SAGD horizontal well starting method for fractured heavy oil reservoir, SAGD horizontal well pipe column system and application of SAGD horizontal well pipe column system

Abstract

The invention belongs to the technical field of oil exploitation, and provides an SAGD horizontal well starting method for a fractured heavy oil reservoir, an SAGD horizontal well pipe column system and application of the SAGD horizontal well pipe column system. The method comprises the following steps that a plugging agent is injected, and a natural crack or high-permeability strip stratum is plugged and subjected to seal examination; after plugging succeeds, liquid extrusion capacity expansion is conducted on the SAGD horizontal well, and a capacity expansion transformation area is formed; injecting a solvent into the SAGD horizontal well group, and continuously soaking; steam is injected into the SAGD horizontal well for circulation, and a thermal field between injection wells and production wells is established; and after the communication between the SAGD horizontal wells meets the requirement, transferring to SAGD production. According to the method, uniform communication of the SAGD injection-production horizontal wells of the fractured heavy oil reservoir can be achieved, the preheating period is greatly shortened, and the steam injection amount is reduced; and through reservoir capacity expansion, the permeability of the reservoir around the horizontal well is improved, a foundation is provided for subsequent injection of a solvent, the SAGD development effect is improved, and green low-carbon development is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of petroleum extraction, and relates to a SAGD horizontal well startup method for a fractured heavy oil reservoir, a SAGD horizontal well string system and applications thereof. Background Art

[0002] Steam-assisted gravity drainage (SAGD) is the main technology for the development of super-heavy oil reservoirs. The basic principle is to deploy a pair of horizontal wells in the reservoir. The upper steam injection horizontal well continuously injects high-dryness steam. The steam flows to the upper part of the reservoir under the action of gravity differentiation and gradually expands to form a steam cavity. The crude oil in the upper part of the reservoir is heated and viscosity is reduced. Under the action of gravity, it flows to the production horizontal well and is produced. The SAGD development stage is divided into a preheating start-up stage and a production stage. The preheating start-up stage mainly adopts conventional steam injection cycle preheating or rapid start-up methods. Steam injection cycle preheating is to inject steam into the two horizontal wells at the same time. The reservoir temperature between the injection and production horizontal wells gradually increases, and finally the injection and production horizontal wells form thermal connection, and then turn to the SAGD production stage. The steam injection cycle preheating process consumes a lot of steam and the preheating time is long, resulting in poor SAGD development efficiency. In order to accelerate the thermal connection between the injection and production wells and shorten the preheating cycle, rapid start-up methods have been proposed, including squeeze expansion, solvent assistance, electric heating and other methods.

[0003] For SAGD horizontal wells in fractured reservoirs, natural fractures or high-permeability zones are developed in such reservoirs. When conventional steam injection circulation preheating is used, steam channeling is serious and steam consumption is high, making it difficult to achieve uniform connectivity of the horizontal sections. When using liquid squeezing expansion startup, there are problems such as difficulty in raising pressure to achieve reservoir expansion and transformation, large solvent loss due to solvent-assisted immersion, and long startup time and high energy consumption due to electric heating startup.

[0004] Chinese invention patent application CN114790879A discloses a method and system for underground production of fractured oil reservoirs by steam-assisted gravity drainage, which mainly includes the following steps: setting the casing in the horizontal section underground, plugging the formation fractures, and preheating by low-pressure steam injection or solvent-assisted preheating. After the preheating is completed, hot fluid is injected into the steam injection well, and a heating cable is lowered for heating, while the production well is pumping oil. This method can realize the start-up of SAGD in fractured heavy oil reservoirs, but the main body adopts the steam injection preheating method, which has the problems of large steam consumption and long preheating time, and the solvent injection assisted preheating has the problems of poor solvent injectability and small injection volume.

[0005] Chinese invention patent CN114790878B discloses a method and system for underground electric preheating of steam-assisted gravity drainage in fractured oil reservoirs, which mainly includes the following steps: setting the casing in the horizontal section of the well, plugging the formation fractures, and then setting the first oil pipe in the casing, and setting the heating cable in the first oil pipe, injecting water and preheating through the heating cable. This method can achieve rapid start-up of SAGD, but the use of high-power heating devices in the wellbore has problems such as high energy consumption, difficult temperature control, and easy damage of the heating device, making it difficult to achieve field application.

