Method for improving SAGD (Steam Assisted Gravity Drainage) development effect of super heavy oil reservoir

Abstract

The invention discloses a method for improving the SAGD (Steam Assisted Gravity Drainage) development effect of a super heavy oil reservoir. The method comprises the following steps: drilling a steam injection well and a production well which are vertically opposite in position in an oil layer; steam is injected into the steam injection well and the production well, the steam injection well and the production well are communicated in a heating mode, an oil drainage channel is built between the steam injection well and the production well, and when the communication degree between the steam injection well and the production well meets the requirement, an SAGD production stage is started; closing the production well, injecting high-temperature, high-pressure and high-speed superheated steam into the steam injection well, and expanding the volume of a reservoir above the steam injection well; after the steam injection pressure of the steam injection well reaches a required value, soaking the steam injection well, and building a liquid level by soaking energy storage; underground environment parameters of the production well are collected, when it is judged that production conditions are met, the steam injection well is kept closed, the production well is opened for production, and liquid drainage energy release extraction is completed; and repeating for multiple rounds until the oil production level of the production well is not increased any more, and then turning to a conventional SAGD production stage. According to the method, the initial yield of SAGD production can be rapidly increased, and the problems that the expansion speed of the steam cavity is slow and underground steam channeling is likely to happen are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of petroleum extraction, and in particular relates to a method for improving the SAGD development effect of super-heavy oil reservoirs. Background Art

[0002] The principle of steam-assisted gravity drainage (SAGD) is to deploy horizontal wells stacked up and down in the same oil layer, continuously inject high-temperature steam with a temperature greater than 200°C into the upper steam injection well, heat the formation and crude oil through steam, reduce the viscosity of the heated crude oil, and the condensed water of the steam flows downward under the action of gravity, and is produced from the horizontal production well at the bottom of the oil layer. The steam occupies the space of the produced crude oil and gradually expands in the formation to form a steam chamber. The expansion process of the steam chamber is the process of heat exchange between the crude oil and steam in the formation and being produced. Its development process is mainly divided into two stages, one is the cycle preheating stage, and the other is the SAGD production stage. The goal of the preheating stage is to achieve uniform heating of the oil layer in the shortest time, so that the steam injection well and the production well are evenly heated and connected, and an oil drainage channel is established between the steam injection well and the production well. When the degree of connectivity between the two wells reaches more than 75%, the SAGD production stage is entered. In the prior art, the startup method using circulating preheating is generally divided into three steps: (1) Steam circulates in the steam injection well and the production well, and the reservoir transfers heat mainly through heat conduction; (2) An inter-well pressure difference is formed between the steam injection well and the production well, and the pressure of the steam injection well is higher than that of the production well, so that the inter-well crude oil flows to the production well, preparing for the transition to full SAGD production; (3) The annulus of the upper steam injection well stops draining liquid, and the lower production well stops injecting steam, and the full SAGD production stage is entered.

[0003] In the SAGD production stage, the conventional SAGD production method is continuous steam injection in the steam injection wells and continuous production in the production wells. The injected steam contacts the crude oil in the reservoir. The crude oil flows downward by gravity along the two sides of the steam injection wells in contact with the cold oil layer, and enters the production wells through the connecting channels between the injection and production wells, and is produced by the production wells. In this process, steam continuously occupies the space of the produced crude oil, forming a steam chamber. Therefore, the expansion and development of the steam chamber is a physical manifestation of the mechanism contained in the SAGD development process. The expansion speed and scale of the steam chamber are directly proportional to the production of the well group. The larger the scale of the steam chamber development, the higher the production. Generally, according to the expansion and development process of the SAGD steam chamber in the production stage, SAGD production is divided into three stages: vertical rise of the steam chamber, lateral expansion of the steam chamber, and descent of the steam chamber.

