A downhole electric heating assisted production method during the initial stage of SAGD conversion to production for dual horizontal wells

Abstract

The present invention discloses a downhole electric heating assisted production method at the initial stage of SAGD conversion to production for dual horizontal wells. The production method comprises the following steps: screening SAGD well groups that have completed cyclic preheating and entered the initial stage of SAGD production; lowering resistance heating cables into the production wellbore; heating the production wellbore using the resistance heating cables; adjusting the steam injection parameters of the steam injection well and the oil production parameters of the production well to achieve electric heating assisted SAGD production; tracking the numerical values and using numerical simulation, and when the steam chamber in the electric heating section rises to the top of the oil layer, stopping the electric heating and switching to steam injection and production. This production method can effectively determine the unconnected section between the production well and the horizontal well, and through electric heating, reduce the viscosity of the crude oil in the unconnected section and let it flow down to the production well, establish a drainage channel, achieve uniform heating and expansion of the steam chamber, effectively solve the problem of uneven development of the steam chamber during the conventional steam cycle heat period, and promote the uniform development of the steam chamber along the horizontal section during the SAGD production stage at a relatively low cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil extraction, and particularly relates to a downhole electric heating assisted production method in the initial stage of the conversion of dual horizontal well SAGD to production. Background Art

[0002] Steam Assisted Gravity Drainage technology (abbreviation: SAGD) was invented by Butler in Canada in 1978 and has been successfully applied in heavy oil reservoirs in oil sand mining areas in Canada, Liaohe Oilfield, Xinjiang Oilfield, etc. Its principle is to deploy a pair of vertically stacked horizontal wells in the same oil layer. High-quality steam is injected into the upper steam injection well. Since the density of steam is much smaller than that of crude oil, the steam overrides upward in the formation to form a steam chamber. As the steam is continuously injected, the steam chamber continuously expands upward and laterally, and heat exchange occurs with the crude oil in the oil layer. The viscosity of the heated crude oil decreases, and it flows downward under the action of gravity together with the condensed water and is produced from the horizontal production well at the lower part of the oil layer. Up to now, SAGD technology has achieved large-scale development in heavy oil reservoirs in Liaohe, Xinjiang and other places.

[0003] Heterogeneous heavy oil reservoirs widely exist. Such reservoirs are characterized by strong heterogeneity. Under the action of high temperature and high pressure of conventional cyclic preheating steam, due to the influence of reservoir heterogeneity, the development degree of steam chambers in the horizontal section is different. During the conventional steam injection cyclic preheating process in the above-mentioned oil layer, under the condition of high-speed steam injection, there is a certain pressure difference between the horizontal sections of the steam injection well and the production well. Under the action of this pressure difference, steam is likely to enter the intermediate oil layer between the steam injection well and the production well along the horizontal high-permeability channel and enter the production wellbore, resulting in preferential thermal communication. It is statistically shown that the connection rate of the horizontal section of SAGD using steam cyclic preheating is less than 70%. The preferential thermal communication section has a great impact on the uniform steam injection in the SAGD production stage, which will cause the preferential development of the steam chamber in this section, resulting in non-uniform utilization of the horizontal section, affecting the production and recovery rate. It is statistically shown that for dual horizontal well SAGD using conventional steam injection cyclic preheating, steam chambers develop only in less than 50% of the horizontal section. When the above-mentioned SAGD well pair is converted to production, the steam chambers developed in the preferential connection section will continue to develop, while it is difficult to utilize the sections where steam chambers have not developed or developed poorly. Conventional measures such as steam foam and string structure adjustment are difficult to effectively utilize the sections where steam chambers have not developed or developed poorly. At present, there is no economically effective technical means to improve the utilization degree of the horizontal section of SAGD. Summary of the Invention

[0004] The purpose of the present invention is to provide a downhole electric heating assisted production method in the initial stage of the conversion of dual horizontal well SAGD to production to solve the problems raised in the above background art.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] The downhole electric heating assisted production method at the initial stage of SAGD conversion of double horizontal wells includes the following steps: screening SAGD well groups that have completed cyclic preheating and entered the initial stage of SAGD production; lowering resistance heating cables into the production wellbore; heating the production wellbore using the resistance heating cables; adjusting the steam injection parameters of the injection well and the oil production parameters of the production well to achieve electric heating assisted SAGD production; tracking the numerical values and using numerical simulation, and when the steam chamber in the electric heating section rises to the top of the oil layer, stop electric heating and switch to steam injection and production. The SAGD herein refers to Steam Assisted Gravity Drainage.