[0006] Chinese invention patent application CN11028486A discloses a method for using a degradable temporary plugging agent to assist SAGD in the exploitation of natural fractured heavy oil reservoirs. The method mainly includes the following steps: injecting a high temperature resistant degradable temporary plugging agent to plug natural fractures or high permeability strips, then injecting hot water or light oil into the injection and production horizontal wells for expansion operations, and finally injecting high temperature steam into the injection and production wells to carry out conventional thermal cycles to form thermal connectivity between the injection and production wells. This method can realize the startup of fractured SAGD horizontal wells, but it also has problems such as high steam consumption and uneven preheating of the horizontal section when using conventional preheating cycles, which is not conducive to the green and low-carbon development of SAGD.

[0007] Generally speaking, existing technologies have not effectively solved the problems of large steam consumption when preheating SAGD horizontal wells due to fractures or high permeability strips, difficulty in solvent injection and uniform utilization of horizontal sections after fracture plugging, and high energy consumption and difficulty in controlling electric heating, and thus cannot achieve green and low-carbon development of SAGD. Summary of the invention

[0008] The present invention aims at the problems of serious steam channeling, large steam consumption, long preheating cycle, and difficulty in achieving uniform connection of horizontal sections in SAGD horizontal wells in fractured heavy oil reservoirs using conventional circulation preheating. A method for starting a SAGD horizontal well in fractured heavy oil reservoirs, a SAGD horizontal well string system and its application are provided. The method sequentially seals and homogenizes natural fractures or high permeability strips, expands the capacity of horizontal wells by injection of liquid, injects solvent to shut down the well, and injects steam circulation at low pressure to achieve connection between two horizontal wells of SAGD and then enter the normal production stage of SAGD. The method can achieve uniform connection of SAGD injection and production horizontal wells in fractured heavy oil reservoirs, greatly reduce the amount of steam injection, and ensure the green and low-carbon benefit development of SAGD.

[0009] To achieve the above object, the present invention provides a method for starting a SAGD horizontal well in a fractured heavy oil reservoir, which specifically comprises the following steps:

[0010] (1) injecting a plugging agent into a SAGD horizontal well to plug the natural fracture or high permeability formation and determine the plugging status. If the plugging is unsuccessful, repeat step (1); if the plugging is successful, perform step (2);

[0011] (2) Squeeze and expand the SAGD horizontal well to form an expansion zone around the horizontal well;

[0012] (3) Injecting solvent into the SAGD horizontal well and continuously shutting down the well;

[0013] (4) Inject steam into the SAGD horizontal well for circulation, establish a thermal field between the injection and production wells, and determine the degree of connectivity between the SAGD horizontal wells; if the degree of connectivity does not meet the requirements, repeat steps (3) and (4); if the degree of connectivity meets the requirements, execute step (5);

[0014] (5) After the connectivity between SAGD horizontal wells reaches the required level, switch to SAGD production.

[0015] Furthermore, in step (1), the blocking step is:

[0016] (1-1) Circulation well washing: Inject well washing fluid into the first tubing of the horizontal well, return it from the second tubing or casing, clean the oil stains in the wellbore and measure the water absorption of the formation;

[0017] (1-2) Inject the front slug, main slug, and displacement slug in sequence;

[0018] (1-3) Waiting for setting: After the plugging section is injected, the well is shut down and the setting is waited for.

[0019] Furthermore, the pre-slug is injected with a polymer solution, the injection volume of which is equal to the horizontal wellbore volume, usually 10-30m 3 .

[0020] Furthermore, the main segment plug is injected with a high temperature resistant gel plugging agent, the high temperature resistant gel plugging agent has a temperature resistance of ≥180°C, a controllable gelling time, and an injection volume determined according to the formation drilling fluid loss situation, which is 10-80m 3 .

[0021] Furthermore, the injection amount of the main segment plugging agent is calculated according to the following formula:

[0022] V=kLπR 2 φ+q

[0023] Where V is the injection volume of the main segment plugging agent, m 3 ; k is the correction coefficient, with a value of 0.5-0.7; L is the length of the horizontal well section where the drilling fluid loss rate is greater than 30%, m; R is the plugging radius, with a value of 1.0m; Φ is the average porosity of the reservoir, %; q is the pipeline and tank bottom retention, with a value of 0.5-1m 3 .

[0024] Furthermore, the displacement plug is injected with a polymer solution, the injection volume of which is equal to the horizontal wellbore volume, usually 10-30m3 .

