CO2 composite energy increasing and efficiency improving method after heavy oil reservoir high-round huff and puff

Abstract

The invention discloses a CO2 composite energy increasing and efficiency improving method after high-round throughput of a heavy oil reservoir. The CO2 composite energy increasing and efficiency improving method comprises the following steps that 101, an appropriate target well is selected from the high-round throughput heavy oil reservoir; 102, a proper amount of CO2 and a foaming agent solution with a certain concentration are sequentially injected into the target well; step 103, soaking the well for a period of time, so that CO2 is fully dissolved in the crude oil and foam is formed; 104, a proper amount of N2 is injected into the target well; 105, conventional steam injection huff and puff operation is conducted on the target well; and 106, the economic benefits of the target well are evaluated, and the CO2 injection stopping opportunity is determined. The method is suitable for the technical field of oil field development, a certain amount of CO2 is injected into the heavy oil reservoir which becomes poor in development effect due to low formation pressure after high-round steam huff and puff, the formation pressure and the oil well liquid production capacity are improved, and the oil well production radius is enlarged; cO2 is promoted to expand and extend to a far wellbore zone, and the CO2 storage rate is increased.

Description

Technical Field

[0001] The invention belongs to the technical field of oilfield development, and in particular is a method for improving the efficiency of CO2 composite energy after high-cycle throughput in a heavy oil reservoir. Background Art

[0002] After more than 30 years of exploration and development, Shengli Oilfield has proved that the geological reserves of heavy oil are 660 million tons. Since the 15th Five-Year Plan, the production of Shengli heavy oil has increased significantly, of which nearly 98% comes from steam injection. The stability and efficiency of the production of the throughput are of great significance. However, with the increase of the throughput round, the production effect of the oil well has deteriorated. The reasons for the poor throughput effect of high rounds are analyzed, and the lack of formation energy caused by exhaustion-type throughput production is an important reason.

[0003] CO2 huff and puff is an effective measure to increase production, and is widely used in heavy oil reservoirs. CO2 huff and puff oil production is to inject CO2 into the reservoir, and then make the carbon dioxide diffuse and miscible by shutting the well to achieve the purpose of increasing the production of a single well. From an environmental perspective, CO2 huff and puff oil production consumes the carbon dioxide waste gas emitted in the heavy industrial production process, solves the problem of waste gas treatment, and slows down the greenhouse effect; from an effect perspective, carbon dioxide can not only replenish formation energy, but also miscible with crude oil, reduce the viscosity of crude oil, etc., and improve the recovery rate; from a benefit perspective, CO2 huff and puff oil production has low investment, fast results, and good returns.

[0004] Patent application CN115478818A discloses a method for improving oil recovery by composite CO-2 and N-2 huff and puff. It includes: step 1, determining the formation pressure maintenance level according to reservoir geology and development data; step 2, determining the ratio and injection volume of composite huff and puff injected gas, as well as the well shut-in 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, starting oil well production until the oil well production drops to the oil well production before the huff and puff treatment, and then ending oil well production. This invention determines the ratio, injection volume and well shut-in time of composite CO-2 and N-2 huff and puff injected gas according to the formation pressure maintenance level, and gives full play to the advantages of composite CO-2 and N-2 huff and puff. However, there are no technical measures to deal with the high gas recovery rate of oil wells.

[0005] Patent application CN112360408A discloses a new method for increasing the recovery rate of heavy oil by injecting carbon dioxide hot fluid. It includes: step 1, heating carbon dioxide gas to 80-100℃ on the ground; step 2, injecting the heated carbon dioxide gas into the formation at an injection pressure 20-30% higher than the original reservoir pressure to heat and reduce the viscosity of the heavy oil; step 3, separating the produced heavy oil-carbon dioxide mixture and recovering carbon dioxide. The present invention organically combines the CO-2 injection and thermal recovery mechanism of heavy oil, and only uses hot CO-2 as the medium for increasing the recovery rate of heavy oil, which simplifies the production process and reduces the production equipment. It not only greatly saves water resources, but also reduces production costs and reduces the safety risks caused by complex procedures in the production process, thus realizing the green and environmentally friendly development of heavy oil reservoirs, and providing a green and efficient mining method for the shallow heavy oil reservoirs in the western region with drought and water shortage. However, the viscosity reduction range of this method is limited, and it is only limited to the near-well area.