[0004] In the vertical rising stage of the steam chamber, the corresponding control policy is formulated for the purpose of "increasing steam stripping liquid and expanding the chamber under high pressure". By continuously increasing steam injection and controlling the higher steam injection pressure, the steam is accelerated to pass through the reservoir. At the same time, according to the underground Sub-cooling, the purpose of increasing steam stripping liquid and expanding the chamber is achieved in accordance with the cycle rhythm of increasing steam-stable production-lifting liquid-stable production, so that the production can quickly reach the production peak. However, for oil reservoirs with low permeability, developed interlayers and strong heterogeneity, on the one hand, due to the low reservoir permeability (generally less than 1000mD), the steam chamber is difficult to expand upward under the steam injection pressure during normal SAGD production, and due to the strong heterogeneity of the reservoir, high permeability channels are likely to exist between the steam injection well and the production well, resulting in the steam being easily directly escaping from the high permeability channel between the steam injection well and the production well after the pressure is increased to inject steam, and being produced from the production well, resulting in the steam chamber not expanding upward, or expanding slowly. Since there is no relevant SAGD plugging technology at present, in order to ensure that steam does not escape from the bottom of the production well, a higher Sub-cool will be maintained at the bottom of the well or the steam injection rate of the steam injection well will be reduced to control a lower steam injection pressure, reduce the pressure difference, ensure that steam does not occur underground and stabilize production. However, due to the low permeability of the reservoir and the low steam injection pressure, although this method can effectively improve the steam utilization rate, the steam chamber expands extremely slowly or even does not expand, and the oil production level is low.

[0005] Existing research shows that increasing the steam injection pressure can effectively increase the expansion speed of the steam chamber. However, since high pressure can easily lead to steam channeling at the bottom of the well, the steam is directly extracted from the production well and cannot expand the chamber upward. There is a practical contradiction between the easy channeling of high-pressure chamber expansion and the slow expansion of low-pressure chamber expansion. In addition, there is no research on improving the development effect of such reservoirs. Summary of the invention

[0006] The purpose of the present invention is to provide a method for improving the SAGD development effect of super heavy oil reservoirs, accelerate the expansion speed of the steam chamber, and improve the oil production level and the oil-steam ratio in view of the problems that the low permeability leads to slow expansion of the steam chamber, the strong heterogeneity leads to low steam channeling utilization, and the high original formation pressure leads to low thermal efficiency during the existing SAGD development of super heavy oil reservoirs.

[0007] In order to achieve the above object, the present invention has the following technical solutions:

[0008] A method for improving the SAGD development effect of super heavy oil reservoirs comprises the following steps:

[0009] Step S10: determining a heterogeneous oil reservoir suitable for steam-assisted gravity drainage development;

[0010] Step S20: drilling two horizontal wells that are located vertically opposite to each other in the oil layer, the upper horizontal well being a steam injection well, and the lower horizontal well being a production well;

[0011] Step S30: Inject steam into the steam injection well and the production well to heat and connect the steam injection well and the production well evenly, and establish an oil leakage channel between the steam injection well and the production well. When the degree of connectivity between the two wells reaches more than 75%, the SAGD production stage is entered;

[0012] Step S40: closing the production well, injecting high-temperature, high-pressure, and high-speed superheated steam into the steam injection well, expanding the reservoir above the steam injection well, changing the effective stress on the rock skeleton, increasing the rock pore volume, increasing the porosity and permeability, and improving the reservoir properties;

[0013] Step S50: When the steam injection pressure of the steam injection well reaches the required value, the steam injection well is shut down to store energy and build up the liquid level;

[0014] Step S60: collecting downhole environmental parameters of the production well, and when it is determined that the production conditions are met, the steam injection well is kept shut down, and the production well is opened for production, so as to complete the drainage and energy release;

[0015] Repeat steps S40 to S60 for multiple rounds. When the oil production level of the production well stops increasing, the steam injection well continues to inject steam and the production well continues to produce liquid, thus entering the conventional SAGD production stage.

[0016] As a preferred scheme, the super-heavy oil reservoir developed by SAGD is a medium-shallow reservoir with a burial depth of 350 to 600 meters, an oil saturation greater than 0.45, an oil layer thickness greater than 10 meters, a horizontal permeability between 600 and 1400 millidarcy, a ratio of vertical permeability to horizontal permeability greater than 0.5, an oil layer porosity greater than 0.28, and there are continuously or discontinuously developed low-physical property reservoirs in the oil layer, the permeability of the low-physical property reservoirs is less than 200 millidarcy, and the degassed crude oil viscosity of the reservoir at 50°C is greater than 50,000 centipoise.

