SAGD Development Mid-to-Late Stage Stable Production Control Methods

Abstract

This invention relates to the field of heavy oil reservoir development technology, specifically a method for stable production control in the mid-to-late stages of SAGD development. The method comprises the following steps: S1, selecting SAGD well groups in the target area that are in the mid-to-late stages of SAGD production, and reducing the operating pressure of each SAGD well group within the set; S2, reducing the downhole sub-cooling threshold range for each SAGD well group and stabilizing production for more than 3 months; S3, adjusting the injection-production points based on the location of the gas cavity connection and fusion within the SAGD well group set; S4, adjusting the injection-production ratio or steam injection volume of the two SAGD well groups within the set. This invention, based on the characteristics of the mid-to-late stages of SAGD development, controls and optimizes operating parameters to accelerate the gas cavity expansion rate, improve the oil-steam ratio, and save steam by adjusting the injection-production points and injection-production modes, thereby improving development efficiency. It is highly operable and applicable.

Description

Technical Field

[0001] This invention relates to the field of heavy oil reservoir development technology, and is a method for stable production control in the mid-to-late stages of SAGD development. Background Technology

[0002] Steam-assisted gravity drainage (SAGD) technology works by deploying horizontal well pairs stacked vertically within the same oil reservoir. Superheated steam is continuously injected into the upper injection well, heating the formation and crude oil. The heated crude oil's viscosity decreases, and the steam condensate flows downwards under gravity, being extracted from the horizontal production well located below the reservoir. The steam occupies the space where the extracted crude oil is extracted and gradually expands within the formation, forming a steam cavity. The expansion of the steam cavity is the process of heat exchange between the crude oil and steam, leading to its extraction. Therefore, the expansion and development of the steam cavity is a physical manifestation of the underlying mechanism in SAGD development and is commonly used to describe the SAGD development process. The SAGD steam cavity expansion and development process is generally divided into four stages: circulating preheating, vertical rise of the steam cavity, lateral expansion of the steam cavity, and descent of the steam cavity.

[0003] As SAGD development continues, some well groups in the longest-developed and best-properly-property-grade extra-heavy oil (Crude oil viscosity at 50℃ is 20,000 to 50,000 mPa·s) reservoirs have exhibited gas cavity connectivity, indicating that development has entered the late stage of lateral expansion, i.e., the gas cavity fusion stage. The gas cavity connectivity stage occurs when the steam cavity of a SAGD well group extends vertically to the top of the oil layer, then laterally along the caprock and connects with the steam cavity of adjacent wells. This typically occurs 7 to 8 years after the steam cavity reaches its top. At this point, the recovery rate of some well groups reaches 40% to 50%, indicating that development has entered the mid-to-late stage, facing challenges such as increased heat loss from the caprock, decreased fluid and oil production levels, increased water cut, and a decreased oil-steam ratio.

[0004] In the early stages of steam cavity development, SAGD development adopts corresponding control policies aimed at "increasing steam and improving fluid volume, and expanding the cavity under high pressure." This involves continuously increasing steam injection and controlling high injection pressure to accelerate cavity expansion while maintaining high downhole sub-cooling to ensure stable well production and prevent steam channeling. However, when the steam cavity enters the lateral expansion-fusion stage, it remains in continuous contact with the top caprock of the oil layer, leading to increased heat loss. Furthermore, the steam cavity has reached its maximum development potential and has no further upward expansion potential, rendering the earlier control policies inapplicable. However, domestic research on control policies for the mid-to-late stages of SAGD development in dual-horizontal wells is still lacking. Therefore, it is necessary to explore a method to improve the effectiveness of mid-to-late stage SAGD development, enhance its efficiency, and improve the entire life-cycle development technology system for SAGD to ensure efficient heavy oil development. Summary of the Invention

[0005] This invention provides a method for stable production control in the mid-to-late stages of SAGD development, which overcomes the shortcomings of the prior art and can effectively solve the problems of decreased liquid and oil production levels and decreased oil-gas ratio in the mid-to-late stages of SAGD development.

