Multi-process integrated efficient exploitation method combining fracturing, exploitation and consolidation for hydrate reservoir

Abstract

A multi-process integrated efficient exploitation method combining fracturing, exploitation and consolidation for a hydrate reservoir, comprising: arranging, in a production well, pressure-resistant pipes for fluid injection that are independent of each other (104); providing openings (201) and nozzles for fracturing, consolidation and exploitation on the production well; respectively connecting the nozzles for fracturing and consolidation to corresponding injection systems by means of the pipes in the well; injecting a prepared fracturing fluid into a hydrate reservoir (103) to form hydraulic fractures; exploiting the reservoir by means of the production well by using depressurization and other approaches; injecting a prepared consolidation agent into the post-exploitation reservoir for consolidation; and repeating the described steps to carry out multi-process integrated efficient exploitation combining fracturing, exploitation and consolidation on the reservoir. In the method, the permeability of the reservoir around the production well is improved by means of the fracturing process, and the stability of the reservoir is improved by means of the consolidation process; thus, multi-process integrated exploitation enhances both the efficiency and safety of the exploitation process, providing a novel multi-process integrated efficient exploitation method for safe and efficient exploitation of deep-sea natural gas hydrates.

Description

A multi-process, efficient exploitation method for hydrate reservoirs, combining fracturing, extraction, and reinforcement. Technical Field

[0001] This invention belongs to the fields of energy engineering and geotechnical engineering technology, and relates to a method for reinforcing and safely and efficiently exploiting natural gas hydrate reservoirs. In particular, it relates to a multi-process combined efficient exploitation method of fracturing, exploitation and reinforcement of hydrate reservoirs, which is suitable for solving the problems of low gas production rate and easy instability of reservoirs during natural gas hydrate exploitation. Background Technology

[0002] Natural gas hydrates are considered the most promising clean energy source to replace conventional oil and gas. It is estimated that the reserves of natural gas hydrates in the deep-sea sediments of the South my country Sea are approximately 80 billion tons of oil equivalent. In my country, natural gas hydrates are mainly found in deep-sea sediments under high pressure and low temperature conditions. Currently, depressurization extraction is widely recognized as the most economical and effective method for natural gas hydrate extraction. The sediments in the South my country Sea hydrate reservoirs are mainly silty mudstone with an average grain size of approximately 12 μm and low permeability, averaging millidarcy level. During depressurization extraction, pressure transmission is slow, hindering the expansion of the depressurization zone and resulting in low extraction efficiency. Active hydraulic fracturing of the surrounding sediments to create fractures around the well is a common method for improving wellbore permeability in conventional underground energy extraction. If applied to natural gas hydrate extraction, it is expected to improve wellbore permeability while simultaneously expanding the depressurization decomposition zone, thereby increasing gas production efficiency.

[0003] Unlike traditional oil and gas extraction, natural gas hydrate extraction is a phase transition process in which the solid phase transforms into liquid water and gaseous methane. The loss of solid phase in hydrate-bearing sediments weakens the cementation and support between soil skeletons. The flow of liquid and gas two-phase flow in the pores often carries a large number of soil particles, increasing the risk of sand production and potentially causing well blockage. Japan's two natural gas hydrate trial productions in the Nankai Trough were forced to stop due to sand production problems. At the same time, the decomposition of the solid phase can reduce the strength of the skeleton, causing reservoir deformation, and even leading to well tilting or reservoir collapse, resulting in serious engineering disasters.

[0004] Currently, the low permeability of hydrate reservoirs in the South my country Sea leads to a small effective exploitation area and low gas production efficiency. Furthermore, the low permeability poses risks of sand production and reservoir instability / collapse, which are bottlenecks hindering the commercial exploitation of natural gas hydrates. Therefore, exploring an efficient and continuous exploitation method for low-permeability sedimentary reservoirs, while ensuring reservoir deformation remains within a safe and controllable range, is the primary key challenge to overcome in achieving the goal of efficient, safe, and long-term exploitation of natural gas hydrate energy. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a multi-process, efficient extraction method for hydrate reservoirs, encompassing fracturing, extraction, and reinforcement. This invention utilizes a specific viscosity fracturing agent containing a high-permeability porous material proppant to hydraulically fracture the reservoir, followed by extraction methods such as depressurization and thermal injection. Simultaneously, the extracted area is reinforced using a cementing agent. Based on this, unexploited areas can be further fracturing as needed to expand the hydrate extraction range, thus filling the gap in the field of multi-process extraction of hydrate reservoirs, integrating fracturing, extraction, and reinforcement.

[0006] The objective of this invention is achieved through the following technical solution: a multi-process combined efficient exploitation method for hydrate reservoirs, including fracturing, extraction, and reinforcement, comprising the following steps:

[0007] Step 1: Install liquid injection pipelines inside the well.