[0017] As a preferred solution, the method is suitable for the well group recovery rate between 5% and 30% after the oil leakage channel is established between the steam injection well and the production well and the SAGD production stage is entered.

[0018] As a preferred solution, when high-temperature, high-pressure and high-velocity steam is injected into the steam injection well, the steam injection pressure is greater than the minimum principal stress and less than the formation fracture pressure of 0.5 MPa.

[0019] As a preferred solution, in step S40, the steam injection well uses a main pipe and a secondary pipe to inject steam simultaneously, and the steam injection rate is 200t / d to 240t / d.

[0020] As a preferred solution, in step S50, the required value of the steam injection pressure of the steam injection well is 9.0 MPa.

[0021] As a preferred solution, in step S50, the well is shut down for 1 to 3 days, and downhole temperature monitoring results of the production well are collected synchronously.

[0022] As a preferred solution, in step S60, the production condition of the production well is that the underground sub-cooling temperature is 20-30°C.

[0023] As a preferred solution, the calculation method of the downhole Sub-cool is: its value is equal to the saturation temperature corresponding to the steam chamber pressure at a certain moment minus the downhole temperature of the production well at that time, which represents the downhole liquid level. The larger the value, the higher the downhole liquid level.

[0024] As a preferred solution, in the step of keeping the steam injection well shut in and opening the production well for production, the production well is firstly produced by self-flowing, and then the oil pumping unit is used for production after the wellhead pressure drops to 2.0 MPa.

[0025] As a preferred solution, in the step of keeping the steam injection well shut in and opening the production well for production, when the fluid production level drops to 50% of that before the method is implemented, a round of fluid drainage and energy release is completed.

[0026] As a preferred solution, when the recovery rate of the well group is between 5% and 15%, after step S30 and before step S40, the following steps are further included:

[0027] Step S33: injecting viscosity reducer into the short steam injection pipe and the long steam injection pipe in the steam injection well at the same time.

[0028] As a preferred solution, the amount of viscosity reducer A used in step S33 is calculated by A=πr 2 ×Φ×S0×ρ×c×L, where L is the horizontal length of the well group, R is the radius of the steam cavity, which is generally 3.0m, Φ is the porosity of the oil layer in the well group, S0 is the oil saturation of the well group, ρ is the density of crude oil, and c is the concentration of the viscosity reducer.

[0029] As a preferred solution, when the recovery rate of the well group is between 15% and 30%, after step S33 and before step S40, the following steps are further included:

[0030] Step S333: injecting non-condensable gas into the steam injection well through the short steam injection pipe and the long steam injection pipe at the same time.

[0031] As a preferred solution, the non-condensable gas injected in step S333 is nitrogen.

[0032] As a preferred solution, the amount of non-condensable gas used in step S33 is equal to the volume of the steam chamber multiplied by the gas injection coefficient. According to numerical modeling research, the best effect is achieved when the coefficient is between 0.02 and 0.025.

[0033] As a preferred solution, the viscosity reducer is first injected, and then nitrogen is used to carry and diffuse the viscosity reducer to the edge of the steam chamber, and then high-temperature and high-pressure steam is injected to accelerate the expansion of the steam chamber by the dual viscosity reducing effects of heat and the viscosity reducer.

[0034] Compared with the prior art, the present invention has at least the following beneficial effects:

[0035] The application of the technical solution of the present invention can quickly increase the initial production of SAGD, solve the problems of slow expansion of the steam chamber and easy steam channeling in the well caused by poor reservoir permeability and strong heterogeneity, and thus significantly improve the economic development benefits. In particular, since the technical solution is carried out after the pumping, when the production well is shut down and the steam injection well is injected with high pressure, the physical properties such as the reservoir permeability change, and the steam expansion speed is accelerated under high pressure conditions. At the same time, since the production well is shut down, energy concentration is achieved, and steam is not easy to be produced from the connecting channel between the production well and the steam injection well, and expands upward under the action of pressure, the goal of accelerating the expansion of the steam chamber and increasing the initial production of SAGD is achieved.