[0006] For blocks with low formation pressure after high-round throughput in Shengli, when CO2-assisted steam throughput is injected into the reservoir, the gas recovery rate of the oil wells is high, which seriously affects the CO2 production-increasing effect and also brings up environmental protection problems again. Summary of the invention

[0007] The purpose of the present invention is to overcome the defects of the prior art and provide a method for improving the efficiency of CO2 composite energy after high-cycle throughput in heavy oil reservoirs.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] A method for improving the efficiency of CO2 composite energy after high-cycle huff-and-puff in a heavy oil reservoir comprises the following steps:

[0010] Step 101: Select a suitable target well in a high-cycle throughput heavy oil reservoir;

[0011] Step 102: injecting an appropriate amount of CO2 and a foaming agent solution of a certain concentration into the target well in sequence;

[0012] Step 103: Immerse the well for a period of time to allow the CO2 to fully dissolve in the crude oil and form foam;

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

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

[0015] Step 106: Evaluate the economic benefits of the target well and determine the timing to stop CO2 injection.

[0016] Preferably, in step 101, the lower limit of the formation pressure of the target well that is subjected to CO2 energy enhancement and efficiency improvement after high-cycle steam stimulation is the minimum pressure required to ensure that the crude oil can be converted into a Newtonian fluid after dissolving a certain amount of CO2.

[0017] Preferably, in step 101, the specific method for obtaining the lower limit of the formation pressure is: 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 the rheological curve, then measure the viscosity of the crude oil under different amounts of CO2 dissolved, and determine the amount of CO2 required to dissolve when the crude oil is converted into a Newtonian fluid.

[0018] Preferably, the step 101 further includes:

[0019] The amount of CO2 dissolved in the crude oil produced from the target block oil wells under different pressures is measured, and the lower limit of the formation pressure that the target well needs to meet is determined based on the amount of CO2 that needs to be dissolved when the crude oil can flow normally in the formation.

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

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

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

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

[0024] Preferably, in step 103, the method for determining the soaking time is:

[0025] By analyzing the mole fraction field diagram of CO2 in the oil phase obtained after numerical simulation calculation, the solubility of CO2 in crude oil at different shut-in times can be judged. When the shut-in time reaches a certain time, the mole fraction of CO2 in the oil phase basically no longer changes. This time is the theoretically appropriate shut-in time.

[0026] Preferably, in step 103, after CO2 and a certain concentration of foaming agent solution are injected and the well is started to be shut down, the change of bottom hole pressure is continuously monitored. When the decrease of bottom hole pressure is monitored to be significantly slowed down, it means that the dissolution of CO2 in crude oil is close to saturation and the well can be stopped.

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

[0028] Preferably, in step 104, a numerical simulation model is used to predict the cumulative oil production of the target well under different N2 injection intensities, and the economic benefits after deducting the operating costs, N2 injection and steam costs are calculated. The appropriate N2 injection amount is when the economic benefits are optimal.

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

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

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

[0032] Preferably, in step 106, when the economic benefit no longer increases with the increase in throughput rounds, this round is the time to stop injecting CO2.

[0033] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0034] In the present invention, a certain amount of CO2 is injected into a heavy oil reservoir whose development effect has deteriorated due to low formation pressure after high-cycle steam huff and puff, thereby increasing the formation pressure and the oil well liquid production and expanding the oil well utilization radius; at the same time, a certain amount of foaming agent is injected to cause CO2 to expand and extend to areas far from the wellbore, thereby increasing the CO2 storage rate; compared with steam huff and puff, the recovery degree is increased, the economic benefits and CO2 gas storage capacity of a single well are increased, and low-carbon economic development of heavy oil reservoirs after high-cycle huff and puff is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0036] Figure 2 This is a graph showing the change of crude oil viscosity with CO2 dissolution in a specific embodiment of the present invention;

[0037] Figure 3 This is a curve diagram showing the variation of CO2 dissolution amount with saturation pressure in a specific embodiment of the present invention;

[0038] Figure 4 It is a curve diagram of the economic benefits of oil wells under different CO2 injection intensities in a specific embodiment of the present invention;