[0008] Several pressure-resistant pipes are installed inside the production well to transport fracturing fluid and reinforcement agent, respectively. The upper end of the pressure-resistant pipes is connected to the corresponding high-pressure liquid injection system on the offshore production platform.

[0009] Step 2: Install mining holes and nozzles on the mining shaft.

[0010] In the part of the production well that comes into contact with the natural gas hydrate reservoir, fracturing, reinforcement and production openings and nozzles are set at regular intervals. The nozzles extend outward from the openings and the outer end of the nozzles is flush with the sand screen.

[0011] Step 3: Connect the nozzles to the corresponding high-pressure liquid injection systems.

[0012] The fracturing and reinforcement nozzles are connected to the lower end of the corresponding pressure-resistant pipes, so that the fracturing and reinforcement nozzles on the production well are connected to the corresponding high-pressure liquid injection system on the offshore production platform, so as to control the fracturing fluid and reinforcement agent to be injected into the hydrate reservoir independently through the nozzles.

[0013] Step 4: Prepare fracturing fluid and inject it into the hydrate reservoir

[0014] Fracturing fluid is prepared and injected into the hydrate reservoir through the fracturing fluid nozzle on the production well using the high-pressure liquid injection system on the offshore production platform to form fracturing fractures in the hydrate reservoir, and the porous material proppant in the fracturing fluid is deposited and fixed in the fractures.

[0015] Step 5: Hydrate Extraction

[0016] The hydrate reservoir is depressurized or depressurization-thermal shock combined with the extraction well to enable the rapid decomposition and production of hydrates in the fracturing zone.

[0017] Step Six: Prepare and inject the consolidating agent into the hydrate reservoir for reinforcement.

[0018] Prepare a consolidating agent and use the high-pressure liquid injection system on the offshore mining platform to inject the consolidating agent into the hydrate reservoir after mining through the consolidating agent nozzle on the mining well. After standing for a period of time, the mined area is reinforced.

[0019] Step 7: Multi-process mining of hydrate reservoirs including fracturing, extraction, and reinforcement.

[0020] Based on the required hydrate extraction range, repeat steps four to six. First, fracture the unexploited hydrate reservoir to form a fractured zone. Then, extract the hydrate in the fractured zone. After the hydrate in the fractured zone is decomposed and extracted, inject a reinforcing agent to transform the fractured zone into a reinforced zone. Then, continue to fracture the unexploited hydrate reservoir to expand the fractured zone. Perform multi-process combined efficient extraction of the hydrate reservoir, including fracturing, extraction, and reinforcement.

[0021] Furthermore, in step one, the pipelines transporting different liquids within the mining well are independent, and the pipelines are pressure-resistant pipelines capable of withstanding the pressure difference between the inside and outside.

[0022] Furthermore, in step two, the well is provided with several mining openings, which serve as transmission channels for the production of liquid gas during the extraction of natural gas hydrates; the outside of the well is wrapped with a sand-proof screen.

[0023] Furthermore, in step two, the nozzles have circular nozzle holes, and each set of nozzles consists of fracturing fluid nozzles and reinforcement agent nozzles. The fracturing fluid nozzle has a nozzle hole for fracturing fluid spraying, and the reinforcement agent nozzle has a reinforcement agent mother liquor nozzle and a reinforcement agent reactant nozzle. Each set of nozzles surrounds a production well opening, and the nozzles extend outward from the well wall, pass through the sand control screen wrapped around the outside of the production well, and the outermost end of the nozzle is flush with the outermost end of the sand control screen.

[0024] Furthermore, in step four, the fracturing fluid is a liquid with viscosity, which can be a high-viscosity fracturing fluid or a low-viscosity fracturing fluid. The high-viscosity fracturing fluid includes guar gum fracturing fluid and silicone oil fracturing fluid, while the low-viscosity fracturing fluid includes sodium chloride solution fracturing fluid.

[0025] Furthermore, in step four, the proppant includes one or more of porous ceramic particles, porous calcium carbonate particles, and polyester fiber materials; the proppant is uniformly mixed in the fracturing fluid to form a suspension.

[0026] Furthermore, in step four, the high-pressure fluid injection system includes constant-pressure injection and constant-flow injection. The pressure or injection rate of the injected fracturing fluid is determined based on the mechanical parameters and pressure conditions of the hydrate reservoir obtained during pre-mining drilling, with a minimum injection pressure p. min The calculation formula is:

[0027] In the formula, K0 is the static earth pressure coefficient at that location in the hydrate reservoir, Φ is the internal friction angle of the sediments in the hydrate reservoir, ρ' is the average effective density of the hydrate reservoir and the overlying sediment layer, g is the gravitational acceleration, z is the burial depth of the hydrate reservoir at that location, and N P c is the cohesive coefficient of hydrates. h This represents the cohesive force of the hydrate.

