Method for preventing explosion risk of DME oil displacement output gas

Abstract

The invention discloses a method for preventing DME flooding output gas explosion risk, and belongs to the technical field of oil and gas field development. The method specifically comprises the following steps: (1) preparing a mixed oil displacement system; (2) optimizing injection process parameters; (3) safety control and dynamic adjustment; and (4) gas recovery and cyclic utilization. DME and CO2 are jointly dissolved in water to be injected into the oil reservoir, the explosion risk of DME is reduced or even eliminated, meanwhile, the purpose of improving the recovery efficiency through synergistic interaction of DME and CO2 is achieved, multiple contradictions between efficient oil displacement and explosion risk of DME, CO2 safety and low efficiency and high consumption of CO2 are broken through by dynamically adjusting the gas dissolution proportion, optimizing the injection process and conducting real-time safety monitoring, and the recovery efficiency of the oil reservoir is improved. And an innovative solution is provided for safe and large-scale application of DME.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas field development, and more particularly to a method for preventing the explosion risk of DME oil displacement produced gas. Background Art

[0002] Dimethyl ether (DME), a combustible organic ether gas, can be used as an additive to significantly enhance oil recovery. Extensive research has been conducted both domestically and internationally on DME's effectiveness in enhancing oil recovery. Results demonstrate significant benefits and significant potential for DME's application. However, safety remains a major constraint to its widespread adoption in the field.

[0003] The explosion risk of DME mixed with air has attracted considerable attention. Early research focused on the properties of DME itself, primarily examining its physicochemical properties. Its explosive limits in air at room temperature and pressure were determined to be 3.7%-18%. As research deepened, researchers began to examine the explosive properties of DME mixed with other combustible gases. For example, the explosive limits of DME, CH₄, and their mixtures were determined at room temperature -80°C and pressures of 0.1-0.3 MPa. The effects of inert gases on the explosive limits of DME and its mixed combustible gases have also been studied. Studies have shown that a critical explosion suppression point is reached when the flame-retardant refrigerant HFC125 and DME have a volume ratio of 4.6. When inert gases are added to a DME-propane system, CO₂ demonstrates superior explosion suppression compared to N₂. Furthermore, patent CN 114439439 A proposes injecting a DME aqueous solution into heavy oil reservoirs to significantly reduce the viscosity of the oil, thereby improving recovery. However, this patent primarily focuses on improving oil recovery and ignores the risk of explosion. Patent CN 101109758 A proposes installing a sensor at a leak-prone location in the filling line. When the DME concentration reaches 3.4%, a buzzer alarm is activated and the gas solenoid valve is shut off, keeping the concentration below the lower explosion limit. Patent CN 202501186 U proposes using a sealing ring made of polytetrafluoroethylene rubber to combat the corrosive properties of DME, preventing DME leakage and thus suppressing explosions.

[0004] In summary, the current research on the explosion characteristics of DME is mainly concentrated in the field of chemical safety. In the field of DME to enhance crude oil recovery, DME is a new gas-phase combustible additive, and its impact on the explosion risk of existing oil and gas production systems needs to be deeply evaluated. How to avoid and control the explosion risk is a difficult problem that must be solved. It is necessary to propose effective and reliable explosion prevention and explosion control measures based on the properties and usage of DME. Summary of the Invention

[0005] In view of this, the object of the present invention is to provide a method for preventing the risk of explosion of DME oil production gas, so as to address the deficiencies in the prior art.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preventing the risk of explosion of DME flooding produced gas comprises the following steps:

[0008] (1) Preparation of mixed flooding system

[0009] Under normal temperature and high pressure conditions on the ground, DME and CO2 are added to the injection water to prepare a DME+CO2 aqueous solution;

[0010] The amount of DME dissolved in the injected water is 0% to 100% of the saturation state under formation conditions, and the amount of CO2 dissolved in the injected water is also 0% to 100% of the saturation state under formation conditions.

