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

Abstract

The invention relates to the technical field of petroleum and natural gas engineering, in particular to a geothermal energy, differential pressure energy and pressure-dissolved gas multi-energy fusion comprehensive development and utilization method which comprises a first-class development well and a second-class development well. The first-class development well is arranged at the top of the entrapment structure where the pressure-dissolved gas is located; the second-class development well is used for exploiting reservoir high-heat-energy formation water and arranged at the bottom of the entrapment structure where the pressure dissolved gas is located, natural gas exploited by the first-class development well can be used for differential pressure power generation, and the high-heat-energy formation water exploited by the second-class development well can be used for geothermal / kinetic energy power generation. According to the system and method, collaborative development of high-heat-energy formation water, pressure-dissolved gas and free natural gas under the high-temperature and high-pressure conditions can be achieved, and multi-energy fusion efficient development and utilization of geothermal energy, differential pressure energy, pressure-dissolved gas and natural gas are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil and gas field development engineering, and in particular relates to a method for comprehensive development and utilization of geothermal energy, pressure difference energy and pressure-dissolved gas multi-energy integration. Background Art

[0002] With the continued growth of global energy demand, the development of conventional oil and gas reservoirs has gradually entered a late stage, with declining resources, increasing extraction difficulties, and rising costs becoming increasingly prominent. Conventional reservoirs are primarily concentrated in shallow and medium-deep formations. After long-term development, their resource potential is nearing exhaustion, and remaining resources are mostly located in areas with complex geological conditions and difficult development. 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. Numerous natural gas reservoir types have been discovered. The most common forms of natural gas occurrence include free gas and water-dissolved gas. The former is typically concentrated free gas, often referred to as conventional gas formations, while the latter is natural gas dissolved in water. However, gas-water coexistence is observed in high-temperature and high-pressure reservoirs, such as pressure-dissolved gas zones, which contain a certain amount of dispersed free gas and saturated solution gas. The natural gas contained in these gas-water zones and water-dissolved gas within high-pressure reservoirs is called pressure-dissolved gas. Furthermore, due to the high temperature and high pressure, the fluids within high-pressure reservoirs possess high kinetic energy, high pressure energy, and high thermal energy.

[0003] Conventional development of such pressure-dissolved gas reservoirs can lead to rising bottom water levels, high reservoir abandonment pressures, and a significant amount of pressure-dissolved and water-dissolved gas remaining within the structure, making it difficult to maximize economic benefits. To improve the development efficiency of pressure-dissolved gas, the present invention provides a method for the integrated development and utilization of geothermal energy, pressure differential energy, and pressure-dissolved gas. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for the comprehensive development and utilization of geothermal energy, pressure differential energy and pressure-dissolved gas, so as to achieve comprehensive utilization of multiple energies while improving the overall development effect within the closed structure.

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

[0006] A first type of development well, wherein the first type of development well is used to extract natural gas and is located at the top of a trap structure where pressure-dissolved gas is located;

[0007] The second type of development well is used to produce formation water, and the second type of development well is set at the bottom of the trap structure where the pressure solution gas is located.

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

[0009] Furthermore, the formation water produced from the second type of development wells is used for geothermal / kinetic power generation.

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

[0011] Furthermore, the natural gas produced from the first type of development wells is used for pressure difference power generation.

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

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

[0014] Drilling exploration wells, predicting the geological reserves of pressure-dissolved gas, testing the physical properties of formation water and pressure-dissolved gas in pressure-dissolved gas reservoirs, and determining the feasibility of development;

[0015] Drilling a second type of development well, the second type of development well being located at the bottom of the trap structure where the pressure solution gas is located, and utilizing the second type of development well to produce formation water;

[0016] A first type of development well is drilled, 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 of development well is used to extract the formation natural gas.

[0017] Furthermore, it also includes determining reserves using the material balance equation, where 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] Among them, G is the original geological reserves, G p is the cumulative gas production, B g is the volume coefficient of the gas phase in the current state; W e is the water intrusion; W p is the cumulative water production; B w is the volume coefficient of the water phase; B giis the volume coefficient of the gas phase in the initial state; V w,initial is the volume of the water body in the initial state; R swi is the dissolved gas-water ratio in the initial state; R swi is the dissolved gas-water ratio in the current state.

