Geothermal energy, differential pressure energy and pressure solution gas multi-energy fusion comprehensive development and utilization method

Abstract

The present application relates to the technical field of oil and gas engineering, and particularly relates to a method for comprehensive development and utilization of geothermal energy, pressure difference energy and pressure solution gas, which comprises a first type of development well and a second type of development well, the first type of development well is used for mining natural gas, and the first type of development well is arranged at the top position of a trap structure where pressure solution gas is located; the second type of development well is used for mining high-heat-energy formation water, and the second type of development well is arranged at the bottom position of the trap structure where pressure solution gas is located, wherein the natural gas mined by the first type of development well can be used for pressure difference power generation, and the high-heat-energy formation water mined by the second type of development well can be used for geothermal / dynamic energy power generation. The system and method provided by the present application can realize the coordinated development of high-heat-energy formation water, pressure solution gas and free natural gas under high-temperature and high-pressure conditions, and realize the multi-energy fusion efficient development and utilization of geothermal energy, pressure difference energy, pressure solution gas and natural gas.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field development engineering technology, and in particular relates to a method for the integrated development and utilization of geothermal energy, differential pressure energy and pressure dissolved gas. Background Technology

[0002] With the continued growth of global energy demand, the development of conventional oil and gas reservoirs has gradually entered the later stages, with problems such as decreasing resource volume, increased extraction difficulty, and rising costs becoming increasingly prominent. Conventional reservoirs are mainly concentrated in shallow and medium-deep layers. After long-term development, their resource potential is nearing depletion, and the remaining resources are mostly distributed in areas with complex geological conditions and high development difficulty. This situation has prompted the energy industry to turn its attention to unconventional reservoirs such as shale gas, natural gas hydrates, and pressure-dissolved gas. There are many types of proven natural gas accumulation. The most common natural gas occurrence states include free gas and water-dissolved gas. The former is the commonly understood accumulated free gas, i.e., conventional gas layers, while the latter is natural gas dissolved in water. However, gas-water coexistence phenomena are observed in high-temperature and high-pressure reservoirs, such as pressure-dissolved gas zones. These zones contain a certain amount of dispersed free gas and saturated dissolved gas. The natural gas contained in the gas-water zone and water-dissolved gas within these high-pressure reservoirs is called pressure-dissolved gas. At the same time, due to the effects of high temperature and pressure, the fluids within high-pressure reservoirs have characteristics such as high kinetic energy / pressure energy and high thermal energy.

[0003] Developing such pressure-dissolved gas reservoirs using conventional methods would lead to rising bottom water, high reservoir abandonment pressure, and a massive amount of residual pressure-dissolved gas and water-dissolved gas within the structure, making it difficult to maximize economic benefits. Therefore, to improve the development efficiency of pressure-dissolved gas, this invention provides a multi-energy integrated development and utilization method combining geothermal energy, pressure differential energy, and pressure-dissolved gas. Summary of the Invention

[0004] The purpose of this invention is to provide a method for the integrated development and utilization of geothermal energy, differential pressure energy, and pressure dissolved gas, in order to achieve integrated utilization of multiple energy sources while improving the overall development effect within the trap structure.

[0005] To achieve the above objectives, the present invention provides a pressure dissolved gas development system, comprising the following technical features:

[0006] The first type of development well is used to extract natural gas and is located at the top of the trap structure where the pressure-dissolved gas is located.

[0007] The second type of development well is used to extract formation water and is located at the bottom of the trap structure where the pressure-dissolved gas is located.

[0008] Furthermore, the formation temperature of the reservoir containing the dissolved gas is greater than 150°C, and the pressure coefficient is greater than 1.5.

[0009] Furthermore, the formation water extracted from the second type of development well can be used for geothermal / kinetic power generation.

[0010] Furthermore, the wellhead production of the second type of development well is greater than 800 cubic meters per day.

[0011] Furthermore, the natural gas extracted from the first type of development well is used for differential pressure power generation.

[0012] Furthermore, the number of the first type of development well and the second type of development well is one or more.

[0013] On the other hand, the present invention provides a method for the integrated development and utilization of geothermal energy, differential pressure energy, and dissolved gas, comprising the following steps:

[0014] Drill exploration wells to predict the geological reserves of dissolved gas, test the formation water and physical properties of dissolved gas in the dissolved gas reservoir, and determine its exploitability.

[0015] Drill a second type of development well, which is located at the bottom of the trap structure where the pressure-dissolved gas is located, and use the second type of development well to extract formation water;

[0016] Drill a first-type development well, which is located at the top of the trap structure where the pressure-dissolved gas is located. When the formation pressure drops to a preset pressure value, the first-type development well is used to extract formation natural gas.