[0036] Furthermore, in the process of conventional SAGD production, the method of the present invention uses nitrogen to carry the viscosity reducer to diffuse to the edge of the steam chamber, and then injects steam. By injecting a high-temperature dispersant to act on the periphery of the steam chamber, non-condensable gas assists the lateral expansion of the steam chamber, thereby achieving multi-media collaborative steam mass and heat transfer, increasing the oil leakage rate, and further accelerating the expansion of the steam chamber. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The following description and drawings, which constitute a part of this application, are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0038] Figure 1 Schematic diagram of the early production mode of a low-quality reservoir with dual horizontal wells;

[0039] Figure 2 Schematic diagram of high-pressure throughput and cavity expansion mechanism according to an embodiment of the present invention;

[0040] FIG3( a ) is a cross-sectional view of temperature parameters at the end of the throughput expansion cavity according to an embodiment of the present invention;

[0041] FIG3( b ) is a cross-sectional view of pressure parameters at the end of the throughput expansion cavity according to an embodiment of the present invention;

[0042] FIG3( c ) is a cross-sectional view of porosity parameters at the end of the throughput expansion of an embodiment of the present invention;

[0043] FIG3( d ) is a cross-sectional view of permeability parameters at the end of the throughput expansion cavity according to an embodiment of the present invention;

[0044] Figure 4A graph showing the change in porosity with injection pressure during the expansion process of an embodiment of the present invention. DETAILED DESCRIPTION

[0045] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0046] It should be noted that, unless otherwise specified, all technical and scientific terms used in this application have the same meanings as commonly understood by ordinary technicians in the technical field to which this application belongs.

[0047] In view of the problems existing in the existing SAGD production steam stripping liquid cavity expansion process, the present invention proposes a method for improving the SAGD development effect of super-heavy oil reservoirs, which overcomes the practical contradiction that high-pressure cavity expansion is easy to collide and low-pressure cavity expansion is slow, and is a measure generally applicable to improving the SAGD development effect of double horizontal wells in super-heavy oil reservoirs. The double horizontal well production mode is changed in stages, and the reservoir physical properties are changed by high-temperature and high-pressure steam injection, and nitrogen and viscosity reducers are used to accelerate the steam cavity expansion speed, thereby improving the oil production level and the oil-gas ratio. In particular, the method has strong adaptability in the early and middle stages of developing oil reservoirs using the double horizontal well steam-assisted gravity drainage mode.

[0048] like Figure 1 As shown in the figure, in the early production mode of the dual horizontal well inferior reservoir oil reservoir, the original formation pressure is 4.5MPa, which is a relatively high pressure area. After switching to SAGD production, due to the high original formation pressure and the connection between the I and P wells as a low pressure area, the steam is easier to expand downward, resulting in steam being produced. However, for oil reservoirs with low permeability, developed interlayers and strong heterogeneity, on the one hand, due to the low reservoir permeability (generally less than 1000mD), the steam chamber is difficult to expand upward under the steam injection pressure during normal SAGD production, and due to the strong reservoir heterogeneity, there is a high permeability channel between the steam injection well and the production well, resulting in the steam being easily directly out of the high permeability channel between the steam injection well and the production well after the pressure is increased and the steam is injected, and is produced from the production well, resulting in the steam chamber not expanding upward, or expanding slowly. Since there is no relevant SAGD plugging technology at present, in order to ensure that steam does not escape from the bottom of the production well, a higher Sub-cool is maintained at the bottom of the well or the steam injection rate of the steam injection well is reduced to control a lower steam injection pressure, reduce the pressure difference, ensure that steam does not escape from the well and stabilize production. However, due to the low permeability of the reservoir and the low steam injection pressure, although this method effectively improves the steam utilization rate, the steam chamber expands extremely slowly or even does not expand, and the oil production level is low.