[0019] The present invention provides a method for the comprehensive development and utilization of geothermal energy, pressure differential energy, and pressure-dissolved gas, wherein a second type of development well is set up to exploit formation water under high-temperature and high-pressure conditions, and the high-temperature formation water is used for geothermal / kinetic power generation; due to the effect of formation water development, unconventional natural gases such as pressure-dissolved gas and water-soluble gas will be converted into free gas, thereby increasing gas reservoir reserves; at the same time, a first type of development well is set up to develop natural gas, and the high-pressure characteristics of the produced natural gas are used to generate pressure differential power. The method provided by this application realizes the efficient development of pressure-dissolved gas, and realizes the coordinated development of multiple energy sources of geothermal energy, pressure differential energy, and pressure-dissolved gas, which is conducive to the high efficiency and sustainable development of multi-energy systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic diagram of the pressure-dissolved gas trap structure of the present invention and a conventional development method;

[0021] Figure 2 Schematic diagram of the method for comprehensive development and utilization of geothermal energy, pressure differential energy and pressure-dissolved gas provided by the present invention;

[0022] Figure 3 It is a schematic diagram of the capillary pressure curve and phase permeability curve corresponding to the trapped structure where the pressure solution gas is located and its layer section. DETAILED DESCRIPTION

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

[0024] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present 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 only used to explain the present invention and are not intended to limit the present 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 occurrence forms of natural gas are continuous free gas, dispersed free gas, saturated dissolved gas, and unsaturated dissolved gas, in order, with the gas abundance per unit volume of the formation decreasing in turn. Figure 1 The figure shows a typical geological structure trap diagram of pressure-dissolved gas, which refers to the natural gas stored in the gas-water zone and water-dissolved gas zone in the high-pressure reservoir. Figure 1As shown in the figure, during the accumulation process, due to the combined effects of gravity differentiation and capillary force, the trap structure is generally distributed from bottom to top with water layer 1, water-soluble gas zone 2, pressure-soluble gas zone 3, and gas cap zone 4. The fluid at the bottom of water layer 1 is water, that is, the pure water zone. The gas saturation S in the pore medium of the formation is g It can be regarded as 0. Above the water layer 1 is the water-soluble gas zone 2, which contains dissolved gas. This gas exists in the porous medium in the form of unsaturated-saturated dissolved gas. Above the water-soluble gas zone 2 is the pressure-dissolved gas zone 3, which is mainly composed of dispersed free gas and continuous free gas. The gas top layer 4 only produces gas, such as Figure 3 As shown in FIG, it corresponds to a pure gas zone (containing only irreducible water) with a water saturation lower than the irreducible water saturation and a reservoir zone (containing some free water) with a water saturation between the irreducible 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] Wherein, h is the thickness of the pressure-dissolved gas zone 3, is the capillary pressure of gas and water phases under formation conditions, ρ w , ρ g are the densities of water phase and gas phase, respectively.

[0029]

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

[0031] In the vertical direction, the pressure-dissolved gas zone 3 has the characteristics of coexistence of continuous free gas, dispersed free gas and dissolved gas and their mutual conversion. Among them, dispersed free gas refers to natural gas existing in the high-pressure storage space in the form of microbubbles and bubbles; continuous free gas refers to natural gas existing in the high-pressure storage space in the form of gas columns and continuous gas phases; saturated dissolved gas refers to natural gas dissolved saturated in high-pressure formation water.

[0032] In the prior art, Figure 1As shown, gas reservoir development often focuses on the gas cap 4. Conventional development of such pressure-dissolved gas reservoirs typically involves setting up first-type development wells at the top of the reservoir's trap structure to extract natural gas from the gas cap 4. However, after a certain period of development, this approach results in both gas and water being produced from the first-type development wells. This approach suffers from the disadvantages of rapid bottomwater buildup, high reservoir abandonment pressure, and the inability to further develop the vast amount of pressure-dissolved and water-dissolved gas remaining in the trap structure, making it difficult to maximize economic benefits. Furthermore, high-abundance pressure-dissolved gas is often found in deep, high-temperature, and high-pressure geological environments, further complicating exploration and development.

[0033] Based on the technical problems of poor economic benefits and great development difficulty of pressurized dissolved gas in the existing technology, this application creatively proposes a new idea for gas reservoir development, which fully utilizes the high temperature and high pressure storage characteristics of pressurized dissolved gas to achieve efficient coordinated development of multiple energy sources such as geothermal energy, pressure difference energy and pressurized 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 the preservation of natural gas; second, a large amount of formation water in the pressure system to ensure that a large amount of natural gas can form a thick pressure-dissolved gas zone under an overpressure environment and a large amount of free gas can be saturated and dissolved in the formation water. Based on the above characteristics of pressure-dissolved gas, the present invention provides a method suitable for pressure-dissolved gas development, such as Figure 3 As shown, a first type of development well is set at the top of the trap structure, primarily for extracting natural gas. A second type of development well is set in the water body, primarily for extracting formation water at the bottom of the pressure-dissolved gas reservoir. The second type of development well is located at the bottom of the trap structure containing the gas reservoir, preferably in the formation where water layer 1 is located. The first type of development well is located at the top of the trap structure containing the gas reservoir, preferably in the formation where gas cap layer 4 is located.