[0006] The technical solution of this invention is achieved through the following measures: a method for stable production control in the mid-to-late stage of SAGD development, which is carried out according to the following steps:

[0007] S1. Select SAGD well sets in the target area that are in the middle and late stages of SAGD production to reduce the operational pressure of each SAGD well set in the SAGD well set.

[0008] S2, reduce the downhole sub-cool threshold range for each SAGD well group and maintain stable production for more than 3 months;

[0009] S3, adjust the injection and production points according to the location of the connection and fusion of the gas chambers of the SAGD well group within the SAGD well group;

[0010] S4, adjust the injection-production ratio or steam injection rate of the two SAGD well groups in the SAGD well group suite.

[0011] The following are further optimizations and / or improvements to the above-mentioned technical solution:

[0012] In step S1 above, the operating pressure of each SAGD well group is gradually reduced from 1 MPa to 2.0 MPa above the original formation pressure to the original formation pressure.

[0013] In step S2 above, the downhole sub-cool threshold range for each SAGD well group is reduced to 5°C to 15°C.

[0014] In step S3 above, the adjustment of the injection and production points is specifically as follows: the injection and production points of the two SAGD well groups with connected gas chambers are adjusted from the position where the gas chambers are connected and merged to the position where the gas chambers are not connected.

[0015] In step S4 above, adjusting the injection-production ratio of the SAGD well group specifically involves adjusting the injection-production ratio of the lower wells in the SAGD well group to 1.3 to 1.5 and the injection-production ratio of the upper wells to 0.6 to 0.8.

[0016] In step S4 above, adjusting the steam injection volume of the SAGD well group specifically involves: increasing the steam injection volume of the upper well to 110% to 150% of the original steam injection volume, reducing the steam injection volume of the lower well to less than 50% of the original steam injection volume, or shutting off the steam injection well of the lower well.

[0017] The present invention has the following advantages:

[0018] 1. By reducing the operating pressure, the steam heat utilization rate can be effectively improved, and the oil-steam ratio can be increased; by reducing the sub-cool (downhole fluid level), the amount of steam heating the fluid level can be reduced, and the development of the lower part of the steam chamber of the well group can be promoted, the steam sweep volume can be expanded, and the production level and oil-steam ratio can be improved; by adjusting the injection and production points and injection and production modes, the balanced development of the steam chamber can be promoted, untapped reserves can be utilized, steam can be saved, and the development effect can be improved.

[0019] The increased volume of the steam chamber leads to higher oil production levels and a higher oil-to-steam ratio.

[0020] After the application of the 90 well group in the field, the oil production level of the single well group increased by 2.1t / d, the production-injection ratio increased by 0.15, and the oil-gas ratio increased by 0.024. Attached Figure Description

[0021] Appendix Figure 1 These are schematic diagrams of two SAGD development modes in this invention. Figure A is a schematic diagram of the fusion of steam chambers in a pair of SAGD well groups affected by the formation dip angle, and Figure B is a schematic diagram of the fusion of steam chamber development in a pair of SAGD well groups affected by three-dimensional development.

[0022] Appendix Figure 2 This invention presents a comparison of the expansion of the bottom angle of the steam chamber under different Sub-cool conditions during the lateral expansion stage of the steam chamber in the SAGD well group.

[0023] Appendix Figure 3 These are microgravity monitoring diagrams and numerical simulation diagrams of the gas cavity development of FHW001 and FHW002 in Embodiment 7 of the present invention. Detailed Implementation

[0024] The present invention is not limited to the following embodiments, and specific implementation methods can be determined according to the technical solutions and actual conditions of the present invention.

[0025] The present invention will be further described below with reference to embodiments:

[0026] Example 1: The method for stable production control in the mid-to-late stage of SAGD development is carried out according to the following steps:

[0027] S1. Select SAGD well sets in the target area that are in the middle and late stages of SAGD production to reduce the operational pressure of each SAGD well set in the SAGD well set.

