Method for determining application boundary of conglomerate oil reservoir carbon dioxide huff and puff and carbon dioxide-water displacement

Abstract

The invention belongs to the technical field of oil exploitation, and particularly relates to a method for determining the application limit of conglomerate oil reservoir carbon dioxide huff and puff and carbon dioxide-water displacement. The method solves the problem of low crude oil extraction efficiency caused by unreasonable application boundaries of carbon dioxide huff and puff and carbon dioxide-water displacement of conglomerate oil reservoirs at present. According to the technical scheme, the method comprises the steps that a conglomerate oil reservoir standard matrix and fractured cores are obtained, the cores are arranged according to a harmonic average method, the cores are sequentially loaded into a long core displacement device according to the arrangement sequence, and the initial state of the oil reservoir is established; respectively carrying out carbon dioxide huff and puff and carbon dioxide-water displacement experiments to obtain the crude oil exploitation efficiency of each experiment, establishing a fracture ratio and crude oil exploitation efficiency plate, and determining the application limit of the conglomerate oil reservoir carbon dioxide huff and puff and carbon dioxide-water displacement through the plate; according to the new method, an oil reservoir development scheme can be optimized, and higher economic benefits and operation flexibility are achieved.

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 "A method for oil production by integrating multi-media displacement and throughput in heavy oil reservoirs" with publication number CN118029982A realizes a method for oil production by integrating injection and production in multiple well groups by injecting multiple displacement media into the injection wells and acting synchronously with the viscosity reduction and energy enhancement system in the production wells, significantly improving the recovery rate of ultra-deep heavy oil reservoirs with high water content exceeding 1,800 meters and broadening the technical boundaries of heavy oil extraction; the "A new CO2 displacement and throughput system and method" with publication number CN116591647A can simulate the formation temperature and pressure conditions, and analyze the influence of these factors and their sensitivity on the development effect through the displacement or throughput development effect of underground oil and gas reservoirs through multiple media.

[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 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, the number of fracture cores is continuously increased, 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] The fifth step is to conduct CO2 huff-and-puff experiments and CO2-water displacement experiments using a long core displacement device to obtain the crude oil recovery efficiency of each experiment;

[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 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. cWhen 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 throughput and carbon dioxide-water displacement in conglomerate reservoirs, the steps of obtaining the crude oil recovery efficiency of each experiment are:

[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 carried out displacement by continuous alternating injection at an injection ratio of 1:2.

[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 injection experiment and the CO2-water displacement experiment;

[0026] The third step is to calculate the crude oil recovery efficiency of the CO2 huff-and-puff experiment and the CO2-water displacement experiment, and establish a crude oil recovery efficiency calculation model.

[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 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, the number of fracture cores is continuously increased, 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] The fifth step is to conduct CO2 huff-and-puff experiments and CO2-water displacement experiments using a long core displacement device to obtain the crude oil recovery efficiency of each experiment;

[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 each experiment are:

[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 carried out displacement by continuous alternating injection at an injection ratio of 1:2.

[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 injection experiment and the CO2-water displacement experiment;

[0054] The third step is to calculate the crude oil recovery efficiency of the CO2 huff-and-puff experiment and the CO2-water displacement experiment, and establish a crude oil recovery efficiency calculation model.

[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 certain 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, and carbon dioxide and water were alternately injected at a ratio of 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] Table 2 Crude oil recovery efficiency of CO2 huff-and-puff experiment

[0061] Table 3 Crude oil recovery efficiency of CO2-water displacement experiment

[0062] 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.

[0063] 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 establish a fracture ratio calculation model. ， 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, the steps of carrying out a CO2 huff-and-puff experiment and a CO2-water displacement experiment by using a long core displacement device to obtain the crude oil recovery efficiency of each experiment are as follows: S501, a carbon dioxide injection experiment was conducted using carbon dioxide as the medium, and a carbon dioxide-water displacement experiment was conducted using carbon dioxide-water as the medium, with a continuous alternating injection method at an injection ratio of 1:2; S502, when there is no crude oil flowing out of the outlet, the experiment is stopped, and the cumulative oil production of the carbon dioxide injection experiment and the carbon dioxide-water displacement experiment is recorded; S503, calculating the crude oil recovery efficiency of the carbon dioxide huff-and-puff experiment and the carbon dioxide-water displacement experiment, and establishing a crude oil recovery efficiency calculation model, ， 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.

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