Method and system for developing natural gas hydrate reservoirs

Abstract

The invention relates to the field of natural gas extraction, in particular to a method and system for developing a natural gas hydrate reservoir. The method comprises the following steps: a, introducing a CO2 material flow into the waste hot oil reservoir to obtain a hot material flow, and carrying out first gas-liquid separation on the hot material flow to obtain a hot CO2 material flow and a hot liquid phase; b, introducing the hot CO2 material flow into the natural gas hydrate reservoir to obtain an extraction material flow, and carrying out second gas-liquid separation on the extraction material flow to obtain an extraction liquid phase and an extraction gas phase; and c, heat exchange is conducted on the produced liquid phase and the hydrothermal liquid phase, the produced liquid phase obtained after heat exchange is circulated back to the natural gas hydrate reservoir, and the hydrothermal liquid phase obtained after heat exchange is circulated back to the waste hot oil recovery reservoir. According to the method, the heat injection cost of the hydrate reservoir can be greatly reduced, the problem that the heat injection cost is too high in a traditional heat injection exploitation method is solved, the development productivity of the natural gas hydrate reservoir can be improved, meanwhile, CO2 burying can be achieved, and the greenhouse effect is reduced.

Description

Technical Field

[0001] The invention relates to the field of natural gas exploitation, and in particular to a method and system for developing natural gas hydrate reservoirs. Background Art

[0002] The total amount of natural gas hydrate resources in my country's sea areas exceeds 80 billion tons of oil equivalent, mainly distributed in the continental slope of the South China Sea and its deep sea, which is about twice the amount of conventional natural gas resources. At the same time, it has the advantages of being clean and efficient, and is regarded as one of the most promising successor resources. At present, most ideas for the development of natural gas hydrates are basically to first consider how to decompose the natural gas hydrates stored in the sediments, and then extract the natural gas to the ground. Generally speaking, changing the temperature and pressure at which natural gas hydrates exist stably to cause their decomposition is the main way to develop natural gas hydrate resources. The main methods for exploiting natural gas hydrates at present include pressure reduction method, heat injection method, etc.

[0003] By reducing the pressure, the equilibrium curve of natural gas hydrate stability is moved, thereby achieving the purpose of promoting the decomposition of hydrates. Generally, the natural gas pressure is "reduced" or a natural gas cavity is formed in the free gas accumulation layer under the hydrate layer (which can be artificially formed by thermal excitation or chemical reagents), making the hydrate unstable and decomposing into natural gas and water. Exploiting the free gas under the hydrate layer is an effective way to reduce reservoir pressure. The biggest feature of the depressurization method is that it does not require expensive continuous excitation, so it may become one of the effective methods for large-scale exploitation of natural gas hydrates in the future. However, the speed of natural gas exploitation using only the depressurization method is very slow, and the decomposition of natural gas hydrate reservoirs is an endothermic reaction. At the same time, the heat energy contained in natural gas hydrate reservoirs is limited. Therefore, the results of two test productions show that it is difficult to meet the minimum production capacity required for commercial development using a single depressurization development method.

[0004] Thermal recovery is the most studied and most in-depth natural gas hydrate recovery technology. Thermal recovery uses drilling technology to install pipelines in the natural gas hydrate stable layer, heat the hydrate formation, increase the reservoir temperature, cause the natural gas hydrate to decompose, and then use pipelines to collect the decomposed natural gas. The heat injection method can provide the required heat energy for hydrate decomposition, thereby greatly increasing production capacity, but the conventional heat injection method faces the problem of high heat injection costs and poor economic efficiency.

