Method for improving carbon dioxide flooding miscible phase degree of tight oil reservoir through water injection energy supplementation

Abstract

The invention relates to a method for improving the carbon dioxide flooding miscible degree of a tight oil reservoir through water injection energy supplementation, which comprises the following steps of: performing advanced water injection on a target reservoir in a target low-permeability tight oil reservoir block, and increasing the average pressure of the target reservoir to be above the minimum miscible pressure of a carbon dioxide-crude oil system; carbon dioxide is injected into the target reservoir through the gas injection well, so that the carbon dioxide and the crude oil in the target reservoir are mixed; production well production; in the carbon dioxide injection process, when the production gas-oil ratio in the target low-permeability tight oil reservoir block is increased to 1000 m < 3 > / m < 3 > or the gas channeling wells account for 10%-20% of the total number of production wells, carbon dioxide injection is changed into the original water injection well, water injection is changed into the original gas injection well, and single-well alternating driving is achieved; and when the production gas-oil ratio in the target low-permeability tight oil reservoir block is increased to 1000 m < 3 > / m < 3 > or the gas channeling wells account for 30%-50% of the total number of the production wells, the production wells on the injection well row are converted into water-gas alternating wells in the dominant seepage direction, carbon dioxide injection is crossed with the water injection wells, and the injection-production relation is enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of enhanced oil recovery in low-permeability tight oil reservoirs, and particularly to a method for improving the miscibility of carbon dioxide flooding in tight oil reservoirs by water injection for energy supplementation. Background Technique

[0002] With the continuous increase in global energy demand and the decreasing of conventional oil and gas resources, low-permeability tight oil reservoirs are playing an increasingly important role in China's energy strategic layout. Low-permeability tight oil reservoirs are rich in reserves, accounting for more than 58% of China's oil resources, and are the key sectors for domestic oil and gas exploration and development. However, the development of low-permeability tight oil reservoirs is difficult, and the calibrated recovery rates of different types of low-permeability and tight oil reservoirs are only 10% - 23%, with great potential for further improving the recovery rate. Carbon dioxide has strong seepage ability and can reduce viscosity, expand and extract after reacting with crude oil. Therefore, carbon dioxide flooding is considered one of the effective means to improve the crude oil recovery rate in low-permeability oil reservoirs and has been widely applied in many countries such as the United States and Canada. At the same time, carbon dioxide is one of the main greenhouse gases. Injecting carbon dioxide into oil reservoirs can, to a certain extent, achieve geological sequestration of carbon dioxide. Under the background of the national dual-carbon goal, it is of great significance for the low-carbon and green transformation and development of the oil and gas industry.

[0003] Due to the low formation pressure coefficient of the reservoirs in continental sedimentary low-permeability tight oil reservoirs in China, it is difficult for formation crude oil to be miscible with carbon dioxide under the original formation pressure conditions, and it is mostly immiscible or near miscible. The low miscibility of carbon dioxide and crude oil has become one of the main limiting factors affecting the effect of carbon dioxide flooding. Therefore, it is particularly necessary to improve the reservoir pressure and enhance the miscibility of carbon dioxide flooding in low-permeability oil reservoirs to improve the effect of carbon dioxide flooding.

[0004] Based on the advanced water injection practice experience previously obtained in the water injection technology of Changqing Oilfield, the most typical low-permeability oilfield in China, it is proposed to carry out advanced gas injection in the carbon dioxide test area to optimize the effect of carbon dioxide flooding in low-pressure tight oil reservoirs. However, the relevant on-site test results show that the effect of energy supplementation by advanced carbon dioxide injection is limited. Combining the carbon dioxide dissolution theory in crude oil and indoor physical simulation experiments, it is considered that due to the strong compressibility, strong solubility in crude oil and strong penetration ability in oil reservoirs of carbon dioxide, compared with injecting the same volume of rigid fluid water, the energy supplementation and pressure boosting effect of injecting carbon dioxide is slightly insufficient. Based on this, the technical method of "using advanced water injection to increase the reservoir pressure for energy supplementation and subsequent gas injection to give full play to the high-efficiency miscible displacement of carbon dioxide under high pressure" is proposed. Summary of the Invention

[0005] The present invention aims at the above problems and proposes a method of using advanced water injection to increase the reservoir pressure for energy supplementation and subsequent gas injection to give full play to the high-efficiency miscible displacement of carbon dioxide under high pressure.

