Method for improving recovery efficiency of heavy oil reservoir

Abstract

The invention provides a method for improving the recovery efficiency of a heavy oil reservoir. The method comprises the steps that a target well is determined, a reservoir where the bottom of the target well is located is a heavy oil reservoir subjected to steam development, and the average water saturation of the target well is 0.3-0.7; injecting an active aqueous solution into a reservoir in which the bottom of the target well is located, wherein the active aqueous solution comprises at least one of an ammonium bicarbonate aqueous solution, an ammonium carbonate aqueous solution and a sulfonate type anionic surfactant aqueous solution; the reservoir near the bottom of the target well is heated, so that water, including the active water solution, in the reservoir near the bottom of the target well is gasified to form a steam slug; non-condensed gas is injected into a reservoir where the bottom of the target well is located, a steam slug is pushed to the deep part of the oil reservoir, and then the target well is soaked; and opening the well for production after the soaking of the target well is finished.

Description

Technical Field

[0001] The invention belongs to the technical field of oil field production, and in particular relates to a method for improving the recovery rate of a heavy oil reservoir. Background Art

[0002] Heavy oil reservoirs refer to reservoirs where the viscosity of degassed crude oil is greater than 100 mPa·s at reservoir temperature. Thermal recovery technology is currently widely used in the development of heavy oil reservoirs. Existing thermal recovery technologies mainly include steam-assisted gravity drainage, steam huff and puff, and steam flooding.

[0003] Steam Assisted Gravity Drainage (SAGD) has now developed into a mature commercial exploitation application technology. Its production method is: deploy a pair of parallel horizontal wells at the bottom of the reservoir, and inject a large amount of high-dryness steam into the reservoir through the upper horizontal well. The density difference between steam and crude oil forces the steam to overlap upward and release heat in contact with the cold crude oil above. The condensed water and heated crude oil flow to the vicinity of the lower horizontal well under the influence of gravity and are produced through the lower horizontal well; with the gradual injection of steam, a gradually expanding steam chamber is formed above the injection well, and the steam chamber gradually spreads to the upper and side parts of the reservoir, gradually heating the entire reservoir and producing the crude oil therein.

[0004] Steam huff and puff is the most widely used thermal recovery technology in heavy oil reservoirs. Its production method is: inject wet steam into the same well, and then shut down the well after reaching the designed injection volume. After the bottom well heat gradually diffuses to the depth of the reservoir, the well is started for production. After the daily oil production is lower than the critical value or the water content exceeds the critical value, the production cycle is stopped, and wet steam is continuously injected into the well to start the next round of huff and puff.

[0005] Steam drive is different from steam-assisted gravity drainage and steam huff and puff. Its production method is: based on a certain form of injection-production well network, high-dryness or low-dryness steam is continuously injected into the reservoir through the injection well, and continuous production is carried out through the production well adjacent to the injection well; the injected steam heats the crude oil to reduce the viscosity, making the crude oil between the injection well and the production well easier to flow, and the hot water formed by the condensation of the steam is produced together with the heated crude oil through the production well.

[0006] The main problems of existing thermal recovery technology for heavy oil reservoirs are as follows:

[0007] Steam throughput: As the number of throughput rounds increases, the efficiency gradually decreases, which is specifically reflected in the decrease in daily oil production, the increase in water content, and the shortening of the cycle.

[0008] Steam drive: Due to its heat loss characteristics, the oil-gas ratio decreases, the development efficiency decreases, and the water content increases in the middle and late stages of steam drive.

[0009] Steam-assisted gravity drainage: only applicable to the development of thick-layer reservoirs, with a small scope of application and high requirements for reservoir conditions; for thin-layer reservoirs, there are problems such as low oil-gas ratio and slow oil production rate.

[0010] In the development process of heavy oil reservoirs, crude oil emulsification plays an important role in improving crude oil recovery. Through the formation of emulsion, the mobility of heavy oil can be improved, a pseudo-single-phase flow can be formed in the reservoir to reduce water channeling, and a volume replacement effect can be formed to expand the production range.

[0011] At present, research on crude oil emulsification has been widely carried out. Existing crude oil emulsification is usually achieved by adding emulsifiers to crude oil to form an emulsion. However, there are many problems with existing crude oil emulsification technology, such as: (1) it is difficult to achieve an ideal emulsified state under the conditions of heavy oil reservoirs; (2) it is too dependent on the performance of emulsifiers; (3) it has strict requirements on the water content and crude oil saturation of heavy oil reservoirs. As a result, it is difficult for existing crude oil emulsification technology to achieve the ideal laboratory effect when it is actually applied to heavy oil reservoir development, and it is not very operable.

