Safe and efficient unconventional oil gas in-situ low-temperature ignition agent and ignition process

Abstract

The invention discloses a safe and efficient unconventional oil gas in-situ low-temperature ignition agent and an ignition process, and belongs to the technical field of oil gas development, and the ignition agent comprises, by mass, a coated slow-release oxidant, a high-calorific-value fuel, a catalyst, and the balance an auxiliary agent. The process comprises the following steps: firstly, injecting a dispersion system A containing a catalyst to pre-treat a reservoir; then, injecting the B dispersion system containing the coated slow-release oxidizing agent and the C dispersion system containing the high-calorific-value fuel into the pretreated reservoir in an alternate injection or synchronous injection mode, so that the coated slow-release oxidizing agent and the high-calorific-value fuel are uniformly distributed in the reservoir and are physically isolated; and finally, injecting a D dispersion system containing an initiator as a trigger source. Through a novel chemical ignition agent system and a reasonable implementation process, rapid, safe and self-heating ignition under a low-temperature reservoir condition is realized, so that cost reduction and benefit improvement of in-situ conversion mining are realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of oil and gas development, and particularly relates to a safe and efficient unconventional oil and gas in-situ low-temperature ignition agent and ignition process. BACKGROUND

[0002] Unconventional oil and gas resources such as oil shale, low-mature shale oil and oil-rich coal are extremely rich in reserves in China, but their large-scale development is highly dependent on in-situ conversion technology.

[0003] In-situ conversion technology converts organic matter into light oil and gas by artificially heating the reservoir to the cracking temperature of cheese root and asphaltene (usually up to 350℃), and then mining. However, the entire heating process consumes a huge amount of energy, which has become a core bottleneck restricting the popularization and application of the technology.

[0004] To reduce the input of external energy, underground combustion technology and self-heating in-situ conversion technology use the oxidation exothermic effect of fixed carbon in organic matter or semi-coke in the reservoir to continuously heat the reservoir, significantly reducing the demand for external energy. However, this preheating process takes a long time, consumes a lot of energy, and has a low heat conduction rate, resulting in a sharp increase in development costs. Underground ignition devices have inherent defects such as high sealing requirements, high costs and poor reliability, making ignition difficult, especially in deep or low-permeability reservoirs. The in-situ conversion development of resources cannot be guaranteed in terms of technical and economic feasibility. Chemical ignition agent technology is considered an effective way to break through the above limitations. Existing research has explored a variety of chemical ignition agents, but they still need to be ignited reliably at temperatures above 220℃. This temperature requirement is still too high for low-temperature reservoirs such as shallow oil shale or low-maturity shale oil, and has limited practical value, failing to fundamentally solve the ignition startup problem. In particular, oil shale, low-mature shale oil and oil-rich coal are generally characterized by shallow burial, low temperature, poor permeability and other geological characteristics, further exacerbating the inadaptability of existing ignition technology.

[0005] Therefore, there is an urgent need to develop a chemical ignition agent and process that can quickly self-ignite at low-temperature reservoir conditions, is safe and controllable, and is environmentally friendly, to break through the dual bottlenecks of in-situ conversion technology in terms of economy and reliability, and to provide a feasible solution for the efficient development of unconventional oil and gas resources. SUMMARY

[0006] In order to overcome the above-mentioned defects of the prior art, the purpose of the present application is to provide a safe and efficient unconventional oil and gas in-situ low-temperature ignition agent and ignition process for overcoming the problems of long preheating time (5-10 days are needed), high energy consumption, low ignition success rate and poor adaptability to low-temperature reservoirs in the in-situ conversion mining of oil shale, medium and low mature shale oil and oil-rich coal, and to realize the cost reduction and efficiency increase of in-situ conversion mining by realizing rapid, safe and self-generating heat ignition under low-temperature reservoir conditions through a new type of chemical ignition agent system and a reasonable implementation process.

[0007] In order to achieve the above-mentioned purpose, the present application is realized by the following technical means: According to the first aspect of the present application, a safe and efficient unconventional oil and gas in-situ low-temperature ignition agent is provided, the ignition agent comprises the following raw materials in percentage by mass: 30-55% of a coated slow-release oxidizing agent, 25-45% of a high-calorific fuel, 3-8% of a catalyst, and the balance of an additive, the additive comprises 5-15% of an initiator; the initiator is selected from a carbamide-organic acid system, a coated active metal or coated nano calcium oxide particles; the carbamide-organic acid system is composed of a carbamide-organic acid compound, a composite catalyst and a sulfonate; the mass ratio of the carbamide-organic acid compound to the composite catalyst is 1:1; the mass ratio of the composite catalyst to the sulfonate is 3:7; the carbamide-organic acid compound is composed of carbamide and organic acid in a mass ratio of 11:9; the organic acid is propionic acid or butyric acid; the composite catalyst is composed of sodium nitrite and hypochlorous acid in a mass ratio of 1:1; the sulfonate is sodium dodecyl sulfonate; the coated active metal is an active metal coated with stearic acid and / or paraffin; the active metal is sodium, potassium or rubidium; the coated nano calcium oxide particles are nano calcium oxide particles coated with paraffin.

[0008] Further, the additive further comprises 2-5% of a surfactant, and the surfactant is selected from at least one of sodium dodecyl sulfate SDS, sodium dodecyl benzene sulfonate SDBS, fatty alcohol polyoxyethylene ether AEO, octyl phenol OP and polysorbate-80.

[0009] Further, the additive further comprises 0.5-5% of a stabilizer, and the stabilizer is selected from sodium thiosulfate or sodium silicate.

[0010] Further, the additive further comprises 1-3% of a pH regulator, and the pH regulator is selected from at least one of citric acid, acetic acid, sodium hydroxide, sodium bicarbonate and calcium carbonate.