[0006] The technical solution of the present invention lies in: A method for improving the miscibility of carbon dioxide flooding in tight oil reservoirs by water injection energy supplementation, the method is as follows: Make the target low-permeability tight oil reservoir block in a relatively independent pressure system, and deploy gas injection wells and water injection wells crosswise along the dominant seepage orientation inside the injection-production well pattern; Through the water injection well, advance water injection into the target reservoir in the target low-permeability tight oil reservoir block, and raise the average pressure of the target reservoir above the minimum miscibility pressure of the carbon dioxide-crude oil system; Then inject carbon dioxide into the target reservoir through the gas injection well to achieve miscibility between the carbon dioxide and the crude oil located in the target reservoir; the production well produces; During the process of injecting carbon dioxide, when the produced gas-oil ratio in the target low-permeability tight oil reservoir block rises to 1000 m 3 / m 3 or more, or when the gas channeling wells account for 10% - 20% of the total number of production wells, the original water injection well is changed to inject carbon dioxide, and the original gas injection well is changed to inject water to achieve single-well alternating flooding; When the produced gas-oil ratio in the target low-permeability tight oil reservoir block rises to 1000 m 3 / m 3 or more, or when the gas channeling wells account for 30% - 50% of the total number of production wells, along the dominant seepage orientation, the production wells on the injection well row are converted into water and gas alternating wells, and the injection of carbon dioxide is crossed with the water injection wells to strengthen the injection-production relationship.

[0007] The target low-permeability tight oil reservoir block is a target low-permeability tight oil reservoir block with good integrity of the injection-production well pattern and good well conditions. The method of making the target low-permeability tight oil reservoir block in a relatively independent pressure system is specifically achieved by setting peripheral water injection wells around the target low-permeability tight oil reservoir block to form a block closed-loop water wall.

[0008] During the advance water injection, the bottom hole flowing pressure of the water injection well does not exceed the fracture pressure of the target reservoir.

[0009] During the production of the production well, the bottom hole flowing pressure of the production well is higher than the bubble point pressure.

[0010] The alternating cycle of the single-well alternating flooding and the water and gas alternating well is half a year to one year.

[0011] The single-well water injection volume during the advance water injection > the single-well water injection volume after the single-well alternation.

[0012] Before and after the single-well alternating flooding, the injection rate of carbon dioxide remains unchanged.

[0013] The continuous effect of the present invention lies in: (1) By cross - deploying injection wells and gas injection wells in the target low - permeability tight oil reservoir block, using the peripheral injection wells and injection wells to inject water in advance, the overall pressure of the low - permeability tight oil reservoir is efficiently lifted, the miscibility degree in the subsequent carbon dioxide flooding process is effectively improved, thereby enhancing the carbon dioxide flooding effect; meanwhile, the reservoir pressure - sensitive effect caused by pressure reduction production in the low - permeability tight oil reservoir is avoided. (2) In the target low - permeability tight oil reservoir block, injection wells and gas injection wells are cross - deployed. Subsequently, the production wells located on the injection well row along the dominant seepage direction are converted into water - gas alternating wells, and the carbon dioxide injection intersects with the injection wells. A micro water wall is formed through the injection wells on both sides of the dominant seepage direction to inhibit the cross - flow of carbon dioxide gas across the injection - production well pattern, improve the carbon dioxide sweep volume, and maximize the carbon dioxide flooding recovery degree. (3) The well pattern deployment method proposed by the present invention is easy to carry out single - well alternating transformation and well pattern densification, while ensuring the relative stability of the gas source demand. The single - well water - gas alternating injection can effectively improve the vertical sweep volume and enhance the crude oil recovery degree of each injection - production well pattern. The row - shaped injection well pattern can improve the overall injection - production ratio and injection intensity of the block, and further enhance the carbon dioxide flooding development effect of the low - permeability tight oil reservoir. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the injection - production well pattern deployment for the target low - permeability tight oil reservoir block.

