A method for CO2 composite energy enhancement and efficiency improvement after high cycle huff and puff of a heavy oil reservoir

Abstract

The application discloses a CO2 composite energy-increasing and efficiency-improving method for high-cycle steam soaking of a heavy oil reservoir, and comprises the following steps: step 101, selecting a proper target well in the heavy oil reservoir subjected to high-cycle steam soaking; step 102, sequentially injecting appropriate CO2 and a foam agent solution with a certain concentration into the target well; step 103, stewing the well for a period of time, so that the CO2 is fully dissolved in the crude oil and foam is formed; step 104, injecting appropriate N2 into the target well; step 105, performing a conventional steam injection and soaking operation on the target well; and step 106, evaluating the economic benefits of the target well and determining the CO2 injection stopping time. The application is suitable for the technical field of oilfield development, and a certain amount of CO2 is injected into the heavy oil reservoir subjected to high-cycle steam soaking and subjected to poor development effect due to low formation pressure, so that the formation pressure and the liquid production of the oil well are improved, the drainage radius of the oil well is expanded, the CO2 is extended to a far-well zone, and the CO2 storage rate is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of oilfield development, and specifically relates to a CO2 composite energy-increasing and efficiency-improving method after high-cycle huff and puff of a heavy oil reservoir. BACKGROUND

[0002] After more than 30 years of exploration and development, the proven heavy oil geological reserves of Shengli Oilfield are 660 million tons. Since the "Tenth Five-Year Plan", the heavy oil production of Shengli has increased significantly, of which nearly 98% of the production comes from steam injection and puffing. The stability of huff and puff production and the development of benefits are of great significance. However, as the huff and puff cycles increase, the production effect of the oil well becomes worse. Analysis of the reasons for the poor effect of high-cycle huff and puff shows that one of the important reasons is the lack of formation energy caused by depletion-type huff and puff development.

[0003] CO2 huff and puff is an effective stimulation measure and has been widely used in heavy oil reservoirs. CO2 huff and puff is to inject CO2 into the reservoir, and then to diffuse and mix CO2 further through soaking to improve the production of single wells. From the environmental protection point of view, CO2 huff and puff consumes the CO2 waste gas discharged from the production process of heavy industry, solves the problem of waste gas treatment, and slows down the greenhouse effect. From the effect point of view, CO2 not only can supplement the formation energy, but also can mix with crude oil to reduce the viscosity of crude oil and improve the recovery efficiency. From the benefit point of view, CO2 huff and puff has low investment, quick effect and good benefits.

[0004] Patent application CN115478818A is a method for improving recovery by CO-2 and N-2 composite huff and puff. It includes the following steps: step 1, determining the formation pressure maintenance level according to the reservoir geology and development data; step 2, determining the proportion and injection volume of the composite huff and puff injection gas and the soaking time according to the formation pressure maintenance level, and then performing huff and puff treatment; step 3, after the huff and puff treatment is completed, oil well production is started, and when the oil well production decreases to the oil well production before the huff and puff treatment, the oil well production is ended. The application determines the proportion and injection volume of CO-2 and N-2 composite huff and puff injection gas and the soaking time according to the formation pressure maintenance level, and plays the advantages of CO-2 and N-2 composite huff and puff. However, there is no technical measure to deal with high gas recovery rate of oil wells.

[0005] Patent application CN112360408A A new method for improving heavy oil recovery by injecting carbon dioxide hot fluid. It includes: step 1, heating carbon dioxide gas to 80-100 DEG C on the ground; step 2, injecting the heated carbon dioxide gas into the formation to heat and reduce the viscosity of heavy oil at a pressure higher than the original reservoir pressure by 20-30%; step 3, separating the produced heavy oil-carbon dioxide mixture and recovering carbon dioxide. The present application combines the mechanisms of CO-2 injection and thermal recovery of heavy oil, and only uses hot CO-2 as a heavy oil enhanced recovery medium, which simplifies the production process, reduces the production equipment, not only greatly saves water resources, but also reduces the production cost, reduces the safety risk caused by complex procedures in the production process, realizes the green and environmental protection development of heavy oil reservoir, and provides a green and efficient exploitation method for the shallow heavy oil reservoir in the arid and water shortage west. But this method has limited viscosity reduction range, only for near wellbore.

