Ignition method for oil reservoir air injection development

Abstract

The invention provides an ignition method for oil reservoir air injection development, which comprises the following steps: aiming at an oil reservoir for air injection development, in-situ crude oil is injected into an injection well, and the injection amount of the in-situ crude oil is determined according to the residual oil saturation at the bottom of the injection well; a catalytic mixing aid and a crude oil slug are injected into the injection well; a bridge plug is installed in the injection well, water-based foam liquid is injected, and the bridge plug is used for replacing the catalytic mixing aid and the crude oil slug till the bridge plug falls into the well bottom; injecting foam liquid into the injection well; and air is injected into the injection well to be mixed with the catalytic mixing aid to ignite the oil layer. According to the ignition method, the threshold temperature of combustion is reduced for oil reservoirs capable of implementing air injection development, especially for ultra-deep wells with the depth larger than 2000 m, and efficient and safe ignition is achieved through the formation temperature of the oil reservoirs; efficient oxygen consumption is achieved, complex procedures and fine regulation and control of a conventional ignition technology are avoided, operability is high, and the implementation success rate is high.

Description

Technical Field

[0001] This invention belongs to the field of oil production technology, specifically relating to an ignition method for air injection development of oil reservoirs. Background Technology

[0002] Air-injected thermal miscible flooding (AIMF) is a secondary oil recovery method used to enhance oil recovery. Its principle involves using a high-temperature, high-pressure mixture of gas (usually a mixture of injected hot air and crude oil) to drive the crude oil towards the production well. It boasts low operating costs and wide applicability, making it a highly promising technology for oilfield development. AIMF is primarily applied to light oil and condensate gas reservoirs. The key to successful implementation lies in ignition. Under safe conditions, the crude oil within the formation must be ignited, meaning the mixture of crude oil and air must produce a high-temperature oxidation reaction. This process has two crucial factors: sufficient air injection and reaching the combustion threshold temperature. Studies show that for different crude oils with combustion temperatures between 250-550℃, artificial ignition, including electric heating and chemical ignition, is required to achieve the necessary conditions.

[0003] Electric heating ignition can achieve ignition at different temperatures (200-600℃) depending on the properties of crude oil in different reservoirs, and can be implemented at depths exceeding 900m. However, electric ignition technology uses continuous cable heating, resulting in high equipment costs and complex processes. Furthermore, the heating cable placed at the oil layer location is perpendicular to the wellbore. If crude oil remains in the wellbore or flows back into the wellbore, it can easily cause an internal explosion. This is especially true for ultra-deep wells with high pressure conditions at depths greater than 2000m, where the safety risks are even greater, and the requirements for the ignition process are more stringent. It also has special requirements in terms of monitoring, safety control, and supporting tools. Currently, conventional supporting process technologies cannot meet the high-pressure ignition requirements.

[0004] Compared to electric heating ignition, chemical ignition is more flexible and safer. CN102071918A discloses a method for combustion-assisted ignition in heavy oil reservoir fire-driven oil recovery, which involves injecting high-temperature steam into the injection well to raise the formation temperature to 210-260℃, and then injecting a mixture of combustion-assisted agent and crude oil. CN107100604A discloses a method for fire-induced oil layer extraction using nano-combustion-assisted ignition, which involves injecting a steam slug into a heavy oil reservoir to maintain the temperature at the oil layer location above 100℃, then injecting nano-combustion-assisted agent and allowing it to stand, followed by injecting air to achieve spontaneous ignition. However, the above ignition methods uniformly use high-temperature steam injection and catalyst ignition, requiring high ignition temperatures. When igniting gas injection wells in oil layers at depths of 2000m and above, it is necessary to ensure the wellbore gas tightness and use thermal recovery completion, which greatly increases the cost of gas injection wells. Furthermore, due to the high temperature inside the wellbore, there is also the possibility of combustion inside the wellbore. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide an ignition method for reservoir air injection development, which lowers the threshold temperature for crude oil combustion to around 50°C. For ultra-deep wells with a depth greater than 2000m, reservoir temperature can be utilized to safely and efficiently ignite the oil layer.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] This invention provides an ignition method for air injection development in oil reservoirs, the ignition method comprising the following steps:

[0008] (1) For reservoirs developed by air injection, formation crude oil is injected into the injection well, and the injection volume of the formation crude oil is determined based on the remaining oil saturation at the bottom of the injection well.

