A method for determining the application limit of carbon dioxide huff-and-puff and carbon dioxide-water displacement in conglomerate reservoirs

Abstract

The invention belongs to the technical field of oil production, and particularly relates to a method for determining the application limit of carbon dioxide throughput and carbon dioxide-water displacement in a conglomerate oil reservoir; the method solves the problem that the current unreasonable application limit of carbon dioxide throughput and carbon dioxide-water displacement in conglomerate oil reservoirs leads to low crude oil production efficiency; the technical scheme is: obtaining a standard matrix and fracture cores of a conglomerate oil reservoir, arranging the cores in order according to the harmonic mean method, sequentially loading them into a long core displacement device in the arrangement order, establishing an initial state of the oil reservoir, firstly conducting experiments with all matrix core combinations, continuously increasing the proportion of fractures, conducting carbon dioxide throughput and carbon dioxide-water displacement experiments respectively, obtaining the crude oil production efficiency of each experiment, establishing a fracture proportion and crude oil production efficiency chart, and determining the application limit of carbon dioxide throughput and carbon dioxide-water displacement in the conglomerate oil reservoir through the chart; the new method in the invention can optimize the oil reservoir development plan and achieve higher economic benefits and operational flexibility.

Description

Technical Field

[0001] The invention belongs to the technical field of petroleum extraction, and in particular relates to a method for determining the application limit of carbon dioxide throughput and carbon dioxide-water displacement in a conglomerate oil reservoir. Background Art

[0002] In the field of oil extraction, choosing the right extraction method is crucial; the huff-and-puff method uses pressure changes to drive oil flow through periodic gas injection and oil production; the displacement method displaces crude oil in the reservoir by injecting fluids (such as water, gas, etc.); for conglomerate reservoirs, there is no clear method to define the best application scenarios for these two technologies, which will lead to the failure to fully tap the potential of the reservoir.

[0003] After extensive research, the publication number CN118029982A, "A method for oil recovery by combining multi-media displacement and throughput in heavy oil reservoirs", injects multiple displacement media into the injection wells and works synchronously with the viscosity reduction and energy enhancement system in the production wells to achieve a multi-well group injection and production linkage oil recovery method, which significantly improves the recovery rate of ultra-deep heavy oil reservoirs with a high water content of more than 1,800 meters and broadens the technical boundaries of heavy oil recovery; the publication number CN116591647A, "A new type of CO 2 The Displacement and Huff & Puff System and Method can simulate the displacement or huff & puff development effects of underground oil and gas reservoirs through various media under the conditions of simulating formation temperature and pressure, and analyze the influence of these factors and their sensitivity on the development effect.

[0004] In general, there are many methods for determining the application limits of throughput and displacement. However, these methods have their own limitations. Therefore, it is particularly important to study a scientific method for determining the application limits of carbon dioxide throughput and carbon dioxide-water displacement in conglomerate reservoirs. This will not only help optimize mining strategies and achieve higher economic benefits and operational flexibility, but also improve the accuracy of decision-making. Summary of the invention

[0005] The purpose of the present invention is to solve the problem of low crude oil production efficiency caused by unreasonable application limits of carbon dioxide throughput and carbon dioxide-water displacement in conglomerate reservoirs. The present invention adopts a combination of experimental and theoretical means to obtain standard matrix and fracture cores of conglomerate reservoirs, arrange the cores in order according to the harmonic mean method, and sequentially load them into a long core displacement device in the arrangement order to establish the initial state of the reservoir. First, all matrix core combinations are used to carry out experiments, and the proportion of fractures is continuously increased. Carbon dioxide throughput and carbon dioxide-water displacement experiments are carried out respectively to obtain the crude oil production efficiency of each experiment, and a fracture proportion and crude oil production efficiency chart is established. The application limits of carbon dioxide throughput and carbon dioxide-water displacement in conglomerate reservoirs can be determined through the chart, and the calculation is fast and accurate.

[0006] To achieve the above object, the present invention provides a method for determining the application limit of carbon dioxide throughput and carbon dioxide-water displacement in conglomerate reservoirs, the method comprising the following steps:

[0007] The first step is to obtain conglomerate reservoir rock samples, cut and fracture them, and obtain standard matrix and fracture cores;

[0008] The second step is to arrange the cores in order according to the permeability of the matrix and fracture cores using the harmonic mean method;

[0009] The third step is to add gaskets between the two cores and install them into the long core displacement device in the order of arrangement. Under the conditions of temperature 80℃ and confining pressure 55MPa, the device is pressurized to saturate the formation water, and then driven with crude oil to a water saturation of 50%. Then, it is sealed for 48 hours to establish the initial state of the reservoir.