[0007] Furthermore, the SAGD well group meets the following conditions: the length of the unproduced section > 80m; the effective thickness of the oil layer ≥ 15m; the oil saturation > 63%; the viscosity of crude oil at 50°C > 20,000 mPa·s; the permeability > 720 mD; the permeability ratio between the unproduced section and the produced section < 7.

[0008] Furthermore, the resistance heating cable includes a heating cable conductive section and a heating cable heating section. The specific operation of lowering the resistance heating cable into the production wellbore is as follows: the heating cable heating section is lowered to the horizontal section position in the area where the steam chamber in the production well has not developed, and the remaining section of the resistance heating cable is the heating cable conductive section.

[0009] Furthermore, the resistance heating cable is measured for temperature using a thermocouple. The resistance heating cable and the thermocouple are pre-arranged in parallel in the tubing and lowered to the end of the horizontal section. The heating cable heating section is 40 - 60m away from the end of the horizontal section.

[0010] Furthermore, the highest surface temperature of the resistance heating cable is 10 - 30°C below the coking temperature of the crude oil in the oil layer, and the heating power of the resistance heating cable is 800 - 1000W / m.

[0011] Furthermore, the adjustment of the steam injection parameters of the injection well and the adjustment of the oil production parameters of the production well include: the peak steam injection rate of the injection well, the bottom hole pressure difference between the injection well and the production well, the Sub-cool control parameter of the production well, and the injection-production ratio between the injection well and the production well.

[0012] Furthermore, the operating pressure of the steam chamber is 5.5MPa in the rising stage, gradually decreases from 5.5MPa to 5.0MPa in the expanding stage, and gradually decreases from 5.0MPa to 3.5MPa in the falling stage.

[0013] Furthermore, the peak steam injection rate of the injection well is 80 - 107m 3 / d.

[0014] Furthermore, the optimization of the bottom-hole pressure difference between the steam injection well and the production well is as follows: when the electric heating lasts for 1 - 2 years, the pressure difference is 0.4 - 0.5 MPa; when the electric heating lasts for 3 - 5 years, the pressure difference is 0.5 - 0.6 MPa; when the steam chambers of adjacent well groups merge, the pressure difference is 0.4 - 0.5 MPa.

[0015] Furthermore, the optimization of the Sub-cool control parameter of the production well is as follows: when the electric heating lasts for 1 - 2 years, the Sub-cool of the developed steam chamber section is 10 - 25 °C, and that of the electric heating section is 0 - 15 °C; when the electric heating lasts for 3 - 5 years, the Sub-cool of the developed steam chamber section is 5 - 25 °C, and that of the electric heating section is 5 - 20 °C; when the steam chambers of adjacent well groups merge, the Sub-cool of the non-developed steam chamber section and the developed steam chamber section after fusion is 10 - 30 °C. The Sub-cool control parameter of the production well is the difference between the saturation steam temperature corresponding to the bottom-hole flowing pressure of the production well and the actual temperature of the fluid.

[0016] Furthermore, the optimization of the injection-production ratio between the steam injection well and the production well is as follows: when the electric heating lasts for 1 - 2 years, the injection-production ratio is 1.0 - 1.1; when the electric heating lasts for 3 - 5 years, the injection-production ratio is 1.1 - 1.3; when the steam chambers of adjacent well groups merge, the injection-production ratio is 1.1 - 1.2.

[0017] Furthermore, the optimization of the minimum bottom-hole dryness of the steam injected into the steam injection well is > 70%.

[0018] The technical effects and advantages of the present invention: This downhole electric heating assisted production method during the initial production stage of the dual horizontal well SAGD conversion can use the electric heating technology to specifically increase the temperature of the horizontal section, heat the crude oil in the near-well area, establish an oil drainage channel, promote the development of the steam chamber, and improve the utilization degree of the horizontal section; this production method uses heating cables to supplement energy to the formation and effectively increase the steam dryness. The electric heating can increase the temperature of the near-well area to 350 °C - 400 °C, causing the interlayers in the steam chamber to rupture, thereby improving the development effect of the steam chamber; this production method has strong pertinence, high energy utilization rate, promotes the uniform development of the SAGD steam chamber, improves the crude oil recovery rate, and has obvious economic benefits. Brief Description of the Drawings

[0019] Figure 1 It is a schematic diagram of the downhole electric heating assisted production method during the initial production stage of the dual horizontal well SAGD conversion of the present invention.