[0049] See also Figure 2 The method for improving the SAGD development effect of super heavy oil reservoirs according to the embodiment of the present invention comprises the following steps:

[0050] Step S10: determining a heterogeneous oil reservoir suitable for steam-assisted gravity drainage development;

[0051] Step S20: drilling two horizontal wells that are located vertically opposite to each other in the oil layer, the upper horizontal well being a steam injection well, and the lower horizontal well being a production well;

[0052] Step S30: Inject steam into the steam injection well and the production well to heat and connect the steam injection well and the production well evenly, and establish an oil leakage channel between the steam injection well and the production well. When the degree of connectivity between the two wells reaches more than 75%, the SAGD production stage is entered;

[0053] Step S40: closing the production well, injecting high-temperature, high-pressure, and high-speed superheated steam into the steam injection well, expanding the reservoir above the steam injection well, changing the effective stress on the rock skeleton, increasing the rock pore volume, increasing the porosity and permeability, and improving the reservoir properties;

[0054] Step S50: When the steam injection pressure of the steam injection well reaches the required value, the steam injection well is shut down to store energy and build up the liquid level;

[0055] Step S60: collecting downhole environmental parameters of the production well, and when it is determined that the production conditions are met, the steam injection well is kept shut down, and the production well is opened for production, so as to complete the drainage and energy release;

[0056] Repeat steps S40 to S60 for multiple rounds. When the oil production level of the production well stops increasing, the steam injection well continues to inject steam and the production well continues to produce liquid, thus entering the conventional SAGD production stage.

[0057] In a possible implementation manner, the super-heavy oil reservoir developed by SAGD in the embodiment of the present invention is a medium-shallow reservoir with a burial depth of 350 to 600 meters, an oil saturation greater than 0.45, an oil layer thickness greater than 10 meters, a horizontal permeability between 600 and 1400 millidarcy, a ratio of vertical permeability to horizontal permeability greater than 0.5, an oil layer porosity greater than 0.28, and the presence of continuously or discontinuously developed low-physical property reservoirs in the oil layer, the permeability of the low-physical property reservoirs is less than 200 millidarcy, and the degassed crude oil viscosity of the reservoir at 50°C is greater than 50,000 centipoise.

[0058] In a possible implementation manner, the method described in the embodiment of the present invention is applicable to the well group recovery rate between 5% and 30% after the steam injection well and the production well establish the oil drainage channel and enter the SAGD production stage.

[0059] In a possible implementation, when high-temperature, high-pressure, and high-velocity steam is injected into the steam injection well, the steam injection pressure is greater than the minimum principal stress and less than the formation fracture pressure of 0.5 MPa.

[0060] In a possible implementation, in step S40, the steam injection well uses a main pipe and a secondary pipe to inject steam simultaneously, and the steam injection rate is 200-240 t / d.

[0061] In a possible implementation, in step S50, the required value of the steam injection pressure of the steam injection well is 9.0 MPa.

[0062] In a possible implementation, in step S50, the well is shut down for 1 to 3 days, and downhole temperature monitoring results of the production well are collected simultaneously.

[0063] In a possible implementation, in step S60, the production condition of the production well is that the downhole sub-cooling is 20-30°C.

[0064] Furthermore, the calculation method of the downhole Sub-cool is: its value is equal to the saturation temperature corresponding to the steam chamber pressure at a certain moment minus the downhole temperature of the production well at that time, which represents the downhole liquid level. The larger the value, the higher the downhole liquid level.

[0065] In a possible implementation, in the step of keeping the steam injection well shut in and opening the production well for production, the production well is first produced by self-flowing, and then a pumping unit is used for production after the wellhead pressure drops to 2.0 MPa.

[0066] In a possible implementation, in the step of keeping the steam injection well shut in and opening the production well for production, when the fluid production level drops to 50% of that before the method is implemented, a round of fluid drainage and energy release is completed.

[0067] In a possible implementation manner, when the recovery rate of the well group is between 5% and 15%, after step S30 and before step S40, the method further includes:

[0068] Step S33: injecting viscosity reducer into the short steam injection pipe and the long steam injection pipe in the steam injection well at the same time.

[0069] In a possible implementation manner, the amount A of the viscosity reducing agent used in step S33 is calculated by the formula A=πr 2 ×Φ×S0×ρ×c×L, where L is the horizontal length of the well group, R is the radius of the steam cavity, which is generally 3.0m, Φ is the porosity of the oil layer in the well group, S0 is the oil saturation of the well group, ρ is the density of crude oil, and c is the concentration of the viscosity reducer.