[0011] (2) Optimization of injection process parameters

[0012] The DME+CO2 aqueous solution is injected into the ground through a plunger pump, and the bottom hole flow pressure does not exceed the formation fracture pressure;

[0013] The injection method is continuous injection or slug injection, and the slug size can be optimized according to the recovery effect and gas production pattern;

[0014] (3) Safety control and dynamic adjustment

[0015] Downhole sensors monitor the concentrations of DME, CO2, and major hydrocarbon gases such as CH4 and C2H6 in the produced gas in real time. The data is fed back to the control system, triggering an automatic adjustment mechanism to dynamically adjust the amount and ratio of DME and CO2 dissolved in the injected water to ensure that the CO2 content in the produced gas is high enough to completely suppress the risk of explosion.

[0016] The indoor experimental results show that Figure 1 and Figure 2As shown, when the output gas is mainly CO2+DME, and the volume ratio of CO2 to DME is greater than 6.5, that is, the CO2 content is higher than 86.67%, the explosion risk will disappear. When the output gas is mainly CO2+CH4, and the volume ratio of CO2 to CH4 is greater than 3.4, that is, the CO2 content is higher than 77.27%, the explosion risk will disappear. When the output gas is mainly CO2+ethane, and the volume ratio of CO2 to ethane is greater than 7.3, that is, the CO2 content in the system is higher than 87.95%, the explosion risk will disappear. When the output gas is mainly CO2+DME+CH4+ethane, the explosion risk just disappears, and the corresponding volume ratio of CO2 to combustible gas (DME+CH4+ethane) is between 3.4-7.3, and the CO2 content is between 77.27-87.95%. For safety reasons and to make timely adjustments, the volume ratio of CO2 to combustible gas of 7.3 and the CO2 content of 87.95% are selected as the triggering standards for dynamic adjustment. That is, when it is monitored that the volume ratio of CO2 to combustible gas is less than 7.3 and the CO2 content is lower than 87.95%, the amount and ratio of DME and CO2 dissolved in the injected water are adjusted dynamically in time.

[0017] (4) Gas recovery and recycling

[0018] After the wellhead produced fluid is separated into three phases, based on the separation accuracy and process cost, two options, a and b, can be selected, corresponding to different technical routes and economic characteristics respectively;

[0019] Plan a: If Figure 3 As shown, a high-precision three-phase separation system is used to separate the fluid into high-precision oil phase, water phase and gas phase (separation technologies include but are not limited to: multi-stage centrifugal separation technology and membrane separation technology), and secondary separation of the gas phase components (low-temperature fractionation and selective adsorption can be used) is performed to obtain high-purity DME, CO2 and major hydrocarbon gases such as CH4 and C2H6. The obtained DME and CO2 are injected into the water phase after three-phase separation according to a preset ratio to form a DME+CO2 aqueous solution with controllable concentration;

[0020] Plan b: If Figure 4 As shown, a conventional three-phase separation system is used to preliminarily separate the oil phase, water phase and gas phase with lower precision. The high water solubility of CO2 and DME is utilized to physically degas and discharge the water-insoluble hydrocarbon gas through a water absorption device. The remaining DME and CO2 mixed gas is supplemented with industrial-grade DME and CO2 in an adjusted ratio and then injected into the water phase after three-phase separation to form a DME+CO2 aqueous solution with controllable concentration.

[0021] The DME+CO₂ aqueous solution re-formed in Schemes A and B of the present invention is pressurized and then reinjected into the formation, achieving the recycling of the oil displacement medium. Scheme A trades high costs for precise control and high recovery rates, while Scheme B prioritizes economic efficiency and reduces costs through process simplification. The two form a complementary technical system that can be flexibly selected based on oilfield geological conditions, gas composition characteristics, and economic efficiency goals.

[0022] In the present invention, the core purpose of preparing the mixed oil recovery system in step (1) is to ensure that the DME+CO2 aqueous solution prepared on the ground does not degas under formation conditions. The solubility and ratio of DME and CO2 in the injected water can be flexibly adjusted according to the requirements of the oil recovery effect and the risk control of produced gas explosion.

[0023] The core purpose of optimizing the injection process parameters in step (2) is to improve the oil recovery efficiency of reservoirs with different permeabilities through dynamic adaptation of pressure and injection mode.

[0024] The core purpose of step (3) safety control and dynamic regulation is to eliminate the risk of explosion and ensure that the DME concentration in the produced gas is lower than the safety threshold.