[0005] There are heavy oil thermal recovery reservoirs in my country's South China Sea and East China Sea. After the thermal recovery reservoirs are abandoned, there is still a lot of residual heat in the formation. 2 The development of natural gas hydrate reservoirs with the residual heat from heavy oil thermal recovery reservoirs can significantly reduce the heat injection cost of natural gas hydrate reservoirs, increase the development capacity of natural gas hydrate reservoirs, and achieve CO 2This method overcomes the problem of high heat injection cost in traditional heat injection mining method, has the advantages of simple equipment and strong operability, and provides technical support for the economic and efficient development of natural gas hydrate reservoirs. Summary of the invention

[0006] The purpose of the present invention is to overcome the problem of high heat injection cost in traditional heat injection exploitation method and provide a method and system for developing natural gas hydrate reservoirs, which has the characteristics of low heat injection cost.

[0007] In order to achieve the above-mentioned object, the first aspect of the present invention provides a method for developing a natural gas hydrate reservoir, the method comprising: a. 2 The material flow is introduced into the abandoned thermal recovery reservoir to obtain hot material flow, which is then separated into hot CO after the first gas-liquid separation. 2 Logistics and hot liquid phase; b. Heat CO 2 The logistics is passed into the natural gas hydrate reservoir to obtain the produced logistics, and the produced logistics undergoes a second gas-liquid separation to obtain a produced liquid phase and a produced gas phase; c. The produced liquid phase is heat exchanged with the hot liquid phase, and the produced liquid phase after heat exchange is circulated back to the natural gas hydrate reservoir, and the hot liquid phase is circulated back to the abandoned thermal recovery reservoir after heat exchange.

[0008] The second aspect of the present invention provides a system for developing a natural gas hydrate reservoir, the system comprising: a natural gas hydrate reservoir, including a central well and a corner well, a second gas-liquid separation device is arranged at the outlet of the corner well for separating the produced flow to obtain a produced liquid phase and a produced gas phase, and the central well is used to separate the produced liquid phase after heat exchange and the hot CO 2 Flow into gas hydrate reservoirs; abandoned thermal recovery reservoirs, including CO 2 The first gas-liquid separation device is set at the outlet of the hot logistics production well to separate the hot CO 2 Logistics and thermal phase, CO 2 The logistics injection well is used to transfer the liquid phase and CO after the hot liquid phase heat exchange. 2 The logistics raw material is introduced into the abandoned thermal recovery oil reservoir; the heat exchange device is used for heat exchange between the hot liquid phase separated by the first gas-liquid separation device and the produced liquid phase separated by the second gas-liquid separation device; and, CO 2 Logistics raw material supply device and produced gas phase enrichment device.

[0009] Through the above technical solution, the present invention has the following advantages:

[0010] 1. The present invention utilizes CO 2 Developing natural gas hydrate reservoirs with residual heat from thermal recovery oil reservoirs can significantly reduce the heat injection cost of hydrate reservoirs, overcoming the problem of too high heat injection cost in traditional heat injection recovery methods;

[0011] 2. The present invention uses the extracted hot CO 2Reinject it into the gas hydrate reservoir, and use a heat exchanger to extract heat energy from the produced hot water, heat the produced water from the gas hydrate reservoir and inject it back into the gas hydrate reservoir, promote the decomposition of hydrates in the gas hydrate reservoir, and help improve the development capacity of the gas hydrate reservoir;

[0012] 3. The present invention injects CO into the abandoned thermal recovery reservoir. 2 The produced hot CO 2 Reinjection into natural gas hydrate reservoirs can achieve CO 2 Storage to reduce greenhouse effect;

[0013] 4. The target natural gas hydrate reservoir and the abandoned thermal oil reservoir of the present invention are preferably developed using the same offshore platform, which is beneficial to reducing the development costs of the hydrate reservoir and the thermal oil reservoir. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a system schematic diagram and flow chart for developing natural gas hydrate reservoirs according to a preferred embodiment of the present invention.