[0012] In summary, there is a need to study technologies applicable to heavy oil reservoirs that have undergone thermal recovery, which can induce emulsification of crude oil in such reservoirs and improve the development effect of such reservoirs. Summary of the invention

[0013] The object of the present invention is to provide a method for improving the recovery rate of a heavy oil reservoir that has undergone steam development, which can promote the emulsification of heavy oil in the heavy oil reservoir that has undergone steam development, can improve the utilization degree of the heavy oil reservoir that has undergone steam development, can improve the steam utilization rate and development efficiency of the heavy oil reservoir that has undergone steam development, and effectively realize the improvement of the recovery rate and development effect of the heavy oil reservoir.

[0014] In order to achieve the above object, the present invention provides a method for improving the recovery rate of heavy oil reservoirs, wherein the method comprises:

[0015] 1) Determine the target well; wherein the reservoir at the bottom of the target well is a heavy oil reservoir that has undergone steam development (such as steam stimulation, steam flooding, steam-assisted gravity drainage) and the average water saturation of the reservoir near the bottom of the target well is 0.3-0.7; wherein the reservoir near the bottom of the well refers to the reservoir area within 10m of the reservoir at the bottom of the well;

[0016] 2) injecting an active aqueous solution into the reservoir at the bottom of the target well; wherein the active aqueous solution comprises one or a combination of two or more of an aqueous solution of ammonium bicarbonate, an aqueous solution of ammonium carbonate and an aqueous solution of a sulfonate type anionic surfactant;

[0017] 3) heating the reservoir near the bottom of the target well to vaporize the water in the reservoir near the bottom of the well, including the active aqueous solution, to form a steam slug;

[0018] 4) Inject non-condensable gas into the reservoir where the bottom of the target well is located to push the steam slug to the deep part of the reservoir, and then soak the target well; wherein the deep well in the reservoir refers to the reservoir area in the reservoir where the bottom of the well is located with a horizontal distance of more than 10m from the bottom of the well;

[0019] 5) After the target well is shut down, it is started for production.

[0020] In the method for improving the recovery rate of heavy oil reservoirs provided by the present invention, the water-continuous aqueous phase containing ammonium bicarbonate, ammonium carbonate and / or sulfonate type anionic surfactants around the wellbore is reheated into a steam state, and diffused to the deep part of the reservoir under the impetus of non-condensable gas. During the diffusion process of steam, the steam contacts the crude oil over a large area and the steam dissipates heat and condenses, and the volume of the steam (gas phase) is sharply reduced to a liquid phase. The crude oil is heated by steam and has good fluidity, occupying the original space of the steam (gas phase). With the assistance of the surfactant material after the pyrolysis of ammonium bicarbonate, the surfactant material after the pyrolysis of ammonium carbonate and / or the sulfonate type anionic surfactant, an oil-in-water emulsion is formed. In the above process, the injected non-condensable gas dissolves in the liquid phase under high pressure, and the pressure gradually decreases after the well is opened for production. The non-condensable gas precipitates into small bubbles in the liquid phase, releasing elastic energy. Thus, a stable quasi-single-phase flow is formed in the reservoir. The method for improving the recovery rate of heavy oil reservoirs provided by the present invention improves the problem of continuous distribution of water phase in the late stage of steam development of heavy oil reservoirs and reduces the water content of the reservoir. On the other hand, a stable water-in-oil emulsion is formed to improve the fluidity and relative permeability of the oil phase. On the other hand, the gas phase diffused into the oil phase occupies the space where the crude oil is located to a certain extent, increasing the volume of the crude oil, thereby improving the recovery of the crude oil. The method for improving the recovery rate of heavy oil reservoirs provided by the present invention causes the water phase near the bottom of the well to undergo a secondary phase change into steam, which is then transported to the deep of the reservoir to form a water-in-oil emulsion. Compared with the steam development process, the action range of steam is expanded, and in a preferred embodiment, the recovery rate can be increased by 35-40%.

[0021] Preferably, the reservoir where the bottom of the target well is located is a heavy oil reservoir that has undergone steam stimulation.

[0022] Preferably, the reservoir at the bottom of the target well where the target well is located has undergone more than 10 rounds of steam huff and puff development or the recovery rate of steam huff and puff development has reached more than 15%.