[0039] Figure 5 It is a resistance factor variation curve diagram under different foaming agent concentrations in a specific embodiment of the present invention;

[0040] Figure 6 It is a curve diagram of the change of the mole fraction of CO2 in the oil phase at different soaking times in a specific embodiment of the present invention;

[0041] Figure 7 It is a curve diagram of the economic benefits of oil wells under different N2 injection amounts in a specific embodiment of the present invention;

[0042] Figure 8 This is a curve diagram of the economic benefits of oil wells under different numbers of CO2-assisted steam throughput cycles in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0043] The following is combined with Figure 1-8 , further illustrating a specific implementation of a CO2 composite energy enhancement and efficiency improvement method after high-cycle huff and puff of a heavy oil reservoir of the present invention. A CO2 composite energy enhancement and efficiency improvement method after high-cycle huff and puff of a heavy oil reservoir of the present invention is not limited to the description of the following embodiments.

[0044] Embodiment 1:

[0045] A method for improving the efficiency of CO2 composite energy after high-cycle huff-and-puff in heavy oil reservoirs, such as Figure 1 As shown, the following steps are included:

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

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

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

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

[0050] Step 105: performing 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 to stop CO2 injection.

[0052] Embodiment 2:

[0053] A method for improving the efficiency of CO2 composite energy after high-cycle huff-and-puff in heavy oil reservoirs, such as Figure 1As shown, other steps are similar to Example 1. Furthermore, in step 101, the lower limit of the formation pressure of the target well for CO2 energy enhancement and efficiency improvement after high-cycle steam stimulation is the minimum pressure required to ensure that the crude oil can be converted into a Newtonian fluid after dissolving a certain amount of CO2.

[0054] Embodiment 3:

[0055] A method for improving the efficiency of CO2 composite energy after high-cycle huff-and-puff in heavy oil reservoirs, such as Figure 1 As shown, other steps are similar to those of Example 2. Furthermore, in step 101, the specific method for obtaining the lower limit of the formation pressure is as follows: first, the viscosity of the crude oil when it is converted into a Newtonian fluid is determined based on the crude oil viscosity-temperature curve and the rheological curve, and then the viscosity of the crude oil under different amounts of CO2 dissolved is measured to determine the amount of CO2 required to dissolve when the crude oil is converted into a Newtonian fluid.

[0056] Embodiment 4:

[0057] A method for improving the efficiency of CO2 composite energy after high-cycle huff-and-puff in heavy oil reservoirs, such as Figure 1 As shown, other steps are similar to those in Example 3. Further, step 101 further includes:

[0058] The amount of CO2 dissolved in the crude oil produced from the target block oil wells under different pressures is measured, and the lower limit of the formation pressure that the target well needs to meet is determined based on the amount of CO2 that needs to be dissolved when the crude oil can flow normally in the formation.

[0059] Embodiment 5:

[0060] A method for improving the efficiency of CO2 composite energy after high-cycle huff-and-puff in heavy oil reservoirs, such as Figure 1 As shown, the other steps are similar to those in Example 1. Furthermore, in step 102, the injected CO2 is in liquid state.

[0061] Furthermore, in step 102, a numerical simulation model is used to predict the cumulative oil production of the target well under different CO2 injection intensities, and the economic benefits after deducting the operating costs, CO2 injection and steam costs are calculated, and the appropriate CO2 injection amount is determined according to the principle of optimal economic benefits.

[0062] Embodiment 6:

[0063] A method for improving the efficiency of CO2 composite energy after high-cycle huff-and-puff in heavy oil reservoirs, such as Figure 1 As shown, other steps are similar to those of Example 5. Further, in step 102, the resistance factors of foaming agent solutions of different concentrations measured in the laboratory, the foaming agent solution concentration corresponding to the maximum resistance factor is the appropriate foaming agent concentration.

[0064] Furthermore, in step 102, during the injection of CO2 and a foaming agent solution of a certain concentration, the change of the bottom hole flow pressure is continuously monitored.