[0006] For the block with low formation pressure after high cycle huff and puff in Shengli, when CO2 assisted steam huff and puff is injected into the reservoir, the gas recovery rate of the oil well is high, which seriously affects the play of CO2 production increasing effect, and also brings environmental protection problem again. SUMMARY

[0007] The purpose of the present application is to overcome the defects of the prior art and provide a CO2 composite energy increasing and efficiency improving method for heavy oil reservoir after high cycle huff and puff.

[0008] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0009] A CO2 composite energy increasing and efficiency improving method for heavy oil reservoir after high cycle huff and puff, comprising the following steps:

[0010] Step 101: selecting a suitable target well in the heavy oil reservoir after high cycle huff and puff;

[0011] Step 102: injecting appropriate amount of CO2 and foam agent solution with certain concentration into the target well in turn;

[0012] Step 103: soak for a period of time to make CO2 fully dissolve in crude oil and form foam;

[0013] Step 104: injecting appropriate amount of N2 into the target well;

[0014] Step 105: performing conventional steam injection and huff and puff operation on the target well;

[0015] Step 106: evaluating the economic benefit of the target well to determine the timing of stopping injecting CO2.

[0016] Preferably, in step 101, the lower limit of formation pressure of the target well for CO2 stimulation after high-cycle steam stimulation is the minimum pressure required for the crude oil to be converted into Newtonian fluid after dissolving a certain amount of CO2.

[0017] Preferably, in step 101, the lower limit of formation pressure is determined by first determining the viscosity of the crude oil when it is converted into Newtonian fluid according to the viscosity-temperature curve and the rheological curve, and then determining the amount of CO2 to be dissolved for the conversion of the crude oil into Newtonian fluid.

[0018] Preferably, in step 101, it further comprises:

[0019] The amount of CO2 dissolved in the produced crude oil of the target block under different pressures is determined, and the lower limit of formation pressure required by the target well is determined according to the amount of CO2 to be dissolved for the normal flow of the crude oil in the formation.

[0020] Preferably, in step 102, the injected CO2 is in liquid state.

[0021] Preferably, in step 102, the cumulative oil production of the target well under different CO2 injection intensities is predicted by using a numerical simulation model, the economic benefits after deducting the operating costs, CO2 injection and steam costs are calculated, and the appropriate amount of CO2 injection is determined according to the principle of optimal economic benefits.

[0022] Preferably, in step 102, the resistance factor of the foam solution of different concentrations is measured in the laboratory, and the concentration of the foam solution corresponding to the maximum resistance factor is the appropriate concentration of the foam.

[0023] Preferably, in step 102, the change of bottom hole flowing pressure is continuously monitored during the injection of CO2 and the foam solution of a certain concentration.

[0024] Preferably, in step 103, the determination method of soak time is:

[0025] The solubility of CO2 in crude oil under different soak times is determined by analyzing the molar fraction field diagram of CO2 in oil phase obtained after numerical simulation calculation, and when the molar fraction of CO2 in oil phase basically does not change after a certain soak time, this time is the appropriate soak time in theory.

[0026] Preferably, in step 103, after the injection of CO2 and the foam solution of a certain concentration, the change of bottom hole flowing pressure is continuously monitored, and when the decrease of bottom hole flowing pressure is significantly slowed down, it indicates that the dissolution of CO2 in crude oil has approached saturation, and the soak can be ended.

[0027] Preferably, in the step 104, the N2 injection amount is determined by the same method as the optimization of the CO2 injection amount in the step 102.

[0028] Preferably, in the step 104, the cumulative oil production of the target well under different N2 injection intensities is predicted by using a numerical simulation model, and the economic benefits after deducting the operation cost, the N2 injection cost and the steam injection cost are calculated, and the appropriate N2 injection amount corresponds to the optimal economic benefits.