[0015] Figure 2 It is a schematic diagram of the injection - production well pattern deployment after well pattern densification for a specific experimental case.

[0016] Figure 3 It is a graph showing the relationship between carbon dioxide flooding efficiency and miscibility degree.

[0017] Figure 4 It is a comparison graph of the fluid volume expansion after injecting the same underground volume of carbon dioxide and water.

[0018] Figure 5 It is a graph of the numerical simulation predicted recovery rate results under different schemes for the target low - permeability tight oil reservoir block. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] Example 1 A method for improving the miscibility degree of carbon dioxide flooding in a tight oil reservoir by water injection energy supplementation is as follows: Make the target low - permeability tight oil reservoir block in a relatively independent pressure system, and cross - deploy gas injection wells and injection wells along the dominant seepage azimuth within the injection - production well pattern of the block. Inject water in advance into the target reservoir in the target low - permeability tight oil reservoir block through the injection wells to raise the average pressure of the target reservoir above the minimum miscibility pressure of the carbon dioxide - crude oil system. Then, carbon dioxide is injected into the target reservoir through an injection well, enabling the carbon dioxide to achieve miscibility with the crude oil located within the target reservoir; production is carried out from the production well; During the process of injecting carbon dioxide, when the produced gas-oil ratio in the target low-permeability tight oil reservoir block rises to 1000 m 3 / m 3 or above, or when the gas channeling wells account for 10% - 20% of the total number of production wells, the original water injection wells are converted to inject carbon dioxide, and the original gas injection wells are converted to inject water to achieve single-well alternate flooding; When the produced gas-oil ratio in the target low-permeability tight oil reservoir block rises to 1000 m 3 / m 3 or above, or when the gas channeling wells account for 30% - 50% of the total number of production wells, along the dominant seepage direction, the production wells on the injection well row are converted into water-alternating-gas wells and the carbon dioxide injection and water injection wells are crossed to strengthen the injection-production relationship.

[0020] Example 2 Based on Example 1, it further includes: the target low-permeability tight oil reservoir block is a target low-permeability tight oil reservoir block with good integrity of the injection-production well pattern and good well conditions. Making the target low-permeability tight oil reservoir block in a relatively independent pressure system is specifically achieved by setting peripheral water injection wells around the target low-permeability tight oil reservoir block to form a block closed-loop water wall.

[0021] Example 3 Based on Example 2, it further includes: during the early water injection, the bottom-hole flowing pressure of the water injection well does not exceed the fracture pressure of the target reservoir. During the production of the production well, the bottom-hole flowing pressure of the production well is higher than the bubble point pressure. The alternate period of the single-well alternate flooding and the water-alternating-gas well is from half a year to one year.

[0022] Example 4 Based on Example 3, it further includes: the single-well water injection volume during the early water injection > the single-well water injection volume after the single-well alternation. Before and after the single-well alternate flooding, the injection rate of carbon dioxide remains unchanged.

[0023] Specific experimental case - a certain test area in the Ordos Basin A method for improving the miscibility degree of carbon dioxide flooding in tight oil reservoirs by water injection for energy supplementation is as follows.

[0024] Step 1: Screen the target low-permeability tight oil reservoir block; In a certain test area in the Ordos Basin, the average porosity of the reservoir of the oil reservoir is 9.4%, and the average permeability is 0.27 mD, belonging to a low-permeability tight oil reservoir, and its original formation pressure is 18.5 MPa; through relevant slim tube experiments, it is measured that the minimum miscibility pressure of the carbon dioxide - crude oil system in this block is 18.87 MPa, and the injected carbon dioxide and crude oil are mostly in a near-miscible displacement state (formation crude oil viscosity < 600 mPa·s, formation crude oil density < 993.0 kg / m3 , with reservoir depth > 900 m and oil saturation > 30%); Based on relevant fluid phase experiments, it is found that when injecting the same volume of carbon dioxide and water, due to the large amount of carbon dioxide dissolved in the formation crude oil, its pressure boosting and energy supplementing effect is slightly insufficient compared with water ( Figure 4 ); Therefore, pressure can be increased in the formation by early water injection for energy supplement; Therefore, taking this block as the target low-permeability and tight oil reservoir block, its injection-production well pattern is complete, which is a rhombic inverted nine-spot well pattern, and the long axis direction of the rhombic well pattern is consistent with the dominant seepage orientation of this block (NE65°), and the well conditions are good; There are a total of 121 wells and 16 injection-production well patterns in the target low-permeability and tight oil reservoir block.