[0070] In a possible implementation manner, when the recovery degree of the well group is between 15% and 30%, after step S33 and before step S40, the method further includes:

[0071] Step S333: injecting non-condensable gas into the steam injection well through the short steam injection pipe and the long steam injection pipe at the same time.

[0072] In a possible implementation manner, the non-condensable gas injected in step S333 is nitrogen.

[0073] Furthermore, the amount of non-condensable gas used in step S33 is equal to the volume of the steam chamber multiplied by the gas injection coefficient. According to numerical simulation research, the best effect is achieved when the coefficient is between 0.02 and 0.025.

[0074] In one possible implementation, a viscosity reducer is first injected, and then nitrogen is used to carry and diffuse the viscosity reducer to the edge of the steam cavity, and then high-temperature and high-pressure steam is injected to accelerate the expansion of the steam cavity by the dual viscosity reducing effects of heat and the viscosity reducer.

[0075] See also Figure 3(a) to Figure 3(d) as well as Figure 4 In the method for improving the SAGD development effect of super-heavy oil reservoirs in the embodiment of the present invention, the mechanism of the throughput expansion technology is as follows: 1) Increasing the pressure to inject steam to accelerate the expansion speed of the steam chamber: When the reservoir is an elastic-plastic body, when the steam injection pressure is higher than the minimum principal stress, the reservoir rock particles begin to expand and deform. The numerical simulation of coupled rock mechanics shows that when the pressure is increased to 8MPa-9MPa, the porosity increases by 5%-10%, and the permeability increases by 1.0 times-1.5 times. Under the same reservoir conditions and the same time, the operating pressure is increased from 5MPa to 8MPa, and the steam chamber volume increases by 25%; 2) Injection-production separation realizes uniform use of the horizontal section: During normal SAGD production, affected by the strong heterogeneity of the reservoir, high-pressure steam injection is easy to cause steam channeling in the high-permeability section, forming a dominant channel, and part of the steam flash is directly produced, while suppressing the low and medium permeability sections. mobilization; in order to achieve the purpose of high-pressure cavity expansion, the steam injection and oil production processes are separated. During high-pressure steam injection, the oil production wells are shut down to ensure that the steam expands upward. After the steam injection is completed, the oil production wells are in production and the steam injection wells are shut down to maximize the utilization of energy and heat, avoid the possibility of steam breakthrough, and ensure the uniform utilization of the horizontal section; 3) Multiple rounds of high-speed throughput to reduce environmental pressure: Through multiple rounds of steam injection-oil production throughput, the formation pressure is effectively reduced; the steam injection rate is increased from 60t / d in normal SAGD production to 220t / d of throughput steam injection, which reduces the heat loss of steam along the way and improves the bottom hole dryness; 4) Medium-assisted optimization and upgrade: During the implementation process, high-temperature dispersant is injected to act on the periphery of the steam cavity, and non-condensable gas assists the lateral expansion of the steam cavity, realizing multi-media synergistic steam mass and heat transfer, increasing the oil leakage rate, and further accelerating the expansion of the steam cavity.

[0076] The method for improving the SAGD development effect of super heavy oil reservoirs of the present invention has verified the technical effect through actual production.

[0077] Taking the FHW3080 well group as an example, the horizontal section is 430 meters long, the permeability is 1066mD, the oil layer thickness is 20 meters, and the reservoir is buried at a depth of 450 meters. The well group was put into production in June 2015 and switched to SAGD production in November 2015. There is an advantageous connecting channel at 755 meters to 820 meters in the horizontal section, which leads to the temperature of these two points being above 240℃ during normal steam injection (steam injection pressure 5MPa), the bottom of the well Sub-cool is 0, and steam channeling occurs frequently. The temperature monitored in the observation well reflects that the steam chamber has not expanded. As of 2021, the recovery degree of more than 7 years of production is only 10.9%, the oil production level is 7.6t / d, and the oil-gas ratio is 0.116, showing the characteristics of low oil production level and oil-gas ratio.