[0015] Description of Reference Numerals

[0016] 1- natural gas hydrate reservoir, 2- top and bottom caprock, 3- abandoned thermal recovery reservoir, 4- injection well, 5- production well, 6- center well, 7- corner well, 8- CO 2 Logistics raw material supply device, 9-abandoned thermal recovery oil reservoir hot logistics separation device, 10-heat exchange device, 11-natural gas hydrate reservoir production logistics separation device, 12-produced gas phase enrichment device. DETAILED DESCRIPTION

[0017] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0018] The present invention provides a method for developing a natural gas hydrate reservoir, the method comprising: a. 2 The material flow is introduced into the abandoned thermal recovery reservoir to obtain hot material flow, which is then separated into hot CO after the first gas-liquid separation. 2 Logistics and hot liquid phase; b. Heat CO 2 The logistics is passed into the natural gas hydrate reservoir to obtain the produced logistics, and the produced logistics undergoes a second gas-liquid separation to obtain a produced liquid phase and a produced gas phase; c. The produced liquid phase is heat exchanged with the hot liquid phase, and the produced liquid phase after heat exchange is circulated back to the natural gas hydrate reservoir, and the hot liquid phase is circulated back to the abandoned thermal recovery reservoir after heat exchange.

[0019] According to a preferred embodiment of the present invention, the reservoir temperature of the abandoned thermal recovery oil reservoir is not less than 100° C. By adopting the above preferred solution, the heat injection cost for developing natural gas hydrate reservoirs can be further reduced.

[0020] According to a preferred embodiment of the present invention, the thickness of the natural gas hydrate reservoir is not less than 20 m, and the permeability is not less than 50 mD.

[0021] According to a preferred embodiment of the present invention, the development method of the natural gas hydrate reservoir is five-point well network depressurization development; preferably, when the five-point well network depressurization development is carried out, the distance between the central well and any corner well should be no less than 70m, and the bottom hole flow pressure range is 1.5-6MPa. By adopting the above preferred scheme, the heat injection cost of developing the natural gas hydrate reservoir can be further reduced.

[0022] According to a preferred embodiment of the present invention, the CO 2 The speed of logistics into abandoned thermal recovery reservoir is 100-500m 3 By adopting the above preferred solution, the heat injection cost for developing natural gas hydrate reservoirs can be further reduced.

[0023] According to a preferred embodiment of the present invention, in the produced gas phase, the critical daily gas production is 1 / 2-1 / 5 of the maximum daily gas production. When the average daily gas production of the natural gas hydrate reservoir is lower than the critical daily gas production, the well is shut down to terminate the production.

[0024] According to a preferred embodiment of the present invention, the heat exchange method is countercurrent heat exchange. By adopting the above preferred solution, the heat injection cost for developing natural gas hydrate reservoirs can be further reduced.

[0025] According to a preferred embodiment of the present invention, at least one CO 2 a stream injection well and at least one hot stream production well.

[0026] According to a preferred embodiment of the present invention, the natural gas hydrate reservoir and the abandoned thermal oil reservoir are developed using the same offshore platform. The aforementioned preferred solution is conducive to reducing the development costs of the hydrate reservoir and the thermal oil reservoir.

[0027] The present invention provides a system for developing a natural gas hydrate reservoir, the system comprising:

[0028] The natural gas hydrate reservoir includes a central well and a corner well. A second gas-liquid separation device is provided at the outlet of the corner well to separate the produced flow to obtain a produced liquid phase and a produced gas phase. The central well is used to separate the produced liquid phase after heat exchange and the hot CO 2The logistics is passed into the natural gas hydrate reservoir;

[0029] Abandoned thermal recovery reservoirs, including CO 2 The first gas-liquid separation device is set at the outlet of the hot logistics production well to separate the hot CO 2 Logistics and thermal phase, CO 2 The logistics injection well is used to transfer the liquid phase and CO after the hot liquid phase heat exchange. 2 Logistics raw materials are passed into abandoned thermal recovery reservoirs;

[0030] A heat exchange device, used for heat exchange between the hot liquid phase separated by the first gas-liquid separation device and the produced liquid phase separated by the second gas-liquid separation device;

[0031] And, CO 2 Logistics raw material supply device and produced gas phase enrichment device.