[0020] In the figure: 1 - casing; 21 - tubing; 22 - sucker rod; 23 - pumping; 31 - long tube; 32 - conductive section of heating cable; 33 - heating section of heating cable; 4 - screen pipe; 51 - steam chamber development area; 52 - steam chamber non-development area. Detailed Description of the Invention

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0022] The present invention provides a downhole electric heating assisted production method during the initial stage of the conversion from SAGD with dual horizontal wells to production as Figure 1 shown.

[0023] The production method includes the following steps: screening SAGD well groups that have completed cyclic preheating and entered the initial stage of SAGD production; lowering resistance heating cables into the production wellbore; heating the production wellbore using the resistance heating cables; adjusting the steam injection parameters of the injection wells and the oil production parameters of the production wells to achieve electric heating assisted SAGD production; tracking the numerical values and using numerical simulation, and when the steam chamber in the electric heating section rises to the top of the oil layer, stop the electric heating and switch to steam injection and production.

[0024] During the initial stage of SAGD production, thermal cycle startup is required, and steam is injected into the production wells and injection wells. The startup of steam injection cyclic preheating is generally divided into three steps: 1) Steam circulates between the production well and the injection well, and the reservoir mainly transfers heat through heat conduction; (2) An inter-well pressure difference is formed between the production well and the injection well, and the pressure of the injection well is higher than that of the production well, causing the crude oil between the wells to flow towards the production well to prepare for the conversion to full SAGD production; (3) The annulus of the upper steam injection well stops discharging liquid, and the lower production well stops injecting steam and enters the full SAGD production stage.

[0025] The SAGD well group meets the following conditions: the length of the unexploited section > 80 m; the effective thickness of the oil layer ≥ 15 m; the oil saturation > 63%; the viscosity of crude oil at 50 °C > 20,000 mPa·s; the permeability > 720 mD; the permeability ratio between the unexploited section and the exploited section < 7.

[0026] The resistance heating cable includes a heating cable conductive section 32 and a heating cable heating section 33. The specific operation of lowering the resistance heating cable into the production wellbore is as follows: the heating cable heating section 33 is lowered to the horizontal section position of the un-developed area 52 of the production well steam chamber, and the remaining section of the resistance heating cable is the heating cable conductive section 32, as Figure 1 shown.

[0027] The resistance heating cable is measured for temperature using a thermocouple. The resistance heating cable and the thermocouple are pre-arranged in parallel into the tubing 21 and lowered to the end of the horizontal section. The heating cable heating section 33 is 40 - 60 m away from the end of the horizontal section.

[0028] The maximum surface temperature of the resistance heating cable is 10 - 30 °C below the coking temperature of the crude oil in the oil layer, and the heating power of the resistance heating cable is 800 - 1000 W / m. During the surface temperature measurement process of the resistance heating cable, the power is automatically controlled by a power control box set on the ground.

[0029] The adjustment of the steam injection parameters of the steam injection well and the adjustment of the oil production parameters of the production well include: the peak steam injection rate of the steam injection well, the bottom hole pressure difference between the steam injection well and the production well, the Sub-cool control parameter of the production well, and the injection-production ratio between the steam injection well and the production well.

[0030] The operating pressure of the steam chamber is 5.5 MPa in the rising stage, gradually decreases from 5.5 MPa to 5.0 MPa in the expanding stage, and gradually decreases from 5.0 MPa to 3.5 MPa in the falling stage.

[0031] The peak steam injection rate of the steam injection well is 80 - 107 m 3 / d.

[0032] The optimization of the bottom hole pressure difference between the steam injection well and the production well is as follows: the pressure difference is 0.4 - 0.5 MPa in the case of electrical heating for 1 - 2 years, 0.5 - 0.6 MPa in the case of electrical heating for 3 - 5 years, and 0.4 - 0.5 MPa in the case of the merger of steam chambers in adjacent well groups.

[0033] The optimization of the Sub-cool control parameter of the production well is as follows: in the case of electrical heating for 1 - 2 years, Sub-cool is 10 - 25 °C in the developed steam chamber section and 0 - 15 °C in the electrical heating section; in the case of electrical heating for 3 - 5 years, Sub-cool is 5 - 25 °C in the developed steam chamber section and Sub-cool is 5 - 20 °C in the electrical heating section; in the case of the merger of steam chambers in adjacent well groups, Sub-cool is 10 - 30 °C for the fusion of the undeveloped steam chamber section and the developed steam chamber section. The Sub-cool control parameter of the production well is the difference between the saturation steam temperature corresponding to the bottom hole flowing pressure of the production well and the actual temperature of the fluid.