[0028] S2, reduce the downhole sub-cool threshold range for each SAGD well group and maintain stable production for more than 3 months;

[0029] S3, adjust the injection and production points according to the location of the connection and fusion of the gas chambers of the SAGD well group within the SAGD well group;

[0030] S4, adjust the injection-production ratio or steam injection rate of the two SAGD well groups in the SAGD well group suite.

[0031] This invention is applicable to SAGD well groups in shallow extra-heavy oil reservoirs with a continuous thickness greater than 10m, initially using a dual-horizontal-well steam-assisted gravity drainage method, and progressing into the mid-to-late stage where the steam chamber is in the lateral expansion phase. For example... Figure 1 As shown, there are currently two SAGD development models, both employing a single SAGD well group comprising two SAGD well groups. Each SAGD well group consists of two parallel horizontal wells, one above the other. Specifically, each SAGD well group includes a steam injection horizontal well and a production horizontal well. The upper part is the steam injection well, and the lower part (approximately 5 meters below) is the production well. Once the steam injection and production wells are connected, steam is continuously injected from the steam injection well. The injected steam expands upwards, heating the crude oil. The crude oil in the oil layer flows downwards due to gravity and is eventually extracted by the lower production well. One of these models involves deploying two SAGD well groups within the same conventional oil reservoir (i.e., developing a single SAGD well group within the same layer), as shown in the attached diagram. Figure 1 As shown in Figure A, the connection of the gas cavity is mainly affected by the formation dip angle. The connection method is that the two SAGD well groups gradually connect from the top of the reservoir. Due to the formation dip, the two SAGD well groups form a vertical height difference, with the one located at the top being the upper well (see Appendix). Figure 1 Figure A shows the SAGD2 well group, with the lower well being the lower section (see appendix). Figure 1 Figure A shows the SAGD1 well group. One type is a vertical development model, which involves deploying two SAGD well groups (one vertical and one horizontal) within the same oil-bearing formation (i.e., a single SAGD well group set in a three-dimensional development approach), as shown in the attached figure. Figure 1 As shown in Figure B, its connection method is from the lower well (see appendix). Figure 1 The top and upper wells of the SAGD1 well group (see attached diagram) Figure 1 The bottom of well group B (SAGD2 well group) is connected. (See attached diagram) Figure 3 As shown in the figure, Figure A shows the phenomenon of gradual connection of the steam chambers in the later stage of production of a SAGD well group developed in the same layer. This is mainly affected by the formation dip angle. The connection method is that the two well groups are gradually connected from the top of the reservoir. Figure B shows the fusion of steam chambers in the vertical development mode. This is because two SAGD well groups are deployed in the same oil layer. The connection method is that the top of the lower well group and the bottom of the upper well group are connected.

[0032] Example 2: As an optimization of the above example, in step S1, the operating pressure of each SAGD well group is gradually reduced from 1 MPa higher than the original formation pressure to 2.0 MPa to the original formation pressure.

[0033] In this invention, the operating pressure is the pressure within the steam chamber of the SAGD well group. During SAGD development, after the injection well and production well are connected, the steam injected from the injection well continuously expands upwards, heating the crude oil. The crude oil in the reservoir flows downwards under gravity and is eventually extracted by the lower production well. As crude oil is continuously extracted from the reservoir pores, the upper injection well continuously injects steam, which gradually occupies the crude oil production space, forming a steam chamber. The pressure of this steam chamber is the operating pressure. Steam-assisted gravity drainage (SAGD) technology utilizes the latent heat of vaporization of steam. According to the properties of saturated steam, the lower the steam pressure, the greater the latent heat enthalpy. By reducing the pressure in the steam chamber, on the one hand, the available steam enthalpy for SAGD development increases, and more enthalpy is used to heat the crude oil, improving the steam heat utilization rate and increasing the ratio of oil production to steam injection level (i.e., the oil-steam ratio); on the other hand, the decrease in steam chamber pressure releases the heat stored in the rock skeleton inside the steam chamber, further improving steam utilization.

[0034] Example 3: As an optimization of the above example, in step S2, the downhole sub-cool threshold range for each SAGD well group is reduced to 5°C to 15°C.