[0011] Further, the coated slow-release oxidant is coated with a temperature-sensitive coating material or a pH-responsive coating material on the surface of the oxidant; the oxidant is selected from at least one of potassium permanganate, potassium dichromate, potassium ferrate, potassium perchlorate, potassium nitrate, potassium chlorate, sodium nitrate, and calcium nitrate; the temperature-sensitive coating material is selected from at least one of stearic acid, paraffin, or rosin; and the pH-responsive coating material is a chitosan-sodium tripolyphosphate particle, the particle size of the chitosan-sodium tripolyphosphate particle ranges from 650 nm, and the chitosan-sodium tripolyphosphate particle is depolymerized and broken in an environment with a pH value greater than 6.5.

[0012] Further, the high-calorific-value fuel has a calorific value ranging from 5000 kJ / kg to 45000 kJ / kg, and the high-calorific-value fuel is selected from at least one of aluminum powder, magnesium powder, iron powder, boron powder, charcoal, carbon powder, polyhydric alcohol, ferrocene, and tung oil; the polyhydric alcohol is selected from at least one of ethylene glycol, propylene glycol, or glycerol; and the boron powder is modified by ammonium perchlorate, polyvinylidene fluoride, and bismuth oxide.

[0013] Further, the catalyst is selected from iron nitrate, copper nitrate, cerium nitrate, sodium chloride, iron chloride, zinc chloride, copper sulfate, zinc sulfate, copper oxide, nickel oxide, molybdenum disulfide, iron naphthenate, cobalt naphthenate, iron oleate, ferrocene, metal-loaded nano Y-type molecular sieve, and a solid mixed acid of iron oxide and cobalt oxide.

[0014] According to a second aspect of the present application, a safe and efficient unconventional oil and gas in-situ low-temperature ignition process is provided, which uses the ignition agent to ignite, and specifically comprises the following steps: Step 1: injecting an A dispersion system containing a catalyst into a target reservoir to perform reservoir pretreatment; Step 2: injecting a B dispersion system containing a coated slow-release oxidant and a C dispersion system containing a high-calorific-value fuel into the pretreated reservoir in an alternating injection or synchronous injection manner, so that the coated slow-release oxidant and the high-calorific-value fuel are uniformly distributed and physically isolated in the reservoir; Step 3: injecting a D dispersion system containing an initiator into the reservoir, and the initiator triggers an exothermic reaction of the ignition agent system; Wherein, the initial heat released by the exothermic reaction melts the coating material of the coated slow-release oxidant, so that the oxidant is released slowly and undergoes a redox reaction with the high-calorific-value fuel to continuously release heat energy, and the temperature of the reservoir is raised to the ignition point of the target oil and gas.

[0015] Further, a surfactant and / or a stabilizer are added according to the stability of the system when the B dispersion system and / or the C dispersion system is injected.

[0016] In the present application, the surfactant and / or the stabilizer are added according to the stability of the system, and the judgment criteria and technical principles are as follows: Surfactants: When an oil-water miscible component is present in the injected dispersion system, a surfactant needs to be added. Its function is to reduce the interfacial tension between oil and water, forming a stable adsorption film on the surface of the dispersed phase droplets, thereby preventing phase separation and maintaining the stability of the entire dispersion system. For example, when tung oil is used as the high-calorific-value fuel, it is not easily miscible with the aqueous solution as the continuous phase; in this case, adding a surfactant to the C dispersion system is necessary.

[0017] Stabilizers: When the dispersion system injected into the reservoir is a thermodynamically unstable heterogeneous system, or when its components have large density differences and are prone to sedimentation or stratification, stabilizers are required. Stabilizers prevent the aggregation and sedimentation of dispersed phase particles by increasing the viscosity of the dispersion medium or utilizing steric hindrance, ensuring that the components are uniformly distributed within the reservoir. Stabilizers can be used for any system with heterogeneous mixing and a tendency for phase separation to ensure the smooth progress of the injection process and the stability of the system in the reservoir.

[0018] According to specific embodiments of the present invention, dispersion system A uses a catalyst as the main functional substance and is supplemented with a pH adjuster; dispersion system B uses a coated slow-release oxidant as the core component and also contains a surfactant; dispersion system C is based on high-calorific-value fuel and uses surfactants and stabilizers in combination.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: High safety: A coating layer is applied to the surface of the oxidant to form a coated slow-release oxidant, preventing the oxidant from reacting prematurely with high-calorific-value fuel in the wellbore; the contact sequence of each component is precisely controlled through a segmented injection process, and the reaction start-up timing is controlled by the final injection of the initiator, so as to achieve delayed release of the coated slow-release oxidant, preventing sudden runaway reaction from the source and ensuring safety throughout the entire process.

[0020] Economical and efficient: It utilizes the spontaneous reaction of chemical ignition agents to generate heat and form stable combustion, achieving energy self-sufficiency and reducing external energy consumption; catalysts and additives promote the full reaction, and combined with the oil displacement effect of increased reservoir pressure, it significantly improves oil and gas extraction efficiency and recovery rate; the segmented injection process design ensures that each component is evenly distributed in the reservoir pores, improves reactant contact efficiency, reduces energy and material waste, and combines economy and efficiency.

[0021] Low-temperature flammability: The initiator triggers a self-generated heat reaction to rapidly increase the reservoir temperature. Even in low-temperature environments below 70°C, the heat released by the reaction can still bring the reservoir temperature to the ignition point of the oil and gas layer. The selected oxidant coating material can melt within 100°C to achieve slow release of the oxidant, which is suitable for low-temperature reservoir conditions and solves the problem of oil and gas reservoirs being difficult to ignite in low-temperature environments, thus achieving low-temperature flammability.