[0017] Furthermore, this also includes determining reserves using a material balance equation, wherein the material balance equation is: GB gi =(GG p B g +(W e -W p B w +G transition,initial (B gi -B g )+[V w,initial R swi -(V w,initia +W e / B w -W p )R sw B g

[0018] Where G represents the original geological reserves, G p To calculate the cumulative gas production, B g W is the volume coefficient of the gas phase in its current state. e For water intrusion; W p B represents the cumulative water production. w B is the volume coefficient of the aqueous phase; giV is the volume coefficient of the gas phase in its initial state; w,initial R represents the initial volume of the water body. swi R represents the initial dissolved gas-to-water ratio. swi This represents the dissolved air-to-water ratio at the current state.

[0019] This invention provides a method for the integrated development and utilization of geothermal energy, differential pressure energy, and dissolved gas. A second type of development well is set up to extract formation water under high temperature and high pressure conditions, and this high-temperature formation water is used for geothermal / kinetic power generation. The development of formation water leads to the conversion of unconventional natural gas such as dissolved gas and water-soluble gas into free gas, thereby increasing gas reservoir reserves. Simultaneously, a first type of development well is set up to develop natural gas, utilizing the high-pressure characteristics of the extracted natural gas for differential pressure power generation. The method provided in this application achieves efficient development of dissolved gas and realizes the synergistic development of multiple energy sources, including geothermal energy, differential pressure energy, and dissolved gas, which is beneficial to the high efficiency and sustainable development of multi-energy systems. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the closed structure where the pressure dissolved gas is located according to the present invention and a conventional development method;

[0021] Figure 2 A schematic diagram of the integrated development and utilization method of geothermal energy, differential pressure energy and pressure dissolved gas provided by the present invention;

[0022] Figure 3 This is a schematic diagram of the capillary pressure curve and relative permeation curve of the closed structure where the pressure dissolved gas is located and its corresponding layer segment in this invention. Detailed Implementation

[0023] The present invention will now be described in detail with reference to the accompanying drawings.

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0025] Generally speaking, the vertical structure of conventional high-pressure natural gas reservoirs can be divided into gas layers, pressure-dissolved gas zones, and water layers. The main forms of natural gas occurrence are, in order, continuous free gas, dispersed free gas, saturated dissolved gas, and unsaturated dissolved gas, with the gas abundance per unit volume of formation decreasing in that order. Figure 1 The diagram illustrates a typical geological structural trap for pressure-dissolved gas, which refers to natural gas contained in the gas-water zone and water-dissolved gas zone within a high-pressure reservoir. Figure 1As shown, during the hydrocarbon accumulation process, due to the combined effects of gravity differentiation and capillary forces, the trap structure generally consists of, from bottom to top, a water layer 1, a water-dissolved gas zone 2, a pressure-dissolved gas zone 3, and a gas-top layer 4. The fluid at the bottom of water layer 1 is water, which is the pure water zone. The gas saturation S in the formation pore medium is... g This can be considered as 0. Above water layer 1 is water-soluble gas zone 2, which contains dissolved gas, existing in the porous medium in an unsaturated to saturated dissolved gas state. Above water-soluble gas zone 2 is pressure-soluble gas zone 3, which mainly consists of dispersed free gas and continuous free gas. The gas layer 4 only produces gas, such as... Figure 3 As shown, it corresponds to the pure gas zone (containing only bound water) with a water saturation lower than the bound water saturation and the storage zone (containing some free water) with a water saturation between the bound water saturation and the critical water saturation.

[0026] According to the basic principles of gas reservoir engineering, the thickness h of the pressure-dissolved gas zone 3 can be expressed as:

[0027]

[0028] Where h is the thickness of the pressure-dissolved gas zone 3. ρ is the capillary pressure of the gas-water two-phase system under formation conditions. w ρ g These are the densities of the aqueous phase and the gas phase, respectively.

[0029]

[0030] in, This refers to the two-phase capillary pressure under formation pressure; σ is the capillary pressure of mercury injection under laboratory conditions. gw The interfacial tension between the gas and water phases; θ gw σ is the contact angle between the gas and water phases; Hg The interfacial tension between mercury and air is mN / m; θ Hg This is the contact angle between mercury and air.

[0031] In the vertical direction, the pressure-dissolved gas zone 3 has the characteristics of continuous free gas, dispersed free gas and dissolved gas coexisting and being able to transform into each other. Among them, dispersed free gas refers to natural gas in the form of microbubbles or bubbles in the high-pressure reservoir space; continuous free gas refers to natural gas in the form of gas columns or continuous gas phases in the high-pressure reservoir space; and saturated dissolved gas refers to natural gas that is saturated with dissolved gas in the high-pressure formation water.