[0009] (2) Injecting catalyst mixing agent and crude oil slug into the injection well;

[0010] (3) Install a bridge plug into the injection well and inject water-based foam liquid to replace the catalyst mixing agent and crude oil slug described in step (2) until the bridge plug falls to the bottom of the well.

[0011] (4) Inject foam fluid into the injection well;

[0012] (5) Inject air into the injection well to achieve the mixing point of the fuel layer with the catalytic mixer.

[0013] The ignition method provided by this invention first injects an appropriate amount of formation crude oil into the reservoir, adjusts the gas intake profile around the injection well, saturates the area around the long-term water injection well where the crude oil volume is too low, adjusts the underground oil-water saturation distribution, uses a catalytic mixing agent to reduce the combustion threshold temperature to about 50°C, reduces the miscibility pressure, injects foam liquid twice, uses the foam liquid to push the catalytic mixing agent into the oil layer, cleans the wellbore, ensures that there is no residual oil and catalytic mixing agent adhering to the wall, avoids combustion in the wellbore when air is injected, and finally injects air to ignite the crude oil using the formation temperature.

[0014] For reservoirs where air injection is feasible, especially for ultra-deep wells with a depth greater than 2000m, the threshold temperature for combustion is lowered, and efficient and safe ignition is achieved by utilizing the reservoir formation temperature. Furthermore, during ignition, oxygen is completely consumed through the thermal front, achieving efficient oxygen consumption. This avoids the complex process and fine control required by conventional ignition technologies, making it highly operable and with a high success rate.

[0015] Preferably, in step (1), the remaining oil saturation at the bottom of the injection well is ≥30%, and the injection volume of the formation crude oil is 20-30m³. 3 For example, it could be 20m 3 22m 3 24m 3 25m 3 26m3 28m 3 or 30m 3 However, this does not limit the listed values; other unlisted values ​​within the range are also applicable.

[0016] Preferably, the remaining oil saturation at the bottom of the injection well is <30%, and the injection volume of the formation crude oil is 30m³. 3 Or 12.56 × hm 3 The larger value of , where h is the oil layer thickness.

[0017] Preferably, the injection temperature of the formation crude oil in step (1) is 40-50℃, for example, it can be 40℃, 42℃, 44℃, 45℃, 46℃, 48℃ or 50℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0018] Preferably, the catalytic additive in step (2) comprises oxides of nickel and / or cobalt, and a mixture of potassium permanganate and sodium nitrate.

[0019] The metal oxides of nickel and cobalt can react rapidly with oxygen. At the same time, the mixture of potassium permanganate and sodium nitrate has a low flash point and is easily ignited, enabling a rapid oxidation reaction to occur in the 50°C oil reservoir and ignite the oil layer.

[0020] Preferably, the amount of crude oil in step (2) is 1-5 wt% of the total amount of catalytic additive and crude oil, for example, it can be 1 wt%, 2 wt%, 3 wt%, 4 wt% or 5 wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0021] Preferably, the injection volume of the catalyst mixing agent and crude oil slug in step (2) is (2-7) × hm 3 For example, it could be 2h m 3 3h m 3 4h m 3 5h m 3 6h m 3 or 7h m 3 However, it is not limited to the listed values; other unlisted values ​​within the range are also applicable, where h is the oil layer thickness.

[0022] Preferably, the injection temperature of the catalyst mixing agent and crude oil slug in step (2) is 40-50°C, for example, it can be 40°C, 42°C, 44°C, 45°C, 46°C, 48°C or 50°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] Preferably, the injection volume of the foam liquid in step (4) is twice the volume of the wellbore.

[0024] Preferably, the injection speed of the foam liquid in step (4) is 8-12m. 3 / h, for example, could be 8m 3 / h、9m 3 / h, 10m 3 / h、11m 3 / h or 12m 3 / h, but not limited to the listed values, other unlisted values ​​within the range also apply.

[0025] Preferably, the temperature of the foam liquid in step (4) is ≥40℃, for example, it can be 40℃, 45℃, 50℃, 60℃ or 80℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0026] Preferably, the air injection intensity in step (5) is 500-25000 Nm. 3 / m, for example, could be 500Nm 3 / m、1000Nm 3 / m, 5000Nm 3 / m、10000Nm 3 / m, 15000Nm 3 / m、20000Nm 3 / m or 25000Nm 3 / m, but not limited to the listed values, other unlisted values ​​within the range also apply.