[0022] High adaptability: The components and coating materials can be flexibly selected and adjusted according to the specific reservoir conditions such as temperature and pH value, thereby improving the coverage range while ensuring the advanced nature and practicality of the technology, providing a universal, economical and safe solution for the in-situ conversion of unconventional oil and gas resources. Attached Figure Description

[0023] Figure 1 This is a flowchart of a safe and efficient unconventional in-situ cryogenic ignition process for oil and gas in an embodiment of the present invention. Detailed Implementation

[0024] This invention addresses the problems encountered during the in-situ thermal conversion or underground combustion extraction of unconventional oil and gas resources such as oil shale, medium-to-low maturity shale oil, and oil-rich coal, including long preheating cycles (typically 5-10 days) and high energy consumption due to the injection of high-temperature fluids, low underground ignition success rates of igniters, and the difficulty of adapting traditional chemical ignition agents to low-temperature reservoirs. It proposes a safe and efficient unconventional in-situ low-temperature ignition agent and ignition process for oil and gas. By constructing a chemical ignition agent system that can be directly injected underground, and utilizing the synergistic effect of coated slow-release oxidizers, high-calorific-value fuels, catalysts, and various additives, a large amount of heat energy is released instantaneously underground, achieving rapid and reliable ignition in the reservoir, thereby promoting the autogenous thermal chain-like thermal cracking and extraction of unconventional oil and gas reservoirs.

[0025] Compared to traditional methods relying on external heating such as electric ignition or downhole heaters, this invention uses chemical ignition agents for underground ignition, eliminating the need for complex external heating equipment and lengthy preheating processes. This significantly reduces energy consumption and operational complexity, improving economic efficiency and engineering adaptability. The developed chemical ignition agent system features easy initiation at low temperatures, controllable reaction, high safety, and strong reservoir adaptability, making it particularly suitable for low-temperature conditions (such as reservoirs below 200°C), overcoming the dependence of existing ignition agents on high-temperature environments. Furthermore, this chemical ignition agent system can achieve precise management of the heating temperature gradient and thermal propulsion process by accurately controlling the component distribution ratios and injection parameters, thereby effectively improving oil and gas recovery rates and extraction efficiency.

[0026] This invention proposes a safe and efficient unconventional in-situ cryogenic ignition agent suitable for low-temperature, low-permeability reservoirs such as oil shale, medium-to-low maturity shale oil, and oil-rich coal. The agent comprises a coated slow-release oxidant, high-calorific-value fuel, catalyst, and additives. The additives include an initiator, and depending on the specific application, may also include surfactants, pH adjusters, and stabilizers. The core of this ignition agent lies in achieving safe and efficient reservoir ignition at low temperatures (below 70°C) through the synergistic effect and controlled release mechanism of its components, while maintaining the continuous advancement of the autogenous heating reaction or combustion front, thus ensuring the in-situ conversion and exploitation of unconventional oil and gas. In the formulation design of this ignition agent, the selection and proportion range of each component have been fully optimized and experimentally verified to ensure its broad applicability and adjustability.

[0027] The ignition agent proposed in this invention comprises, by mass percentage, the following raw materials: 30%–55% coated slow-release oxidant, 25%–45% high-calorific-value fuel, 3%–8% catalyst, and the balance being additives, wherein the sum of the mass percentages of the coated slow-release oxidant, high-calorific-value fuel, catalyst, and additives is 100%. The additives include 5%–15% initiator, and depending on the actual application requirements, the additives may also include 2%–5% surfactant, 0.5%–5% stabilizer, and 1%–3% pH adjuster.

[0028] In the encapsulated slow-release oxidant, the oxidant is encapsulated by an encapsulating material to control its release rate. The oxidants include not only conventional oxidants such as potassium permanganate, potassium dichromate, potassium ferrate, potassium perchlorate, potassium nitrate, potassium chlorate, sodium nitrate, and calcium nitrate, but also encapsulated oxidants using encapsulation processes. Specifically, this includes encapsulating oxidants with temperature-sensitive materials such as stearic acid, paraffin wax, and rosin, and encapsulating oxidants with pH-responsive chitosan-sodium tripolyphosphate particles. The aim is to prevent premature reaction of the oxidant with other components in the wellbore by utilizing the slow-release, dissolving, or triggered release characteristics of encapsulating materials such as stearic acid, paraffin wax, rosin, and chitosan-sodium tripolyphosphate particles, and to adapt to different reservoir temperature and pH environments. Chitosan-sodium tripolyphosphate particles are a CS submicron particle system prepared by iontophoresis of chitosan (CS) and sodium tripolyphosphate (TPP). The mass ratio of chitosan (CS) to sodium tripolyphosphate (TPP) during the preparation process is 5:1, and the particle size range of this CS submicron particle system is 650 nm. It undergoes depolymerization and rupture in an environment with a pH value greater than 6.5.

[0029] The selection of high-calorific-value fuels covers metal powders (such as aluminum powder, magnesium powder, and iron powder), non-metallic carbonaceous fuels (such as charcoal and carbon powder), and organic fuels (such as polyols, ferrocene, and tung oil, with the polyol selected from at least one of ethylene glycol, propylene glycol, or glycerol). The calorific value of the high-calorific-value fuels is controlled within the range of 5000 kJ / kg to 45000 kJ / kg, and the mass percentage of high-calorific-value fuels is 25% to 45% to ensure sufficient heat output and controllable rate of reaction. Boron powder can also be selected as a high-calorific-value fuel, and the boron powder is modified with ammonium perchlorate (AP), polyvinylidene fluoride (PVDF), and bismuth oxide (Bi2O3). This is prior art and the specific modification process will not be described in detail here.

[0030] The catalysts include, but are not limited to, water-soluble nitrates (such as ferric nitrate, copper nitrate, and cerium nitrate), chlorides (such as sodium chloride, ferric chloride, and zinc chloride), sulfates (such as copper sulfate and zinc sulfate), metal oxides (such as copper oxide and nickel oxide), metal sulfides (such as molybdenum disulfide), organometallic salts (such as ferric naphthenate, cobalt naphthenate, ferric oleate, and ferrocene), supported nanomolecular sieves (such as metal-supported nano-Y-type molecular sieves), and multi-metal solid acids (such as a mixed solid acid of ferric oxide and cobalt oxide). The catalysts promote the exothermic oxidation reaction of organic matter in the reservoir at a lower temperature by reducing the activation energy of the reaction.