[0032] According to a preferred embodiment of the present invention, a pumping device and / or a switch is provided on the communication passage of each unit.

[0033] like Figure 1 The present invention provides a system schematic diagram and flow chart for developing natural gas hydrate reservoirs. Figure 1 The process for developing a gas hydrate reservoir carried out by the device shown includes:

[0034] a. Put CO 2 CO in logistics raw material supply units 2 The logistics is introduced into the abandoned thermal recovery oil reservoir through the injection well, and the production well obtains the hot logistics. The hot logistics passes through the first gas-liquid separation of the hot logistics separation device of the abandoned thermal recovery oil reservoir to obtain hot CO 2 Logistics and hot liquid phase; b. Heat CO 2 The logistics is passed into the natural gas hydrate reservoir through the central well, and the corner wells obtain the produced logistics. The produced logistics passes through the second gas-liquid separation of the natural gas hydrate reservoir produced logistics separation device to obtain the produced liquid phase and the produced gas phase; c. The produced liquid phase and the hot liquid phase are passed into the heat exchange device for heat exchange. The produced liquid phase after heat exchange is circulated back to the natural gas hydrate reservoir from the central well. After heat exchange, the hot liquid phase is circulated back to the abandoned thermal recovery oil reservoir from the injection well, and the produced gas phase is passed into the produced gas phase enrichment device.

[0035] The present invention will be described in detail below through examples.

[0036] Example 1

[0037] Development of Gas Hydrate Reservoirs:

[0038] (1) Selection of gas hydrate reservoirs and abandoned heavy oil thermal recovery reservoirs: Based on the well logging and deep seabed reflection data in the study area, a gas hydrate reservoir with a thickness of 25 m and a permeability of 100 mD was selected as the target for exploitation. Based on the geographical location of the target gas hydrate reservoir, an abandoned heavy oil thermal recovery reservoir with a reservoir temperature of 120 °C was selected nearby;

[0039] (2) Depressurization method for exploiting natural gas hydrate reservoirs: A five-point well pattern with 1 central well and 4 corner wells is used to depressurize and exploit natural gas hydrate reservoirs. The distance between the central well and the corner wells is 75 m, and the bottom hole flowing pressure is 4 MPa.

[0040] (3) Select injection wells and production wells, and inject CO into the injection wells 2 , Production well production: select two abandoned wells with complete wellbore structure with a distance of 75m in the abandoned heavy oil thermal recovery reservoir and no cross-flow channel between the wells, one of which is used as an injection well and the other as a production well. 3 CO is injected into the injection well at a rate of / d 2

[0041] (4) CO produced from production wells 2 The CO in the produced fluid of the production well is recycled after the water is captured by thermal energy: the surface separation device of the abandoned heavy oil thermal recovery reservoir is used to separate the CO 2 The produced water in the corner wells is separated and injected into the central well, the water in the produced fluid in the production well is transported to the high-temperature working fluid inlet end of the heat exchanger, flows out from the high-temperature working fluid outlet end after heat exchange and is reinjected into the abandoned heavy oil thermal recovery reservoir through the injection well, the produced water in the corner wells is separated by a ground separation device for the natural gas hydrate reservoir and transported to the low-temperature working fluid inlet end of the heat exchanger, flows out from the low-temperature working fluid outlet end after heat exchange and is reinjected into the natural gas hydrate reservoir through the central well, the produced gas in the corner wells directly enters the gas storage tank, and the heat exchange mode of the heat exchanger is countercurrent heat exchange;

[0042] (5) When the average daily gas production of the natural gas hydrate reservoir is lower than the critical daily gas production, production is stopped: the critical daily gas production (20000m 3 / d) is the maximum daily gas production (80000m 3 / d) is 1 / 4.

[0043] The target natural gas hydrate reservoir and the abandoned heavy oil thermal recovery reservoir are developed on the same offshore platform.