[0029] Preferably, in the step 105, in addition to the normal steam injection amount, a certain amount of steam is additionally injected for heat compensation.

[0030] Preferably, in the step 105, a certain amount of steam is additionally injected for compensating the heat absorbed by the injected CO2 after entering the oil layer.

[0031] Preferably, in the step 106, the cumulative oil production of the target well after different rounds of the stimulation according to the steps 101-5 is predicted, and the economic benefits after deducting the cumulative cost of all rounds of operation cost, CO2 injection cost, N2 injection cost and steam injection cost are calculated.

[0032] Preferably, in the step 106, when the economic benefits no longer increase with the increase of the stimulation rounds, the round is the CO2 injection stop opportunity.

[0033] In summary, due to the adoption of the above technical solutions, the present application has the following beneficial effects:

[0034] In the present application, by injecting a certain amount of CO2 into the heavy oil reservoir with poor development effect due to low formation pressure after high-round steam stimulation, the formation pressure and the liquid production of the oil well are improved, and the drainage radius of the oil well is expanded; meanwhile, by injecting a certain amount of foam agent to promote the extension of CO2 to the far-well zone, the CO2 storage rate is improved; compared with steam stimulation, the recovery degree is improved, the economic benefits and the CO2 gas storage amount of a single well are increased, and the low-carbon economic development of the heavy oil reservoir after high-round stimulation is realized. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 is the flow chart of the present application;

[0036] Figure 2 is the curve graph of the change of the crude oil viscosity with the CO2 dissolution amount in the specific embodiment of the present application;

[0037] Figure 3 is the curve graph of the change of the CO2 dissolution amount with the saturation pressure in the specific embodiment of the present application;

[0038] Figure 4 is the curve graph of the change of the economic benefits of the oil well under different CO2 injection intensities in the specific embodiment of the present application;

[0039] Figure 5 This is a graph showing the variation of the drag factor under different foaming agent concentrations in a specific embodiment of the present invention;

[0040] Figure 6 This is a graph showing the change in the mole fraction of CO2 in the oil phase under different well-closing times in a specific embodiment of the present invention;

[0041] Figure 7 This is a graph showing the economic benefits of oil wells under different N2 injection volumes in a specific embodiment of the present invention.

[0042] Figure 8 This is a graph showing the change in the economic benefits of oil wells under different CO2-assisted steam huff and puff cycles in a specific embodiment of the present invention. Detailed Implementation

[0043] The following is in conjunction with the appendix Figures 1-8 This invention further illustrates the specific implementation of a CO2-based energy enhancement and efficiency improvement method for heavy oil reservoirs after high-cycle huff and puff. The method is not limited to the descriptions in the following embodiments.

[0044] Example 1:

[0045] A method for enhancing efficiency and improving the combined capacity of CO2 after high-cycle huff and puff in heavy oil reservoirs, such as... Figure 1 As shown, it includes the following steps:

[0046] Step 101: Select a suitable target well in a high-cycle heavy oil reservoir;

[0047] Step 102: Inject appropriate amounts of CO2 and a foaming agent solution of a certain concentration into the target well in sequence;

[0048] Step 103: Simmer the well for a period of time to allow CO2 to fully dissolve in the crude oil and form foam;

[0049] Step 104: Inject an appropriate amount of N2 into the target well;

[0050] Step 105: Perform conventional steam injection and huff-and-puff operations on the target well;

[0051] Step 106: Evaluate the economic benefits of the target well and determine the timing for stopping CO2 injection.

[0052] Example 2:

[0053] A method for enhancing efficiency and improving the combined capacity of CO2 after high-cycle huff and puff in heavy oil reservoirs, such as... Figure 1As shown, other steps are similar to example 1, further, in step 101, the lower limit value of the formation pressure of the target well after high-cycle steam stimulation and CO2 energy enhancement is the minimum pressure required to convert the crude oil into Newtonian fluid after dissolving a certain amount of CO2.