[0027] Preferably, the ignition method further includes: after igniting the fuel layer in step (5), continuously injecting air for more than seven days, and then gradually increasing the injection speed until the designed injection volume is reached.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] The ignition method provided by this invention is designed for oil reservoirs where air injection is feasible, especially for ultra-deep wells with a depth greater than 2000m. It lowers the combustion threshold temperature and utilizes the reservoir formation temperature to achieve efficient and safe ignition. Furthermore, during ignition, oxygen is completely consumed through the thermal front, achieving efficient oxygen consumption. This avoids the complex process and fine control required by conventional ignition techniques, making it highly operable and with a high success rate. Detailed Implementation

[0030] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0031] Example 1

[0032] This embodiment provides an ignition method for air injection development in oil reservoirs.

[0033] This embodiment is for an oil reservoir that can be developed by air injection. The average burial depth of the layer in this block is 2800m, the effective oil layer thickness is 20m, the current gas injection pressure is about 17-20MPa, the formation temperature is 102℃, and the oil saturation is 55%.

[0034] Before ignition, after completing the injection string, inject annular fluid into the annulus at a rate of 20m / s. 3 / h, until the oil sleeve annulus returns and the packer expands to seal.

[0035] The ignition method includes the following steps:

[0036] (1) Inject 30m into the injection well 3 Formation crude oil, injection temperature 40℃, injection rate 10m 3 / h, maximum injection pressure 30MPa;

[0037] (2) Inject 30m into the ignition well 3 Catalytic additive and crude oil slug, wherein the amount of crude oil is 1 wt% of the total amount of catalytic additive and crude oil, the injection temperature is 40℃, and the injection rate is 10 m / s. 3 / h, maximum injection pressure 30MPa;

[0038] (3) Inject 10m into the ignition well. 3 Water-based foaming fluid, combined with a pre-bridge plug to replace the catalyst mixing agent and crude oil slug, is injected at a speed of 1m. 3 / h, maximum injection pressure 30MPa, when the bridge plug naturally falls to the bottom of the well, the catalyst mixing agent and crude oil slug are completely pushed into the interior of the oil layer;

[0039] (4) Inject 20m into the ignition well. 3 Hot foam liquid, the temperature of the hot foam liquid is 40℃, and the injection speed is 10m. 3 / h, maximum injection pressure 30MPa, clean the wellbore to ensure no residual oil clings to the wall, and the catalytic mixing agent enters the oil layer to a distance of more than 2m from the bottom of the well.

[0040] (5) Seamless continuous air injection, injection speed 13000 Nm 3 / d, igniting crude oil;

[0041] (6) Gradually increase the injection rate and observe the changes in wellhead pressure. After 6 hours, the injection rate is increased to 28,800 Nm. 3 / d, and after 7 days the injection rate increased to 57600 Nm 3 / d, and the injection rate increased to 86400 Nm after 30 days. 3 / d, with stable air supply.

[0042] Example 2

[0043] This embodiment provides an ignition method for air injection development in oil reservoirs.

[0044] This embodiment is for an oil reservoir that can be developed by air injection. The average burial depth of the layer in this block is 2800m, the effective oil layer thickness is 20m, the current gas injection pressure is about 17-20MPa, the formation temperature is 102℃, and the oil saturation is 55%.

[0045] Before ignition, after completing the injection string, inject annular fluid into the annulus at a rate of 20m / s. 3 / h, until the oil sleeve annulus returns and the packer expands to seal.

[0046] The ignition method includes the following steps:

[0047] (1) Inject 20m into the injection well 3 Formation crude oil, injection temperature 50℃, injection rate 10m 3 / h, maximum injection pressure 30MPa;

[0048] (2) Inject 140m into the ignition well 3 The catalyst blending agent and crude oil slug are used, wherein the amount of crude oil is 5 wt% of the total amount of catalyst blending agent and crude oil, the injection temperature is 50℃, and the injection speed is 10m. 3 / h, maximum injection pressure 30MPa;

[0049] (3) Inject 10m into the ignition well. 3 Water-based foaming fluid, combined with a pre-bridge plug to replace the catalyst mixing agent and crude oil slug, is injected at a speed of 1m. 3 / h, maximum injection pressure 30MPa, when the bridge plug naturally falls to the bottom of the well, the catalyst mixing agent and crude oil slug are completely pushed into the interior of the oil layer;

[0050] (4) Inject 20m into the ignition well. 3 Hot foam liquid, the temperature of the hot foam liquid is 45℃, and the injection speed is 10m. 3 / h, maximum injection pressure 30MPa, clean the wellbore to ensure no residual oil clings to the wall, and the catalytic mixing agent enters the oil layer to a distance of more than 2m from the bottom of the well.