[0035] The (bottom-hole vapor-liquid interface) is the difference between the saturation temperature corresponding to the vapor chamber pressure in the SAGD well group and the bottom-hole fluid temperature in the production well. It corresponds to the liquid level in the production well; 5℃ to 15℃ corresponds to a liquid level of 0.5m to 1.0m. In the early stages of SAGD well development, during the rising phase of the vapor chamber, the principle is to increase vapor production, lift liquid, and enhance utilization. Sub-cooling is controlled at a relatively high level, maintained between 20℃ and 30℃, to ensure no vapor channeling occurs in the well group and to stabilize production while increasing the utilization of the horizontal section. As the SAGD well group enters the middle and later stages of development, the vapor chamber development scale is large, and the vapor chambers in the SAGD wells are generally in a stage of lateral expansion and fusion, with a high utilization of the horizontal section and strong liquid production capacity. (Appendix) Figure 2 This is a comparison diagram of the expansion of the bottom angle of the steam chamber under different sub-cooling conditions during the lateral expansion stage of the SAGD steam chamber. (Attached is a diagram.) Figure 2 Figure a shows that when the Sub-cool value is 15℃, the bottom angle of the SAGD steam chamber continuously increases as the steam chamber expands laterally, and the bottom steam chamber continues to develop. Figure 2Figure b shows that when the Sub-cool value is 20℃, the bottom angle of the SAGD steam chamber does not change with the lateral expansion of the steam chamber and remains unchanged. At this time, the bottom steam chamber cannot develop, so the reserves cannot be utilized. A comparative study of the expansion of the bottom angle of the steam chamber under different Sub-cool conditions during the lateral expansion stage revealed that: 1) the higher the Sub-cool, the lower the oil-steam ratio; 2) during the lateral expansion stage, Sub-cool affects the development of the steam chamber. When Sub-cool is less than 15℃, the bottom angle of the steam chamber changes; when Sub-cool is greater than 15℃, the bottom angle of the steam chamber remains basically unchanged, and the lower steam chamber does not develop. Therefore, considering all factors, after the SAGD well enters the middle and late stages of development, the Sub-cool should be adjusted to 5 to 15℃ to maintain its production capacity.

[0036] Example 4: As an optimization of the above example, in step S3, the adjustment of the injection and production points is specifically as follows: the injection point and production point of the two SAGD well groups with connected gas chambers are adjusted from the position where the gas chambers are connected and merged to the position where the gas chambers are not connected.

[0037] In conventional SAGD development, the well spacing between adjacent SAGD well groups is 70m to 100m. In the early stages of development, production wells use short-tube fluid production, while steam injection wells use long-tube steam injection. However, in the later stages of development, when the steam cavity develops to a large scale, it may connect with the steam cavity of adjacent SAGD wells along the caprock at the top boundary of the oil layer. Due to reservoir heterogeneity, the development of steam cavities varies along the horizontal section of the SAGD well group. At this point, it is necessary to adjust the injection and production points. The steam injection and fluid production points of the two SAGD well groups with connected steam cavities should be moved from a point where the steam cavities are connected to a point where they are not connected. In other words, the steam injection and fluid production points of the SAGD well groups should be moved from a point where the steam cavities are not developed or are relatively poorly developed, to promote balanced steam cavity development. If the steam cavity development in the front section of the two SAGD well groups is good, after the steam cavity connects in the front section of the horizontal section, the fluid production point of the two SAGD well groups needs to be moved from the front to the rear. If the steam injection point is already at the rear, no adjustment is needed. This also means that the steam injection point and liquid production point of both well groups will be adjusted from the connected section to the disconnected section in order to promote the balanced development of the steam cavity.

[0038] Example 5: As an optimization of the above example, in step S4, the injection-production ratio of the SAGD well group is adjusted as follows: the injection-production ratio of the lower wells in the SAGD well group is adjusted to 1.3 to 1.5, and the injection-production ratio of the upper wells is adjusted to 0.6 to 0.8.