[0032] In existing technologies, such as Figure 1As shown, gas reservoir development often focuses on the development of the top layer 4. That is, when developing this type of pressure-dissolved gas reservoir using conventional methods, the first-type development well is typically located at the top of the gas trap structure to develop the natural gas in the top layer 4. However, after a certain development period, this method leads to the simultaneous emergence of gas and water from the first-type development well. Therefore, this development method suffers from drawbacks such as rapid rise of bottom water in the gas reservoir, high abandoned pressure in the gas reservoir, and the inability to further develop the huge amount of pressure-dissolved gas and water-dissolved gas remaining in the trap structure, making it difficult to maximize economic benefits. Furthermore, high-abundance pressure-dissolved gas is mostly located in high-temperature, high-pressure, deep geological environments, which further increases the difficulty of exploration and development.

[0033] Based on the technical problems of poor economic benefits and high development difficulty of pressure-dissolved gas in existing technologies, this application creatively proposes a new approach to gas reservoir development, which makes full use of the high temperature and high pressure storage characteristics of pressure-dissolved gas to achieve efficient and coordinated development of multiple energy sources such as geothermal energy, pressure difference energy and pressure-dissolved gas.

[0034] The formation and storage of a certain scale of pressure-dissolved gas reservoirs require two conditions: first, a high-pressure or ultra-high-pressure formation pressure system to provide favorable conditions for natural gas preservation; and second, a large amount of formation water within the pressure system to ensure that a large amount of natural gas can form a thick pressure-dissolved gas zone under ultra-high pressure, and that a large amount of free gas can be saturated and dissolved in the formation water. Based on the above characteristics of pressure-dissolved gas, this invention provides a method suitable for pressure-dissolved gas development, such as... Figure 3 As shown, a first-type development well is set at the top of the trap structure, primarily for natural gas extraction. A second-type development well is set in the water body section, for extracting formation water at the bottom of the solution-treated gas reservoir. The second-type development well is located at the bottom of the trap structure containing the gas reservoir, preferably in the stratum containing water layer 1. The first-type development well is located at the top of the trap structure containing the gas reservoir, preferably in the stratum containing the top gas layer 4.

[0035] During development, the second type of development wells extract water. Due to the extraction of formation water, the formation pressure decreases. As the pressure decreases, on the one hand, the saturated dissolved gas in the water-dissolved gas zone 2 undergoes desolvation, transforming into dispersed or continuous free gas; on the other hand, the decrease in formation pressure also causes a reduction in the thickness of the pressure-dissolved gas zone 3 (e.g., Figure 2 As shown in the diagram, the change in pore capillary pressure in the transition zone causes the dispersed free gas in the dissolved gas 2 to transform into continuous free gas. All of the above factors play a role in replenishing the gas source for the development of the gas reservoir. At the same time, the water production and pressure reduction of the second type of development well can also delay the rise of the bottom water in the first type of development well.

[0036] It should be noted that the first type of development well in this invention is mainly used for extracting natural gas, but the fluid extracted from the first type of development well may also include some formation water; similarly, the second type of development well is mainly used for extracting formation water, but the fluid extracted from the second type of development well may also include some natural gas (dissolved gas precipitation).

[0037] In the high-temperature and high-pressure storage environment, dissolved gas possesses high kinetic / pressure energy and thermal energy, providing favorable conditions for multi-energy integrated development. Considering that dissolved gas is located in a high-pressure and high-energy reservoir environment, the formation water extracted from the second type of development wells has a high temperature. Therefore, the formation water extracted from the second type of development wells can be used for geothermal / kinetic energy power generation. Meanwhile, the natural gas used in the first type of development wells has high pressure energy, so the natural gas extracted from the first type of development wells can be used for differential pressure power generation, thus achieving efficient utilization of pressure energy.

[0038] Based on this development approach, this application provides a method for developing pressure-dissolved gas, comprising the following steps:

[0039] Drill exploration wells, measure the parameters of free gas zone, pressure-dissolved gas zone, water-dissolved gas zone and pure water layer reservoir, predict the geological reserves of free gas, pressure-dissolved gas and water-dissolved gas, and test the formation water in pressure-dissolved gas reservoir as well as the physical properties of pressure-dissolved gas and water-dissolved gas.