[0035] During the development process, the second type of development wells produce water. As the formation water is developed, the formation pressure decreases. As the pressure decreases, on the one hand, the saturated dissolved gas in the water-soluble gas zone 2 will be desolvated and converted into dispersed free gas or continuous free gas; on the other hand, the decrease in formation pressure will also cause the thickness of the pressure-dissolved gas 3 to decrease (e.g. Figure 2 Therefore, the change in pore capillary pressure in the transition zone causes the dispersed free gas in the water-soluble gas 2 to transform into continuous free gas. The above factors all 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 in the second type of development wells can also play a role in delaying the rise of bottom water in the first type of development wells.

[0036] It should be noted that the first type of development wells in the present invention are mainly used to extract natural gas, but the fluid produced by the first type of development wells may also include some formation water; similarly, the second type of development wells are mainly used to extract formation water, but the fluid produced by the second type of development wells may also include some natural gas (dissolved gas precipitation).

[0037] In high-temperature, high-pressure storage environments, pressure-dissolved gas is accompanied by high kinetic / pressure energy and thermal energy, creating favorable conditions for multi-energy development. Given the high-pressure, high-energy reservoir environment of pressure-dissolved gas, the formation water produced from Type II development wells has a relatively high temperature. Therefore, this water can be used for geothermal / kinetic power generation. Natural gas from Type I development wells, on the other hand, possesses a relatively high pressure energy, so it can be used for pressure differential power generation, achieving efficient utilization of pressure energy.

[0038] Based on this development idea, the present application provides a method for developing pressurized dissolved gas, comprising the following steps:

[0039] Drilling exploration wells, measuring reservoir parameters of free gas zones, pressure-dissolved gas zones, water-dissolved gas zones and pure water layers, predicting geological reserves of free gas, pressure-dissolved gas and water-dissolved gas, and testing the physical properties of formation water, pressure-dissolved gas and water-dissolved gas in pressure-dissolved gas reservoirs;

[0040] Based on the reservoir characteristics of the pressure-dissolved gas zone, the thickness and gas saturation of the pressure-dissolved gas zone are predicted after a certain period of development when the formation pressure drops. The amount of pressure-dissolved gas and dissolved gas converted to free gas is also predicted to determine the development feasibility.

[0041] Drilling second-type development wells, located at the bottom of the trapped structure where pressure-dissolved gas is located, to extract high-thermal formation water for geothermal kinetic power generation. The number of second-type development wells is set based on the pressure reduction requirements of the trapped structure to achieve the purpose of controlling the rise of bottom water and promoting the conversion of pressure-dissolved gas and dissolved gas into free gas;

[0042] The first type of development wells are drilled. The first type of development wells are located at the top of the closed structure where the pressure-dissolved gas is located. They are mainly used to produce free gas at the top of the structure and free gas converted from pressure-dissolved gas and dissolved gas during the development cycle.

[0043] Among them, the initial thickness of pressure-dissolved gas, gas saturation and pressure-dissolved gas reserves can be determined based on the exploration well logging data. Combined with the temperature and pressure characteristics of the reservoir, the dissolved gas reserves in the structural water body can be determined.

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

[0045] Furthermore, in order to improve the synergistic development effect of pressure-dissolved gas, formations with a formation temperature greater than 150°C and a pressure coefficient greater than 1.5 are selected as development layers. Under the pressure and temperature conditions of this formation, there are relatively thick pressure-dissolved gas zones and water-soluble 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 is greater than 800 cubic meters per day.

[0047] To determine the overall gas production during the development cycle, the following method can be used to estimate the changes in geological reserves of pressurized solution gas during the production cycle.

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

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

[0050] Among them, G free,initial is the original free gas reserves in the gas cap 4; G transition,initial is the original gas reserves in the pressure solution gas 3; G dissolved,initial is the original dissolved gas reserve in the water-soluble gas zone 2.