[0010] The fourth step is to first use all matrix core combinations to carry out experiments, including CO2 injection and CO2-water displacement experiments. After the different experiments, the cores should be cleaned and dried to re-establish the initial state of the reservoir. Each time, one matrix core is replaced with a fracture core, and the number of fracture cores is continuously increased to obtain core combinations with different fracture ratios, and a fracture ratio calculation model is established.

[0011] ,

[0012] Among them, R f is the crack ratio, unit is %; N f is the number of fracture cores, in pieces; N s is the number of matrix cores, in pieces;

[0013] Step 5: For each group of core combinations with different fracture ratios in Step 4, CO2 huff-and-puff and CO2-water displacement experiments are performed independently through a long core displacement device to obtain the crude oil recovery efficiencies of CO2 huff-and-puff experiments and CO2-water displacement experiments under different core combinations with different fracture ratios.

[0014] The sixth step is to combine the crude oil recovery efficiency data of the carbon dioxide huff and puff experiment and the carbon dioxide-water displacement experiment to establish a fracture ratio and crude oil recovery efficiency chart. With the increase of fracture ratio, the crude oil recovery efficiency continues to decrease under the carbon dioxide huff and puff method, and the carbon dioxide huff and puff effect becomes worse. However, under the carbon dioxide-water displacement method, the crude oil recovery efficiency gradually increases. The fracture ratio corresponding to the intersection of the two curves in the fracture ratio and crude oil recovery efficiency chart is the application limit R of carbon dioxide huff and puff and carbon dioxide-water displacement. c , when the crack ratio is less than the application limit R cWhen the proportion of fractures is greater than the application limit R, the efficiency of crude oil recovery by CO2 injection is higher than that of CO2-water injection. c When the carbon dioxide-water displacement method is used, the crude oil recovery efficiency is higher than the carbon dioxide throughput, and the oil reservoir should be exploited by the carbon dioxide-water displacement method.

[0015] In the above method for determining the application boundary of carbon dioxide huff-and-puff and carbon dioxide-water displacement in conglomerate reservoirs, the steps of obtaining standard matrix and fracture cores are:

[0016] The first step is to drill representative conglomerate samples from the target reservoir, cut them to obtain matrix cores, and use a triaxial stress testing system to create fractures in the matrix cores to obtain fracture cores.

[0017] In the second step, the matrix and fracture cores were washed and dried, and the length, diameter, weight, permeability and porosity were measured.

[0018] In the above method for determining the application limit of carbon dioxide huff and puff and carbon dioxide-water displacement in conglomerate reservoirs, the step of arranging the cores according to the harmonic mean method is as follows:

[0019] The first step is to calculate the harmonic mean permeability of the core by the harmonic mean method.

[0020] ,

[0021] Among them, K h is the harmonic average permeability of the core, in mD; L is the total length of all cores, in m; L i is the length of the i-th core, in m; K i is the permeability of the i-th core, in mD; n is the end value of the summation, in dimensionless units;

[0022] The second step is to compare the harmonic average permeability of the core with the permeability of all cores, and place the core with the smallest absolute value of the difference between the permeability and the harmonic average permeability of the core in the first place at the exit. Then calculate the harmonic average permeability of the remaining cores, compare the newly calculated harmonic average permeability of the cores with the remaining cores, and place the core with the smallest absolute value of the difference between the permeability and the new harmonic average permeability of the core in the second place at the exit. According to this step, arrange the order of all cores.

[0023] In the above method for determining the application limit of carbon dioxide huff and puff and carbon dioxide-water displacement in conglomerate reservoirs, the steps of obtaining the crude oil recovery efficiency of the carbon dioxide huff and puff experiment and the carbon dioxide-water displacement experiment under different fracture ratio core combinations are as follows:

[0024] In the first step, carbon dioxide was used as the medium for the carbon dioxide injection experiment. The carbon dioxide-water displacement experiment used carbon dioxide-water as the medium, and the injection ratio of carbon dioxide to water was 1:2, and the displacement was carried out by continuous alternating injection.

[0025] The second step is to stop the experiment when there is no crude oil flowing out of the outlet, and record the cumulative oil production of the CO2 huff-and-puff experiment and the CO2-water displacement experiment under different core combinations with different fracture ratios.