[0023] Preferably, the daily oil production of the target well is less than 0.5 tons / day.

[0024] Preferably, the water content of the produced fluid of the target well is above 80%.

[0025] Preferably, the sulfonate type anionic surfactant includes one or a combination of two or more of sodium dodecylbenzenesulfonate, sodium hexadecylbenzenesulfonate, sodium α-olefinsulfonate and sodium methylenebisnaphthalenesulfonate; more preferably, the active aqueous solution contains two or more sulfonate type anionic surfactants, which helps to reduce the oil-water interfacial tension and promote better oil-water emulsification.

[0026] Preferably, based on the total mass of the active aqueous solution being 100%, the total mass concentration of ammonium bicarbonate, ammonium carbonate and sulfonate type anionic surfactant in the active aqueous solution is not less than 20%.

[0027] Preferably, the injection amount of the active aqueous solution is 10-150 tons / (m reservoir thickness).

[0028] Preferably, when heating the reservoir near the bottom of the target well, the average reservoir temperature of the reservoir near the bottom of the target well is increased to above the saturated steam temperature corresponding to the bottom hole pressure of the target well; at this time, it can be effectively ensured that the water in the reservoir near the bottom of the target well, including the active aqueous solution and formation water, is basically completely vaporized, and the ammonium bicarbonate and ammonium carbonate in the active aqueous solution can also be completely decomposed to produce surfactant substances.

[0029] Preferably, the heating of the reservoir near the bottom of the target well is achieved by:

[0030] A heater is lowered into the wellbore of the target well, and the heater temperature is set to 20-40°C above the saturated steam temperature corresponding to the reservoir pressure of the reservoir at the bottom of the target well. Heating is performed at this temperature. During the heating process, the bottom hole pressure of the target well and the average reservoir temperature of the reservoir near the bottom of the target well are monitored. If the average reservoir temperature of the reservoir near the bottom of the target well rises to above the saturated steam temperature corresponding to the bottom hole pressure of the target well, heating is stopped.

[0031] Preferably, the heating of the reservoir near the bottom of the target well is achieved by:

[0032] Superheated steam with a superheat degree of >40° is injected into the reservoir at the bottom of the target well through the target well, which triggers the phase change and gasification of water in the reservoir near the bottom of the well, including the active aqueous solution, to form a steam slug.

[0033] Preferably, the heating of the reservoir near the bottom of the target well is achieved by:

[0034] Injecting a high-temperature mixed gas of superheated steam and non-condensable gas into the reservoir at the bottom of the target well through the target well to induce phase change and gasification of water in the reservoir near the bottom of the well, including the active aqueous solution, to form a steam slug;

[0035] This method can improve the formation energy while heating the reservoir near the bottom of the target well.

[0036] Preferably, the heating of the reservoir near the bottom of the target well is achieved by:

[0037] Inject combustion-supporting agent and air into the reservoir at the bottom of the target well through the target well, trigger combustion at the bottom of the well, and heat generated by the combustion heats the reservoir near the bottom of the target well; this method releases heat and replenishes energy in situ inside the reservoir, which can effectively trigger the phase change and gasification of water in the reservoir near the bottom of the well, including the active aqueous solution, to form a steam slug;

[0038] More preferably, the injection amount of the combustion aid is 80-120 tons;

[0039] More preferably, the amount of air injected is 400,000-800,000 cubic meters.

[0040] Preferably, the non-condensable gas includes but is not limited to one or a combination of two or more of air, nitrogen, carbon dioxide and flue gas; more preferably, the non-condensable gas injected into the reservoir at the bottom of the target well includes carbon dioxide, and the injection of carbon dioxide helps to enhance the recovery of formation energy and improve the flowability of crude oil.

[0041] Preferably, the injection of non-condensable gas into the reservoir at the bottom of the target well to push the steam slug into the deep part of the reservoir is achieved by:

[0042] The steam slug is pushed to the deep part of the reservoir by injecting normal temperature non-condensable gas into the reservoir at the bottom of the target well.

[0043] Preferably, the injection of non-condensable gas into the reservoir at the bottom of the target well to push the steam slug into the deep part of the reservoir is achieved by:

[0044] Through the target well, a combustion-supporting agent and air are injected into the reservoir at the bottom of the target well, and then combustion is triggered at the bottom of the well. The non-condensable gas after combustion pushes the steam slug to the deep part of the reservoir. This method not only uses non-condensable gas to push the steam slug to the deep part of the reservoir, but also releases heat and replenishes energy in situ inside the reservoir;

[0045] More preferably, the injection amount of the combustion aid is 60-90 tons;

[0046] More preferably, the amount of air injected is 300,000-500,000 cubic meters.