[0028] Furthermore, in step six, the reinforcing agent consists of a reinforcing mother liquor and a reactant. The ratio of the reinforcing mother liquor to the reactant is determined according to the required reaction time and reinforcement strength. The reinforcing mother liquor is injected into the mined hydrated reservoir through the reinforcing mother liquor pipeline and the reinforcing mother liquor nozzle on the reinforcing agent nozzle for reinforcement. The reactant is injected into the mined hydrated reservoir through the reinforcing reactant pipeline 209 and the reinforcing reactant nozzle on the reinforcing agent nozzle for reinforcement. The reinforcement process is as follows: first, the reinforcing mother liquor is injected for a period of time, and then the reactant is injected to uniformly fill the pores of the soil skeleton. After standing for a period of time, the cement or crystals are generated, thus completing the reinforcement of the mined area.

[0029] Furthermore, when the reinforcing mother liquor and the reactant react, a cement or crystal is formed in the pores of the hydrate reservoir, and the formation principle is shown in the following formula:

[0030] The cement or crystals are porous and are formed at the contact points with the soil skeleton.

[0031] Furthermore, in step six, the pressure during reinforcement injection is less than or equal to the minimum injection pressure p of the fracturing fluid. min .

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] This invention is applicable to the field of offshore natural gas hydrate extraction. It can improve the permeability of the wellbore hydrate reservoir and form a dominant seepage path by using active fracturing. It can also reinforce the hydrate reservoir after fracturing by using chemical reaction or microbial induced crystallization reinforcement methods. Furthermore, through a multi-process combined method of fracturing-extraction-reinforcement, the fracturing area and hydrate decomposition area are repeatedly expanded to improve the efficiency of hydrate extraction and reservoir stability.

[0034] This invention presents a novel and clear approach, filling the gap in multi-process combined efficient extraction technology for natural gas hydrate reservoirs, including fracturing, extraction, and reinforcement. It provides new technology for the safe and efficient extraction of deep-sea natural gas hydrates, and solves the problems of low gas production rate due to low reservoir permeability and well blockage and reservoir instability caused by sand production during current natural gas hydrate extraction. Attached Figure Description

[0035] Figure 1 is a schematic diagram of the site layout and multi-process combined high-efficiency mining process of natural gas hydrate extraction in this invention, including fracturing, extraction and reinforcement. In Figure 1, (a) is a schematic diagram of the fracturing and extraction process; and (b) is a schematic diagram of the reinforcement and secondary fracturing process.

[0036] Figure 2 is a schematic diagram of the wellbore, nozzle arrangement, and internal pipeline structure in this invention; wherein, (a) in Figure 2 is a front view of the well; (b) in Figure 2 is a radial cross-sectional view of the well; (c) in Figure 2 is an axial cross-sectional view of the well; and (d) in Figure 2 is another axial cross-sectional view of the well.

[0037] Figure 3 is a flowchart of the multi-process combined high-efficiency mining method of hydrate reservoir fracturing-mining-consolidation in this invention.

[0038] In the diagram, the components are: reinforced zone 101, fracturing zone 102, hydrate reservoir 103, production well 104, overlying seawater 105, overlying soil layer 106, underlying layer 107, offshore production platform 108, production opening 201, fracturing fluid nozzle 202, reinforcer nozzle 203, production access channel 204, sand control screen 205, production well wall 206, fracturing fluid pipeline 207, reinforcer mother liquor pipeline 208, reinforcer reactant pipeline 209, reinforcer mother liquor nozzle 210, and reinforcer reactant nozzle 211. Detailed Implementation

[0039] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims. It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not intended to limit this application.

[0040] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0041] It should be understood that although the terms first, second, third, etc., may be used in this application to describe various information, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "in response to determination," or "includes." Moreover, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process or method that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process or method. Without further limitations, an element defined by the phrase "comprising a..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0042] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings. Unless otherwise specified, the features in the following embodiments and implementations can be combined with each other.

[0043] As shown in Figures 1 and 2, the hydrate reservoir 103 described in this invention is located in deep-sea seabed sediments. The hydrate reservoir 103 is covered from top to bottom by overlying seawater 105 and overlying soil 106, with an underlying layer 107 at the bottom. The multi-process combined high-efficiency extraction method of the hydrate reservoir using fracturing, extraction, and reinforcement of this invention involves firstly, the extraction well 104 penetrating from the offshore extraction platform 108 through the overlying seawater 105 and overlying soil 106 into the unextracted hydrate reservoir 103. The wellbore 206 is equipped with extraction openings 201, fracturing fluid nozzles 202, and reinforcement nozzles 203 at intervals. Four extraction openings 201 are symmetrically arranged circumferentially in the figures; however, the arrangement density can be changed according to requirements. The fracturing fluid nozzles 202 and reinforcement nozzles 203 form a group of nozzles surrounding the extraction openings 201. The outer side of the wellbore 206 is covered with a sand-proof screen 205, and the outermost end of the nozzle is flush with the outermost end of the sand-proof screen 205. Fracturing fluid pipeline 207, reinforcement agent mother fluid pipeline 208, and reinforcement agent reactant pipeline 209 are installed inside the wellbore 104 to connect the nozzle to the high-pressure liquid injection system on the offshore production platform 108. The pipelines inside the well correspond to the nozzles and are arranged symmetrically in a central manner. The produced liquid and gas are generated through the production channel 204 inside the well.