[0026] The third step is to establish a calculation model for crude oil recovery efficiency and calculate the crude oil recovery efficiency of the carbon dioxide injection experiment and the carbon dioxide-water displacement experiment under different fracture ratio core combinations.

[0027] ,

[0028] Among them, R o is the crude oil extraction efficiency, unit is %; V o is the cumulative oil production, in m³; B o is the volume coefficient of crude oil, unit is dimensionless quantity; d is the diameter of the long core, unit is m; L is the total length of all cores, unit is m; P is the average porosity of the long core, unit is %; S oi is the initial oil saturation, in %.

[0029] Compared with the prior art, the present invention has the following advantages: (1) high working efficiency; (2) simple method and rapid application; (3) high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In the attached picture:

[0031] Figure 1 It is the overall technical roadmap of the method;

[0032] Figure 2 This is a chart showing the proportion of fractures and the efficiency of crude oil extraction. DETAILED DESCRIPTION

[0033] The present invention will be further described below in conjunction with the embodiments and accompanying drawings;

[0034] The present invention provides a method for determining the application limit of carbon dioxide throughput and carbon dioxide-water displacement in conglomerate oil reservoirs. Figure 1 It is the overall technical roadmap of the method, which includes the following steps:

[0035] The first step is to obtain conglomerate reservoir rock samples, cut and fracture them, and obtain standard matrix and fracture cores;

[0036] The second step is to arrange the cores in order according to the permeability of the matrix and fracture cores using the harmonic mean method;

[0037] The third step is to add gaskets between the two cores and install them into the long core displacement device in the order of arrangement. Under the conditions of temperature 80℃ and confining pressure 55MPa, the device is pressurized to saturate the formation water, and then driven with crude oil to a water saturation of 50%. Then, it is sealed for 48 hours to establish the initial state of the reservoir.

[0038] The fourth step is to first use all matrix core combinations to carry out experiments, including CO2 injection and CO2-water displacement experiments. After the different experiments, the cores should be cleaned and dried to re-establish the initial state of the reservoir. Each time, one matrix core is replaced with a fracture core, and the number of fracture cores is continuously increased to obtain core combinations with different fracture ratios, and a fracture ratio calculation model is established.

[0039] ,

[0040] Among them, R f is the crack ratio, unit is %; N f is the number of fracture cores, in pieces; N s is the number of matrix cores, in pieces;

[0041] Step 5: For each group of core combinations with different fracture ratios in Step 4, CO2 huff-and-puff and CO2-water displacement experiments are performed independently through a long core displacement device to obtain the crude oil recovery efficiencies of CO2 huff-and-puff experiments and CO2-water displacement experiments under different core combinations with different fracture ratios.

[0042] The sixth step is to combine the crude oil recovery efficiency data of the carbon dioxide huff and puff experiment and the carbon dioxide-water displacement experiment to establish a fracture ratio and crude oil recovery efficiency chart. With the increase of fracture ratio, the crude oil recovery efficiency continues to decrease under the carbon dioxide huff and puff method, and the carbon dioxide huff and puff effect becomes worse. However, under the carbon dioxide-water displacement method, the crude oil recovery efficiency gradually increases. The fracture ratio corresponding to the intersection of the two curves in the fracture ratio and crude oil recovery efficiency chart is the application limit R of carbon dioxide huff and puff and carbon dioxide-water displacement. c , when the crack ratio is less than the application limit R c When the proportion of fractures is greater than the application limit R, the efficiency of crude oil recovery by CO2 injection is higher than that of CO2-water injection. c When the carbon dioxide-water displacement method is used, the crude oil recovery efficiency is higher than the carbon dioxide throughput, and the oil reservoir should be exploited by the carbon dioxide-water displacement method.

[0043] Further, the steps of obtaining the standard matrix and fracture core are:

[0044] The first step is to drill representative conglomerate samples from the target reservoir, cut them to obtain matrix cores, and use a triaxial stress testing system to create fractures in the matrix cores to obtain fracture cores.

[0045] In the second step, the matrix and fracture cores were washed and dried, and the length, diameter, weight, permeability and porosity were measured.

[0046] Further, the step of arranging the cores according to the harmonic mean method is:

[0047] The first step is to calculate the harmonic mean permeability of the core by the harmonic mean method.