[0065] Embodiment 7:

[0066] A method for improving the efficiency of CO2 composite energy after high-cycle huff-and-puff in heavy oil reservoirs, such as Figure 1 As shown, the other steps are similar to those in Example 1. Further, in step 103, the method for determining the soaking time is:

[0067] By analyzing the mole fraction field diagram of CO2 in the oil phase obtained after numerical simulation calculation, the solubility of CO2 in crude oil at different shut-in times can be judged. When the shut-in time reaches a certain time, the mole fraction of CO2 in the oil phase basically no longer changes. This time is the theoretically appropriate shut-in time.

[0068] Embodiment 8:

[0069] A method for improving the efficiency of CO2 composite energy after high-cycle huff-and-puff in heavy oil reservoirs, such as Figure 1 As shown, the other steps are similar to Example 7. Furthermore, in step 103, after the CO2 and a certain concentration of foaming agent solution are injected and the well is started to be shut down, the change of the bottom hole pressure is continuously monitored. When it is monitored that the decline of the bottom hole pressure is significantly slowed down, it means that the dissolution of CO2 in crude oil has approached saturation, and the well can be stopped.

[0070] Embodiment 9:

[0071] A method for improving the efficiency of CO2 composite energy after high-cycle huff-and-puff in heavy oil reservoirs, such as Figure 1 As shown, other steps are similar to those in Example 1. Further, in step 104, the N2 injection amount is determined by the same method as the CO2 injection amount optimization in step 102.

[0072] Embodiment 10:

[0073] A method for improving the efficiency of CO2 composite energy after high-cycle huff-and-puff in heavy oil reservoirs, such as Figure 1 As shown, other steps are similar to Example 9. Furthermore, in step 104, a numerical simulation model is used to predict the cumulative oil production of the target well under different N2 injection intensities, and the economic benefits after deducting the operating costs, N2 injection and steam costs are calculated. The appropriate N2 injection amount is when the economic benefits are optimal.

[0074] Embodiment 11:

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

[0076] Embodiment 12:

[0077] A method for improving the efficiency of CO2 composite energy after high-cycle huff-and-puff in heavy oil reservoirs, such as Figure 1 As shown, the other steps are similar to those of Example 10. Furthermore, in step 105, a certain amount of steam is additionally injected to compensate for the heat absorbed by the injected CO2 after entering the oil layer.

[0078] Embodiment 13:

[0079] A method for improving the efficiency of CO2 composite energy after high-cycle huff-and-puff in heavy oil reservoirs, such as Figure 1 As shown, other steps are similar to Example 1. Furthermore, in step 106, the cumulative oil production of the target well after different rounds of throughput according to steps 101 to 5 is predicted, and the economic benefits after deducting the operating costs of all rounds, CO2 injection, N2 injection, and steam injection cumulative costs are calculated.

[0080] Embodiment 14:

[0081] A method for improving the efficiency of CO2 composite energy after high-cycle huff-and-puff in heavy oil reservoirs, such as Figure 1 As shown, the other steps are similar to those in Example 13. Furthermore, in step 106, when the economic benefit no longer increases with the increase in throughput rounds, this round is the time to stop injecting CO2.

[0082] Method mechanism analysis:

[0083] In step 101, the process of selecting suitable target wells for CO2 energy enhancement and efficiency improvement after high-cycle huff-and-puff of heavy oil reservoirs is as follows: first, the viscosity of the crude oil produced from the target block oil wells under different CO2 amounts dissolved is measured, and the viscosity of the crude oil when converted into a Newtonian fluid is obtained by combining the crude oil viscosity-temperature curve and the rheological curve, and the amount of CO2 required to be dissolved when the crude oil can flow normally in the formation is determined, and then the amount of CO2 dissolved in the crude oil produced from the target block oil wells under different pressures is measured, and the lower limit of the formation pressure that the target wells need to meet is determined according to the amount of CO2 required to be dissolved when the crude oil can flow normally in the formation, and wells with formation pressures above this lower limit are selected as target wells for implementing CO2 energy enhancement and efficiency improvement.