[0044] Example 2

[0045] Development of Gas Hydrate Reservoirs:

[0046] (1) Selection of gas hydrate reservoirs and abandoned heavy oil thermal recovery reservoirs: Based on the well logging and deep seabed reflection data in the study area, a gas hydrate reservoir with a thickness of 40 m and a permeability of 120 mD was selected as the target for exploitation. Based on the geographical location of the target gas hydrate reservoir, an abandoned heavy oil thermal recovery reservoir with a reservoir temperature of 110 °C was selected nearby;

[0047] (2) Depressurization method for exploiting natural gas hydrate reservoirs: A five-point well pattern with 1 central well and 4 corner wells is used to depressurize and exploit natural gas hydrate reservoirs. The distance between the central well and the corner wells is 90 m, and the bottom hole flowing pressure is 5 MPa.

[0048] (3) Select injection wells and production wells, and inject CO into the injection wells 2 , Production well production: select two abandoned wells with intact wellbore structure with a distance of 90m in the abandoned heavy oil thermal recovery reservoir and no cross-flow channel between the wells, one of which is used as an injection well and the other as a production well. 3 CO is injected into the injection well at a rate of / d 2

[0049] (4) CO produced from production wells 2 The CO in the produced fluid of the production well is recycled after the water is captured by thermal energy: the surface separation device of the abandoned heavy oil thermal recovery reservoir is used to separate the CO 2 The produced water in the corner wells is separated and injected into the central well, the water in the produced fluid in the production well is transported to the high-temperature working fluid inlet end of the heat exchanger, flows out from the high-temperature working fluid outlet end after heat exchange and is reinjected into the abandoned heavy oil thermal recovery reservoir through the injection well, the produced water in the corner wells is separated by a ground separation device for the natural gas hydrate reservoir and transported to the low-temperature working fluid inlet end of the heat exchanger, flows out from the low-temperature working fluid outlet end after heat exchange and is reinjected into the natural gas hydrate reservoir through the central well, the produced gas in the corner wells directly enters the gas storage tank, and the heat exchange mode of the heat exchanger is countercurrent heat exchange;

[0050] (5) When the average daily gas production of the natural gas hydrate reservoir is lower than the critical daily gas production, production is stopped: the critical daily gas production (30000m 3 / d) is the maximum daily gas production (150000m 3 / d) is 1 / 5.

[0051] The target natural gas hydrate reservoir and the abandoned heavy oil thermal recovery reservoir are developed on the same offshore platform.

[0052] Example 3

[0053] Development of Gas Hydrate Reservoirs:

[0054] (1) Selection of gas hydrate reservoirs and abandoned heavy oil thermal recovery reservoirs: Based on the well logging and deep seabed reflection data in the study area, a gas hydrate reservoir with a thickness of 25 m and a permeability of 60 mD was selected as the target for exploitation. Based on the geographical location of the target gas hydrate reservoir, an abandoned heavy oil thermal recovery reservoir with a reservoir temperature of 130 °C was selected nearby;

[0055] (2) Depressurization method for exploiting natural gas hydrate reservoirs: A five-point well pattern with 1 central well and 4 corner wells was used to depressurize and exploit natural gas hydrate reservoirs. The distance between the central well and the corner wells was 100 m, and the bottom hole flowing pressure was 6 MPa.

[0056] (3) Select injection wells and production wells, and inject CO into the injection wells 2 , Production well production: select two abandoned wells with complete wellbore structure with a distance of 75m in the abandoned heavy oil thermal recovery reservoir and no cross-flow channel between the wells, one of which is used as an injection well and the other as a production well. 3 CO is injected into the injection well at a rate of / d 2