[0078] In June 2022, the method for improving the SAGD development effect of super-heavy oil reservoirs of the present invention was carried out, and the throughput expansion measures were implemented. First, 13,000 standard cubic meters of nitrogen and 8.2 tons of viscosity reducer were injected, and finally steam was injected into the steam injection well at a steam injection rate of 200t / d, while the production well remained shut-in. When the steam injection pressure reached 8.5MPa, the steam injection well was shut down and the downhole temperature was observed. When the downhole temperature dropped below 240°C, the production well was started for production, first through self-flowing production in the production well, and then mechanical pumping was carried out when the wellhead pressure dropped to 2.0MPa. When the liquid production level dropped to 50% of the level before the measures, the above steps were repeated until four cycles later, and then normal SAGD production was entered, that is, the steam injection well continued to inject steam, and the production well continued to produce liquid. In this process, nitrogen is used to carry steam to the edge of the steam chamber due to its strong penetration ability, and then a viscosity reducer is injected to reduce viscosity by both thermal and viscosity reducer effects. At the same time, steam is injected at a steam injection pressure of 0.5 MPa lower than the formation fracture pressure, causing plastic deformation of the formation porosity. The permeability in the steam chamber is increased by more than 1.6 times, and the expansion speed of the steam chamber is accelerated, thereby increasing the steam swept volume and improving development efficiency. After implementation, the liquid production level of FHW3082 increased by a total of 20 t / d, the oil production level increased by 14.2 t / d, the production-injection ratio increased by 0.12, and the oil-steam ratio increased by 0.14, with significant results.

[0079] ① In the field application of 9 well groups, the oil production level of a single well group increased by more than 6.4 tons, an increase of 1.5 to 2.0 times, and the oil-gas ratio increased by 0.12, an increase of 1.5 to 2.0 times;

[0080] ②The steam chamber expansion speed increased by more than 3 times, and the oil production speed increased by 1.5 to 2.0 times.

[0081] Obviously, the embodiments described above are only some embodiments of the present invention, not all embodiments. Based on the embodiments described in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0082] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0083] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein.

[0084] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for improving the SAGD development effect of super heavy oil reservoirs, characterized in that: The following steps are involved: Step S10: determining a heterogeneous oil reservoir suitable for steam-assisted gravity drainage development; Step S20: drilling two horizontal wells that are located vertically opposite to each other in the oil layer, the upper horizontal well being a steam injection well, and the lower horizontal well being a production well; Step S30: Inject steam into the steam injection well and the production well to heat and connect the steam injection well and the production well evenly, and establish an oil leakage channel between the steam injection well and the production well. When the degree of connectivity between the two wells reaches more than 75%, the SAGD production stage is entered; Step S40: closing the production well, injecting high-temperature, high-pressure, and high-speed superheated steam into the steam injection well, expanding the reservoir above the steam injection well, changing the effective stress on the rock skeleton, increasing the rock pore volume, increasing the porosity and permeability, and improving the reservoir properties; Step S50: When the steam injection pressure of the steam injection well reaches the required value, the steam injection well is shut down to store energy and build up the liquid level; Step S60: collecting downhole environmental parameters of the production well, and when it is determined that the production conditions are met, the steam injection well is kept shut down, and the production well is opened for production, so as to complete the drainage and energy release; Repeat steps S40 to S60 for multiple rounds. When the oil production level of the production well stops increasing, the steam injection well continues to inject steam, and the production well continues to produce liquid, and the conventional SAGD production stage is entered.

2. The method for improving the SAGD development effect of super heavy oil reservoirs according to claim 1, characterized in that: The super-heavy oil reservoir developed by SAGD is a medium-shallow reservoir with a burial depth of 350 to 600 meters, an oil saturation greater than 0.45, an oil layer thickness greater than 10 meters, a horizontal permeability between 600 and 1400 millidarcy, a ratio of vertical permeability to horizontal permeability greater than 0.5, an oil layer porosity greater than 0.28, and the presence of continuously or discontinuously developed low-physical property reservoirs in the oil layer, the permeability of the low-physical property reservoirs being less than 200 millidarcy, and the degassed crude oil viscosity of the reservoir at 50°C being greater than 50,000 centipoise.