[0044] In this invention, fracturing, mining and reinforcement are carried out in sequence. The high-pressure pump of the high-pressure liquid injection system injects the fracturing fluid on the offshore mining platform 108 into the unmined hydrate reservoir 103 through the fracturing fluid pipeline 207 and the fracturing fluid nozzle 202, thereby generating fracturing fractures and forming a fracturing zone 102. The proppant in the fracturing fluid can prevent the fractures from closing. Extraction can be carried out using the depressurization method. After the hydrates in the fracturing zone 102 have decomposed, CaCl2, urea, and water are uniformly mixed in proportion on the offshore extraction platform 108 to prepare the consolidation mother liquor of the consolidation agent. DSM33 bacteria, urease, nutrient solution, and water are uniformly mixed in proportion to prepare the reaction agent of the consolidation agent. Using a high-pressure pump of the high-pressure liquid injection system, the consolidation mother liquor and the reaction agent of the consolidation agent are injected into the fracturing zone 102 through the consolidation agent mother liquor pipeline 208 and the consolidation agent reaction agent pipeline 209, respectively, via the consolidation agent nozzle 203. After standing for a period of time to allow crystallization and consolidation, the extracted fracturing zone 102 is transformed into the consolidation zone 101. After the consolidation zone 101 is consolidated, the high-pressure pump continues to inject fracturing fluid into the unextracted hydrate reservoir 103. Secondary fracturing transforms a portion of the unextracted hydrate reservoir 103 into the fracturing zone 102. The subsequent multi-stage process of extraction, consolidation, and fracturing is repeated to continuously expand the hydrate extraction range.

[0045] As shown in Figure 3, the embodiments of the present invention and their implementation process include the following steps:

[0046] Step 1: Install liquid injection pipelines inside the well.

[0047] Several pressure-resistant pipes are installed in the production well 104 to transport fracturing fluid and reinforcement agent, respectively. The upper end of the pressure-resistant pipes is connected to the corresponding high-pressure liquid injection system on the offshore production platform 108.

[0048] Furthermore, the pipelines for transporting different liquids within the mining well 104 are independent to ensure that the independent injection of different liquids can be controlled. The pipelines are pressure-resistant pipelines capable of withstanding internal and external pressure differences.

[0049] Specifically, four fracturing fluid pipelines 207, four consolidation agent mother liquor pipelines 208, and four consolidation agent reactant pipelines 209 are installed in the production well 104. The three types of pressure-resistant pipelines are respectively connected to the consolidation agent mother liquor nozzle 210 and the consolidation agent reactant nozzle 211 of the fracturing fluid nozzle 202 and the consolidation agent nozzle 203. The upper end of the pressure-resistant pipeline is connected to the corresponding high-pressure liquid injection system on the offshore production platform 108. They are used to transport fracturing fluid and consolidation agent, respectively. The pipelines transporting different liquids are independent to achieve independent injection control of different liquids.

[0050] Step 2: Install mining holes and nozzles on the mining shaft.

[0051] In the part of the production well 104 that comes into contact with the natural gas hydrate reservoir 103, fracturing, reinforcement and production openings and nozzles are set at regular intervals. The nozzles extend outward from the openings and the outer end of the nozzles is flush with the sand screen 205.

[0052] Furthermore, the production well 104 is provided with several production openings 201, which serve as transmission channels for the production of liquid gas during the extraction of natural gas hydrates; the outside of the production well 104 is wrapped with a sand-proof screen 205, which can prevent sand from the hydrate reservoir 103 from clogging the production openings 201 on the production well 104 and the liquid gas production channels including the production well 104 during the extraction process.

[0053] Furthermore, the nozzles have circular nozzle holes. Each set of nozzles consists of a fracturing fluid nozzle 202 and a consolidation agent nozzle 203. The fracturing fluid nozzle 202 has one nozzle hole for fracturing fluid ejection. The consolidation agent nozzle 203 has two nozzle holes for the consolidation mother liquor and the consolidation agent reactant ejection, respectively. Each set of nozzles surrounds a production well 201 to inject different liquids into the hydrate reservoir 103. The nozzles extend outward from the well wall 206 of the production well and pass through the sand control screen 205 wrapped around the outside of the production well 104. The outermost end of the nozzle is flush with the outermost end of the sand control screen 205.