[0025] The core purpose of step (4) gas recovery and recycling is to achieve closed-loop utilization of resources and improve economic benefits and environmental compatibility.

[0026] It can be seen from the above technical solution that compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] To explore safe ways to apply DME to significantly enhance crude oil recovery, this paper proposes a comprehensive technical solution that balances DME flooding efficiency, explosion risk mitigation, and gas recycling. Specifically, DME and CO2 are dissolved in water and injected into the reservoir to reduce or even eliminate the DME explosion risk, while simultaneously achieving the synergistic effect of DME and CO2 on oil recovery. By dynamically adjusting the gas dissolution ratio, optimizing the injection process, and implementing real-time safety monitoring, this approach overcomes the multiple contradictions between DME's high oil recovery efficiency and explosion risk, and CO2's safety and low efficiency and high consumption, providing an innovative solution for the safe and large-scale application of DME. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is the explosion limit of methane / ethane / DME+CO2;

[0029] Figure 2 The effect of CO2 on the explosion limits of methane / ethane / DME;

[0030] Figure 3 This is a schematic diagram of the process of gas recovery and recycling using a high-precision three-phase separation system in Scheme A;

[0031] Figure 4 This is a schematic diagram of the process of gas recovery and recycling using a conventional three-phase separation system in Scheme B;

[0032] Figure 5 To assess the explosion risk of produced gas in DME / +CO2 water flooding experiments. DETAILED DESCRIPTION

[0033] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0034] Example 1

[0035] When the explosion risk of DME+CH4+CO2 system disappears, the ratio of CO2 to DME+CH4 content should be between 3.4-6.5. For the sake of conservatism, 6.5 is selected as the standard for judging whether the produced gas has explosion risk. According to the composition of the produced gas in the DME+CO2 water flooding experiment, the volume ratio of CO2 to DME+CH4 and other combustible gas components is calculated and compared with 6.5. The results are as follows Figure 5 As shown. Through analysis, we can get:

[0036] (1) When the volume ratio of CO2 to combustible gases such as DME+CH4 in the output gas is greater than 6.5, there is no explosion risk; when the ratio of CO2 to combustible gases is less than 6.5, there is an explosion risk.

[0037] (2) Generally, as DME+CO2 water flooding progresses, the DME content in the produced gas increases, the CO2 content decreases, and the explosion risk increases. The specific situation is also affected by the release of associated hydrocarbons such as CH4 when crude oil is produced in the oil gathering zone.

[0038] (3) Under the conditions of 0.5wt% DME + 100% saturated CO2 water flooding, the CO2 content in the produced gas is high, and there is no explosion risk throughout the process. Under the conditions of 5wt% DME + 100% saturated CO2 water flooding, the CO2 content is high in the initial stage, and there is no explosion risk after the delayed DME production. In the middle and late stages, as the DME content in the produced gas increases, the volume ratio of CO2 to combustible gases such as DME + CH4 gradually decreases and remains near the critical value. There is a certain explosion risk, but it is relatively small. Therefore, the 0.5-5wt% DME + 100% saturated CO2 aqueous solution system is recommended, which can improve the recovery factor by 19.25%-22.30%.

[0039] Example 2

[0040] The method for preventing the risk of explosion of DME flooding produced gas specifically comprises the following steps:

[0041] (1) Preparation of mixed flooding system

[0042] Under normal temperature and high pressure conditions on the ground, DME and CO2 were added to the injection water to prepare a 0.5wt% DME + 100wt% saturated CO2 aqueous solution;

[0043] (2) Optimization of injection process parameters

[0044] The DME+CO2 aqueous solution was injected into the ground through a plunger pump. The bottomhole pressure did not exceed the formation fracture pressure. 2PV of normal water flooding was continuously injected, followed by 3PV of DME+CO2 mixed solution flooding. The cumulative gas production was 0.54L.

[0045] (3) Safety control and dynamic adjustment

[0046] Downhole sensors monitor the concentrations of DME, CO2, and hydrocarbon gases in the produced gas in real time. The data is fed back to the control system, triggering an automatic adjustment mechanism to dynamically adjust the amount and ratio of dissolved DME and CO2 in the injected water.