[0084] In a possible implementation, the dissolved 0-107.5 m 3 / tCO2, and draw a curve of crude oil viscosity changing with CO2 dissolution, such as Figure 2As shown in the figure, according to the viscosity-temperature curve and rheological curve of crude oil, the viscosity of crude oil when converted into Newtonian fluid is 201 mPa·s, so in order to make the crude oil flow, at least 11.5 m 3 / t CO2; then measure the amount of CO2 dissolved in crude oil at pressures of 0 to 17 MPa, such as Figure 3 As shown, according to the minimum required to dissolve 11.5m3 of crude oil to make it flow 3 / t CO2 can determine that the required minimum pressure is 3.5 MPa, and select wells with formation pressure above 3.5 MPa in the target block as target wells for implementing CO2 energy enhancement and efficiency improvement. The process enters step 102.

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

[0086] In one possible implementation, the numerical model predicts the cumulative oil production of the target wells when CO2 with an intensity of 6.8 to 34 t / m is injected. Based on the oil price of US$50 / barrel and CO2 of RMB357 / ton (0.638 yuan / m 3 ), the price of steam is 340 yuan / ton to calculate the economic benefits of oil wells at different CO2 injection intensities, and draw a curve of the economic benefits of oil wells at different CO2 injection intensities. The CO2 injection intensity corresponding to the maximum economic benefit point on the curve is 27.2t / m. Figure 4 As shown in the figure, the appropriate CO2 injection amount for the target well is calculated to be 300t based on the intensity. At the same time, the resistance factor of the solution when the foaming agent concentration is 0-1.0% is measured in the laboratory. When the foaming agent concentration exceeds 0.5%, the resistance factor of the foaming agent solution increases significantly slower, as shown in the figure below. Figure 5 As shown, the appropriate concentration of the foaming agent is 0.5%, and the injection volume of the foaming agent solution matches the CO2 injection volume of 1000m 3 During the process of injecting CO2 and foaming agent solution into the target well, the change of bottom hole flow pressure is continuously monitored. The process proceeds to step 103.

[0087] In step 103, the theoretical soaking time after the CO2 and foaming agent solution are injected is calculated by numerical simulation. In actual operation of the mine, under the guidance of the theoretical soaking time, the change of the bottom hole pressure after the CO2 and foaming agent solution are injected is continuously monitored, and the soaking can be ended when the decrease of the bottom hole pressure is significantly slowed down.

[0088] In a possible implementation, numerical simulation is used to calculate the mole fraction field of CO2 in the oil phase at different soaking times after the injection of CO2 and foaming agent solution. It can be seen that CO2 is mainly concentrated near 20m of the wellbore after injection. As the soaking time increases, CO2 gas continues to expand into the formation, and the expansion radius is about 44m. A curve is drawn showing the relationship between soaking days and the mole fraction of CO2 in the oil phase, such as Figure 6 As shown in the figure, after 5 to 7 days of soaking, the molar fraction of CO2 in oil changes little, indicating that CO2 no longer dissolves and expands in the reservoir, which is the theoretically appropriate soaking time. In actual field operations, by continuously monitoring the changes in the bottom flow pressure of the target well during soaking after the injection of CO2 and foaming agent solution, it is found that after 7 to 10 days of soaking after the injection of CO2, the formation pressure decreases significantly, indicating that the CO2 dissolution has approached saturation, and the soaking can be ended, and the process enters step 104.

[0089] In step 104, after the CO2 and foaming agent solution are injected and the well is soaked, a certain amount of N2 is injected into the formation to promote the further expansion of CO2 to the far well area and isolate the foaming agent solution from direct contact with subsequent high-temperature steam to avoid foaming agent failure. The N2 injection amount is determined by the same method as the CO2 injection amount optimization in step 10102.

[0090] In one possible implementation, the numerical model predicts that after the CO2 and foam solution are injected into the target well, 0 to 60,000 m 3 The cumulative oil production when the N2 is 50 US dollars per barrel, CO2 357 yuan per ton (0.638 yuan per m 3 ), N21.5 yuan / m 3 The economic benefits of oil wells at different N2 injection rates are calculated based on the prices of foaming agent 10,000 yuan / ton and steam 340 yuan / ton. The economic benefit curve of oil wells at different N2 injection rates is also drawn. The N2 injection rate corresponding to the maximum economic benefit point on the curve is 20,000m 3 ,like Figure 7 As shown, gaseous N2 is injected into the target well according to the amount. The process proceeds to step 105.

