model under the simulated temperature and pressure conditions is solved, and the calculation formula is shown in formula (5): （5）； In the formula, V s — CO2 gas volume under simulated temperature and pressure conditions, mL; n i — amount of CO2 substance injected into the long core analog model, mol; Z s — CO2 gas compressibility factor, dimensionless; R - molar gas constant, J / (mol-K); T s - analog temperature, K; P s - simulated pressure, MPa; (4) carry out a round of huff and puff and collect data: First, huff and puff; if the simulation of thermal assisted CO2 huff and puff is carried out, heat the device to the specified temperature and then huff and puff; Then, after the huff and puff is finished, flow back the fluid to atmospheric pressure, take out the core in the order arranged in S5 of step (1), and mark the inlet and outlet end surface of the core; Finally, use the GR-HSE pulse sequence and CPMG pulse sequence of nuclear magnetic resonance equipment to collect the axial HSE signal and T2 spectrum of all cores after a round of huff and puff in the order arranged in S5 of step (1); (5) if multiple rounds of huff and puff experiment are required, repeat the above steps (3)-(4); (6) analyze the sweep range and oil washing characteristics of CO2 in each huff and puff round: a, calculate the CO2 sweep efficiency in each huff and puff round, and the calculation formula is shown in formula (6): （6）； wherein η s - CO2 sweep efficiency per throughput cycle, %; L Hi — the length of the HSE signal attenuation in the long core simulation model, cm i the length of the HSE signal attenuation in the long core, cm d i — long core analog model in the first i Diameter of the block core, cm; φ i — long core simulation model in the first i porosity of the block core, L i — 1st i Length of core corresponding block, cm; b, calculate the CO2 oil washing efficiency in each huff and puff round, and the calculation formula is shown in formula (7): （7）； wherein η w - CO2 wash oil efficiency per throughput cycle, %; T 2o — the sum of all core initial T2 map signal values in the long core simulation model, dimensionless; T 2a — the sum of the T2 map signal values of all cores in the long core simulation model after core throughput, dimensionless; η s - CO2 sweep efficiency per throughput cycle, %; c. The formula for calculating the expansion rate of the wave efficiency is shown as equation (8): （8）； In the formula, D s - expansion rate of the conformance, %; η sn — first n Pass CO2 sweep efficiency, %; η s(n+1) - 1st n +1st pass CO2 sweep efficiency, %; d. The formula for calculating the attenuation rate of the oil washing efficiency is shown as equation (9): （9）； In the formula, D w - wash oil efficiency decay rate, %; η wn - 1st n Round CO2 wash oil efficiency, %; η w(n+1) - 1st n +1st cycle CO2 wash oil efficiency, %; e. The formula for calculating the wave uniformity index is shown as equation (10): （10）； wherein I u - spread uniformity index, dimensionless; η w - CO2 wash oil efficiency per throughput cycle, %; I i Spread uniformity evaluation index, %.

2. The method for quantitatively evaluating the sweep volume and oil displacement efficiency of carbon dioxide and heat-assisted carbon dioxide in a tight reservoir according to claim 1, characterized in that, The long core holder front-end tubing volume in step (3) of formula (4) V d The measurement was performed by: The impermeable columnar iron block is placed in the long core holder, and CO2 gas is driven into the long core holder at constant pressure. When the overall pressure is stable, the injection volume of the displacement pump is the volume of the front-end pipeline of the long core holder V d .

3. The method for quantitatively evaluating the sweep volume and oil displacement efficiency of carbon dioxide and heat-assisted carbon dioxide in a tight reservoir according to claim 1, characterized in that, The wave and uniformity evaluation index in the formula (10) of the step (6) I i The average oil displacement efficiency is calculated by the CO2 huff and puff experiment of each core.

4. A simulation device for quantitatively evaluating the method of claim 1 to 3 for the sweep volume and oil displacement efficiency of carbon dioxide and heat-assisted carbon dioxide in a compact reservoir, characterized by, The CO2 cylinder, CO2 gas container, oil container, low-field nuclear magnetic resonance equipment and long core holder in the thermostat are included. The CO2 cylinder is connected with the gas pressurizing pump through pipeline and two-way valve No.1; the gas pressurizing pump is connected with the left port of three-way No.1 through pipeline and two-way valve No.2; the lower port of three-way No.1 is connected with the top end of the CO2 gas container through pipeline; the bottom end of the CO2 gas container is connected with the displacement pump No.1 through pipeline and two-way valve No.3; the upper port of three-way No.1 is connected with the left port of three-way No.2 through pipeline and two-way valve No.4, and pressure gauge No.1 is arranged on the pipeline segment between the upper port of three-way No.1 and two-way valve No.4; the lower port of three-way No.2 is connected with the vent valve; the right port of three-way No.2 is connected with the left end of the long core holder; the fracture core and matrix core are placed in the long core holder; the top of the long core holder is connected with the hand pump through pipeline and two-way valve No.5, and pressure gauge No.3 is arranged on the pipeline segment between the top of the long core holder and two-way valve No.5; the right end of the long core holder is connected with the top of the oil container through pipeline and two-way valve No.6, and pressure gauge No.4 is arranged on the pipeline segment between the right end of the long core holder and two-way valve No.6; the bottom of the oil container is connected with the displacement pump No.2 through pipeline and two-way valve No.7.

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