[0040] Based on the reservoir characteristics of the pressure-dissolved gas zone, the changes in the thickness and gas saturation of the pressure-dissolved gas zone after the formation pressure decreases after a certain development period are predicted. The amount of pressure-dissolved gas and dissolved gas converted into free gas is predicted to determine the exploitability.

[0041] Drill a second type of development well, which is located at the bottom of the trap structure where the pressure-dissolved gas is located. Use the second type of development well to extract high-energy formation water for geothermal power generation. The number of second type development wells is set according to the pressure reduction requirements of the trap structure to control the rise of bottom water and promote the conversion of pressure-dissolved gas and dissolved gas into free gas.

[0042] Drilling a Type I development well, located at the top of the trap structure where the pressure-dissolved gas is located, is mainly used to produce free gas at the top of the structure as well as free gas converted from pressure-dissolved gas and dissolved gas during the development cycle.

[0043] Among them, by using well logging data from exploration wells, the initial thickness of pressure-dissolved gas, gas saturation and pressure-dissolved gas reserves can be determined. Combined with the temperature and pressure characteristics of the reservoir, the dissolved gas reserves of the tectonic water body can be determined.

[0044] After a certain period of mining, the formation pressure of Class I and Class II development wells decreases. The changes in the thickness and reserves of dissolved gas can be calculated. The established material balance method can be used to predict the amount of dissolved gas produced during the mining cycle, thereby conducting an assessment of economic and technical feasibility.

[0045] Furthermore, in order to improve the synergistic development effect of pressure-dissolved gas, a formation with a formation temperature greater than 150℃ and a pressure coefficient greater than 1.5 was selected as the development layer. Under the pressure and temperature conditions of this formation, there are thick pressure-dissolved gas zones and water-dissolved gas zones.

[0046] Furthermore, in order to improve the development effect of geothermal energy, it is preferred that the wellhead water production of the second type of development wells be greater than 800 cubic meters / day.

[0047] To determine the total gas production during the development cycle, the following methods can be used to estimate the changes in pressure dissolved gas geological reserves during the extraction cycle.

[0048] Furthermore, when predicting the changes in characteristic parameters of the pressure-dissolved gas zone reservoir after a certain development period and subsequent decrease in formation pressure, the following principles can be used. The total original geological reserves G consist of three parts:

[0049] G = G free,initial +G transition,initial +G dissolved,initial

[0050] Among them, G free,initial The primary free gas reserves in the top layer 4; G transition,initial G represents the original gas reserves in the dissolved gas 3. dissolved,initial This represents the original dissolved gas reserves in water-soluble gas zone 2.

[0051] As mining progresses, the formation pressure decreases, and the solubility R of the water-soluble gas zone increases. sw As the pressure dissolves, gas is released; the thickness of the gas-dissolved layer decreases, and the gas expands, releasing some of it into the top layer. Based on these physical processes, a dynamic mass balance equation can be established:

[0052] GB gi =(GG p B g +(W e -W p B w +G transition,initial (B gi -B g )+[V w,initial R swi -(V w,initia +W e / B w -W p )R swB g

[0053] Among them, G p To calculate the cumulative gas production, B g W is the volume coefficient of the gas phase in its current state. e For water intrusion; W p B represents the cumulative water production. w B is the volume coefficient of the aqueous phase; gi V is the volume coefficient of the gas phase in its initial state; w,initial R represents the initial volume of the water body. swi R represents the initial dissolved gas-to-water ratio. swi This represents the dissolved air-to-water ratio at the current state.

[0054] It should be noted that the original gas reserves in pressure-dissolved gas zone 3 can be obtained through the following methods:

[0055] G transition,initial =A*h transition,initial *φ*S g,initial / B gi

[0056] Where A is the area of ​​the pressure-dissolved gas in the gas reservoir; h transition,initial φ represents the initial thickness of the pressure-dissolved gas; φ represents the porosity of the pressure-dissolved gas; S g,initial The initial gas saturation of the pressure-dissolved gas is given by the above parameters, which can be obtained from exploration well logging data.

[0057] S within the transition zone g It varies with altitude and can be obtained using the following methods:

[0058]

[0059] As mining progresses, the formation pressure decreases, and gas expansion causes changes in gas saturation. When the formation pressure P... r As the pressure dissolved gas decreases, the volume of free gas in the gas increases, and the gas saturation S increases. g The change can be represented as:

[0060]

[0061] Among them, V t S represents the total pore volume; g0 ΔS represents the initial gas saturation. g To increase gas saturation; ΔV 游离 The volume of free gas released due to pressure drop consists of two parts:

[0062] 1) Capillary-driven gas-water redistribution: C f1) Pore compressibility coefficient; 2) Dissolved gas escape: It is related to the release of dissolved gas under Henry's Law.