[0054] Specifically, in the part of the production well 104 that contacts the unexploited natural gas hydrate reservoir 103, four circumferentially symmetrical production openings 201 are set at 2-meter intervals along the axis. Each production opening 201 is surrounded by one fracturing fluid nozzle 202 and one reinforcement nozzle 203. The nozzles extend outward from the opening and out of the production well wall 206, with the outer end of the nozzle flush with the sand screen 205.

[0055] Step 3: Connect the nozzles to the corresponding high-pressure liquid injection systems.

[0056] The fracturing and reinforcement nozzles are connected to the lower ends of the corresponding pressure-resistant pipes, so that the fracturing and reinforcement nozzles on the production well 104 are connected to the corresponding high-pressure liquid injection systems on the offshore production platform 108, so as to control the fracturing fluid and reinforcement agent to be injected independently into the hydrate reservoir 103 through the nozzles.

[0057] Specifically, the fracturing fluid nozzle 202 and the reinforcement agent nozzle 203 are respectively connected to the lower end of the corresponding pressure-resistant pipes, that is, the fracturing fluid nozzle 202 is connected to the lower end of the fracturing fluid pipe 207. The two nozzles (i.e., the reinforcement agent mother liquor nozzle 210 and the reinforcement agent reactant nozzle 211) provided on the reinforcement agent nozzle 203 are respectively connected to the lower end of the reinforcement agent mother liquor pipe 208 and the reinforcement agent reactant pipe 209. This allows the fracturing fluid nozzle 202 and the reinforcement agent nozzle 203 to be connected to the corresponding high-pressure liquid injection system on the offshore mining platform 108 through the corresponding pressure-resistant pipes. This enables the fracturing fluid and the reinforcement agent to be injected independently into the hydrate reservoir 103 through the corresponding fracturing fluid nozzle 202 and the reinforcement agent nozzle 203.

[0058] Step 4: Prepare fracturing fluid and inject it into the hydrate reservoir

[0059] Fracturing fluid is prepared and injected into the hydrate reservoir 103 through the fracturing fluid nozzle 202 on the production well 104 using the high-pressure liquid injection system on the offshore production platform 108. This forms fracturing fractures in the hydrate reservoir 103, and the porous proppant in the fracturing fluid is deposited and fixed in the fractures to support them and prevent them from closing. This can improve the permeability of the fracturing zone 102 and form a dominant seepage channel.

[0060] Furthermore, the fracturing fluid is a liquid with a specific viscosity. When injected into the hydrate reservoir 103, the pressure of the liquid is used to split the hydrate reservoir 103, forming fracturing fractures. The fracturing fluid can be a high-viscosity fracturing fluid such as guar gum or silicone oil, or a low-viscosity fracturing fluid such as sodium chloride solution. When the hydrate saturation of the hydrate reservoir 103 is high, a low-viscosity fracturing fluid can be used, which facilitates the removal of the fracturing fluid during extraction; when the hydrate saturation of the hydrate reservoir 103 is low, a high-viscosity fracturing fluid can be used, which can reduce the loss of fracturing fluid in the hydrate reservoir 103 and successfully split the hydrate reservoir 103.

[0061] The components of the guar gum fracturing fluid are: 0.55% guar gum powder, 0.6% crosslinking agent, 0.2% ammonium persulfate, 0.2% soybean lecithin, and water; the components of the sodium chloride solution fracturing fluid are: 3.5% sodium chloride aqueous solution.

[0062] Furthermore, the proppant in the fracturing fluid can be one or more of the following materials: porous ceramic particles, porous calcium carbonate particles, polyester fibers, etc. The proppant is uniformly mixed in the fracturing fluid to form a suspension, that is, the fracturing fluid is a suspension.

[0063] Furthermore, the high-pressure fluid injection system includes two injection methods: constant pressure injection and constant flow injection. Utilizing the high-pressure fluid injection system on the offshore mining platform 108, fracturing fluid is injected into the unexploited hydrate reservoir 103 through the fracturing fluid nozzle 202 to form fracturing fractures, thus converting a portion of the unexploited hydrate reservoir 103 into a fracturing zone 102. The injection pressure or injection rate of the fracturing fluid is determined based on the mechanical parameters and pressure conditions of the hydrate reservoir 103 obtained through pre-mining drilling. The minimum injection pressure p... min The specific calculation formula is shown in formula (1):

[0064] In the formula, K0 is the static earth pressure coefficient at the hydrate reservoir 103, Φ is the internal friction angle of the sediment in the hydrate reservoir 103, ρ' is the average effective density of the hydrate reservoir 103 and the overlying sediment layer, g is the gravitational acceleration, z is the burial depth of the hydrate reservoir 103, and N is the static earth pressure coefficient at the hydrate reservoir 103. P c is the cohesive coefficient of hydrates. h This represents the cohesive force of the hydrate.