[0057] (4) CO produced from production wells 2 The CO in the produced fluid of the production well is recycled after the water is captured by thermal energy: the surface separation device of the abandoned heavy oil thermal recovery reservoir is used to separate the CO 2 The produced water in the corner wells is separated and injected into the central well, the water in the produced fluid in the production well is transported to the high-temperature working fluid inlet end of the heat exchanger, flows out from the high-temperature working fluid outlet end after heat exchange and is reinjected into the abandoned heavy oil thermal recovery reservoir through the injection well, the produced water in the corner wells is separated by a ground separation device for the natural gas hydrate reservoir and transported to the low-temperature working fluid inlet end of the heat exchanger, flows out from the low-temperature working fluid outlet end after heat exchange and is reinjected into the natural gas hydrate reservoir through the central well, the produced gas in the corner wells directly enters the gas storage tank, and the heat exchange mode of the heat exchanger is countercurrent heat exchange;

[0058] (5) When the average daily gas production of the natural gas hydrate reservoir is lower than the critical daily gas production, production is stopped: the critical daily gas production (8000m 3 / d) is the maximum daily gas production (32000m 3 / d) is 1 / 4.

[0059] The target natural gas hydrate reservoir and the abandoned heavy oil thermal recovery reservoir are developed on the same offshore platform.

[0060] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for developing a natural gas hydrate reservoir, It is characterized in that The method includes: a. Put CO 2 The material flow is introduced into the abandoned thermal recovery reservoir to obtain hot material flow, which is then separated into hot CO after the first gas-liquid separation. 2 Logistics and hydrothermal phases; b. Heat CO 2 The logistics is introduced into the natural gas hydrate reservoir to obtain a produced logistics, and the produced logistics is subjected to a second gas-liquid separation to obtain a produced liquid phase and a produced gas phase; c. The produced liquid phase is heat exchanged with the hot liquid phase, and the produced liquid phase after heat exchange is circulated back to the natural gas hydrate reservoir, and the hot liquid phase is circulated back to the abandoned thermal oil reservoir after heat exchange.

2. The method according to claim 1, in, The reservoir temperature of the abandoned thermal recovery oil reservoir is not less than 100°C.

3. The method according to claim 1 or 2, in, The thickness of the natural gas hydrate reservoir is not less than 20m and the permeability is not less than 50mD.

4. The method according to any one of claims 1 to 3, in, The development method of the natural gas hydrate reservoir is five-point well network pressure reduction development; preferably, When the five-point method well network is used for pressure reduction development, the distance between the central well and any corner well should be no less than 70m, and the bottom hole flow pressure range is 1.5-6MPa.

5. The method according to any one of claims 1 to 4, in, The CO 2 The speed of logistics into abandoned thermal recovery reservoir is 100-500m 3 / d; and / or In the produced gas phase, the critical daily gas production is 1 / 2-1 / 5 of the maximum daily gas production.

6. The method according to any one of claims 1 to 5, in, The heat exchange method is countercurrent heat exchange.

7. The method according to any one of claims 1 to 6, in, There is at least one CO 2 a stream injection well and at least one hot stream production well.

8. The method according to any one of claims 1 to 7, in, The natural gas hydrate reservoir and the abandoned thermal oil reservoir are developed using the same offshore platform.

9. A system for developing a natural gas hydrate reservoir, It is characterized in that The system includes: The natural gas hydrate reservoir includes a central well and a corner well. A second gas-liquid separation device is provided at the outlet of the corner well to separate the produced flow to obtain a produced liquid phase and a produced gas phase. The central well is used to separate the produced liquid phase after heat exchange and the hot CO 2 The logistics is passed into the natural gas hydrate reservoir; Abandoned thermal recovery reservoirs, including CO 2 The first gas-liquid separation device is set at the outlet of the hot logistics production well to separate the hot CO 2 Logistics and thermal phase, CO 2 The logistics injection well is used to transfer the liquid phase and CO after the hot liquid phase heat exchange. 2 Logistics raw materials are passed into abandoned thermal recovery reservoirs; A heat exchange device, used for heat exchange between the hot liquid phase separated by the first gas-liquid separation device and the produced liquid phase separated by the second gas-liquid separation device; And, CO 2 Logistics raw material supply device and produced gas phase enrichment device.

10. The system according to claim 9, in, A pumping device and / or a switch is provided on the communication passage of each unit.

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