3. The method for improving the SAGD development effect of super heavy oil reservoirs according to claim 1, characterized in that: The method is applicable to the well group recovery degree between 5% and 30% after the oil drainage channel is established between the steam injection well and the production well and the SAGD production stage is entered.

4. The method for improving the SAGD development effect of super heavy oil reservoirs according to claim 1, characterized in that: When high-temperature, high-pressure and high-speed steam is injected into the steam injection well, the steam injection pressure is greater than the minimum principal stress and less than the formation fracture pressure of 0.5 MPa.

5. The method for improving the SAGD development effect of super heavy oil reservoirs according to claim 1, characterized in that: In step S40, the steam injection well uses a main pipe and a secondary pipe to inject steam simultaneously, and the steam injection rate is 200-240 t / d.

6. The method for improving the SAGD development effect of super heavy oil reservoirs according to claim 1, characterized in that: In step S50, the required value of the steam injection pressure of the steam injection well is 9.0 MPa.

7. The method for improving the SAGD development effect of super heavy oil reservoirs according to claim 1, characterized in that: In step S50, the well is shut down for 1 to 3 days, and the downhole temperature monitoring results of the production well are collected simultaneously.

8. The method for improving the SAGD development effect of super heavy oil reservoirs according to claim 1, characterized in that: In step S60, the production condition of the production well is that the underground sub-cooling temperature is 20-30°C.

9. The method for improving the SAGD development effect of super heavy oil reservoirs according to claim 8, characterized in that: The calculation method of the downhole Sub-cool is: its value is equal to the saturation temperature corresponding to the steam chamber pressure at a certain moment minus the downhole temperature of the production well at that time, which represents the downhole liquid level. The larger the value, the higher the downhole liquid level.

10. The method for improving the SAGD development effect of super heavy oil reservoirs according to claim 1, characterized in that: In the step of keeping the steam injection well shut in and opening the production well for production, the production well is firstly produced by self-flowing, and then the oil pumping unit is used for production after the wellhead pressure drops to 2.0 MPa.

11. The method for improving the SAGD development effect of super heavy oil reservoirs according to claim 1, characterized in that: In the step of keeping the steam injection well shut in and opening the production well for production, when the fluid production level drops to 50% of the level before the method is implemented, a round of fluid drainage and energy release is completed.

12. The method for improving the SAGD development effect of super heavy oil reservoirs according to claim 1, characterized in that: When the recovery rate of the well group is between 5% and 15%, after step S30 and before step S40, the following steps are further included: Step S33: injecting viscosity reducer into the short steam injection pipe and the long steam injection pipe in the steam injection well at the same time.

13. The method for improving the SAGD development effect of super heavy oil reservoirs according to claim 12, characterized in that: The calculation formula for the amount of viscosity reducing agent A used in step S33 is A=πr 2 ×Φ×S0×ρ×c×L, where L is the horizontal length of the well group, R is the radius of the steam cavity, Φ is the oil layer porosity of the well group, S0 is the oil saturation of the well group, ρ is the density of crude oil, and c is the concentration of the viscosity reducer.

14. The method for improving the SAGD development effect of super heavy oil reservoirs according to claim 12, characterized in that: When the recovery rate of the well group is between 15% and 30%, after step S33 and before step S40, the following steps are further included: Step S333: injecting non-condensable gas into the steam injection well through the short steam injection pipe and the long steam injection pipe at the same time.

15. The method for improving the SAGD development effect of super heavy oil reservoirs according to claim 13, characterized in that: The non-condensable gas injected in step S333 is nitrogen.

16. The method for improving the SAGD development effect of super heavy oil reservoirs according to claim 15, characterized in that: The amount of the non-condensable gas used in step S33 is equal to the volume of the steam chamber multiplied by the gas injection coefficient.

17. The method for improving the SAGD development effect of super heavy oil reservoirs according to claim 15, characterized in that: First, the viscosity reducer is injected, and then nitrogen is used to carry and diffuse the viscosity reducer to the edge of the steam chamber. Then, high-temperature and high-pressure steam is injected to accelerate the expansion of the steam chamber by the dual viscosity reducing effects of heat and viscosity reducer.

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