[0065] The fracturing fluid creates splitting fractures in the hydrate reservoir 103. Subsequently, the porous proppant material in the fracturing fluid is deposited and fixed in the fractures, supporting the fractures, preventing the fractures from closing during the mining process, and improving the permeability of the fracturing zone 102.

[0066] Step 5: Hydrate Extraction

[0067] The hydrate reservoir 103 is exploited by depressurization or depressurization-thermal shock combined methods through the production opening 201 on the production well 104, so that the hydrate in the fracturing zone 102 can be rapidly decomposed and produced. The gas production duration is determined according to the gas production rate characteristics.

[0068] Step Six: Prepare and inject the consolidating agent into the hydrate reservoir for reinforcement.

[0069] A consolidating agent is prepared and injected into the hydrate reservoir 103 after extraction through the consolidating agent nozzle 203 on the extraction well 104 using the high-pressure liquid injection system on the offshore extraction platform 108. After a period of settling, the extracted area is reinforced.

[0070] Furthermore, the reinforcing agent consists of a reinforcing mother liquor and a reactant. The ratio of the reinforcing mother liquor to the reactant is determined according to the required reaction time and reinforcement strength. The reinforcing mother liquor and the reactant are injected into the mined hydrate reservoir 103 through their respective independent pressure-resistant pipes (i.e., the reinforcing mother liquor pipe 208 and the reinforcing reactant pipe 209) and the corresponding reinforcing mother liquor nozzle 210 and reinforcing reactant nozzle 211 on the reinforcing agent nozzle 203 for reinforcement. The reinforcement process is as follows: first, the reinforcing mother liquor is injected for a period of time, and then the reactant is injected to uniformly fill the pores of the soil skeleton. After standing for a period of time, the cement or crystals are generated to complete the reinforcement of the mined area and achieve the reinforcement effect.

[0071] Furthermore, when the mother liquor and the reactant react, a cement or crystal is formed in the pores of the hydrate reservoir 103, which can play a supporting and cementing role. The reaction between the two can be a chemical reaction or a biological reaction. The formation principle of the cement or crystal is shown in formula (2):

[0072] Furthermore, the resulting cement or crystals have high strength and are porous. The cement or crystals are mainly generated at the contact points of the soil skeleton, which play a role in cementing, fixing and reinforcing the soil skeleton, while maintaining its pore channels and not affecting the reservoir permeability.

[0073] Specifically, the concentration ratio of each component in the mother liquor of the consolidating agent is as follows: CaCl2 concentration 2 mol / L, urea concentration 3 mol / L, and sufficient water; the concentration ratio of each component in the reactant of the consolidating agent is as follows: nutrient solution 6 g / L, urease 2 g / L, lyophilized DSM33 bacteria 1 g / L, and sufficient water. The chemical reaction equations for the bacterial-induced formation of calcium carbonate crystals are shown in formulas (3) and (4):

[0074] Specifically, using the high-pressure liquid injection system on the offshore mining platform 108, the reinforcing mother liquor is first injected into the fractured zone 102 after mining through the reinforcing mother liquor nozzle 210 of the reinforcing agent nozzle 203 on the mining well 104. Then, the reactant is injected into the fractured zone 102 after mining through the reinforcing agent reactant nozzle 211 of the reinforcing agent nozzle 203 to fill the pores of the soil skeleton. The volume ratio of the reinforcing mother liquor and reactant injected into the hydrate reservoir 103 is 1:1. After standing for a period of time, calcium carbonate crystallizes and deposits, thus reinforcing the mined area.

[0075] Furthermore, the pressure during reinforcement injection should be less than or equal to the minimum injection pressure p of the fracturing fluid. min To ensure that the reinforcing agent can fully fill the pores between the soil skeleton without disturbing the soil skeleton, the injection pressure should not exceed the minimum injection pressure p. minUnder the premise of increasing the injection rate of the reinforcing agent as much as possible, the reinforcement efficiency can be improved.

[0076] Step 7: Multi-process mining of hydrate reservoirs including fracturing, extraction, and reinforcement.

[0077] Based on the required hydrate extraction range, steps four through six are repeated. First, the unexploited hydrate reservoir 103 is fractured to form a fracture zone 102. Then, the hydrate in the fracture zone 102 is extracted. After the hydrate in the fracture zone 102 is decomposed and extracted, a reinforcing agent is injected to transform the fracture zone 102 into a reinforced zone 101. Then, the unexploited hydrate reservoir 103 is fractured again to expand the fracture zone 102. The hydrate reservoir 103 is subjected to a multi-process combined efficient extraction of fracturing, extraction, and reinforcement. The range of the fracture zone 102 and the reinforced zone 101 is continuously expanded, the extraction range is increased, the permeability of the hydrate reservoir 103 and the stability of the soil skeleton around the extraction well 104 are improved, the extraction efficiency of depressurization and other methods is increased, and the risk of instability of the soil skeleton around the extraction well 104 is reduced.