[0025] Furthermore, the waiting time is determined according to the gelling properties of the plugging agent, as follows:

[0026] Determine the gelling time of the plugging agent under different temperature conditions, and establish a standard curve corresponding to the gelling time of the plugging agent and the temperature; during the on-site construction process, determine the waiting time for the plugging agent based on the temperature of the horizontal section thermocouple when the plugging agent segment is injected and the standard curve; usually 5-24h.

[0027] Furthermore, the well washing fluid is de-oiled hot water.

[0028] In step (1), the injection of the pre-slug can improve the formation adhesion and provide a basis for the subsequent injection of the slug.

[0029] Furthermore, during the plugging process, the injection pressure and injection displacement fluctuation range are maintained at less than 10%, and the bottom hole pressure is ensured not to exceed the formation fracture pressure.

[0030] Furthermore, in step (1), the blocking condition is determined by the following method:

[0031] Close the casing valve, inject de-oiled hot water from the first or second oil pipe, then stop the pump and soak the well. If the wellhead pressure drops less than 0.5MPa within half an hour, it indicates that the plugging is successful.

[0032] Furthermore, in step (2), the specific steps of squeezing liquid to expand the volume include:

[0033] (2-1) Circulation well washing; the circulation well washing steps are the same as step (1-1) of step (1);

[0034] (2-2) Pressure increase and fluid squeezing: Increase the bottom hole pressure to inject water, and stop when the bottom hole pressure rises to 95% of the formation fracture pressure; during this process, the injection pressure is the main control parameter, and the injection displacement is the auxiliary control parameter. The bottom hole pressure is increased in sequence according to the pressure gradient of 0.5MPa;

[0035] In this process, the pump truck on the ground maintains a constant injection displacement, and then controls the pressure through the opening of the casing or the second oil pipe external discharge valve; when the external discharge opening increases, the injection pressure decreases; conversely, the injection pressure increases;

[0036] (2-3) Pulse expansion: The injection pressure is further increased by pulse by increasing the displacement, from 50 L / min to 250 L / min according to the displacement gradient of 50 L / min;

[0037] During this process, the casing or the second oil pipe external discharge valve is in a closed state, and the displacement of the pump truck is increased, and the corresponding injection pressure also increases accordingly.

[0038] Furthermore, in step (2-2), the bottom hole pressure is equal to the sum of the surface injection pressure and the liquid injection pressure in the wellbore.

[0039] In step (2), pulse expansion can cause microcracks in the reservoir around the horizontal well, improve the permeability of the reservoir, and provide a basis for subsequent solvent injection.

[0040] Further, in step (3), the solvent injection step is:

[0041] (3-1) Close the wellhead casing valve and inject solvent into the first and second oil pipes of the horizontal well at the same time. The injection pressure ensures that the bottom hole pressure does not exceed the formation fracture pressure;

[0042] (3-2) Clean water displacement: After the solvent is injected, clean water is injected to displace the solvent to the deep part of the formation, forming a solvent immersion zone.

[0043] Furthermore, the solvent is No. 0 diesel and / or coking diesel.

[0044] Furthermore, during the solvent injection process, the SAGD horizontal wells (double wells) are injected simultaneously or alternately, and the injection displacement is adjusted in a pulsed manner.

[0045] Furthermore, the displacement of the solvent during injection is 50-250 L / min; the solvent single-well injection volume is determined according to the length of the horizontal section and the reservoir porosity.

[0046] The solvent injection volume per well is calculated according to the following formula:

[0047]

[0048] Where Q is the solvent injection volume per well, m 3 ; h is the length of the horizontal section, m; Φ is the average porosity of the reservoir, %; k is the correction factor, which is 0.5; D is the solvent sweep diameter, which is 1.2 m; d is the screen diameter, which is 0.073 m.

[0049] Furthermore, during the solvent injection process, the pressure difference between the injection and production horizontal wells is ensured not to exceed 0.3 MPa.

[0050] Furthermore, in step (3), the soaking time is determined according to the viscosity of the reservoir crude oil, generally 60-90 days, and is specifically determined as follows:

[0051] Under formation conditions, when the viscosity of crude oil is less than 10,000 mPa·s, the soaking time is 60 days; when the viscosity of crude oil is between 10,000-20,000 mP·s, the soaking time is 75 days; when the viscosity of crude oil is greater than 20,000 mPa·s, the soaking time is 90 days.

[0052] Furthermore, in step (4), the steam injection pressure during the steam injection cycle is controlled to be 60-80% of the preheating steam injection pressure of the SAGD well group in the adjacent heavy oil reservoir.

[0053] Furthermore, in step (4), when the degree of connectivity between SAGD horizontal wells is ≥ 70%, SAGD production is switched; otherwise, steps (3) and (4) are repeated.