[0047] Preferably, the stewing time is 3-9 days.

[0048] Preferably, the method for improving oil recovery in a heavy oil reservoir further comprises:

[0049] 6) When the target well is started to produce until the daily oil production is lower than the oil production threshold or the water content of the produced fluid is higher than the water content threshold, repeat steps 2) to 5);

[0050] More preferably, the oil production threshold is less than 0.5 tons / day;

[0051] More preferably, the moisture content threshold is 80% or more.

[0052] The method for improving the recovery rate of heavy oil reservoirs provided by the present invention is a method for promoting emulsification formation and improving the development effect of heavy oil reservoirs, which can promote the emulsification of heavy oil in heavy oil reservoirs that have undergone steam development, can improve the utilization degree of heavy oil reservoirs that have undergone steam development, can improve the steam utilization rate and development efficiency of heavy oil reservoirs that have undergone steam development, and effectively improve the recovery rate and development effect of heavy oil reservoirs. Compared with the prior art, it has the following advantages:

[0053] (1) The technical solution provided by the present invention takes into account the actual reservoir conditions of heavy oil reservoirs that have undergone steam development, and utilizes the continuous water phase near the wellbore after steam development, thereby improving the utilization rate of steam.

[0054] (2) The technical solution provided by the present invention combines the phase change of steam underground with emulsification to improve the recovery rate, greatly improving the efficiency of the entire process and reducing operating costs.

[0055] (3) The technical solution provided by the present invention re-gasifies the stored water near the wellbore to form a steam plug and pushes it into the deep of the reservoir, effectively expanding the scope of utilization. At the same time, the injected non-condensable gas and steam plug cooperate to increase the elastic energy of the formation, increase the swept volume and increase the oil production rate.

[0056] (4) The technical solution provided by the present invention can be used to extend the steam development cycle. Compared with conventional steam development, the oil production rate can be increased by about 25%, the cost per ton of oil can be reduced by more than 20%, and the overall recovery rate of heavy oil reservoirs can reach about 70%. DETAILED DESCRIPTION

[0057] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the protection scope of the present invention.

[0058] A specific embodiment of the present invention provides a method for improving the recovery of heavy oil reservoirs, wherein the method comprises:

[0059] Step S1: determining a target well; wherein the reservoir at the bottom of the target well is a heavy oil reservoir that has undergone steam development (e.g., steam stimulation, steam flooding, steam-assisted gravity drainage) and the average water saturation of the reservoir near the bottom of the target well is 0.3-0.7; wherein the reservoir near the bottom of the well refers to a reservoir area within 10 m of the reservoir at the bottom of the well;

[0060] Step S2: injecting an active aqueous solution into the reservoir at the bottom of the target well; wherein the active aqueous solution comprises one or a combination of two or more of an aqueous solution of ammonium bicarbonate, an aqueous solution of ammonium carbonate and an aqueous solution of a sulfonate type anionic surfactant;

[0061] Step S3: heating the reservoir near the bottom of the target well to vaporize water in the reservoir near the bottom of the well including the active aqueous solution to form a steam slug;

[0062] Step S4: injecting non-condensable gas into the reservoir where the bottom of the target well is located to push the steam slug to the deep part of the reservoir, and then soaking the target well; wherein the deep well in the reservoir refers to the reservoir area in the reservoir where the bottom of the well is located, the horizontal distance from the bottom of the well being greater than 10m;

[0063] Step S5: After the target well is shut down, it is started for production.

[0064] Furthermore, the reservoir where the bottom of the target well is located is a heavy oil reservoir that has experienced steam stimulation; further, the reservoir where the bottom of the target well is located has experienced more than 10 rounds of steam stimulation development or the recovery degree of steam stimulation development has reached more than 15%.

[0065] Further, the daily oil production of the target well is less than 0.5 tons / day.

[0066] Furthermore, the water content of the produced fluid of the target well is above 80%.

[0067] Furthermore, the remaining oil saturation of the reservoir where the target well is located is greater than 0.50.

[0068] Furthermore, the reservoir thickness of the reservoir where the bottom of the target well is located is >10.0m.