[0091] In step 105, in addition to injecting a normal amount of water vapor according to the thickness of the oil layer, an additional 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 results of numerical model optimization, the appropriate steam injection intensity for the target well is 240t / m, the average thickness of the oil layer within the control range of the well is 9.72m, and the required normal steam injection volume is 2332t. The outlet temperature of the CO2 tank is minus 14℃, the temperature after injection into the bottom of the well is 15℃, and the reservoir temperature is 60℃. To make the injected 300tCO2 reach the same temperature as the reservoir, it needs to absorb 1080×10 4 KJ. One ton of 300℃ steam injected underground can release 135.64×10 4 KJ, then injecting 300tCO2 consumes about 8t of steam heat, and the total amount of steam injected into the target well is 2340t. The process proceeds to step 106.

[0093] In step 106, the cumulative oil production of the target well after 5 to 14 rounds of huff and puff according to steps 10101 to 105 is predicted, which is the timing to stop CO2 injection.

[0094] In one possible implementation, the numerical model predicts the cumulative oil production of the target well after different rounds of throughput according to steps 101 to 105, based on an oil price of $50 per barrel and CO2 of 357 yuan per ton (0.638 yuan per m 3 ), N21.5 yuan / m 3 The economic benefits of the oil wells at different throughput cycles are calculated with the prices of foam agent 10,000 yuan / ton and steam 340 yuan / ton, and the economic benefit change curve of the oil wells at different throughput cycles of CO2-assisted steam is drawn. When the throughput cycle is greater than 10 cycles, the economic benefits basically no longer increase. Figure 8 As shown, the appropriate time to stop CO2 injection is after 10 cycles.

[0095] In summary: by injecting a certain amount of CO2 into the heavy oil reservoirs whose development effect has deteriorated due to low formation pressure after high-cycle steam huff and puff, the formation pressure can be increased by 39%, the oil well liquid production can be increased by 28%, and the oil well utilization radius can be expanded by 20m; at the same time, by injecting a certain amount of foaming agent, CO2 can be extended to the far well area by 40m, and the CO2 storage rate can be increased by 11.2 percentage points; this CO2 composite energy enhancement and efficiency improvement method can increase the recovery rate by 4.7 percentage points compared with steam huff and puff, increase the economic benefits of a single well by 800,000 yuan, and store 1534t of CO2 gas, realizing the low-carbon economic development of heavy oil reservoirs after high-cycle huff and puff.

[0096] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A method for improving the efficiency of CO2 composite energy after high-cycle huff-and-puff in heavy oil reservoirs, characterized in that: The following steps are involved: Step 101: Select a suitable target well in a high-cycle throughput heavy oil reservoir; Step 102: injecting an appropriate amount of CO2 and a foaming agent solution of a certain concentration into the target well in sequence; Step 103: Immerse the well for a period of time to allow the CO2 to fully dissolve in the crude oil and form foam; Step 104: injecting an appropriate amount of N2 into the target well; Step 105: performing 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 to stop CO2 injection.

2. A method for improving the efficiency of CO2 composite energy after high-cycle huff-and-puff in a heavy oil reservoir according to claim 1, characterized in that: In step 101, the lower limit of the formation pressure of the target well for CO2 energy enhancement and efficiency improvement after high-cycle steam stimulation is the minimum pressure required to ensure that the crude oil can be converted into a Newtonian fluid after dissolving a certain amount of CO2.

3. A method for improving the efficiency of CO2 composite energy after high-cycle huff-and-puff in a heavy oil reservoir as claimed in claim 2, characterized in that: In step 101, the specific method for obtaining the lower limit of the formation pressure is: first, the viscosity of the crude oil when it is converted into a Newtonian fluid is determined based on the crude oil viscosity-temperature curve and the rheological curve, and then the viscosity of the crude oil under different amounts of CO2 dissolved is measured to determine the amount of CO2 required to dissolve when the crude oil is converted into a Newtonian fluid.

4. A method for improving the efficiency of CO2 composite energy after high-cycle huff-and-puff in heavy oil reservoirs according to claim 1, characterized in that: The step 101 further includes: The amount of CO2 dissolved in the crude oil produced from the target block oil wells under different pressures is measured, and the lower limit of the formation pressure that the target well needs to meet is determined based on the amount of CO2 that needs to be dissolved when the crude oil can flow normally in the formation.