[0051] (5) Seamless continuous air injection, injection speed 13000 Nm 3 / d, igniting crude oil;

[0052] (6) Gradually increase the injection rate and observe the changes in wellhead pressure. After 6 hours, the injection rate is increased to 28,800 Nm. 3 / d, and after 7 days the injection rate increased to 57600 Nm 3 / d, and the injection rate increased to 86400 Nm after 30 days. 3 / d, with stable air supply.

[0053] Comparative Example 1

[0054] This comparative example provides an ignition method for reservoir air injection development. Compared with Example 1, step (2) only involves injecting a catalytic mixing agent slug, while the rest is the same as in Example 1.

[0055] Mixing the catalyst with crude oil can further ensure that after the catalytic oxygen-consuming slug is ignited, the crude oil and catalyst slug can also be ignited, thus buffering the continued combustion. Injecting only the catalytic mixing agent slug would lead to unstable ignition and operation.

[0056] In summary, the ignition method provided by this invention is designed for oil reservoirs where air injection is feasible, especially for ultra-deep wells with a depth greater than 2000m. It lowers the combustion threshold temperature and utilizes the reservoir formation temperature to achieve efficient and safe ignition. Furthermore, during ignition, oxygen is completely consumed through the thermal front, achieving efficient oxygen consumption. This avoids the complex process and fine control required by conventional ignition techniques, making it highly operable and with a high success rate.

[0057] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An ignition method for air injection development of an oil reservoir, characterized in that, The ignition method includes the following steps: (1) For reservoirs developed by air injection, formation crude oil is injected into the injection well, and the injection volume of the formation crude oil is determined based on the remaining oil saturation at the bottom of the injection well. (2) Injecting catalyst mixing agent and crude oil slug into the injection well; (3) Install a bridge plug into the injection well and inject water-based foam liquid to replace the catalyst mixing agent and crude oil slug described in step (2) until the bridge plug falls to the bottom of the well. (4) Inject foam fluid into the injection well; (5) Inject air into the injection well to achieve the mixing point of the fuel layer with the catalytic mixer.

2. The ignition method according to claim 1, characterized in that, In step (1), the remaining oil saturation at the bottom of the injection well is ≥30%, and the injection volume of the formation crude oil is 20-30m³. 3 The remaining oil saturation at the bottom of the injection well is <30%, and the injection volume of the formation crude oil is 30m³. 3 and 12.56×hm 3 The larger value of , where h is the oil layer thickness.

3. The ignition method according to claim 1 or 2, characterized in that, The injection temperature of the formation crude oil in step (1) is 40-50℃.

4. The ignition method according to any one of claims 1-3, characterized in that, The catalyst additive in step (2) includes oxides of nickel and / or cobalt, and a mixture of potassium permanganate and sodium nitrate.

5. The ignition method according to any one of claims 1-4, characterized in that, The amount of crude oil mentioned in step (2) is 1-5 wt% of the total amount of catalyst blending agent and crude oil.

6. The ignition method according to any one of claims 1-5, characterized in that, The injection volume of the catalyst mixing agent and crude oil slug in step (2) is (2-7) × hm 3 , where h is the oil layer thickness.

7. The ignition method according to any one of claims 1-6, characterized in that, The injection temperature of the catalyst mixing agent and crude oil slug in step (2) is 40-50℃.

8. The ignition method according to any one of claims 1-7, characterized in that, The injection volume of the foam liquid in step (4) is twice the volume of the wellbore; Preferably, the temperature of the foam liquid in step (4) is ≥40℃.

9. The ignition method according to any one of claims 1-8, characterized in that, The air injection intensity in step (5) is 500-25000 Nm. 3 / m.

10. The ignition method according to any one of claims 1-9, characterized in that, The ignition method further includes: after igniting the fuel layer in step (5), continuously injecting air for more than seven days, and then gradually increasing the injection speed until the designed injection volume is reached.