[0054] Furthermore, in step (5), after the SAGD horizontal well group is switched to production, solvent is injected again into the SAGD steam injection horizontal well. The solvent is vaporized under high temperature conditions in the formation and mixed with steam to accelerate crude oil production and promote steam chamber expansion.

[0055] The present invention also provides a SAGD horizontal well tubing system using the above-mentioned SAGD horizontal well startup method, the SAGD system comprising: casing, a first oil pipe and a second oil pipe, the casing is lowered from the vertical section of the SAGD horizontal well, and extends through the inclined well section and the horizontal section, the first oil pipe and the second oil pipe are arranged in the casing, and the first oil pipe is longer than the second oil pipe; the casing of the vertical section and the inclined well section of the SAGD horizontal well is a blind pipe, the casing of the horizontal section of the SAGD horizontal well is a combined tubing of a blind pipe and a screen pipe, the blind pipe is arranged in a loss section with a preset proportion of the drilling fluid loss rate in the horizontal section; the screen pipe is arranged in the remaining horizontal sections.

[0056] Furthermore, the blind pipe is arranged in the leakage section of the horizontal section where the drilling fluid loss rate is greater than 30%; and the screen pipe is arranged in the remaining horizontal sections.

[0057] Furthermore, the first oil pipe or the second oil pipe is respectively selected from a flat oil pipe and a combined tubing string, and the combined tubing string is a combination of an insulated oil pipe and a flat oil pipe; the first oil pipe and the second oil pipe are placed in parallel in the casing, wherein the first oil pipe is lowered to the toe end of the horizontal section, and the second oil pipe is lowered to the heel end of the horizontal section, and a continuous temperature measuring thermocouple is lowered into the first oil pipe of the SAGD horizontal well.

[0058] Furthermore, the temperature measuring thermocouple is a continuous steel armored cable testing instrument, which is lowered into the rear end of the horizontal section from the first oil pipe and can measure the temperature data of the horizontal section during steam injection, well soaking and oil pumping in real time.

[0059] The present invention also provides the application of the above-mentioned SAGD horizontal well startup method or the above-mentioned SAGD horizontal well tubular system in steam-assisted gravity drainage (SAGD).

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] (1) The present invention provides a method for starting a SAGD horizontal well in a fractured heavy oil reservoir. Compared with the prior art, the method can promote uniform and efficient connectivity between SAGD injection and production wells in fractured oil reservoirs by plugging the reservoir, squeezing liquid to expand the capacity, injecting solvents, and circulating steam, greatly shorten the preheating period, reduce the amount of steam injection, and enable green and low-carbon development of SAGD.

[0062] (2) In the present invention, the reservoir is expanded before solvent injection, thereby increasing the permeability of the reservoir around the horizontal well and providing a basis for subsequent solvent injection;

[0063] (3) In the present invention, the solvent can be injected again after the SAGD production stage to accelerate the viscosity reduction of crude oil and promote the accelerated expansion of the steam chamber, thereby improving the SAGD development effect;

[0064] (4) The method of the present invention can ensure that the utilization degree of the horizontal section of the SAGD horizontal well reaches more than 80%, and the average daily liquid production and the average daily oil production are greatly improved (the average daily liquid production is increased by 26%, and the average daily oil production is increased by 120%);

[0065] (5) The chemical plugging agent and solvent used in the present invention are commonly used in oil fields, are cheap, safe and reliable, and the injection process is simple and easy to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 It is a schematic diagram of the SAGD horizontal well string system and the plugging agent injection slug in fractured heavy oil reservoirs;

[0067] Figure 2 It is a schematic diagram of SAGD horizontal well expansion and solvent injection in fractured heavy oil reservoirs;

[0068] Figure 3 Implementation flow chart for SAGD horizontal well startup method in fractured heavy oil reservoirs;

[0069] Figure 4 It is the standard curve corresponding to the gelling time and temperature of the main segment plugging agent.

[0070] Figure numerals: 10, casing; 11, horizontal section heel end; 12, horizontal section toe end; 110, screen tube; 120, blind pipe; 20, first oil pipe; 210, temperature measuring thermocouple; 30, second oil pipe; 40, natural fracture or high permeability strip; 50, plugging agent segment plug; 510, front segment plug; 520, main segment plug; 530, replacement segment plug; 60, expansion and transformation area; 610, micro fracture; 70, solvent immersion area. DETAILED DESCRIPTION

[0071] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs. In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail with specific embodiments in conjunction with the accompanying drawings.