[0069] Furthermore, the horizontal permeability of the reservoir where the target well is located is >1000md and the ratio of vertical to horizontal permeability is >0.1.

[0070] Furthermore, the porosity of the reservoir where the bottom of the target well is located is >0.20.

[0071] Furthermore, there are no continuously distributed impermeable mud and shale interlayers in the reservoir where the target well is located.

[0072] Furthermore, the sulfonate type anionic surfactant includes one or a combination of two or more of sodium dodecylbenzenesulfonate, sodium hexadecylbenzenesulfonate, sodium α-olefinsulfonate and sodium methylenebisnaphthalenesulfonate; further, the active aqueous solution contains two or more sulfonate type anionic surfactants.

[0073] Furthermore, based on the total mass of the active aqueous solution as 100%, the total mass concentration of ammonium bicarbonate, ammonium carbonate and sulfonate type anionic surfactant in the active aqueous solution is not less than 20%.

[0074] Furthermore, the injection amount of the active aqueous solution is 10-150 tons / (m reservoir thickness).

[0075] Furthermore, when heating the reservoir near the bottom of the target well, the average reservoir temperature of the reservoir near the bottom of the target well is increased to above the saturated steam temperature corresponding to the bottom pressure of the target well.

[0076] Further, heating the reservoir near the bottom of the target well is achieved by at least one of the following methods:

[0077] Method 1: Place a heater in the wellbore of the target well, set the heater temperature to 20-40°C above the saturated steam temperature corresponding to the reservoir pressure of the reservoir at the bottom of the target well, and heat at this temperature. During the heating process, monitor the bottom pressure of the target well and the average reservoir temperature of the reservoir near the bottom of the target well. If the average reservoir temperature of the reservoir near the bottom of the target well rises to above the saturated steam temperature corresponding to the bottom pressure of the target well, stop heating.

[0078] Method 2: inject superheated steam with a superheat degree of >40° into the reservoir at the bottom of the target well through the target well;

[0079] Method 3: injecting a high-temperature mixture of superheated steam and non-condensable gas into the reservoir at the bottom of the target well through the target well;

[0080] Method 4: injecting combustion aid and air into the reservoir at the bottom of the target well through the target well to trigger combustion at the bottom of the well. The heat generated by the combustion heats the reservoir near the bottom of the target well. The injection amount of the combustion aid is preferably 80-120 tons; the injection amount of air is preferably 400,000-800,000 cubic meters.

[0081] Furthermore, the non-condensable gas includes but is not limited to one or a combination of two or more of air, nitrogen, carbon dioxide and flue gas; further, the non-condensable gas injected into the reservoir at the bottom of the target well includes carbon dioxide.

[0082] Furthermore, the injection of non-condensable gas into the reservoir at the bottom of the target well to push the steam slug into the deep part of the reservoir is achieved by at least one of the following methods:

[0083] Method 1: injecting normal temperature non-condensable gas into the reservoir at the bottom of the target well through the target well to push the steam slug into the deep part of the reservoir;

[0084] Method 2: inject combustion aid and air into the reservoir at the bottom of the target well through the target well, and then trigger combustion at the bottom of the well. The non-condensable gas after combustion pushes the steam segment plug to the deep part of the reservoir; among them, the injection amount of combustion aid is preferably 60-90 tons; the injection amount of air is preferably 300,000-500,000 cubic meters.

[0085] Furthermore, the duration of stewing the well is 3-5 days.

[0086] Furthermore, the method for improving oil recovery in heavy oil reservoirs further comprises:

[0087] Step S6: when the target well is started to produce until the daily oil production is lower than the oil production threshold or the water content of the produced fluid is higher than the water content threshold, repeat steps S2 to S5;

[0088] Furthermore, the oil production threshold is less than 0.5 tons / day;

[0089] Furthermore, the moisture content threshold is 80% or more.

[0090] Example 1

[0091] This embodiment provides a method for improving the recovery of a heavy oil reservoir, which is used to improve the recovery of a heavy oil reservoir A that has undergone steam stimulation development.

[0092] The burial depth of heavy oil reservoir A is 530m, the effective thickness of the reservoir is 42.0m>10.0m, the net-to-total thickness ratio is 0.92, the average porosity is 36.5%>0.20, the initial reservoir pressure is 5.8MPa, the average horizontal permeability is 5540md>1000md, the ratio of horizontal permeability to vertical permeability is 0.7 (the ratio of vertical to horizontal permeability is>0.1), there is no pure mudstone interlayer in the reservoir, and the crude oil viscosity under reservoir conditions is 2.2×10 4 cp, heavy oil reservoir A has been developed with vertical wells for steam stimulation for 10 years, with 12 rounds of stimulation, stage recovery degree of 20.7%, production decline rate of 23.4%, formation pressure of 2-3MPa, and remaining oil saturation>0.50.