[0054] Example 3:

[0055] A CO2 composite energy enhancement method for heavy oil reservoir after high-cycle stimulation, as shown in Figure 1 As shown, other steps are similar to example 2, further, in step 101, the specific method for determining the lower limit value of the formation pressure is: first, determine the viscosity of the crude oil when it is converted into Newtonian fluid according to the viscosity-temperature curve and the rheological curve, then measure the viscosity of the crude oil when it dissolves different amounts of CO2, and determine the amount of CO2 that needs to be dissolved when the crude oil is converted into Newtonian fluid.

[0056] Example 4:

[0057] A CO2 composite energy enhancement method for heavy oil reservoir after high-cycle stimulation, as shown in Figure 1 As shown, other steps are similar to example 3, further, in step 101, it also includes:

[0058] Determine the amount of CO2 dissolved in the produced crude oil of the target well under different pressures, and determine the lower limit value of the formation pressure that the target well needs to meet according to the amount of CO2 that needs to be dissolved when the crude oil can flow normally in the formation.

[0059] Example 5:

[0060] A CO2 composite energy enhancement method for heavy oil reservoir after high-cycle stimulation, as shown in Figure 1 As shown, other steps are similar to example 1, further, in step 102, the injected CO2 is in liquid state.

[0061] Further, in step 102, use numerical simulation model to predict the cumulative oil production of the target well under different CO2 injection intensities, calculate the economic benefits after deducting operating costs, CO2 injection and steam costs, and determine the appropriate CO2 injection amount according to the principle of optimal economic benefits.

[0062] Example 6:

[0063] A CO2 composite energy enhancement method for heavy oil reservoir after high-cycle stimulation, as shown in Figure 1 As shown, other steps are similar to example 5, further, in step 102, the resistance factor of the foam agent solution of different concentrations is measured in the laboratory, and the concentration of the foam agent solution corresponding to the maximum resistance factor is the appropriate concentration of the foam agent.

[0064] Further, in step 102, the change of the bottom hole flowing pressure is continuously monitored during the injection of CO2 and the solution of the foam agent with a certain concentration.

[0065] Example 7

[0066] A CO2 compound energy-increasing and efficiency-improving method for a heavy oil reservoir after high-cycle huff and puff, as shown in Figure 1 The other steps are similar to those in Example 1, and further, in step 103, the determination method of the soak time is as follows:

[0067] The dissolution of CO2 in the crude oil at different soak times is determined by analyzing the CO2 molar fraction field in the oil phase obtained after numerical simulation calculation. When the soak time reaches a certain time, the CO2 molar fraction in the oil phase basically no longer changes, and this time is the theoretically appropriate soak time.

[0068] Example 8

[0069] A CO2 compound energy-increasing and efficiency-improving method for a heavy oil reservoir after high-cycle huff and puff, as shown in Figure 1 The other steps are similar to those in Example 7, and further, in step 103, after the injection of CO2 and the solution of the foam agent with a certain concentration is completed, the change of the bottom hole flowing pressure is continuously monitored. When it is monitored that the decrease of the bottom hole flowing pressure significantly slows down, it indicates that the dissolution of CO2 in the crude oil has approached saturation, and the soak can be ended.

[0070] Example 9

[0071] A CO2 compound energy-increasing and efficiency-improving method for a heavy oil reservoir after high-cycle huff and puff, as shown in Figure 1 The other steps are similar to those in Example 1, and further, in step 104, the N2 injection amount is determined by using the same method as that for the optimization of the CO2 injection amount in step 102.

[0072] Example 10

[0073] A CO2 compound energy-increasing and efficiency-improving method for a heavy oil reservoir after high-cycle huff and puff, as shown in Figure 1 The other steps are similar to those in Example 9, and further, in step 104, the cumulative oil production of the target well under different N2 injection intensities is predicted by using a numerical simulation model, and the economic benefits after deducting the operating costs, N2 injection and steam costs are calculated. When the economic benefits are optimal, the corresponding N2 injection amount is the appropriate N2 injection amount.