5. The method for improving the efficiency of CO2 composite energy after high-cycle huff-and-puff in heavy oil reservoirs according to claim 1, characterized in that: In step 102, the injected CO2 is in liquid state.

6. A method for improving the efficiency of CO2 composite energy after high-cycle huff-and-puff in a heavy oil reservoir according to claim 1, characterized in that: In step 102, a numerical simulation model is used to predict the cumulative oil production of the target well under different CO2 injection intensities, and the economic benefits after deducting the operating costs, CO2 injection and steam costs are calculated, and the appropriate CO2 injection amount is determined according to the principle of optimal economic benefits.

7. A method for improving the efficiency of CO2 composite energy after high-cycle huff-and-puff in a heavy oil reservoir as claimed in claim 1, characterized in that: In step 102, the resistance factors of foaming agent solutions of different concentrations are measured in the laboratory. The foaming agent solution concentration corresponding to the maximum resistance factor is the appropriate foaming agent concentration.

8. The method for improving the efficiency of CO2 composite energy after high-cycle huff-and-puff in heavy oil reservoirs according to claim 1, characterized in that: In step 102, during the injection of CO2 and a foaming agent solution of a certain concentration, the change of the bottom hole flow pressure is continuously monitored.

9. A method for improving the efficiency of CO2 composite energy after high-cycle huff-and-puff in heavy oil reservoirs according to claim 1, characterized in that: In step 103, the method for determining the soaking time is: By analyzing the mole fraction field diagram of CO2 in the oil phase obtained after numerical simulation calculation, the solubility of CO2 in crude oil at different shut-in times can be judged. When the shut-in time reaches a certain time, the mole fraction of CO2 in the oil phase basically no longer changes. This time is the theoretically appropriate shut-in time.

10. The method for improving the efficiency of CO2 composite energy after high-cycle huff-and-puff in heavy oil reservoirs according to claim 1, characterized in that: In step 103, after CO2 and a certain concentration of foaming agent solution are injected and the well is started to be shut down, the change of the bottom hole pressure is continuously monitored. When the decrease of the bottom hole pressure is monitored to be significantly slowed down, it means that the dissolution of CO2 in the crude oil has approached saturation, and the well can be shut down.

11. A method for improving the efficiency of CO2 composite energy after high-cycle huff-and-puff in heavy oil reservoirs according to claim 1, characterized in that: In step 104, the N2 injection amount is determined using the same method as the CO2 injection amount optimization in step 102.

12. A method for improving the efficiency of CO2 composite energy after high-cycle huff-and-puff in heavy oil reservoirs according to claim 11, characterized in that: In step 104, a numerical simulation model is used to predict the cumulative oil production of the target well under different N2 injection intensities, and the economic benefits after deducting the operating costs, N2 injection and steam costs are calculated. The appropriate N2 injection amount is the one that corresponds to the optimal economic benefits.

13. The method for improving the efficiency of CO2 composite energy after high-cycle huff-and-puff in heavy oil reservoirs according to claim 1, characterized in that: In step 105, in addition to the normal amount of steam injection, a certain amount of steam is additionally injected to perform heat compensation.

14. A method for improving the efficiency of CO2 composite energy after high-cycle huff-and-puff in heavy oil reservoirs according to claim 13, characterized in that: In step 105, a certain amount of steam is additionally injected to compensate for the heat absorbed by the injected CO2 after entering the oil layer.

15. The method for improving the efficiency of CO2 composite energy after high-cycle huff-and-puff in heavy oil reservoirs according to claim 1, characterized in that: In step 106, the cumulative oil production of the target well after different rounds of throughput according to steps 101 to 5 is predicted, and the economic benefits after deducting the operating costs of all rounds, CO2 injection, N2 injection, and steam injection accumulated costs are calculated.

16. A method for improving the efficiency of CO2 composite energy after high-cycle huff-and-puff in heavy oil reservoirs according to claim 15, characterized in that: In step 106, when the economic benefit no longer increases with the increase in throughput rounds, this round is the time to stop injecting CO2.

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