[0034] The optimization of the injection-production ratio between the steam injection well and the production well is as follows: the injection-production ratio is 1.0 - 1.1 in the case of electrical heating for 1 - 2 years, 1.1 - 1.3 in the case of electrical heating for 3 - 5 years, and 1.1 - 1.2 in the case of the merger of steam chambers in adjacent well groups.

[0035] The optimization of the minimum bottom hole dryness of the steam injected by the steam injection well is > 70%.

[0036] In view of the problem that the development degree of the steam chamber in the SAGD horizontal section is poor due to the influence of reservoir heterogeneity, the present invention uses the electric heating technology to fix-point increase the temperature of the horizontal section, heat the crude oil in the near-well zone, establish an oil drainage channel, promote the development of the steam chamber, and improve the utilization degree of the horizontal section. The present invention uses heating cables to supplement energy to the formation and effectively improve the steam dryness. Electric heating can raise the temperature of the near-well zone to 350°C - 400°C, causing the interlayers in the steam chamber to rupture, thereby improving the development effect of the steam chamber. The present invention adopts the electric heating technology to assist the horizontal well SAGD production technology at the initial stage of the production cycle in heterogeneous reservoirs, which has strong pertinence, high energy utilization rate, promotes the uniform development of the SAGD steam chamber, improves the crude oil recovery rate, and has obvious economic benefits.

[0037] For the conventional steam injection SAGD technology in the Fengcheng Oilfield operation area, the average utilization degree of the horizontal section is 58%, and the daily oil production level is 10 - 25 t / d; under the same reservoir conditions, when using electric heating-assisted SAGD, the development scale of the steam chamber along the horizontal section (i.e., the utilization degree of the horizontal section) reaches 98%, and the oil production rate increases by more than 15%.

[0038] Exemplarily, the production method includes the following steps: screening SAGD well groups that have completed cyclic preheating and transferred to the initial stage of SAGD production; lowering resistance heating cables into the production wellbore; using the resistance heating cables to heat the production wellbore; adjusting the steam injection parameters of the steam injection well and the oil production parameters of the production well to achieve electric heating-assisted SAGD production; tracking the numerical values and using numerical simulation. When the steam chamber in the electric heating section rises to the top of the oil layer, stop the electric heating and switch to steam injection and production.

[0039] The SAGD well group has the following conditions: the length of the unutilized section is 200 m, the effective thickness of the oil layer is 21 m, the oil saturation is 67%, the viscosity of the crude oil at 50°C is 32,000 mPa·s, the permeability is 1050 mD, and the permeability ratio between the unutilized section and the utilized section is 6.2.

[0040] The heating cable heating section 33 is lowered to the position of the horizontal section where the steam chamber in the production well has not developed, and the remaining section of the resistance heating cable is the heating cable conductive section 32.

[0041] The resistance heating cable uses a thermocouple for temperature measurement. The resistance heating cable and the thermocouple are pre-arranged in parallel on the coiled tubing 21 and lowered to the end of the horizontal section. The heating cable heating section 33 is 50 m away from the end of the horizontal section.

[0042] The highest surface temperature of the resistance heating cable is 20°C below the coking temperature of the crude oil in the oil layer, and the heating power is 900 W / m.

[0043] The operating pressure of the steam chamber is 5.5 MPa in the rising stage, gradually decreases from 5.5 MPa to 5.0 MPa in the expansion stage, and gradually decreases from 5.0 MPa to 3.5 MPa in the falling stage.

[0044] The peak steam injection rate of the steam injection well is 90 m 3 / d.

[0045] The minimum bottom hole dryness of the steam injected by the steam injection well is optimized to be >70%.

[0046] In the field implementation of one well group, the daily oil production level after the measures is 23.1 t / d, an increase of 3.1 t / d. After installing the electric heater, the downhole temperature measuring thermocouple is lowered into the original well. The temperature curve shows that the production mode of the horizontal section changes from a single-peak type to a linear type. The temperature of the entire 590 m - 790 m at the rear end of the original well horizontal section is raised above 150 °C, and the production is more balanced.

[0047] Working principle: This downhole electric heating assisted production method during the initial stage of SAGD conversion of double horizontal wells can effectively determine the unconnected sections between the production well and the horizontal well. Through electric heating, the viscosity of the crude oil in the unconnected sections decreases and drains down to the production well under the action of gravity, establishing an oil drainage channel, achieving uniform heating and uniform expansion of the steam chamber, effectively solving the problems of preferential thermal connection and uneven steam chamber development caused during the conventional steam cycle heating period, and promoting the uniform development of the steam chamber along the horizontal section during the transition to the SAGD production stage at a relatively low cost.