[0074] Example 11

[0075] A CO2 compound energy-increasing and efficiency-improving method for a heavy oil reservoir after high-cycle huff and puff, as shown in Figure 1As shown, other steps are similar to example 1, further, in step 105, in addition to the normal steam injection amount, a certain amount of steam is additionally injected for heat compensation.

[0076] Example 12:

[0077] A CO2 compound energy-increasing and efficiency-improving method for high-cycle huff and puff of a heavy oil reservoir, as shown in Figure 1 As shown, other steps are similar to example 10, further, in step 105, a certain amount of steam is additionally injected for compensating the heat absorbed after the injected CO2 enters the oil layer.

[0078] Example 13:

[0079] A CO2 compound energy-increasing and efficiency-improving method for high-cycle huff and puff of a heavy oil reservoir, as shown in Figure 1 As shown, other steps are similar to example 1, further, in step 106, the cumulative oil production of the target well after different cycles of huff and puff according to steps 101-5 is predicted, and the economic benefit after deducting the cumulative cost of all cycle operation, CO2 injection, N2 injection and steam injection is calculated.

[0080] Example 14:

[0081] A CO2 compound energy-increasing and efficiency-improving method for high-cycle huff and puff of a heavy oil reservoir, as shown in Figure 1 As shown, other steps are similar to example 13, further, in step 106, when the economic benefit no longer increases with the increase of huff and puff cycles, this cycle is the CO2 injection stopping opportunity.

[0082] Method mechanism analysis:

[0083] In step 101, the suitable target well selection process of CO2 energy-increasing and efficiency-improving after high-cycle huff and puff of a heavy oil reservoir is as follows: first, the viscosity of the produced oil of the target block oil well dissolved in different amounts of CO2 is measured, and the viscosity of the oil when it is converted into a Newtonian fluid is obtained by combining the oil viscosity-temperature curve and the rheological curve, to determine the amount of CO2 dissolved in the oil required for normal flow in the formation, and then the dissolution amount of CO2 in the produced oil of the target block oil well under different pressures is determined, and the lower limit value of the formation pressure required by the target well is determined according to the amount of CO2 dissolved in the oil required for normal flow in the formation, and the well with the formation pressure above the lower limit value is selected as the target well for CO2 energy-increasing and efficiency-improving.

[0084] In a possible implementation, the viscosity of the produced oil of the target block oil well dissolved in 0-107.5 m 3 / tCO2 is first measured respectively, and the viscosity curve of the oil with the change of the CO2 dissolution amount is drawn, as shown in Figure 2As shown; based on the crude oil viscosity-temperature curve and rheological curve, the viscosity of the crude oil when converted to a Newtonian fluid is determined to be 201 mPa·s. Therefore, to make the crude oil flow, at least 11.5 m³ of crude oil needs to be dissolved. 3 / t CO2; then measure the solubility of CO2 in crude oil under pressures of 0–17 MPa, such as Figure 3 As shown, the minimum amount of crude oil required to make it flow is 11.5m³. 3 The minimum required pressure for CO2 is determined to be 3.5 MPa. Wells with formation pressures above 3.5 MPa in the target block are selected as target wells for CO2 energy enhancement and efficiency improvement. The process proceeds to step 102.

[0085] In step 102, a numerical simulation model is used to predict the cumulative oil production of the target well under different CO2 injection intensities (t / m of liquid CO2 injection per meter of oil layer thickness). The economic benefits after deducting operating costs, CO2 injection costs, and steam injection costs are calculated, and the appropriate CO2 injection rate is determined based on the magnitude of the economic benefits. Simultaneously, the appropriate concentration of the foaming agent is determined based on the resistance factors of different concentrations of foaming agent solutions measured in the laboratory. Changes in bottom hole flowing pressure are continuously monitored during the injection of CO2 and foaming agent solutions into the target well.