[0078] Furthermore, based on parameters such as the thickness of hydrate reservoir 103, hydrate saturation of hydrate reservoir 103, permeability, and the required exploitation range of hydrate reservoir 103, the operations of steps four to six can be repeated multiple times for fracturing-exploitation-reinforcement. When performing the above operations on the extended area, the fracturing fluid and reinforcing agent can be re-formulated as needed, and the injection rate and injection pressure can be adjusted as required.

[0079] As can be seen from the implementation, this invention innovatively adopts a multi-process combined high-efficiency mining method of fracturing-production-reinforcement, which has the advantages of novel method, simple operation and clear process. It fills the gap in the multi-process combined high-efficiency mining technology of fracturing-production-reinforcement of natural gas hydrate reservoirs, provides new technology for the safe and efficient mining of deep-sea natural gas hydrates, can solve the problems of low gas production rate and easy instability of reservoirs during natural gas hydrate mining, and can achieve the goal of safe, stable and long-term sustainable mining of natural gas hydrates in the field.

[0080] It should be noted that the embodiments of this application are preferred for implementation and are not intended to limit the application in any way. The technical features or combinations of technical features described in the embodiments of this application should not be considered isolated; they can be combined with each other to achieve better technical effects. The scope of the preferred embodiments of this application may also include other implementations, and this should be understood by those skilled in the art to which the embodiments of this application pertain.

[0081] Techniques, methods, and apparatus known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and apparatus should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limiting. Therefore, other examples of exemplary embodiments may have different values.

[0082] The accompanying drawings in this application are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of this application, and are not intended to limit the implementation conditions of this application. Any modifications to the structure, changes in the proportional relationships, or adjustments to the size, without affecting the effects and purposes that this application can produce, should be within the scope covered by the technical content disclosed in this application.

[0083] The above description is merely a description of preferred embodiments of this application and is not intended to limit the scope of this application in any way. Any changes or modifications made by those skilled in the art based on the above-disclosed technical content should be considered as equivalent and valid embodiments and fall within the scope of protection of the technical solution of this application.

Claims

1. A multi-process integrated and efficient exploitation method for hydrate reservoirs, comprising fracturing, extraction, and reinforcement, characterized in that: Includes the following steps: Step 1: Install liquid injection pipelines inside the well. Several pressure-resistant pipes are installed in the production well (104) for transporting fracturing fluid and reinforcement agent respectively. The upper end of the pressure-resistant pipes is connected to the corresponding high-pressure liquid injection system on the offshore production platform (108). Step 2: Install mining holes and nozzles on the mining shaft. In the part of the production well (104) that comes into contact with the natural gas hydrate reservoir (103), openings and nozzles for fracturing, reinforcement and production are set at certain intervals. The nozzles extend outward from the openings and the outer end of the nozzles is flush with the sand screen (205). Step 3: Connect the nozzles to the corresponding high-pressure liquid injection systems. The fracturing and reinforcement nozzles are connected to the lower end of the corresponding pressure-resistant pipes, so that the fracturing and reinforcement nozzles on the production well (104) are connected to the corresponding high-pressure liquid injection system on the offshore production platform (108), so as to control the fracturing fluid and reinforcement agent to be injected independently into the hydrate reservoir (103) through the nozzles. Step 4: Prepare fracturing fluid and inject it into the hydrate reservoir Fracturing fluid is prepared and injected into the hydrate reservoir (103) through the fracturing fluid nozzle (202) on the production well (104) using the high-pressure liquid injection system on the offshore production platform (108) to form fracturing fractures in the hydrate reservoir (103), and the porous material proppant in the fracturing fluid is deposited and fixed in the fractures; Step 5: Hydrate Extraction The hydrate reservoir (103) is depressurized or depressurization-thermal shock combined with the extraction hole (201) on the extraction well (104) so ​​that the hydrate in the fracturing zone (102) can be rapidly decomposed and produced. Step Six: Prepare and inject the consolidating agent into the hydrate reservoir for reinforcement. Prepare a consolidating agent and use the high-pressure liquid injection system on the offshore mining platform (108) to inject the consolidating agent into the hydrate reservoir (103) after mining through the consolidating agent nozzle (203) on the mining well (104). Let it stand for a period of time to reinforce the mined area. Step 7: Multi-process mining of hydrate reservoirs including fracturing, extraction, and reinforcement. According to the requirements of the hydrate mining range, repeat steps four to six. First, the unmined hydrate reservoir (103) is fractured to form a fracture zone (102). Then, the hydrate in the fracture zone (102) is mined. After the hydrate in the fracture zone (102) is decomposed and mined, a reinforcing agent is injected to transform the fracture zone (102) into a reinforcing zone (101). Then, the unmined hydrate reservoir (103) is fractured to expand the fracture zone (102). The hydrate reservoir (103) is subjected to multi-process combined efficient mining of fracturing, mining and reinforcing.