[0031] The initiator is crucial for ensuring low-temperature startup, and its mass fraction is 5%–15%. For ultra-low temperature reservoirs (temperatures below 70°C), a chemithermal initiation system can be selected as the initiator (such as a carbamide-organic acid system, which consists of a carbamide-organic acid complex, a composite catalyst, and a sulfonate; the carbamide-organic acid complex is composed of carbamide and organic acid in a mass ratio of 11:9, wherein the organic acid is propionic acid or butyric acid; the composite catalyst is composed of sodium nitrite and hypochlorous acid in a mass ratio of 1:1; and the sulfonate is sodium dodecyl sulfonate; wherein the carbamide-organic acid complex and the composite catalyst…). The mass ratio of the composite catalyst to the sulfonate is 1:1; the mass ratio of the composite catalyst to the sulfonate is 3:7. This is used to accelerate the dissolution or decomposition of the oxidant coating material and promote the release and reaction of the oxidant. The initiator can also be a substance coated with active metals (such as sodium, potassium or rubidium coated with stearic acid and / or paraffin) and a substance that rapidly releases heat when coated with nano-calcium oxide particles in water. It can work under different triggering mechanisms (heat, water, pH change), which greatly expands the applicable scenarios of ignition agents. The coated nano-calcium oxide particles are nano-calcium oxide particles coated with paraffin.

[0032] The surfactant is selected from at least one of sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (SDBS), fatty alcohol polyoxyethylene ether (AEO), octylphenol (OP), and polysorbate-80; the pH adjuster is selected from at least one of citric acid, acetic acid, sodium hydroxide, sodium bicarbonate, and calcium carbonate. The surfactant and pH adjuster ensure good dispersibility, stability, and chemical compatibility of the injected fluid with the reservoir pores. Furthermore, a stabilizer, selected from sodium thiosulfate or sodium silicate, is incorporated into the ignition agent formulation to further improve reaction efficiency, maintain combustion stability, and suppress unnecessary side reactions.

[0033] The significant advantages of this invention lie in its high customizability and broad adaptability. By selecting different types of oxidant coating materials (such as thermosensitive or pH-responsive coating materials), adjusting the type of initiator (e.g., thermal or water-triggered), and flexibly adjusting the proportions of each component, the designed ignition agent can be applied to a variety of complex geological conditions, covering shallow low-temperature (below 70°C) reservoirs to medium-deep reservoirs, and environments ranging from high water cut to low-permeability acidic conditions. This design not only is compatible with the nitrate-metal fuel system commonly used in existing technologies, but also integrates advanced slow-release technology, nanomaterials (such as coated nano-calcium oxide particles), and a composite initiation mechanism. While expanding the coverage, it ensures technological advancement and practical value, providing an economical, safe, and universally applicable solution for the in-situ conversion of unconventional oil and gas resources.

[0034] The successful implementation of this invention relies on its meticulously designed segmented injection process, which ensures safety, effectiveness, and a high success rate through the principle of spatiotemporal isolation. Specifically, components that may react violently upon encountering each other are physically separated in the wellbore until they are transported to the depths of the target reservoir before being allowed to mix and initiate a reaction. This effectively avoids the risk of premature reactions in the wellbore and improves operational controllability and overall reliability.

[0035] Specifically, in terms of the implementation process, the ignition agent formulation of this invention employs a segmented injection process to ensure construction safety and reaction controllability: First, a catalyst-containing dispersion A is injected to pre-treat the reservoir, creating a basic environment for subsequent reactions; then, dispersion B containing a coated slow-release oxidant and dispersion C containing high-calorific-value fuel are injected alternately or simultaneously, ensuring that the reactants are uniformly distributed but physically isolated within the reservoir. The core purpose of this step is to ensure that the coated slow-release oxidant can uniformly fill the reservoir pores, creating sufficient contact conditions for subsequent oxidation reactions; finally, dispersion D containing an initiator is injected as a trigger source as needed. In this invention, the final injection of the initiator (used for ignition in lower-temperature reservoirs, aiding in the decomposition or dissolution of temperature-sensitive coating materials, releasing the internal oxidant material) is a key step in controlling the reaction initiation. When the initiator is injected into the reservoir, it immediately triggers an autogenous heating reaction, rapidly releasing heat and effectively raising the reservoir temperature. Under the synergistic effect of the heat released by the initiator and the reservoir temperature, the coated oxidant begins to be slowly released. This released oxidant, promoted by the synergistic effect of the catalyst and additives, gradually undergoes a redox reaction with the high-calorific-value fuel in the reservoir, further releasing a large amount of heat. This heat is not only sufficient to ignite the previously injected high-calorific-value fuel, but also to further trigger a continuous exothermic reaction, ultimately forming a stable combustion state, providing a continuous heat source for the pyrolysis of oil shale and the pyrolysis conversion of medium- and low-maturity shale oil.

[0036] This timing control combined with coating technology fundamentally avoids the need for preheating of high-temperature fluids or electric heaters, significantly reducing energy consumption and operational risks. A dispersion system is a system formed by dispersing one or more substances (dispersed phases) into another substance (dispersant). Based on the diameter of the dispersed phase particles, they can be divided into three categories: solutions, colloids, and suspensions, which are existing technologies and will not be discussed in detail here.

[0037] In practical applications, oxidants and high-calorific-value fuels are highly susceptible to reaction if they come into premature contact within the wellbore. To prevent this premature reaction, this invention employs a coating process to modify the surface of the oxidant, forming a coating layer. This coating layer design ensures that after the chemical ignition agent system is delivered to the designated location, the slow-release process of the coated slow-release oxidant is triggered by the natural rise in reservoir temperature, ultimately achieving a delayed reaction. The coating layer is selected based on actual conditions such as reservoir temperature, pH, or the performance of the oxidant. For example: In reservoirs with temperatures ranging from 60℃ to 150℃, temperature-sensitive materials such as stearic acid, paraffin, and rosin are selected. These materials are stable at room temperature and melt to release their contents at reservoir temperatures.