[0048] ,

[0049] Among them, K h is the harmonic average permeability of the core, in mD; L is the total length of all cores, in m; L i is the length of the i-th core, in m; K i is the permeability of the i-th core, in mD; n is the end value of the summation, in dimensionless units;

[0050] The second step is to compare the harmonic average permeability of the core with the permeability of all cores, and place the core with the smallest absolute value of the difference between the permeability and the harmonic average permeability of the core in the first place at the exit. Then calculate the harmonic average permeability of the remaining cores, compare the newly calculated harmonic average permeability of the cores with the remaining cores, and place the core with the smallest absolute value of the difference between the permeability and the new harmonic average permeability of the core in the second place at the exit. According to this step, arrange the order of all cores.

[0051] Further, the steps of obtaining the crude oil recovery efficiency of the carbon dioxide huff-and-puff experiment and the carbon dioxide-water displacement experiment under different fracture ratio core combinations are as follows:

[0052] In the first step, carbon dioxide was used as the medium for the carbon dioxide injection experiment. The carbon dioxide-water displacement experiment used carbon dioxide-water as the medium, and the injection ratio of carbon dioxide to water was 1:2, and the displacement was carried out by continuous alternating injection.

[0053] The second step is to stop the experiment when there is no crude oil flowing out of the outlet, and record the cumulative oil production of the CO2 huff-and-puff experiment and the CO2-water displacement experiment under different core combinations with different fracture ratios.

[0054] The third step is to establish a calculation model for crude oil recovery efficiency and calculate the crude oil recovery efficiency of the carbon dioxide injection experiment and the carbon dioxide-water displacement experiment under different fracture ratio core combinations.

[0055] ,

[0056] Among them, R o is the crude oil extraction efficiency, unit is %; V o is the cumulative oil production, in m³; B o is the volume coefficient of crude oil, unit is dimensionless quantity; d is the diameter of the long core, unit is m; L is the total length of all cores, unit is m; P is the average porosity of the long core, unit is %; S oi is the initial oil saturation, in %.

[0057] Taking a conglomerate reservoir as an example, the original reservoir pressure of the reservoir is 55 MPa, the formation temperature is 80 °C, the initial water saturation is 50%, and the crude oil volume coefficient is 1.14. After fracturing, some wells in the reservoir have a large number of microcracks and strong heterogeneity. Ten fractures and matrix cores of the conglomerate reservoir were obtained. The physical property parameters of each core are shown in Table 1. Carbon dioxide huff and puff experiments were carried out. The carbon dioxide: water injection ratio was 1:2 to carry out carbon dioxide-water displacement experiments. In each experiment, a matrix core was replaced with a fracture core, and the proportion of fractures was continuously increased. The cumulative oil production of each carbon dioxide huff and puff experiment and carbon dioxide-water displacement experiment was recorded respectively. The crude oil recovery efficiency of the carbon dioxide huff and puff experiment was obtained through the crude oil recovery efficiency calculation model, as shown in Table 2, and the crude oil recovery efficiency of the carbon dioxide-water displacement experiment is shown in Table 3.

[0058] Combining the crude oil recovery efficiency data from the CO2 huff-and-puff and CO2-water displacement experiments, a chart of fracture ratio and crude oil recovery efficiency was established. Figure 2 , with the increase of the proportion of fractures, the crude oil recovery efficiency continues to decrease and the throughput effect becomes worse when the carbon dioxide huff and puff method is used, while the crude oil recovery efficiency gradually increases when the carbon dioxide-water displacement method is used. The fracture proportion of 30% corresponding to the intersection of the two curves in the figure is the application limit of carbon dioxide huff and puff and carbon dioxide-water displacement. When the fracture proportion is less than 30%, the crude oil recovery efficiency of the carbon dioxide huff and puff method is higher than that of the carbon dioxide-water displacement method, and the oil reservoir is exploited by the carbon dioxide huff and puff method. When the fracture proportion is greater than 30%, the crude oil recovery efficiency of the carbon dioxide-water displacement method is higher than that of the carbon dioxide huff and puff, and the oil reservoir is exploited by the carbon dioxide-water displacement method.