[0025] Step 2: Make the target low-permeability and tight oil reservoir block in a relatively independent pressure system; Injecting gas wells and water injection wells are cross-deployed along the dominant seepage orientation among the injection wells within its injection-production well pattern; All the wells located at the outer boundary of the target low-permeability and tight oil reservoir block are transformed into outer water injection wells, and a closed-loop water wall of the block is formed by water injection ( Figure 1 in the 1st row, 1st column, 11th row, and 11th column), so that the target low-permeability and tight oil reservoir block is in a relatively independent pressure system; At the same time, injecting gas wells (3-5, 3-9, 5-5, 5-9, 7-5, 7-9, 9-5, and 9-9) and water injection wells (3-3, 3-7, 5-3, 5-7, 7-3, 7-7, 9-3, and 9-7) are cross-deployed along the dominant seepage orientation among the injection wells within the injection-production well pattern, and the result is as Figure 1 shown.

[0026] Step 3: Shut down all the production wells in the block, and conduct early water injection for the 8 deployed water injection wells with a single-well water injection volume of 20 - 30 tons per day, and the cumulative water injection volume is about 0.02 PV, ensuring that the average pressure of the target reservoir is increased from the original 18.5 MPa to above the minimum miscibility pressure of the carbon dioxide - crude oil system, which is 18.87 MPa. During the water injection process, control the bottom-hole flowing pressure of the water injection wells not to exceed the fracture pressure of the target reservoir.

[0027] Step 4: When the average pressure of the target reservoir is greater than the minimum miscibility pressure of the carbon dioxide - crude oil system, the 8 water injection wells continue to inject water with a single-well water injection volume of 10 - 15 tons per day; The injecting gas wells start to inject carbon dioxide into the target reservoir with a single-well gas injection volume of 15 - 25 tons per day; The carbon dioxide achieves miscibility with the crude oil located in the target reservoir, thereby realizing efficient miscible displacement of carbon dioxide for oil; Open the production wells to start oil production, and the bottom-hole flowing pressure of the production wells is 13 - 14 MPa, slightly higher than the bubble point pressure.

[0028] Step 5: When the produced gas - oil ratio in the target low-permeability and tight oil reservoir block rises to 1000 m 3 / m3 When the number of wells with excessive gas production or gas channeling accounts for 10% - 20% of the total number of production wells, the original water injection wells are converted to inject carbon dioxide, and the original gas injection wells are converted to inject water. The water injection volume per well is 10 - 15 tons per day, and the carbon dioxide injection volume is 15 - 25 tons per day. Then, it is adjusted alternately every six months, converting single-well continuous gas flooding / water flooding to single-well water-alternating gas flooding, suppressing gas channeling, preventing premature gas breakthrough and gas channeling in carbon dioxide flooding, improving the crude oil recovery rate of each injection-production well pattern, and ensuring the stability of the gas source supply at the same time.

[0029] Step 6: When the produced gas-oil ratio in the target low-permeability tight oil reservoir block rises to 1000 m 3 / m 3 or more, or when the number of wells with gas channeling accounts for 30% - 50% of the total number of production wells, along the dominant seepage direction, all the production wells on the injection well row are converted to water-alternating gas wells; taking the 3rd row as an example, 3-3, 3-5, 3-7, and 3-9 are all converted to water-alternating gas wells, and at the same time, ensure that the water-alternating gas wells along the dominant seepage direction on the injection well row are cross-injected; taking the 8th row as an example, if 8-4 is in the water injection stage at a certain moment, then 8-6 is in the gas injection stage at that moment, and 8-8 is in the water injection stage at that moment; in this way, the injection-production well pattern is densified, the overall injection-production ratio of the block is increased, the injection intensity is enhanced, and the gas flooding effect is further improved.