[0047] (4) Gas recovery and recycling

[0048] A high-precision three-phase separation system is used to separate the fluid into high-precision oil phase, water phase and gas phase. The gas phase components are separated twice to obtain high-purity DME, CO2 and hydrocarbon gas. The obtained DME and CO2 are injected into the water phase after three-phase separation in a preset ratio to form a DME+CO2 aqueous solution with controllable concentration.

[0049] Example 3

[0050] The method for preventing the risk of explosion of DME flooding produced gas specifically comprises the following steps:

[0051] (1) Preparation of mixed flooding system

[0052] Under normal temperature and high pressure conditions on the ground, DME and CO2 were added to the injection water to prepare a 5wt% DME + 100wt% saturated CO2 aqueous solution;

[0053] (2) Optimization of injection process parameters

[0054] The DME+CO2 aqueous solution was injected into the ground through a plunger pump. The bottomhole pressure did not exceed the formation fracture pressure. 2PV of normal water flooding was continuously injected, followed by 3PV of DME+CO2 mixed solution flooding. The cumulative gas production was 1.36L.

[0055] (3) Safety control and dynamic adjustment

[0056] Downhole sensors monitor the concentrations of DME, CO2, and hydrocarbon gases in the produced gas in real time. The data is fed back to the control system, triggering an automatic adjustment mechanism to dynamically adjust the amount and ratio of dissolved DME and CO2 in the injected water.

[0057] (4) Gas recovery and recycling

[0058] A conventional three-phase separation system is used to preliminarily separate the oil phase, water phase and gas phase with lower precision. The high water solubility of CO2 and DME is utilized to physically degas and discharge the water-insoluble hydrocarbon gas through a water absorption device. The remaining DME and CO2 mixed gas is supplemented with industrial-grade DME and CO2 in an adjusted ratio and then injected into the water phase after three-phase separation to form a DME+CO2 aqueous solution with controllable concentration.

[0059] After testing, the method of Example 2 increased the recovery rate by 19.25%, and the method of Example 3 increased the recovery rate by 22.30%.

[0060] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preventing the risk of explosion of DME flooding gas, characterized in that: The specific steps include: (1) Preparation of mixed flooding system Under normal temperature and high pressure conditions on the ground, DME and CO2 are added to the injection water to prepare a DME+CO2 aqueous solution; (2) Optimization of injection process parameters The DME+CO2 aqueous solution is injected into the ground through a plunger pump, and the bottom hole flow pressure does not exceed the formation fracture pressure; (3) Safety control and dynamic adjustment Downhole sensors monitor the concentrations of DME, CO2, and hydrocarbon gases in the produced gas in real time. The data is fed back to the control system, triggering an automatic adjustment mechanism to dynamically adjust the amount and ratio of dissolved DME and CO2 in the injected water. (4) Gas recovery and recycling Option a: Use a high-precision three-phase separation system to separate the fluid into high-precision oil phase, water phase and gas phase. Perform secondary separation on the gas phase components to obtain high-purity DME, CO2 and hydrocarbon gas. The obtained DME and CO2 are injected into the water phase after three-phase separation in a preset ratio to form a DME+CO2 aqueous solution with controllable concentration. Option b: Use a conventional three-phase separation system to preliminarily separate the oil phase, water phase and gas phase with lower precision. Utilize the high water solubility of CO2 and DME to physically degas and discharge the water-insoluble hydrocarbon gas through a water absorption device. The remaining DME and CO2 mixed gas is supplemented with industrial-grade DME and CO2 in an adjusted ratio and then injected into the water phase after three-phase separation to form a DME+CO2 aqueous solution with controllable concentration.

2. A method for preventing the risk of explosion of DME flooding gas according to claim 1, characterized in that: In step (1), the amount of DME dissolved in the injected water is 0% to 100% of the saturation state under formation conditions.

3. A method for preventing the risk of explosion of DME flooding gas according to claim 1, characterized in that: In step (1), the amount of CO2 dissolved in the injected water is 0% to 100% of the saturation state under formation conditions.

4. A method for preventing the risk of explosion of DME flooding gas according to claim 1, characterized in that: In step (2), the injection method is continuous injection or plug injection.

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