[0059] Table 1 Core physical parameters

[0060]

[0061] Table 2 Crude oil recovery efficiency of CO2 huff-and-puff experiment

[0062]

[0063] Table 3 Crude oil recovery efficiency of CO2-water displacement experiment

[0064]

[0065] Compared with the prior art, the present invention has the following advantages: (1) high working efficiency; (2) simple method and rapid application; (3) high accuracy.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for determining the application limit of carbon dioxide throughput and carbon dioxide-water displacement in conglomerate reservoirs, characterized in that: The method comprises the following steps: S100, the steps of obtaining a conglomerate reservoir rock sample, cutting and creating fractures, and obtaining a standard matrix and fracture core are as follows: S101, drilling a representative conglomerate sample from the target oil reservoir, cutting it to obtain a matrix core, and performing fracture creation on the matrix core using a triaxial stress testing system to obtain a fracture core; S102, the matrix and fracture cores were washed and dried, and the length, diameter, weight, permeability and porosity were measured; S200, according to the size of matrix and fracture core permeability, the steps of arranging the cores by harmonic mean method are as follows: S201, calculate the harmonic mean permeability of the core by the harmonic mean method, ， Among them, K h is the harmonic average permeability of the core, in mD; L is the total length of all cores, in m; L i is the length of the i-th core, in m; K i is the permeability of the i-th core, in mD; n is the end value of the summation, in dimensionless units; S202, comparing the harmonic average permeability of the core with the permeability of all cores, taking the core with the smallest absolute value of difference between the permeability and the harmonic average permeability of the core and placing it at the first position at the outlet, then calculating the harmonic average permeability of the remaining cores, comparing the newly calculated harmonic average permeability value of the core with the remaining cores, taking the core with the smallest absolute value of difference between the permeability and the new harmonic average permeability value of the core and placing it at the second position at the outlet, and arranging the order of all cores according to this step; S300, add gaskets between two cores, install them into the long core displacement device in the order of arrangement, pressurize the device to saturate the formation water under the conditions of temperature 80℃ and confining pressure 55MPa, and then drive with crude oil to 50% water saturation, and then seal it for 48h to establish the initial state of the reservoir; S400, firstly, all experiments were carried out using matrix core combinations, including CO2 huff and puff and CO2-water displacement experiments. After different experiments, the cores were cleaned and dried to re-establish the initial state of the reservoir. Each time, one matrix core was replaced with a fracture core, and the number of fracture cores was continuously increased to obtain core combinations with different fracture ratios, and a fracture ratio calculation model was established. ， Among them, R f is the crack ratio, unit is %; N f is the number of fracture cores, in pieces; N s is the number of matrix cores, in pieces; S500, for each group of fracture ratio core combinations in S400, CO2 huff and puff and CO2-water displacement experiments are independently carried out by a long core displacement device, and the steps of obtaining the crude oil recovery efficiency of CO2 huff and puff experiments and CO2-water displacement experiments under different fracture ratio core combinations are as follows: S501, a carbon dioxide injection experiment is conducted using carbon dioxide as a medium, and a carbon dioxide-water displacement experiment is conducted using carbon dioxide-water as a medium, with a carbon dioxide:water injection ratio of 1:2, and displacement is conducted by continuous alternating injection; S502, when no crude oil flows out from the outlet, the experiment is stopped, and the cumulative oil production of the carbon dioxide huff-and-puff experiment and the carbon dioxide-water displacement experiment under different fracture ratio core combinations is recorded respectively; S503, establish a crude oil recovery efficiency calculation model, calculate the crude oil recovery efficiency of the carbon dioxide huff-and-puff experiment and the carbon dioxide-water displacement experiment under different fracture ratio core combinations, ， Among them, R o is the crude oil extraction efficiency, unit is %; V o is the cumulative oil production, in m³; B o is the volume coefficient of crude oil, unit is dimensionless quantity; d is the diameter of the long core, unit is m; L is the total length of all cores, unit is m; P is the average porosity of the long core, unit is %; S oi is the initial oil saturation, unit is %; S600, combined with the crude oil recovery efficiency data of the CO2 huff and puff experiment and the CO2-water displacement experiment, a fracture ratio and crude oil recovery efficiency chart was established. With the increase of fracture ratio, the crude oil recovery efficiency continued to decrease and the CO2 huff and puff effect became worse when the CO2 huff and puff method was adopted. However, when the CO2-water displacement method was adopted, the crude oil recovery efficiency gradually increased. The fracture ratio corresponding to the intersection of the two curves in the fracture ratio and crude oil recovery efficiency chart is the application limit R of CO2 huff and puff and CO2-water displacement. c , when the crack ratio is less than the application limit R c When the proportion of fractures is greater than the application limit R, the efficiency of crude oil recovery by CO2 injection is higher than that of CO2-water injection. c When the carbon dioxide-water displacement method is used, the crude oil recovery efficiency is higher than the carbon dioxide throughput, and the oil reservoir should be exploited by the carbon dioxide-water displacement method.

Images