[0039] Example 6: As an optimization of the above example, in step S4, adjusting the steam injection volume of the SAGD well group specifically involves increasing the steam injection volume of the upper well to 110% to 150% of the original steam injection volume, reducing the steam injection volume of the lower well to less than 50% of the original steam injection volume, or shutting off the steam injection well of the lower well.

[0040] In this invention, for a single SAGD well group developed at the same level, as shown in the attached figure... Figure 1 As shown in Figure A, due to the influence of the formation dip angle, there is a height difference between the two SAGD wells. The upper well SAGD2 group is "enhanced steam injection," meaning the steam injection level is increased by 10% to 50% above the original level. The lower well SAGD1 group is "reduced / stopped," meaning its steam injection level is reduced or the steam injection well is shut off directly. At this time, the upper well, located in the updip direction, has more injection than production due to enhanced steam injection, and the steam chamber pressure gradually increases. The lower well, due to reduced steam injection or direct shutdown of the steam injection well, maintains normal production, with injection less than production, causing the steam chamber pressure of this well group to decrease. With a pressure difference and connection between the steam chamber pressures of the upper and lower wells, crude oil displacement is accelerated, steam consumption is saved, and crude oil is produced between the two well groups.

[0041] For the two SAGD well groups under the three-dimensional development mode, as shown in the appendix Figure 1 As shown in Figure B, the lower well SAGD1 group improved its production level by adjusting the production system, changing the ratio of produced fluid to injected steam from 1.0 in the early stage of production to 1.3. The upper well SAGD2 group reduced the injected steam, causing the steam chamber pressure in the upper well to drop, which in turn pulled the lower steam chamber to expand upward and gradually submerge the upper well, thereby maximizing the steam sweep volume and improving development efficiency.

[0042] Example 7: This method for improving stable production control in the mid-to-late stages of SAGD development was applied and implemented in the SAGD development area of ​​Fengcheng Oilfield, Xinjiang Oilfield, according to the following steps:

[0043] Basic data on the target reservoir were collected, combined with production characteristic data of SAGD well groups in the region. This basic data included the original formation pressure, reservoir distribution, steam cavity connectivity, steam cavity pressure, downhole temperature data, vertical depth, steam injection rate, and fluid production. One SAGD well group in the target area was selected, with the upper well numbered FHW001 and the lower well numbered FHW002. Both wells were put into production in January 2013 and transitioned to SAGD production in July 2013. Both have been in production for over nine years. Based on the temperature monitoring of the observation wells, reflecting the steam cavity expansion rate, the steam cavities of both well groups reached their peak development in 2017. By the end of 2020, the steam cavities had laterally expanded to connect with the steam cavities of adjacent wells. FHW001... The horizontal sections were used evenly. The last 100 meters of the horizontal section of FHW002 remained unused, and the steam cavity above it was not developed. The vertical depth of FHW001 was 296 meters, and that of FHW002 was 291 meters. FHW002 was located in a higher position, and FHW001 in a lower position. The production level of well FHW001 was 94 t / d, and the steam injection level was 88 t / d. The production level of well FHW002 was 109 t / d, and the steam injection level was 96 t / d. The original formation pressure was 2.7 MPa. The operating pressure of FHW001 and FHW002 was reduced from 4.0 MPa to 2.7 MPa.

[0044] By adjusting the pumping frequency of wells FHW001 and FHW002, the fluid production level was increased, the downhole sub-cool was maintained at 5°C to 15°C, the downhole fluid level was maintained at 0.5m to 1.0m, and stable production was achieved for more than 3 months.

[0045] Because the rear steam chamber of FHW002 is weakly developed, while the steam chamber of the horizontal section of FHW001 is uniformly developed overall, and as monitored by microgravity, as shown in the attached figure... Figure 3 As shown, the steam chamber fusion of the two well groups is clearly defined. The steam injection points and fluid production points of the two SAGD well groups with connected steam chambers are adjusted from the locations where the steam chambers are connected to locations where the steam chambers are not connected. That is, the steam injection points of the two well groups are adjusted to locations where the steam chambers are not well-developed, and the fluid production points are adjusted from the locations where the steam chambers are connected to locations where the steam chambers are not well-developed or poorly developed. The steam injection wells in the FHW001 well group are adjusted to inject steam simultaneously through both long and short pipes, while the steam injection wells in the FHW002 well group inject steam through the long pipe, and the production wells produce fluid through the long pipe.