[0063] Among them, P r0 P is the initial formation pressure. r Given the current formation pressure, S w0 S represents the initial water saturation. w This represents the current water saturation level.

[0064] When the formation pressure decreases, the effective stress increases, which leads to changes in the pore structure of the rock. The changes in porosity φ and permeability K can be calculated using models relating effective stress to porosity and permeability (such as empirical formulas obtained from stress-sensitive experiments).

[0065] A decrease in formation pressure will cause changes in the gas-water interfacial tension and wetting contact angle. Based on the new parameters after the decrease in formation pressure (the changed φ, K, σ...), gw Using models such as θ and capillary pressure, capillary pressures under different gas saturation levels were recalculated. By calculating the current gas-water interface thickness h, the remaining pressure-dissolved gas reserves after a certain extraction cycle can be estimated.

[0066] The method established in this application for developing pressure-dissolved gas can suppress bottom water rise and realize the comprehensive utilization of gas cap gas, pressure-dissolved gas, water-dissolved gas and geothermal energy. In addition, this application considers the impact of free gas, pressure-dissolved gas and water-dissolved gas in the trap on the reserves and provides corresponding material balance methods, which provide a theoretical basis for the dynamic prediction of gas reserves and the optimization of development strategies in pressure-dissolved gas reservoirs.

[0067] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for the integrated development and utilization of multiple energy sources in a pressure dissolved gas development system, characterized in that, The method is applied to pressure-dissolved gas development systems, where the formation temperature of the reservoir containing the pressure-dissolved gas is greater than 150°C and the pressure coefficient is greater than 1.

5. The steps are as follows: Drill exploration wells, test pressure-dissolved gas reservoir parameters, use material balance equations to predict the geological reserves of the reservoir, and test the physical properties of formation fluids; The mass balance equation is: GB gi =(GG p )B g +(W e -IN p )B w +G transition,initial (B gi -B g )+[V w,initial R swi -(V w,initial +W e / B w -IN p )R sw ]B g Where G represents the original geological reserves, G p To calculate the cumulative gas production, B g W is the volume coefficient of the gas phase in its current state. e For water intrusion; W p B represents the cumulative water production. w B is the volume coefficient of the aqueous phase; gi V is the volume coefficient of the gas phase in its initial state; w,initial R represents the initial volume of the water body. swi R represents the initial dissolved gas-to-water ratio. sw The dissolved gas-to-water ratio at the current state; G transition,initial This refers to the original gas reserves in the pressure-dissolved gas; The original geological reserves G are composed of the following: G=G free,initial +G transition,initial +G dissolved,initial Among them, G free,initial The original free gas reserves at the top of the gas layer; G transition,initial This refers to the original gas reserves in the pressure-dissolved gas zone; G dissolved,initial This represents the original dissolved gas reserves in the water-soluble gas zone. Based on the reservoir characteristics of the pressure-dissolved gas zone, predict the changes in reservoir characteristic parameters after the formation pressure decreases after a certain development period, predict the amount of pressure-dissolved gas and dissolved gas converted into free gas, and determine the exploitability. Drill a second type of development well, which is located at the bottom of the trap structure where the pressure-dissolved gas is located, and use the second type of development well to extract formation water; Drill a first-type development well, which is located at the top of the trap structure where the pressure-dissolved gas is located. When the formation pressure drops to a preset pressure value, the first-type development well is used to extract formation natural gas.

2. According to the multi-energy integrated development and utilization method described in claim 1, the wellhead production of the second type of development well is greater than 800 cubic meters per day.

3. The multi-energy integrated development and utilization method according to claim 1, wherein the natural gas extracted from the first type of development well is used for differential pressure power generation.

4. The multi-energy integrated development and utilization method according to claim 1, wherein the number of the first type of development well and the second type of development well is one or more.

5. The multi-energy integrated development and utilization method according to claim 1, wherein the characteristic parameters of the pressure-dissolved gas zone reservoir include thickness and gas saturation.

6. The method for obtaining the original gas reserves in the pressure-dissolved gas zone according to claim 1 is as follows: G transition,initial =A*h transition,initial *φ*S g,initial / B gi in, A represents the area of ​​the pressure-dissolved gas zone in the gas reservoir; h transition,initial φ represents the initial thickness of the pressure-dissolved gas zone; φ represents the porosity of the pressure-dissolved gas zone; S g,initial This represents the initial gas saturation of the pressure-dissolved gas zone; The initial gas saturation within the transition zone varies with altitude and is obtained using the following method:

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