[0093] The method for improving oil recovery in heavy oil reservoirs provided in this embodiment specifically includes:

[0094] 1. Determine the target well;

[0095] A target well A is determined in a vertical well with a bottom located in a heavy oil reservoir A for steam stimulation development of the heavy oil reservoir A; the average water saturation of the reservoir near the bottom of the target well A is 0.4, the current single well oil production is about 0.3 tons / day < 0.5 tons / day, and the current water content of the output fluid is more than 90%, which is a typical low-pressure and low-yield well.

[0096] 2. Inject 420 tons of active aqueous solution into the reservoir at the bottom of target well A; wherein the active aqueous solution is an ammonium carbonate aqueous solution; taking the total mass of the active aqueous solution as 100%, the total mass concentration of ammonium carbonate in the active aqueous solution is 23%; the injection amount of the active aqueous solution is about 10 tons / (m reservoir thickness).

[0097] 3. An electric heater is lowered into the wellbore of target well A, and the temperature of the electric heater is set to 60°C above the saturated steam temperature corresponding to the reservoir pressure of the reservoir at the bottom of target well A (the current reservoir pressure is 1.5MPa, and the saturated steam temperature corresponding to this pressure is about 200°C. The temperature of the electric heater is set to 260°C and the power is 100KW / m). Heating is carried out at this temperature. During the heating process, the bottom hole pressure of target well A and the average reservoir temperature of the reservoir near the bottom of target well A are monitored. The bottom hole pressure begins to rise slowly on the 5th day of heating, rises to 4MPa on the 10th day of heating, and reaches about 6MPa on the 18th day of heating (reaching the initial reservoir pressure level). At this time, if the average reservoir temperature of the reservoir near the bottom of target well A rises to above the saturated steam temperature corresponding to the bottom hole pressure of target well A, the heating is stopped; at this time, the water in the reservoir near the bottom of the well, including the active aqueous solution, is vaporized to form a steam slug, and the ammonium bicarbonate / ammonium carbonate solution has also been completely decomposed.

[0098] 4. Inject 200,000 cubic meters of flue gas into the reservoir at the bottom of target well A to push the steam slug to the deep part of the reservoir, and then soak target well A;

[0099] The flue gas includes CO2, O2, and N2 in a molar ratio of 8:5:87; the flue gas injection rate is 15,000 cubic meters per hour.

[0100] 5. Target well A was opened for production after being kept cold for 6 days.

[0101] 6. Target well A starts production; the daily production of a single well reaches 20 tons / day at the initial stage, with a water cut of less than 30%, and then the production of a single well slowly decreases, with a gas-oil ratio of about 50 cubic meters / cubic meter; after 230 days of production, the daily oil production is less than 0.5 tons / day, and steps 1 to 5 are repeated to start the next round.

[0102] Target well A has been carried out for 5 rounds, with a cumulative oil production of about 30,000 tons in the single well stage, exceeding the cumulative oil production in the throughput stage. The converted oil-gas ratio can reach 0.38, the oil production rate reaches 5%, and the predicted final recovery rate reaches 42.5%; the cost per ton of oil of target well A is reduced from US$59 to about US$42. The cost reduction mainly comes from 1) saving about 1,800 yuan per ton of raw material cost (the converted ton of oil cost is reduced by US$12), and 2) improved production efficiency (producing 1 ton of crude oil reduces the converted steam consumption by 20%, and the converted ton of oil cost is reduced by US$7).

[0103] The block adjacent to the target well A in the heavy oil reservoir A uses well B for continuous steam stimulation development. The oil production rate is only about 1%, the oil-gas ratio is only 0.12, and the final recovery factor is 28%.

[0104] Example 2

[0105] This embodiment provides a method for improving the recovery of a heavy oil reservoir, which is used to improve the recovery of a heavy oil reservoir D that has undergone steam stimulation development.