[0038] For pH-responsive release, a CS submicron particle system prepared using a chitosan-sodium tripolyphosphate (CS-TPP) ionogel system was used as the coating material to achieve sustained release in an acidic environment.

[0039] To improve fuel combustion performance, ammonium perchlorate (AP), polyvinylidene fluoride (PVDF), and bismuth oxide (Bi2O3) are used for modification. The specific modification process is existing technology and will not be described in detail here. It can improve the combustion performance of high-calorific-value fuels such as boron, such as reducing the ignition delay time of boron and increasing the combustion temperature.

[0040] To make it easier to understand, the following will be combined with Figure 1 The safe and efficient unconventional in-situ cryogenic ignition process for oil and gas of the present invention is described in detail, such as... Figure 1 As shown, the process specifically includes: 1. Reservoir stimulation pretreatment: The unconventional oil and gas reservoirs involved in this invention have extremely low permeability, and in-situ conversion processes require reservoir modification. Before injecting the ignition agent, hydraulic fracturing, acidizing, or shock wave fracturing are typically required to create sufficient flow channels, ensuring that the ignition agent can effectively enter and cover the target area. 2. Segmented injection: Phase 1: An A emulsion containing a catalyst and pH adjuster is injected first to pre-activate the reservoir environment; Phase 2: The B emulsion containing coated slow-release oxidant and the C emulsion containing high-calorific-value fuel are injected alternately. The two emulsions can be isolated by an inert fluid (such as nitrogen) slug to prevent them from mixing prematurely in the near-wellbore zone to the greatest extent possible. Phase 3: The D emulsion containing the initiator is injected last, with the initiator serving as the trigger source; 3. Reaction Triggering and Monitoring: After the initiator reaches the predetermined location, it releases heat through its own reaction (such as melting of the coating layer, reaction with water, etc.), triggering the main redox reaction. Successful ignition is determined by monitoring and analyzing the temperature and pressure inside the well, and by analyzing the composition of the gas exiting the production well.

[0041] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of this invention are clearly and completely described below in conjunction with embodiments. Obviously, this invention is not limited to the following embodiments, and specific implementation methods can be determined based on the technical solutions of this invention and actual circumstances. To avoid obscuring the essence of this invention, well-known methods, processes, and procedures are not described in detail.

[0042] Example 1 Reservoir type: shallow, low-temperature oil shale reservoir.

[0043] Reservoir conditions: burial depth 300m, thickness 100m, reservoir temperature 30℃, reservoir pressure 6MPa, reservoir permeability (0.001~0.01)×10 -3 The reservoir has an oil content of 8% within a certain range of μm². Pre-treatment with hydraulic fracturing and shock wave fracturing processes has created an effective fracture network, improving the seepage environment.

[0044] The ignition agent used in this embodiment comprises the following components by mass percentage: Coated slow-release oxidant: 45%, which is composed of potassium nitrate coated with paraffin wax, and the melting point of the paraffin wax coating is 65℃; High-calorific-value fuel: 38%, high-calorific-value fuel is a blend of aluminum powder and magnesium powder in a mass ratio of 3:1; Catalyst: 5%, the catalyst is ferric nitrate; Initiator: 10%, the initiator is a carbamide-propionic acid system; Surfactant: 2%, the surfactant used is sodium dodecyl sulfate (SDS).

[0045] The above-mentioned ignition agent components were prepared into water-based emulsions for downhole injection. The specific preparation methods are as follows: Emulsion A: Mix the catalyst and water at a mass ratio of 1:9 to prepare an emulsion with a mass concentration of 10%, and store it in a sealed container under cold conditions.

[0046] B. Emulsion: Mix the encapsulated slow-release oxidant and 1% surfactant by mass with water at a mass ratio of 1:4 to prepare an emulsion with a mass concentration of 20%, and store it in a sealed container under cold conditions.

[0047] C. Emulsion: Mix high-calorific-value fuel with a surfactant mixture accounting for 1% of the total mass and water at a mass ratio of 1:4 to prepare an emulsion with a mass concentration of 20%, and store it in a sealed container under cold conditions.

[0048] D. Emulsion: Mix the initiator and water at a mass ratio of 1:4 to prepare an emulsion with a mass concentration of 20%, and store it in a sealed container under cold conditions.

[0049] This embodiment employs a dual-tube injection system, including an outer tube and an inner tube, and injects the components in segments in the following order: First, the catalyst-containing emulsion A is injected into the target reservoir through the outer tube; Subsequently, emulsion B containing coated slow-release oxidant and emulsion C containing high-calorific-value fuel were simultaneously injected through the outer and inner pipes, respectively; 1% surfactant by mass was added to both emulsions to promote uniform mixing of oxidant and high-calorific-value fuel in the reservoir. During the injection process, air and CO2 are injected alternately at a slug ratio of 2:1 to enhance fluid mixing and ripple effect; Finally, the reaction is initiated by injecting the catalyst-containing D emulsion through the inner pipe, and oil production begins.

[0050] After employing the aforementioned ignition agent and injection process, the potassium nitrate oxidant in emulsion B is coated with paraffin wax to ensure its inertness before reaching the reservoir. An exothermic reaction is initiated in the reservoir by injecting a carbamide-propionic acid initiator, promoting the release of the oxidant. Oxygen-containing gas is continuously injected into the reservoir. Within 24 hours, the bottomhole temperature rises to over 500°C, successfully igniting the reservoir and forming a stable combustion front. This achieves the goal of synergistically improving shale oil recovery through thermal, gas miscibility, and chemical interactions.

[0051] Example 2 Reservoir type: shallow, low-temperature oil shale reservoir.