[0051] As mining progresses, the formation pressure decreases and the solubility of the water-soluble gas zone 2 R sw As the pressure drops, gas is released; the thickness of the pressure-dissolved gas zone 2 decreases, while the gas expands, and part of the gas is released into the gas top layer 1. Based on the above physical process, a dynamic material 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 sw]B g

[0053] Among them, G p is the cumulative gas production, B g is the volume coefficient of the gas phase in the current state; W e is the water intrusion; W p is the cumulative water production; B w is the volume coefficient of the water phase; B gi is the volume coefficient of the gas phase in the initial state; V w,initial is the volume of the water body in the initial state; R swi is the dissolved gas-water ratio in the initial state; R swi is the dissolved gas-water ratio in the current state.

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

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

[0056] Where A is the area of pressure-dissolved gas in the gas reservoir; h transition,initial is the initial thickness of the pressure-dissolved gas; φ is the porosity of the pressure-dissolved gas; S g,initial is the initial gas saturation of pressure-dissolved gas. The above parameters can be obtained based on the logging data of exploration wells.

[0057] In the transition zone, S g It varies with altitude and can be obtained by:

[0058]

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

[0060]

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

[0062] 1) Gas-water redistribution dominated by capillary forces: C fis the pore compression coefficient; 2) Dissolved gas escape: Related to solution gas release under Henry's law.

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

[0064] When formation pressure decreases, effective stress increases, causing changes in the rock's pore structure. Changes in porosity φ and permeability K can be calculated using models that relate effective stress to porosity and permeability (e.g., empirical formulas derived from stress sensitivity experiments).

[0065] The drop in formation pressure will cause the change of gas-water interfacial tension and wetting contact angle. According to the new parameters after the drop in formation pressure (the changed φ, K, σ gw , θ, etc.) and capillary pressure model to recalculate the capillary pressure at different gas saturations By calculating the current gas-water interface thickness h, we can further estimate the remaining pressure-dissolved gas reserves after a certain period of mining.

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

[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 in the scope of protection of the present invention.

Claims

1. A pressure-dissolved gas development system, characterized in that: The following technical features are included: Category 1 Development wells, wherein the first type of development wells are used to extract natural gas, and the first type of development wells are set at the top of the trap structure where the pressure-dissolved gas is located; The second type of development wells are used to exploit high-thermal energy formation water. The second type of development wells are set at the bottom of the trap structure where the pressure-dissolved gas is located.

2. The pressure-dissolved gas development system according to claim 1, wherein the formation temperature of the reservoir where the pressure-dissolved gas is located is greater than 150°C and the pressure coefficient is greater than 1.

5.

3. The pressure solution gas development system according to claim 1, wherein the high-thermal energy formation water produced by the second type of development well is used for geothermal / kinetic energy power generation.

4. The pressure solution gas development system according to claim 1, wherein the wellhead production of the second type of development well is greater than 800 cubic meters per day.

5. The pressure solution gas development system according to claim 1, wherein the natural gas produced by the first type of development wells is used for pressure difference power generation. 6 . The pressure solution gas development system according to claim 1 , wherein the number of the first type development well and the second type development well is one or more.

7. A method for comprehensive development and utilization of geothermal energy, pressure differential energy and pressure-dissolved gas, characterized in that: The following steps are involved: Drilling exploration wells, testing pressure-dissolved gas reservoir parameters, predicting geological reserves, and testing physical properties of formation fluids; Based on the reservoir characteristics of the pressure-dissolved gas zone, the changes in the characteristic parameters of the pressure-dissolved gas zone after the formation pressure drops after a certain period of development are predicted. The amount of pressure-dissolved gas and dissolved gas converted to free gas is predicted to determine the developability. Drilling a second type of development well, the second type of development well being located at the bottom of the trap structure where the pressure solution gas is located, and utilizing the second type of development well to produce formation water; A first type of development well is drilled, 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 of development well is used to extract the formation natural gas.

8. The method for comprehensive development and utilization of geothermal energy, pressure differential energy, and pressure-dissolved gas according to claim 7 further comprises determining reserves using a material balance equation, wherein the material 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,initia +W e / B w -IN p )R sw ]B g in, G is the original geological reserves, G p is the cumulative gas production, B g is the volume coefficient of the gas phase in the current state; W e is the water intrusion; W p is the cumulative water production; B w is the volume coefficient of the water phase; B gi is the volume coefficient of the gas phase in the initial state; V w,initial is the volume of the water body in the initial state; R swi is the dissolved gas-water ratio in the initial state; R swi is the dissolved gas-water ratio in the current state.

9. According to the method for comprehensive development and utilization of geothermal energy, pressure difference energy and pressure-dissolved gas according to claim 7, the characteristic parameters of the pressure-dissolved gas zone reservoir include thickness and gas saturation.

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