[0086] In one possible implementation, numerical simulations predict the cumulative oil production of the target well when CO2 is injected at intensities of 6.8–34 t / m³, based on an oil price of $50 / barrel and a CO2 price of 357 yuan / ton (0.638 yuan / m³). 3 The economic benefits of oil wells under different CO2 injection intensities were calculated based on a steam price of 340 yuan / ton, and curves showing the changes in economic benefits under different CO2 injection intensities were plotted. The CO2 injection intensity corresponding to the point of maximum economic benefit on the curve is 27.2 t / m. Figure 4 As shown, based on this intensity, the appropriate CO2 injection rate for the target well is calculated to be 300t. Meanwhile, the drag factor of the solution was measured in the laboratory when the foaming agent concentration was 0-1.0%. When the foaming agent concentration exceeded 0.5%, the increase in the drag factor of the foaming agent solution slowed significantly, as shown below. Figure 5 As shown, the appropriate concentration of the foaming agent is 0.5%, and the injection volume of the foaming agent solution is matched to the CO2 injection volume at 1000m³. 3 During the injection of CO2 and foaming agent solution into the target well, the change in bottom hole flowing pressure is continuously monitored. The process then proceeds to step 103.

[0087] In step 103, the theoretical shut-in time after injecting CO2 and foaming agent solution is calculated through numerical simulation. In actual operation at the mine, guided by the theoretical shut-in time, the change in bottom hole flowing pressure after injecting CO2 and foaming agent solution is continuously monitored. The shut-in can be ended when the rate of decrease in bottom hole flowing pressure is significantly slowed down.

[0088] In one possible implementation, numerical simulations were used to obtain the mole fraction field of CO2 in the oil phase at different well-closing times after CO2 and foaming agent solution injection. It can be seen that after injection, CO2 mainly accumulates around 20m in the wellbore. As the well-closing time increases, the CO2 gas continuously expands into the formation, with an expansion radius of approximately 44m. A curve showing the relationship between the number of well-closing days and the mole fraction of CO2 in the oil phase was plotted, as shown below. Figure 6 As shown, after 5-7 days of well shut-in, the change in the molar fraction of CO2 in the oil is small, indicating that CO2 no longer dissolves and expands in the reservoir, which is the theoretically appropriate shut-in time. In actual field operations, by continuously monitoring the change in bottomhole flowing pressure of the target well after CO2 and foaming agent solution injection and shut-in, it was found that after 7-10 days of well shut-in after CO2 injection, the rate of formation pressure decrease slowed significantly, indicating that CO2 dissolution was close to saturation, and well shut-in could be ended, and the process proceeded to step 104.

[0089] In step 104, after the CO2 and foaming agent solution have been injected and the well has been steamed, a certain amount of N2 is injected into the formation to promote the further expansion of CO2 into the far-well zone and to isolate the foaming agent solution from direct contact with subsequent high-temperature steam, thus preventing the foaming agent from failing. The amount of N2 injected is determined using the same method as the CO2 injection amount optimization in step 10102.

[0090] In one possible implementation, the target well predicted by numerical modeling is injected with 0-60,000 m³ of CO2 and foaming agent solution after the well has been saturated. 3 The cumulative oil production during the N2 phase, based on an oil price of $50 / barrel and CO2 production of 357 yuan / ton (0.638 yuan / m³). 3 N21.5 yuan / m 3 The economic benefits of oil wells under different N2 injection volumes were calculated based on the prices of foaming agent (10,000 yuan / ton) and steam (340 yuan / ton). Curves showing the changes in economic benefits under different N2 injection volumes were plotted, with the N2 injection volume corresponding to the point of maximum economic benefit on the curve being 20,000 m³. 3 ,like Figure 7 As shown, gaseous N2 is injected into the target well according to this amount. The process then proceeds to step 105.

[0091] In step 105, in addition to injecting the normal amount of water vapor according to the oil layer thickness, an extra amount of water vapor is injected to compensate for the heat that the bottled CO2 below 0°C needs to absorb after entering the oil layer.