[0048] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, 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 downhole electric heating assisted production method during the initial stage of SAGD conversion to production for dual horizontal wells, characterized in that: The described production method includes the following steps: Screen the SAGD well group at the end of the cyclic preheating and transfer it to the initial stage of SAGD production; Lower the resistance heating cable into the production wellbore; Use the resistance heating cable to heat the production wellbore; Adjust the steam injection parameters of the steam injection well and the oil production parameters of the production well to achieve electrically heated assisted SAGD production; Track the numerical values and use numerical simulation. When the steam chamber in the electrically heated section rises to the top of the oil layer, stop the electrical heating and switch to steam injection and production; The resistance heating cable includes a heating cable conductive section (32) and a heating cable heating section (33). The specific operation of lowering the resistance heating cable into the production wellbore is as follows: The heating cable heating section (33) is lowered to the horizontal section position of the undeveloped area (52) of the production well steam chamber, and the remaining section of the resistance heating cable is the heating cable conductive section (32); The resistance heating cable uses a thermocouple for temperature measurement. The resistance heating cable and the thermocouple are pre-arranged in parallel to the tubing (21) and lowered to the end of the horizontal section. The heating cable heating section (33) is 40 - 60 m away from the end of the horizontal section; The adjustment of the steam injection parameters of the steam injection well and the oil production parameters of the production well includes: the peak steam injection rate of the steam injection well, the bottom hole pressure difference between the steam injection well and the production well, the Sub-cool control parameter of the production well, and the injection-production ratio between the steam injection well and the production well; The peak steam injection rate of the steam injection well is 80 - 107 m 3 / d; The optimization of the bottom hole pressure difference between the steam injection well and the production well is as follows: the pressure difference is 0.4 - 0.5 MPa in the case of electrical heating for 1 - 2 years, the pressure difference is 0.5 - 0.6 MPa in the case of electrical heating for 3 - 5 years, and the pressure difference is 0.4 - 0.5 MPa in the case of the merger of steam chambers in adjacent well groups; The optimization of the Sub-cool control parameter of the production well is as follows: in the case of electrical heating for 1 - 2 years, Sub-cool of the developed steam chamber section is 10 - 25 °C, and Sub-cool of the electrically heated section is 0 - 15 °C; in the case of electrical heating for 3 - 5 years, Sub-cool of the developed steam chamber section is 5 - 25 °C, and Sub-cool of the electrically heated section is 5 - 20 °C. In the case of the merger of steam chambers in adjacent well groups, Sub-cool of the fusion of the undeveloped steam chamber section and the developed steam chamber section is 10 - 30 °C. The Sub-cool control parameter of the production well is the difference between the saturation steam temperature corresponding to the bottom hole flowing pressure of the production well and the actual temperature of the fluid; The optimization of the injection-production ratio between the steam injection well and the production well is as follows: the injection-production ratio is 1.0 - 1.1 in the case of electrical heating for 1 - 2 years, the injection-production ratio is 1.1 - 1.3 in the case of electrical heating for 3 - 5 years, and the injection-production ratio is 1.1 - 1.2 in the case of the merger of steam chambers in adjacent well groups.

2. The downhole electrical heating assisted production method for SAGD conversion to the initial production stage of dual horizontal wells according to claim 1, characterized in that: The SAGD well group meets the following conditions: the length of the unproduced section > 80 m; the effective thickness of the oil layer ≥ 15 m; the oil saturation > 63%; the viscosity of crude oil at 50 °C > 20,000 mPa·s; the permeability > 720 mD; the permeability contrast between the unproduced section and the produced section < 7.

3. The downhole electric heating assisted production method during the initial stage of SAGD conversion in dual horizontal wells according to claim 1, characterized in that: The maximum surface temperature of the resistance heating cable is 10 - 30 °C below the coking temperature of the crude oil in the oil reservoir, and the heating power of the resistance heating cable is 800 - 1000 W / m.

4. The downhole electric heating assisted production method during the initial stage of SAGD conversion in dual horizontal wells according to claim 1, characterized in that: The operating pressure of the steam chamber is 5.5 MPa during the rising stage, gradually decreases from 5.5 MPa to 5.0 MPa during the expansion stage, and gradually decreases from 5.0 MPa to 3.5 MPa during the falling stage.

5. The downhole electric heating assisted production method during the initial stage of SAGD conversion in dual horizontal wells according to claim 1, characterized in that: The minimum bottom dryness of the steam injected into the steam injection well is optimized to be > 70%.

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