[0072] Take a certain oil field as an example, the average burial depth of the oil layer is 600m, the formation fracture pressure is 12.1MPa, the reservoir porosity is 30.2%, the formation crude oil viscosity is 14210mPa·s, the average permeability is 1502mD, the average oil saturation is 71.1%, and the horizontal section length of the SAGD horizontal well is 350m;

[0073] Polymer solution: polyacrylamide, viscosity 30-40 mPa·s;

[0074] Heat-resistant gel plugging agent: chromium gel, viscosity 50-70mPa·s, temperature resistance 200℃, pressure resistance 5MPa;

[0075] De-oiling hot water: hot water from de-oiling of heavy oil produced in oil fields, with a temperature of about 80°C.

[0076] Embodiment 1:

[0077] The SAGD horizontal well string system of the present invention is as follows Figure 1 As shown:

[0078] (1) A pair of SAGD horizontal wells are drilled in the oil reservoir, and the vertical section, the inclined section and the horizontal section of the casing 10 are sequentially lowered into the SAGD double horizontal well, and the first oil pipe 20 and the second oil pipe 30 are lowered into the casing 10; the vertical section and the inclined section of the casing 10 are the blind pipe 120, and the horizontal section of the casing 10 is the combined pipe string of the screen pipe 110 and the blind pipe 120;

[0079] (2) Both the first oil pipe 20 and the second oil pipe 30 are flat oil pipes, and are placed in parallel in the casing 10, wherein the first oil pipe 20 is lowered to the toe end 11 of the horizontal section, and the second oil pipe 30 is lowered to the heel end 12 of the horizontal section, and a continuous temperature measuring thermocouple 210 is lowered into the first oil pipe 20 of the SAGD production horizontal well;

[0080] (3) Determine the lowering position and length of the blind pipe 120 according to the drilling fluid loss situation:

[0081] Drilling fluid loss rate: (imported drilling fluid volume - exported drilling fluid volume) / (imported drilling fluid volume)

[0082] During the SAGD horizontal section drilling process, the horizontal section with a drilling fluid loss rate greater than 30% is marked as a loss section, the loss section in the horizontal section is arranged as a blind pipe 120, and the remaining horizontal sections are arranged with a screen pipe 110.

[0083] Embodiment 2:

[0084] Schematic diagram of SAGD horizontal well string system and plugging agent injection in fractured heavy oil reservoir ( Figure 1 ) and schematic diagram of SAGD horizontal well expansion and solvent injection in fractured heavy oil reservoirs ( Figure 2 ), the SAGD horizontal well start-up method of the present invention is specifically described in the SAGD horizontal well string system of Example 1, and the implementation process is as follows Figure 3 As shown;

[0085] The SAGD horizontal well startup method in fractured heavy oil reservoirs mainly includes the following steps:

[0086] (1) Injecting a plugging agent to plug the natural fracture or high-permeability zone 40 and verify the plugging. The specific steps are as follows:

[0087] ① Circulation well washing: inject well washing fluid into the first oil pipe 20 of the horizontal well, return it from the second oil pipe 30, clean the oil stains in the wellbore and measure the water absorption of the formation; in this embodiment, the well washing fluid uses deoiled hot water;

[0088] ② Injection of pre-slug 510: Inject 0.5% polyacrylamide aqueous solution into the horizontal well to improve the formation adhesion and provide a basis for subsequent slug injection. The injection volume is 30m 3 ; The injection displacement of this process is 160L / min, and the injection pressure is controlled to be less than 5.0MPa;

[0089] ③ Injecting the main segment plug 520: injecting chromium gel plugging agent into the main segment plug 520;

[0090] In this embodiment, during the formation drilling process, the drilling fluid loss rates at well depths of 835m-861m and 946m-977m were 31.1% and 32.6% respectively. The injection amount of the main segment plugging agent was calculated according to the following formula:

[0091] V=kLπR 2 φ+q

[0092] Where V is the injection volume of the main segment plugging agent, m 3 ; k is the correction coefficient, which is 0.5; L is the length of the horizontal well section where the drilling fluid loss rate is greater than 30%, m; R is the plugging radius, which is 1.0 m; Φ is the average porosity of the reservoir, %; q is the pipeline and tank bottom retention, which is 0.5 m 3 .