2. The multi-process combined high-efficiency exploitation method for hydrate reservoir fracturing-exploitation-reinforcement as described in claim 1, characterized in that, In step one, the pipelines that transport different liquids in the mining well (104) are independent and are pressure-resistant pipelines that can withstand the pressure difference between the inside and outside.

3. The multi-process combined high-efficiency exploitation method for hydrate reservoir fracturing-exploitation-reinforcement as described in claim 1, characterized in that, In step two, the mining well (104) is provided with several mining openings (201) as a transmission channel for the production of liquid gas during the mining of natural gas hydrate; the outside of the mining well (104) is wrapped with a sand-proof screen (205).

4. The multi-process combined high-efficiency exploitation method for hydrate reservoir fracturing-exploitation-reinforcement as described in claim 1, characterized in that, In step two, the nozzles have circular nozzles. Each set of nozzles consists of a fracturing fluid nozzle (202) and a reinforcement agent nozzle (203). The fracturing fluid nozzle (202) has a nozzle for fracturing fluid spraying, and the reinforcement agent nozzle (203) has a reinforcement agent mother liquor nozzle (210) and a reinforcement agent reactant nozzle (211). Each set of nozzles surrounds a production well (201). The nozzles extend outward from the well wall (206) of the production well and pass through the sand screen (205) wrapped around the outside of the production well (104). The outermost end of the nozzle is flush with the outermost end of the sand screen (205).

5. The multi-process combined high-efficiency exploitation method for hydrate reservoir fracturing-exploitation-reinforcement according to claim 1, characterized in that, In step four, the fracturing fluid is a liquid with viscosity. The fracturing fluid can be a high-viscosity fracturing fluid or a low-viscosity fracturing fluid. High-viscosity fracturing fluids include guar gum fracturing fluid and silicone oil fracturing fluid, while low-viscosity fracturing fluids include sodium chloride solution fracturing fluid.

6. The multi-process combined high-efficiency exploitation method for hydrate reservoir fracturing-exploitation-reinforcement according to claim 1, characterized in that, In step four, the proppant includes one or more of porous ceramic particles, porous calcium carbonate particles, and polyester fiber materials; the proppant is uniformly mixed in the fracturing fluid to form a suspension.

7. The multi-process combined high-efficiency exploitation method for hydrate reservoir fracturing-exploitation-reinforcement according to claim 1, characterized in that, In step four, the high-pressure fluid injection system includes constant-pressure injection and constant-flow injection. The pressure or injection rate of the injected fracturing fluid is determined based on the mechanical parameters and pressure conditions of the hydrate reservoir (103) obtained from drilling before mining. The minimum injection pressure p min The calculation formula is: In the formula, K0 is the static earth pressure coefficient of the hydrate reservoir (103) at that location, Φ is the internal friction angle of the sediment in the hydrate reservoir (103), ρ' is the average effective density of the hydrate reservoir (103) and the overlying sediment layer, g is the gravitational acceleration, z is the burial depth of the hydrate reservoir (103) at that location, and N P c is the cohesive coefficient of hydrates. h This represents the cohesive force of the hydrate.

8. The multi-process combined high-efficiency exploitation method for hydrate reservoir fracturing-exploitation-reinforcement according to claim 1, characterized in that, In step six, the reinforcing agent consists of a reinforcing mother liquor and a reactant. The ratio of the reinforcing mother liquor to the reactant is determined according to the required reaction time and reinforcement strength. The reinforcing mother liquor is injected into the mined hydrate reservoir (103) through the reinforcing mother liquor pipeline (208) and the reinforcing mother liquor nozzle (203) nozzle hole (210) for reinforcement. The reactant is injected into the mined hydrate reservoir (103) through the reinforcing reactant pipeline (209) and the reinforcing reactant nozzle (203) nozzle hole (211) for reinforcement. The reinforcement process is as follows: first, the reinforcing mother liquor is injected for a period of time, and then the reactant is injected to uniformly fill the pores of the soil skeleton. After standing for a period of time, the cement or crystals are generated to complete the reinforcement of the mined area.

9. The multi-process combined high-efficiency exploitation method for hydrate reservoir fracturing-exploitation-reinforcement according to claim 8, characterized in that, When the reinforcing mother liquor and the reactant react, a cement or crystal is formed in the pores of the hydrate reservoir (103), and the formation principle is shown in the following formula: The cement or crystals are porous and are formed at the contact points with the soil skeleton.

10. The multi-process combined high-efficiency exploitation method for hydrate reservoir fracturing-exploitation-reinforcement according to claim 1, characterized in that, In step six, the pressure during reinforcement injection is less than or equal to the minimum injection pressure p of the fracturing fluid. min .

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