[0052] Reservoir conditions: reservoir depth 350m, reservoir thickness 90m, reservoir temperature 32℃, reservoir pressure 6.5MPa.

[0053] In this embodiment, the ignition agent consists of the following components by mass percentage: Coated slow-release oxidant: 40%, wherein the oxidant contains potassium permanganate, sodium nitrate, potassium nitrate and calcium nitrate, and by mass ratio, potassium permanganate: sodium nitrate: potassium nitrate: calcium nitrate = 7:1:1:1; the oxidant coating material is rosin; High-calorific-value fuel: 40%. High-calorific-value fuel contains aluminum powder, magnesium powder, iron powder, polyol and tung oil. By mass ratio, aluminum powder: magnesium powder: iron powder: polyol: tung oil = 3:3:2:1:1. Catalyst: 5%, the catalyst contains copper nitrate and copper oxide, by mass ratio, copper nitrate: copper oxide = 1:1; Initiator: 10%, which is a carbamide-organic acid system; Surfactant: 3%, the surfactant contains sodium dodecyl sulfate (SDS) and sodium dodecylbenzene sulfonate (SDBS), and the mass ratio of sodium dodecyl sulfate (SDS) to sodium dodecylbenzene sulfonate (SDBS) is 1:1; pH adjuster: 2%, which is citric acid.

[0054] The above-mentioned ignition agent components were prepared into water-based emulsions for downhole injection. The specific preparation methods are as follows: Emulsion A: Mix the catalyst and pH adjuster with water at a mass ratio of 1:9 to prepare an emulsion with a mass concentration of 10%, and store it in a sealed container under cold conditions.

[0055] B. Emulsion: Mix the encapsulated slow-release oxidant and 1% surfactant by mass with water at a mass ratio of 1:4 to prepare an emulsion with a mass concentration of 20%, and store it in a sealed container under cold conditions.

[0056] C. Emulsion: A mixture of high-calorific-value fuel and 1% surfactant by mass is mixed with water at a mass ratio of 1:4 to prepare an emulsion with a mass concentration of 20%, which is then refrigerated and sealed.

[0057] D. Emulsion: Mix the initiator and 1% surfactant by mass with water at a mass ratio of 1:4 to prepare an emulsion with a mass concentration of 20%, and store it in a sealed container under cold conditions.

[0058] Using a large-diameter wellbore suitable for oil shale development, and employing a dual-tube injection system, the emulsions are injected in the following sequence: First, emulsion A is injected into the target reservoir through the outer pipe of the injection well; Subsequently, emulsion B and emulsion C were injected simultaneously through the outer and inner pipes, respectively, to ensure that the oxidant and high-calorific-value fuel were uniformly mixed and distributed in the reservoir. During or between the injection of emulsions B and C, air and CO2 are injected alternately at a slug ratio of 2:1 to enhance fluid drive and mixing.

[0059] Finally, emulsion D is injected through the inner tube to initiate the chemical reaction and begin oil production.

[0060] After the injection of the ignition agent was completed and the reaction was initiated 24 hours later, downhole monitoring data showed that the CO2 concentration in the combustion products was 12.3%, the oxygen concentration decreased by 20%, and the formation pressure increased from 6.5 MPa to 9 MPa. These parameter changes confirmed that a self-sustaining combustion front had been successfully established in the reservoir, ignition was successful, and shale oil production began to be effectively produced.

[0061] Example 3 Reservoir type: Deep, medium- to low-maturity shale oil reservoir.

[0062] Reservoir conditions: reservoir depth 2200m, reservoir temperature 85℃, reservoir pressure 45MPa.

[0063] In this embodiment, the ignition agent consists of the following components by mass percentage: Coated slow-release oxidant: 48%, wherein the oxidant is a mixture of potassium permanganate and potassium chlorate in a mass ratio of 1:1; the oxidant coating material is stearic acid, which controls the oxidation reaction rate through coating and avoids premature activation of high-temperature reservoirs; High-calorific-value fuel: 35%. The high-calorific-value fuel is a blend of magnesium powder and charcoal powder in a mass ratio of 2:1; providing the high-calorific-value output required for continuous combustion. Catalyst: 6%, copper oxide is used as the catalyst to reduce the activation energy of the reaction and promote the combustion chain reaction; Initiator: 8%, the initiator is sodium particles coated with stearic acid, and the coating thickness is 200μm; Stabilizer: 3%, sodium thiosulfate is used as the stabilizer.

[0064] The above-mentioned ignition agent components were prepared into water-based emulsions for downhole injection. The specific preparation methods are as follows: Emulsion A: Mix the catalyst and water at a mass ratio of 1:9 to prepare an emulsion with a mass concentration of 10%, and store it in a sealed container under cold conditions.

[0065] B. Emulsion: Mix the coated slow-release oxidant with water at a mass ratio of 1:4 to prepare an emulsion with a mass concentration of 20%, and store it in a sealed container under cold conditions.

[0066] C. Emulsion: A mixture of high-calorific-value fuel and stabilizer is mixed with water at a mass ratio of 1:4 to prepare an emulsion with a mass concentration of 20%, which is then refrigerated and sealed for storage.

[0067] D. Emulsion: Mix the initiator and water at a mass ratio of 1:4 to prepare an emulsion with a mass concentration of 20%, and store it in a sealed container under cold conditions.

[0068] The injection process remained consistent with Example 2, except that a cooling CO2 slug was injected before injecting emulsions B and C to briefly lower the near-wellbore temperature and further ensure injection safety. The initiator consisted of sodium particles coated with stearic acid that react with water and was activated using reservoir water.

[0069] Five days after the ignition agent was injected, the reservoir pressure increased by 10 MPa, and temperature monitoring showed that the combustion front continued to expand outward, indicating successful ignition.

[0070] Example 4 Reservoir type: High water-cut, oil-rich coal reservoir.