[0106] The heavy oil reservoir D has a burial depth of 300m, an effective reservoir thickness of 23.0m>10.0m, a net-to-total thickness ratio of 0.92, an average porosity of 30.5%>0.20, an initial reservoir pressure of 3.3MPa, an average horizontal permeability of 3158md>1000md, a ratio of horizontal permeability to vertical permeability of 0.5 (the ratio of vertical to horizontal permeability>0.1), no pure mudstone interlayers in the reservoir, and a crude oil viscosity of 8621cp under reservoir conditions. The heavy oil reservoir D has been developed with vertical wells for steam huff and puff for 4 years, and has undergone 4 rounds of huff and puff, with a stage recovery degree of 8%, a production decline rate of 20%, a formation pressure of 2-3MPa, and a remaining oil saturation of>0.50.

[0107] The method for improving oil recovery in heavy oil reservoirs provided in this embodiment specifically includes:

[0108] 1. Determine the target well;

[0109] A target well D is determined in a vertical well with a bottom located in a heavy oil reservoir D for steam stimulation development of the heavy oil reservoir D; the average water saturation of the reservoir near the bottom of the target well D is 0.28, the current single well oil production is about 0.5 tons / day, and the current water content of the output fluid is more than 90%, which is a typical low-pressure and low-yield well.

[0110] 2. Inject 230 tons of active aqueous solution into the reservoir at the bottom of target well D; wherein the active aqueous solution is an ammonium carbonate aqueous solution; based on the total mass of the active aqueous solution as 100%, the total mass concentration of ammonium carbonate in the active aqueous solution is 20%; the injection amount of the active aqueous solution is about 10 tons / (m reservoir thickness).

[0111] 3. An electric heater is lowered into the wellbore of target well D, and the temperature of the electric heater is set to 60°C above the saturated steam temperature corresponding to the reservoir pressure of the reservoir at the bottom of target well D (the current reservoir pressure is 1.5MPa, and the saturated steam temperature corresponding to this pressure is about 200°C. The temperature of the electric heater is set to 260°C and the power is 100KW / m). Heating is carried out at this temperature. During the heating process, the bottom hole pressure of target well D and the average reservoir temperature of the reservoir near the bottom of target well D are monitored. The bottom hole pressure begins to rise slowly on the 5th day of heating, rises to 4MPa on the 10th day of heating, and reaches about 3.2MPa on the 18th day of heating (reaching the initial reservoir pressure level). At this time, if the average reservoir temperature of the reservoir near the bottom of target well D rises to above the saturated steam temperature corresponding to the bottom hole pressure of target well D, the heating is stopped; at this time, the water in the reservoir near the bottom of the well, including the active aqueous solution, is vaporized to form a steam slug, and the ammonium bicarbonate / ammonium carbonate solution has also been completely decomposed.

[0112] 4. Inject 30 tons of combustion aid and 400,000 cubic meters of air at room temperature into the reservoir at the bottom of the target well D, and then trigger combustion at the bottom of the well. The non-condensable gas after combustion pushes the steam segment plug to the deep part of the reservoir, and then the target well D is soaked.

[0113] 5. Target well D was opened for production after being shut down for 6 days.

[0114] 6. Target well D is put into production; the daily production of a single well initially reaches 36 tons / day, with a water cut of less than 20%, and then the production of a single well slowly decreases, with a gas-oil ratio of about 100 cubic meters / cubic meter; after 4250 days of production, the daily oil production is less than 0.5 tons / day, and steps 1 to 5 are repeated to start the next round.

[0115] Target well D has been continuously developed for 5 rounds, with a cumulative oil production of about 34,000 tons in the single well stage, exceeding the cumulative oil production in the throughput stage. The converted oil-gas ratio can reach 1.89, the oil production rate reaches 5%, and the predicted total recovery rate reaches 42.5%. The cost per ton of oil of target well D has been reduced from US$63 to about US$40. The cost reduction mainly comes from 1) saving about 2,400 yuan per ton of raw material cost (the converted ton of oil cost is reduced by US$14), and 2) improved production efficiency (producing 1 ton of crude oil reduces the converted steam consumption by 20%, and the converted ton of oil cost is reduced by US$9).