[0046] The steam injection level of the SAGD well group was adjusted by shutting off the steam injection well FHW001, which is located in a low position, and increasing the steam injection of well FHW002. The steam injection rate of well FHW002 was adjusted from 96t / d to 135t / d. By utilizing the displacement effect of inter-well pressure difference, the fluid production was increased, steam was saved, and development efficiency was improved.

[0047] After the above technical adjustments, the combined fluid production of the two well groups increased by 20 t / d, oil production increased by 5.2 t / d, the production-injection ratio increased by 0.12, and the oil-gas ratio increased by 0.005, and maintained stable production for more than 300 days.

[0048] The present invention has the following advantages:

[0049] 1. By reducing the operating pressure, the steam heat utilization rate can be effectively improved, and the oil-steam ratio can be increased; by reducing the sub-cool (downhole fluid level), the amount of steam heating the fluid level can be reduced, and the development of the lower part of the steam chamber of the well group can be promoted, the steam sweep volume can be expanded, and the production level and oil-steam ratio can be improved; by adjusting the injection and production points and injection and production modes, the balanced development of the steam chamber can be promoted, untapped reserves can be utilized, steam can be saved, and the development effect can be improved.

[0050] The increased volume of the steam chamber leads to higher oil production levels and a higher oil-to-steam ratio.

[0051] After the application of the 90 well group in the field, the oil production level of a single well group can be increased by 2.1t / d, the production-injection ratio can be increased by 0.15, and the oil-gas ratio can be increased by 0.024.

[0052] In summary, the SAGD development mid-to-late stage stable production control method of the present invention is generally applicable to the control of SAGD development mid-to-late stage in dual horizontal wells of extra-heavy oil reservoirs. Based on the characteristics of SAGD development mid-to-late stage, it controls and optimizes operating parameters to accelerate the expansion speed of the gas chamber and increase the oil-gas ratio. By adjusting the injection and production points and injection and production modes, it can save steam and improve development effect. It has strong operability and applicability.

[0053] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A method for stable production control in the mid-to-late stages of SAGD development, characterized in that... Follow these steps: S1. Select SAGD well sets in the target area that are in the middle and late stages of SAGD production to reduce the operational pressure of each SAGD well set in the SAGD well set. S2, reduce the downhole sub-cool threshold range for each SAGD well group and maintain stable production for more than 3 months; S3, adjust the injection and production points according to the location of the connection and fusion of the gas chambers of the SAGD well group within the SAGD well group; S4, adjust the injection-production ratio or steam injection volume of the two SAGD well groups in the SAGD well group suite; In step S2, the downhole sub-cool threshold range for each SAGD well group is reduced to 5°C to 15°C; In step S3, the adjustment of the injection and production points is specifically as follows: the injection and production points of the two SAGD well groups with connected gas chambers are adjusted from the position where the gas chambers are connected and merged to the position where the gas chambers are not connected; In step S4, the injection-production ratio of the SAGD well group is adjusted as follows: the injection-production ratio of the lower wells in the SAGD well group is adjusted to 1.3 to 1.5, and the injection-production ratio of the upper wells is adjusted to 0.6 to 0.

8. In step S4, the steam injection volume of the SAGD well group is adjusted as follows: the steam injection volume of the upper well is increased to 110% to 150% of the original steam injection volume, and the steam injection volume of the lower well is reduced to less than 50% of the original steam injection volume or the steam injection well of the lower well is shut off.

2. The method for stable production control in the mid-to-late stage of SAGD development according to claim 1, characterized in that... In step S1, the operating pressure of each SAGD well group is gradually reduced from 1 MPa to 2.0 MPa above the original formation pressure to the original formation pressure.

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