[0093] According to calculation, the injection volume of the main segment plugging agent is 28m 3 ; During this process, the surface injection displacement is maintained at 160L / min and the injection pressure is controlled to be less than 5.5MPa;

[0094] ④ Injection displacement plug 530: Inject 0.5% polyacrylamide aqueous solution to displace the main plug 520 plugging agent to the natural fracture or high permeability zone 40 deep in the reservoir, with an injection volume of 30m 3 ; The surface injection displacement of this process is 250L / min, and the injection pressure is controlled to be less than 5.0MPa;

[0095] ⑤ Waiting for solidification: After the plugging section plug 50 is injected, the well is shut down for solidification. The plugging agent used in this embodiment is a high temperature resistant chromium gel, which takes about 5 hours to gel at 80°C. When the plugging agent section plug is injected, the horizontal section temperature measuring thermocouple 210 shows that the horizontal section temperature is 78-81°C. According to the standard curve corresponding to the plugging agent gel time and temperature (see Figure 4 ), and the waiting time was determined to be 5h.

[0096] ⑥Seal verification: Close the valve of casing 10, inject de-oiled hot water from the first oil pipe 20, then stop the pump and soak the well. Within half an hour, the wellhead pressure drops to 0.37MPa, which is less than 0.5MPa, indicating that the plugging is successful.

[0097] (2) Squeezing and expanding the SAGD horizontal well to form an expansion and transformation zone 60 around the horizontal well. The specific steps are as follows:

[0098] ① First, inject water into the injection-production well for circulation and well washing: the specific operation is the same as step ① in step (1);

[0099] ② Pressure-raising and squeezing: This process uses injection pressure as the main control parameter and injection displacement as the auxiliary control parameter. The bottom hole pressure is gradually increased to inject water. When the bottom hole pressure rises to 95% of the formation fracture pressure, it stops.

[0100] During this process, the injection displacement of the ground pump truck is maintained at 160L / min. The ground injection pressure is increased by reducing the opening of the second oil pipe external discharge valve. The injection pressure is increased by 0.5MPa each time and maintained for 4 hours after reaching the target pressure.

[0101] The well has a vertical depth of about 600m, the liquid column pressure in the wellbore is about 6.0MPa, and the maximum bottom hole pressure is about 11.5MPa. Therefore, the target pressure is 5.5MPa.

[0102] ③ Pulse expansion: This process further increases the injection pressure by increasing the displacement from 50L / min to 250L / min, increasing by 50L / min each time and maintaining this displacement for 4 hours, so that microcracks 610 are generated in the reservoir around the horizontal well, improving the permeability of the reservoir and providing a basis for subsequent solvent injection;

[0103] This process controls the bottom hole pressure not to exceed the formation fracture pressure of 12.1MPa.

[0104] (3) Injecting solvent into the SAGD horizontal well to form a solvent soaking zone 70, and continuously soaking the well; the specific steps are as follows:

[0105] ① Close the valve of casing 10, and inject No. 0 diesel into the first oil pipe 20 and the second oil pipe 30 simultaneously by SAGD horizontal well simultaneous injection. The injection displacement is controlled at 100L / min, and the injection pressure ensures that the bottom hole pressure does not exceed the formation fracture pressure of 12.1MPa;

[0106] The single well injection volume is calculated according to the horizontal section length and reservoir porosity using the following formula:

[0107]

[0108] Where Q is the solvent injection volume per well, m 3 ; h is the length of the horizontal section, m; Φ is the average porosity of the reservoir, %; k is the correction factor, which is 0.5; D is the solvent sweep diameter, which is 1.2 m; d is the screen diameter, which is 0.073 m;

[0109] According to calculation, the injection volume of a single well is 60m 3 ;

[0110] ② Clean water displacement: After the solvent is injected, clean water is injected to displace the solvent to the deep part of the formation to form a solvent soaking area 70; during the solvent injection process, the pressure difference between the injection and production horizontal wells is ensured not to exceed 0.3MPa;

[0111] ③ After the solvent is injected, the well is shut down; in this embodiment, the viscosity of the formation crude oil is 14210 mPa·s, and the shut down time is determined to be 75 days according to the viscosity of the formation crude oil.

[0112] (4) Inject steam into the SAGD horizontal wells for circulation, establish a thermal field between the injection and production wells, and determine the degree of connectivity between the SAGD horizontal wells; the specific steps are as follows:

[0113] ① Inject steam into the SAGD horizontal well for circulation. This process controls the steam injection rate and pressure of the horizontal well. The steam injection pressure is controlled to be 60%-80% of the circulating preheating steam injection pressure of the adjacent SAGD well group. The average circulating preheating steam injection pressure of the adjacent SAGD horizontal wells is 5.0MPa.