[0092] In a possible implementation, according to the result of the numerical model optimization, the suitable steam injection intensity of the target well is 240 t / m, the average thickness of the reservoir in the control range of the well is 9.72 m, and the calculated normal water-steam injection amount required is 2332 t. The CO2 tank outlet temperature is minus 14 ℃, the temperature after injection into the well bottom is 15 ℃, the reservoir temperature is 60 ℃, and 1080*10 4 KJ of heat is required to make the injected 300 t of CO2 reach the same temperature as the reservoir. Since 1 t of 300 ℃ steam injected into the underground can release 135.64*10 4 KJ of heat when reaching the same temperature as the reservoir, about 8 t of steam heat is required to consume the heat of the injected 300 t of CO2, and the total water-steam injection amount of the target well is 2340 t. The process enters step 106.

[0093] In step 106, the cumulative oil production of the target well after 5-14 cycles of huff and puff according to steps 101-105 is predicted, that is, the CO2 injection stopping time.

[0094] In a possible implementation, the numerical model predicts the cumulative oil production of the target well after different cycles of huff and puff according to steps 101-105, and calculates the economic benefits of the oil well at different huff and puff cycles according to the prices of 50 dollars per barrel of oil, 357 yuan per ton (0.638 yuan / m 3 ) of CO2, 1.5 yuan / m 3 of N2, 10000 yuan per ton of foam agent, and 340 yuan per ton of steam, and makes a curve of the economic benefit changes of the oil well at different huff and puff cycles of CO2 assisted steam, as shown in FIG. 6. When the huff and puff cycles are greater than 10 cycles, the economic benefit basically no longer increases, and thus the suitable CO2 injection stopping time is after 10 cycles. Figure 8

[0095] In summary: by injecting a certain amount of CO2 into the heavy oil reservoir with low formation pressure after high-cycle steam huff and puff, the formation pressure is increased by 39%, the liquid production of the oil well is increased by 28%, and the drainage radius of the oil well is expanded by 20 m; meanwhile, by injecting a certain amount of foam agent to promote the extension of CO2 to the far-well zone by 40 m, the CO2 storage rate is increased by 11.2 percentage points; this CO2 compound energy-increasing and efficiency-improving method can increase the recovery degree by 4.7 percentage points compared with steam huff and puff, increase the economic benefit of a single well by 800,000 yuan, and bury 1534 t of CO2 gas, thereby realizing the low-carbon economic development of the heavy oil reservoir after high-cycle huff and puff.

[0096] The above is a further detailed description of the present application in combination with the specific preferred implementation, and the specific implementation of the present application cannot be limited to these descriptions. For ordinary skilled persons in the technical field to which the present application belongs, some simple deductions or substitutions can be made without departing from the concept of the present application, and all of them shall be regarded as falling within the protection scope of the present application.​