[0030] According to the prediction of the reservoir plan, the water flooding recovery rate of the target low-permeability tight oil reservoir block is 20.77%, the recovery rate of carbon dioxide near-miscible flooding without increasing the reservoir pressure is 29.33%, and the recovery rate of carbon dioxide miscible flooding with energy supplementation by early water injection to increase the reservoir pressure is 35.43%.

[0031] Therefore, by implementing early water injection to supplement energy according to this technology, the carbon dioxide in the target low-permeability tight oil reservoir block is changed from near-miscible to miscible flooding. Finally, the carbon dioxide miscible flooding can increase the recovery rate by 6.10% compared with carbon dioxide near-miscible flooding and by 14.66% compared with water flooding.

Claims

1. A method for improving the miscibility of carbon dioxide flooding in tight oil reservoirs by water injection and energy supplementation, characterized in that: Here’s how: The target low-permeability tight oil reservoir block is placed in a relatively independent pressure system, and the injection wells within the injection-production well network are cross-deployed with gas injection wells and water injection wells along the dominant seepage direction; Pre-inject water into the target reservoir in the target low-permeability tight oil reservoir block through water injection wells to increase the average pressure of the target reservoir to above the minimum miscibility pressure of the carbon dioxide-crude oil system; Then, carbon dioxide is injected into the target reservoir through the gas injection well to make the carbon dioxide and the crude oil in the target reservoir mixed; and production is carried out in the production well; During the injection of carbon dioxide, when the gas-oil ratio in the target low-permeability tight oil reservoir increases to 1000m 3 / m 3 When the number of gas-channeling wells exceeds 10% to 20% of the total number of production wells, the original water injection wells are converted to carbon dioxide injection, and the original gas injection wells are converted to water injection to achieve single-well alternating flooding. When the production gas-oil ratio in the target low-permeability tight oil reservoir increases to 1000 m 3 / m 3 When the above or gas breakthrough wells account for 30% to 50% of the total number of production wells, the production wells on the injection well row will be converted into water-gas alternating wells along the dominant seepage direction, and the carbon dioxide injection will be crossed with the water injection wells to strengthen the injection-production relationship.

2. The method for improving the miscibility of carbon dioxide flooding in tight oil reservoirs by water injection and energy supplementation according to claim 1, characterized in that: The target low-permeability tight oil reservoir block is a target low-permeability tight oil reservoir block with good injection and production well network integrity and good well conditions.

3. The method for improving the miscibility of carbon dioxide flooding in tight oil reservoirs by water injection and energy supplementation according to claim 2, characterized in that: The target low-permeability tight oil reservoir block is placed in a relatively independent pressure system, which is specifically achieved by setting peripheral water injection wells on the periphery of the target low-permeability tight oil reservoir block to form a closed-loop water wall of the block.

4. The method for improving the miscibility of carbon dioxide flooding in tight oil reservoirs by water injection and energy supplementation according to claim 1, characterized in that: During the advance water injection, the bottom hole flow pressure of the water injection well does not exceed the fracture pressure of the target reservoir.

5. The method for improving the miscibility of carbon dioxide flooding in tight oil reservoirs by water injection and energy supplementation according to claim 1, characterized in that: When the production well is in production, the bottom hole flowing pressure of the production well is higher than the bubble point pressure.

6. The method for improving the miscibility of carbon dioxide flooding in tight oil reservoirs by water injection and energy supplementation according to claim 1, characterized in that: The alternating cycle of the single well alternating flooding and the water-gas alternating wells is half a year to one year.

7. The method for improving the miscibility of carbon dioxide flooding in tight oil reservoirs by water injection and energy supplementation according to claim 1, characterized in that: The single well water injection volume during advance water injection is greater than the single well water injection volume after single well alternation.

8. The method for improving the miscibility of carbon dioxide flooding in tight oil reservoirs by water injection and energy supplementation according to claim 1, characterized in that: The injection rate of carbon dioxide remains unchanged before and after the single well alternating flooding.

Images