[0071] Reservoir conditions: reservoir temperature 50℃, water saturation 45%. The large amount of water in the reservoir absorbs heat during ignition, significantly inhibiting temperature rise and easily leading to ignition failure.

[0072] In this embodiment, the ignition agent consists of the following components by mass percentage: Coated slow-release oxidant: 42%, using calcium nitrate or potassium permanganate as the oxidant to provide a continuous oxygen source. The surface of the oxidant is coated with stearic acid to delay release. High-calorific-value fuel: 40%, using aluminum powder to enhance combustion by utilizing its high calorific-value properties; Initiator: 12%, using coated nano-calcium oxide particles. This component reacts rapidly with water and releases a large amount of heat, preferentially vaporizing water in the near-wellbore area. Catalyst: 6%, nickel nitrate was selected to promote the reaction.

[0073] Process Adjustment Instructions: In actual construction, by controlling the addition of the initiator, it is made to react rapidly with the water in the reservoir, generating high-temperature and high-pressure steam. This process can proactively displace some of the reservoir water and preheat the rock formation, thus creating a dry, high-temperature starting environment before the main reaction occurs. Oil-rich coal reservoirs have a high carbon content, and once successfully ignited, they can form a self-sustaining thermal reaction front and effectively propel the reaction.

[0074] Application effect: The ignition barrier of high water-cut reservoirs was successfully overcome, and the reaction temperature was stably maintained above 500℃ after ignition, achieving efficient and stable reservoir ignition.

[0075] Example 5 Reservoir type: Ultra-low permeability tight reservoir.

[0076] The specific implementation process of this embodiment is as follows: 1. Reservoir conditions and stimulation objectives: The target reservoir is an ultra-low permeability tight reservoir with a burial depth of 2000m, a reservoir temperature of 100℃, and which has been modified by supercritical CO2 fracturing. Due to the low degree of organic matter maturation, the natural production capacity of the reservoir does not meet the industrial oil flow standard. It is proposed to adopt a low-temperature oxidation process, which uses chemical ignition to ignite residual hydrocarbons and supplementary fuel in the reservoir to establish a continuous combustion zone, thereby improving crude oil fluidity and ultimate recovery rate.

[0077] 2. Refueling: To improve ignition success rate and promote effective combustion reaction propagation in the reservoir, light crude oil is first injected as supplementary fuel. This light crude oil has good fluidity, easily enters microfractures and pore systems, and improves the overall fuel distribution within the reservoir.

[0078] 3. In this embodiment, the ignition agent, by mass percentage, consists of the following components: Coated slow-release oxidant: 50%, the oxidant is potassium dichromate, and it is coated with chitosan-sodium tripolyphosphate particles to improve its stability and controlled release characteristics; High-calorific-value fuel: 30%. The high-calorific-value fuel uses nano-aluminum powder, which enhances the penetration and dispersion ability in microcracks by utilizing its nanoscale properties. Catalyst: 5%, which is a compound catalyst composed of copper nitrate and ferric nitrate in a mass ratio of 1:1; Initiator: 10%, which is a carbamide-butyric acid system; Additives: 5%, including 3% surfactant and 2% pH adjuster. The surfactant is fatty alcohol polyoxyethylene ether (AEO), and the pH adjuster is citric acid. 4. Preparation of ignition agent emulsion: All emulsions were refrigerated and sealed after preparation. The specific preparation method is as follows: Emulsion A (catalyst system): A mixture of catalyst (copper nitrate and ferric nitrate compound) and pH adjuster (citric acid) is mixed with water at a mass ratio of 1:9 to prepare an emulsion with a mass concentration of 10%.

[0079] B. Emulsion (oxidant system): Mix the coated potassium dichromate with 1% fatty alcohol polyoxyethylene ether (AEO) by mass with water at a mass ratio of 1:4 to prepare an emulsion with a mass concentration of 20%.

[0080] C. Emulsion (high calorific value fuel system): A mixture of nano-aluminum powder and 1% fatty alcohol polyoxyethylene ether (AEO) by mass is mixed with water at a mass ratio of 1:4 to prepare an emulsion with a mass concentration of 20%.

[0081] D. Emulsion (Initiator System): A mixture of carbamide-butyric acid initiator system and 1% fatty alcohol polyoxyethylene ether (AEO) by mass is mixed with water at a mass ratio of 1:4 to prepare an emulsion with a mass concentration of 20%.

[0082] 5. On-site implementation and results: Following supercritical CO2 fracturing, reservoir permeability was significantly improved. Emulsions A, B, C, and D were injected into the reservoir in a predetermined sequence. The chemical ignition agent, synergistically with the pre-injected light supplementary fuel, successfully achieved underground ignition in the ultra-low permeability reservoir and established a stable combustion front, laying the foundation for the effective advancement of subsequent cryogenic oxidation oil recovery technology.

[0083] This invention aims to overcome the ignition technology challenges of low-temperature and low-permeability reservoirs such as oil shale, medium- and low-maturity shale oil, and oil-rich coal. Its core technology requirements revolve around low-temperature flammability to accurately adapt to the low-temperature environment of actual reservoirs.

[0084] To achieve this goal, the present invention has constructed a targeted chemical ignition agent system. In terms of formulation design, the selection and proportion range of each component have been fully optimized and experimentally verified to ensure its wide applicability and adjustability.

[0085] Core heat release combination: With oxidant and high-calorific-value fuel as the core, the strong redox reaction between the two realizes the instantaneous release of heat, providing a key heat source for low-temperature reservoir ignition; Auxiliary functional components: Combined with initiators, surfactants, stabilizers and pH adjusters, the initiator is responsible for rapidly triggering the core exothermic reaction, while the surfactants, stabilizers and pH adjusters ensure that the components of the system are uniformly dispersed and that the reaction starts stably; Safety and controllability assurance: On the one hand, it relies on the pre-injected catalyst, and on the other hand, it combines the coating process and segmented injection technology to coat the oxidant with materials such as stearic acid and paraffin, so as to achieve the slow release of the oxidant at the designated location in the formation. The two measures together meet the core requirements of safety and controllability.