Claims

1. A method for enhancing efficiency and improving the combined capacity of CO2 after high-cycle huff and puff in heavy oil reservoirs, characterized in that, Includes the following steps: Step 101: Select a suitable target well in a high-cycle heavy oil reservoir; Step 102: Inject appropriate amounts of CO2 and a foaming agent solution of a certain concentration into the target well in sequence; Step 103: Simmer the well for a period of time to allow CO2 to fully dissolve in the crude oil and form foam; Step 104: Inject an appropriate amount of N2 into the target well; Step 105: Perform conventional steam injection and huff-and-puff operations on the target well; Step 106: Evaluate the economic benefits of the target well and determine the timing for stopping CO2 injection; In step 101, the target well for CO2 energy enhancement and efficiency improvement after high-cycle steam huff and puff has a formation pressure limit of the minimum pressure required to ensure that crude oil can be converted into a Newtonian fluid after dissolving a certain amount of CO2. In step 101, the specific method for determining the lower limit of formation pressure is as follows: First, determine the viscosity of the crude oil when it is converted into a Newtonian fluid based on the crude oil viscosity-temperature curve and rheological curve. Then, measure the viscosity of the crude oil at different CO2 dissolution rates to determine the amount of CO2 required to be dissolved when the crude oil is converted into a Newtonian fluid. Step 101 further includes: The amount of CO2 dissolved in the crude oil produced from the oil wells in the target block under different pressures was determined. Based on the amount of CO2 required for the crude oil to flow normally in the formation, the lower limit of the formation pressure that the target well needs to meet was determined. In step 102, the cumulative oil production of the target well under different CO2 injection intensities is predicted using a numerical simulation model, the economic benefits after deducting operating costs, CO2 injection and steam costs are calculated, and the appropriate CO2 injection amount is determined based on the principle of optimal economic benefits. In step 102, the resistance factor of foaming agent solutions of different concentrations is measured in the laboratory. The foaming agent solution concentration corresponding to the maximum resistance factor is the appropriate foaming agent concentration. In step 103, after injecting CO2 and a certain concentration of foaming agent solution and starting well shut-in, the change in bottom hole flowing pressure is continuously monitored. When the rate of decrease in bottom hole flowing pressure is significantly slowed down, it indicates that the dissolution of CO2 in crude oil has approached saturation, and well shut-in can be ended. In step 104, the N2 injection amount is determined using the same method as the CO2 injection amount optimization in step 102.

2. The method for enhancing efficiency and improving the combined capacity of CO2 after high-cycle huff and puff in heavy oil reservoirs as described in claim 1, characterized in that: In step 102, the injected CO2 is in liquid state.

3. The method for enhancing efficiency and improving the combined capacity of CO2 after high-cycle huff and puff in heavy oil reservoirs as described in claim 1, characterized in that: In step 102, during the injection of CO2 and a foaming agent solution of a certain concentration, the change in bottom hole flowing pressure is continuously monitored.

4. The method for enhancing efficiency and improving the combined capacity of CO2 after high-cycle huff and puff in heavy oil reservoirs as described in claim 1, characterized in that, In step 103, the method for determining the well-clogging time is as follows: By analyzing the mole fraction field diagram of CO2 in the oil phase obtained from numerical simulation calculations, the dissolution status of CO2 in crude oil under different well-closing times can be determined. When the well-closing time reaches a certain point, the mole fraction of CO2 in the oil phase basically no longer changes. This time is the theoretically appropriate well-closing time.

5. The method for enhancing efficiency and improving the combined capacity of CO2 after high-cycle huff and puff in heavy oil reservoirs as described in claim 1, characterized in that: In step 104, the cumulative oil production of the target well under different N2 injection intensities is predicted using a numerical simulation model. The economic benefits after deducting operating costs, N2 injection and steam costs are calculated, and the appropriate N2 injection amount is the one with the best economic benefits.

6. The method for enhancing efficiency and improving the combined capacity of CO2 after high-cycle huff and puff in heavy oil reservoirs as described in claim 1, characterized in that: In step 105, in addition to the normal amount of steam injected, a certain amount of steam is injected extra to compensate for heat.

7. The method for enhancing efficiency and improving the combined capacity of CO2 after high-cycle huff and puff in heavy oil reservoirs as described in claim 6, characterized in that: In step 105, an additional amount of steam is injected to compensate for the heat absorbed by the injected CO2 after it enters the oil layer.

8. The method for enhancing efficiency and improving the combined capacity of CO2 after high-cycle huff and puff in heavy oil reservoirs as described in claim 1, characterized in that: In step 106, the cumulative oil production of the target well after different cycles of injection and churn in steps 101-5 is predicted, and the economic benefits after deducting the operating costs of all cycles, the cumulative costs of CO2 injection, N2 injection, and steam injection are calculated.

9. The method for enhancing efficiency and improving the combined capacity of CO2 after high-cycle huff and puff in heavy oil reservoirs as described in claim 8, characterized in that: In step 106, when the economic benefits no longer increase with the increase of throughput cycles, this cycle is the time to stop injecting CO2.

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