[0114] ② After 15 days of steam injection circulation in the SAGD horizontal well, the connectivity of the injection and production horizontal sections was tested; at this time, the connectivity was 80%, which met the requirement that the connectivity between the two horizontal wells of SAGD should be greater than 70%, and the production was switched to SAGD.

[0115] After the SAGD horizontal well group was put into production for 90 days, 60m3 of steam was injected into the SAGD steam injection horizontal well again. 3The solvent is mixed with steam after being gasified under high temperature conditions in the formation, which accelerates crude oil production, promotes the expansion of the steam chamber, and further improves the development effect of SAGD.

[0116] After adopting this method, the circulation preheating period of the well is 90 days, which is 50% shorter than that of conventional steam injection circulation preheating. After switching to SAGD production, the temperature of the horizontal section is maintained at 140-180℃, the utilization degree reaches more than 80%, and the average daily liquid production is 64.2 tons and the average daily oil production is 16.5 tons. After the adjacent wells are preheated by conventional steam injection circulation (mainly through the upper and lower horizontal wells to control the pressure and inject steam circulation to establish inter-well thermal connection) and switched to SAGD production, high-temperature steam channeling occurs at the front end of the horizontal section, with a temperature greater than 230℃, while the temperature in the middle and rear ends of the horizontal section is less than 90℃, which shows strong uneven utilization as a whole; the average daily liquid production is 51.2 tons and the daily oil production is 7.5 tons.

[0117] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A method for starting a SAGD horizontal well in a fractured heavy oil reservoir, characterized in that: The following steps are involved: (1) injecting a plugging agent into a SAGD horizontal well to plug the natural fracture or high permeability formation and determine the plugging status. If the plugging is unsuccessful, repeat step (1); if the plugging is successful, perform step (2); (2) Squeeze and expand the SAGD horizontal well to form an expansion zone around the horizontal well; (3) Injecting solvent into the SAGD horizontal well and continuously shutting down the well; (4) Inject steam into the SAGD horizontal well for circulation, establish a thermal field between the injection and production wells, and determine the degree of connectivity between the SAGD horizontal wells; if the degree of connectivity does not meet the requirements, repeat steps (3) and (4); if the degree of connectivity meets the requirements, execute step (5); (5) After the connectivity between SAGD horizontal wells reaches the required level, switch to SAGD production.

2. The SAGD horizontal well startup method according to claim 1, characterized in that: In step (1), the plugging includes a front plug, a main plug and a replacement plug.

3. The SAGD horizontal well startup method according to claim 2, characterized in that: The front slug is injected with a polymer solution, and the injection amount is the wellbore volume of the horizontal well; The main segment plug is injected with a high temperature resistant gel plugging agent, and the high temperature resistant gel plugging agent has a temperature resistance of ≥180°C; the injection amount is determined according to the formation drilling fluid loss situation, and the specific calculation formula is as follows: V=kLπR 2 φ+q Where V is the injection volume of the main segment plugging agent, m 3 ; k is the correction coefficient, with a value of 0.5-0.7; L is the length of the horizontal well section where the drilling fluid loss rate is greater than 30%, m; R is the plugging radius, with a value of 1.0m; Φ is the average porosity of the reservoir, %; q is the pipeline and tank bottom retention, with a value of 0.5-1m 3 ; The displacement plug is injected with a polymer solution, and the injection amount is the wellbore volume of the horizontal well.

4. The SAGD horizontal well startup method according to claim 1, characterized in that: The solvent is No. 0 diesel and / or coking diesel; the displacement of the solvent during injection is 50-250L / min; the solvent single well injection amount is determined according to the horizontal section length and reservoir porosity, and the specific calculation formula is as follows: Where Q is the solvent injection volume per well, m 3 ; h is the length of the horizontal section, m; Φ is the average porosity of the reservoir, %; k is the correction factor, which is 0.5; D is the solvent sweep diameter, which is 1.2 m; d is the screen diameter, which is 0.073 m.

5. The SAGD horizontal well startup method according to claim 1, characterized in that: In step (1), the blocking step is: (1-1) Circulation well washing; (1-2) injecting the front slug, main slug and displacement slug in sequence; (1-3) Waiting for setting: After the plugging section is injected, the well is shut down and the setting is waited for.