[0086] Ultimately, this invention successfully solved key problems in the development of low-temperature, low-permeability reservoirs such as oil shale, medium- and low-maturity shale oil, and oil-rich coal, including difficulties in igniting low-temperature reservoirs, long reservoir preheating time, high preheating costs, and safety hazards in on-site engineering operations.

[0087] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. The present invention is not limited to the above examples. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all embodiments here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A safe and efficient unconventional in-situ cryogenic ignition agent for oil and gas, characterized in that, The ignition agent, by mass percentage, comprises the following raw materials: 30%–55% coated slow-release oxidant, 25%–45% high-calorific-value fuel, 3%–8% catalyst, and the balance being additives, including 5%–15% initiator; the initiator is selected from carbamide-organic acid systems, coated active metals, or coated nano-calcium oxide particles; the carbamide-organic acid system is composed of a carbamide-organic acid complex, a composite catalyst, and a sulfonate; the mass ratio of the carbamide-organic acid complex to the composite catalyst is 1:1; The composite catalyst and sulfonate have a mass ratio of 3:7; the carbamide-organic acid composite is composed of carbamide and organic acid in a mass ratio of 11:9; the organic acid is propionic acid or butyric acid; the composite catalyst is composed of sodium nitrite and hypochlorous acid in a mass ratio of 1:1; the sulfonate is sodium dodecyl sulfonate; the coated active metal is an active metal coated with stearic acid and / or paraffin; the active metal is sodium, potassium, or rubidium; the coated nano-calcium oxide particles are nano-calcium oxide particles coated with paraffin.

2. The safe and efficient unconventional in-situ cryogenic ignition agent for oil and gas as described in claim 1, characterized in that, The additives also include 2% to 5% surfactant, which is selected from at least one of sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (SDBS), fatty alcohol polyoxyethylene ether (AEO), octylphenol (OP), and polysorbate-80.

3. The safe and efficient unconventional in-situ cryogenic ignition agent for oil and gas as described in claim 1, characterized in that, The additives also include 0.5% to 5% stabilizer, which is selected from sodium thiosulfate or sodium silicate.

4. The safe and efficient unconventional in-situ cryogenic ignition agent for oil and gas as described in claim 1, characterized in that, The additives also include 1% to 3% pH adjuster, wherein the pH adjuster is selected from at least one of citric acid, acetic acid, sodium hydroxide, sodium bicarbonate, and calcium carbonate.

5. The safe and efficient unconventional in-situ cryogenic ignition agent for oil and gas according to claim 1, characterized in that, The coated slow-release oxidant is an oxidant surface coated with a thermosensitive coating material or a pH-responsive coating material; the oxidant is selected from at least one of potassium permanganate, potassium dichromate, potassium ferrate, potassium perchlorate, potassium nitrate, potassium chlorate, sodium nitrate, and calcium nitrate; the thermosensitive coating material is selected from at least one of stearic acid, paraffin, or rosin; the pH-responsive coating material is chitosan-sodium tripolyphosphate particles with a particle size range of 650 nm, which depolymerize and break down in an environment with a pH value greater than 6.

5.

6. The safe and efficient unconventional in-situ cryogenic ignition agent for oil and gas as described in claim 1, characterized in that, The calorific value of the high-calorific-value fuel is controlled within the range of 5000 kJ / kg to 45000 kJ / kg. The high-calorific-value fuel is selected from at least one of aluminum powder, magnesium powder, iron powder, boron powder, charcoal, carbon powder, polyol, ferrocene, and tung oil. The polyol is selected from at least one of ethylene glycol, propylene glycol, or glycerol. The boron powder is modified with ammonium perchlorate, polyvinylidene fluoride, and bismuth oxide.

7. The safe and efficient unconventional in-situ cryogenic ignition agent for oil and gas according to claim 1, characterized in that, The catalyst is selected from ferric nitrate, copper nitrate, cerium nitrate, sodium chloride, ferric chloride, zinc chloride, copper sulfate, zinc sulfate, copper oxide, nickel oxide, molybdenum disulfide, ferric naphthenate, cobalt naphthenate, ferric oleate, ferrocene, metal-supported nano-Y-type molecular sieves, and solid mixed acids of ferric oxide and cobalt oxide.

8. A safe and efficient unconventional in-situ cryogenic ignition process for oil and gas, characterized in that, The process utilizes the ignition agent as described in any one of claims 1-7 for ignition, specifically including: Step 1: Inject dispersion system A containing the catalyst into the target reservoir for reservoir pretreatment; Step 2: Inject B dispersion system containing coated slow-release oxidant and C dispersion system containing high-calorific-value fuel into the pretreated reservoir by alternating or synchronous injection, so that the coated slow-release oxidant and the high-calorific-value fuel are uniformly distributed in the reservoir and physically isolated. Step 3: Inject D dispersion system containing initiator into the reservoir, wherein the initiator triggers the autogenous thermal reaction of the ignition agent system; The initial heat released by the self-generated heat reaction melts the coating material of the coated slow-release oxidant, causing the oxidant to be released slowly and react with the high-calorific-value fuel in a redox reaction, continuously releasing heat energy and raising the reservoir temperature to the ignition point of the target oil and gas.

9. The safe and efficient unconventional in-situ cryogenic ignition process for oil and gas as described in claim 8, characterized in that, When injecting dispersion B and / or dispersion C, surfactants and / or stabilizers are added as needed for system stability.

10. The safe and efficient unconventional in-situ cryogenic ignition process for oil and gas as described in claim 9, characterized in that, The A dispersion system containing the catalyst also contains a pH adjuster; the B dispersion system containing the coated slow-release oxidant also contains a surfactant; and the C dispersion system containing the high-calorific-value fuel also contains a surfactant and a stabilizer.

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