Claims

1. A method for improving the recovery of heavy oil reservoirs, wherein: The method includes: 1) Determine the target well; wherein the reservoir at the bottom of the target well is a heavy oil reservoir that has been developed by steam and the average water saturation of the reservoir near the bottom of the target well is 0.3-0.7; wherein the reservoir near the bottom of the well refers to the reservoir area within 10m of the reservoir at the bottom of the well; 2) injecting an active aqueous solution into the reservoir at the bottom of the target well; wherein the active aqueous solution comprises one or a combination of two or more of an aqueous solution of ammonium bicarbonate, an aqueous solution of ammonium carbonate and an aqueous solution of a sulfonate type anionic surfactant; 3) heating the reservoir near the bottom of the target well to vaporize the water in the reservoir near the bottom of the well, including the active aqueous solution, to form a steam slug; 4) Inject non-condensable gas into the reservoir where the bottom of the target well is located to push the steam slug to the deep part of the reservoir, and then soak the target well; wherein the deep well in the reservoir refers to the reservoir area in the reservoir where the bottom of the well is located with a horizontal distance of more than 10m from the bottom of the well; 5) After the target well is shut down, it is started for production.

2. The method according to claim 1, wherein: The reservoir where the bottom of the target well is located is a heavy oil reservoir that has experienced steam stimulation.

3. The method according to claim 2, wherein: The reservoir at the bottom of the target well where the target well is located has experienced more than 10 rounds of steam huff and puff development or the recovery rate of steam huff and puff development has reached more than 15%.

4. The method according to claim 1, wherein: The daily oil production of the target well is less than 0.5 tons / day and / or the water content of the output fluid of the target well is greater than 80%.

5. The method according to claim 1, wherein: The sulfonate type anionic surfactant includes one or a combination of two or more of sodium dodecylbenzene sulfonate, sodium hexadecylbenzene sulfonate, sodium α-olefin sulfonate and sodium methylene bisnaphthalene sulfonate.

6. The method according to claim 1, wherein: Taking the total mass of the active aqueous solution as 100%, the total mass concentration of ammonium bicarbonate, ammonium carbonate and sulfonate type anionic surfactant in the active aqueous solution is not less than 20%.

7. The method according to claim 1, wherein: The injection rate of active aqueous solution is 10-150 tons / (m reservoir thickness).

8. The method according to claim 1, wherein: When heating the reservoir near the bottom of the target well, the average reservoir temperature of the reservoir near the bottom of the target well is increased to above the saturated steam temperature corresponding to the bottom pressure of the target well.

9. The method according to claim 1 or 8, wherein: The heating of the reservoir near the bottom of the target well is achieved by: A heater is lowered into the wellbore of the target well, and the heater temperature is set to 20-40°C above the saturated steam temperature corresponding to the reservoir pressure of the reservoir at the bottom of the target well. Heating is performed at this temperature. During the heating process, the bottom hole pressure of the target well and the average reservoir temperature of the reservoir near the bottom of the target well are monitored. If the average reservoir temperature of the reservoir near the bottom of the target well rises to above the saturated steam temperature corresponding to the bottom hole pressure of the target well, heating is stopped.

10. The method according to claim 1 or 8, wherein: The heating of the reservoir near the bottom of the target well is achieved by: Superheated steam with a superheat degree > 40° is injected into the reservoir at the bottom of the target well through the target well.

11. The method according to claim 1 or 8, wherein: The heating of the reservoir near the bottom of the target well is achieved by: A mixture of superheated steam and non-condensable gas is injected into the reservoir at the bottom of the target well through the target well.

12. The method according to claim 1 or 8, wherein: The heating of the reservoir near the bottom of the target well is achieved by: A combustion-supporting agent and air are injected into the reservoir at the bottom of the target well through the target well to induce combustion at the bottom of the well. The heat generated by the combustion heats the reservoir near the bottom of the target well.

13. The method according to claim 1, wherein: The non-condensable gas includes one or a combination of two or more of air, nitrogen, carbon dioxide and flue gas.

14. The method according to claim 1, wherein: The injection of non-condensable gas into the reservoir at the bottom of the target well to push the steam slug into the deep part of the reservoir is achieved by: The steam slug is pushed to the deep part of the reservoir by injecting normal temperature non-condensable gas into the reservoir at the bottom of the target well.

15. The method according to claim 1, wherein: The injection of non-condensable gas into the reservoir at the bottom of the target well to push the steam slug into the deep part of the reservoir is achieved by: A combustion-supporting agent and air are injected into the reservoir at the bottom of the target well through the target well, and then combustion is triggered at the bottom of the well. The non-condensable gas after combustion pushes the steam segment plug to the deep part of the reservoir.

16. The method according to claim 1, wherein: The method for improving oil recovery in heavy oil reservoirs further comprises: 6) When the target well is started to produce until the daily oil production is lower than the oil production threshold or the water content of the produced fluid is higher than the water content threshold, repeat steps 2) to 5).