6. The SAGD horizontal well startup method according to claim 5, characterized in that: In step (1-3), the waiting time for setting is determined according to the gelling properties of the plugging agent, and the specific method is: A standard curve corresponding to the gelling time and temperature of the plugging agent is established; the waiting time for the plugging agent to be cured is determined based on the temperature of the thermocouple in the horizontal section when the plugging agent segment is injected and the standard curve.

7. The SAGD horizontal well startup method according to claim 1, characterized in that: In step (1), during the plugging process, the injection pressure and injection displacement fluctuation range are maintained at less than 10%, and the bottom hole pressure is ensured not to exceed the formation fracture pressure.

8. The SAGD horizontal well startup method according to claim 1, characterized in that: In step (1), the method for determining the blocking condition is as follows: Close the casing valve, inject de-oiled hot water from the first or second oil pipe, then stop the pump and soak the well. If the wellhead pressure drops less than 0.5MPa within half an hour, it indicates that the plugging is successful.

9. The SAGD horizontal well startup method according to claim 1, characterized in that: In step (2), the specific steps of squeezing liquid to expand the volume include: (2-1) Circulation well washing; (2-2) Pressure increase and fluid squeezing: Increase the bottom hole pressure to inject water, and stop when the bottom hole pressure reaches 95% of the formation fracture pressure; (2-3) Pulse expansion: The injection pressure is further increased by pulses by increasing the displacement from 50 L / min to 250 L / min, causing microcracks in the reservoir around the horizontal well.

10. The SAGD horizontal well startup method according to claim 1, characterized in that: In step (3), the solvent injection step is: (3-1) Close the wellhead casing valve and inject solvent into the first and second oil pipes of the horizontal well at the same time. The injection pressure ensures that the bottom hole pressure does not exceed the formation fracture pressure; (3-2) Clean water displacement: After the solvent is injected, clean water is injected to displace the solvent to the deep part of the formation, forming a solvent immersion zone.

11. The SAGD horizontal well startup method according to claim 10, characterized in that: In step (3-1), during the solvent injection process, the SAGD horizontal wells are injected simultaneously or alternately; the injection displacement is adjusted in a pulse manner, and the displacement is 50-250L / min; during the solvent injection process, the pressure difference between the injection and production horizontal wells is ensured not to exceed 0.3MPa.

12. The SAGD horizontal well startup method according to claim 1, characterized in that: In step (3), the soaking time is determined according to the viscosity of the formation crude oil, specifically: The viscosity of crude oil is less than 10000mPa·s, and the soaking time is 60 days; The viscosity of crude oil is between 10000-20000mP·s, and the soaking time is 75 days; The viscosity of crude oil is greater than 20000mPa·s, and the well soaking time is 90 days.

13. The SAGD horizontal well startup method according to claim 1, characterized in that: In step (4), the steam injection pressure during the steam injection cycle is controlled to be 60-80% of the preheating steam injection pressure of the SAGD well group in the adjacent heavy oil reservoir.

14. The SAGD horizontal well startup method according to claim 1, characterized in that: In step (4), when the connectivity between the SAGD two-horizontal wells is ≥ 70%, the connectivity meets the requirement.

15. A SAGD horizontal well string system using the SAGD horizontal well startup method according to any one of claims 1 to 14, characterized in that: It includes casing, a first oil pipe and a second oil pipe. The casing is lowered from the vertical section of the SAGD horizontal well and extends through the inclined well section and the horizontal section. The first oil pipe and the second oil pipe are arranged in the casing, and the first oil pipe is longer than the second oil pipe. The casing of the vertical section and the inclined well section of the SAGD horizontal well is a blind pipe, and the casing of the horizontal section of the SAGD horizontal well is a combined pipe string of blind pipes and screen pipes. The blind pipe is arranged in the loss section with a preset proportion of the drilling fluid loss rate in the horizontal section; screen pipes are arranged in the remaining horizontal sections.

16. The SAGD horizontal well string system according to claim 15, characterized in that: The first oil pipe or the second oil pipe is selected from a flat oil pipe and a combined tubing string respectively, and the combined tubing string is a combination of an insulated oil pipe and a flat oil pipe; the first oil pipe and the second oil pipe are placed in parallel in the casing, wherein the first oil pipe is lowered to the toe end of the horizontal section, and the second oil pipe is lowered to the heel end of the horizontal section, and a continuous temperature measuring thermocouple is lowered into the first oil pipe of the SAGD horizontal well.

17. Use of the SAGD horizontal well startup method according to any one of claims 1 to 14 or the SAGD horizontal well tubular system according to any one of claims 15 to 16 in steam-assisted gravity drainage (SAGD).

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