Method for generating hydrogen from peridotite serpentine

Abstract

The invention belongs to the technical field of natural hydrogen resource exploration and development and unconventional gas reservoir engineering, and particularly relates to a method for generating hydrogen through peridotite serpentine. According to the method, a main crack channel is constructed by means of directional cutting and erosion of underground water jet in a near-wellbore zone of a target peridotite well section, a reaction cavity with a certain volume and geometric constraint is formed near a wellbore in a dilatation mode, and a main crack-cavity structure is formed. The main crack-cavity structure has the dual functions of a high-specific-surface water accumulation-rock reaction area and a hydrogen local enrichment space. On the basis of the structure, an integrated technical route of near-well fracture and cavity forming, continuous hydrogen generation reaction, well periphery enrichment buffering and dominant channel extraction is formed in cooperation with a staged water injection process of high-pressure water jet fracture and cavity forming and middle-low pressure water injection hydrogen generation enrichment; the serpentine hydrogen generation efficiency and the hydrogen recovery efficiency are remarkably improved, and the risks of hydrogen escape and stratum instability are reduced within the controllable water injection scale and the limited transformation range.

Description

Technical Field

[0001] This invention belongs to the fields of natural hydrogen resource exploration and development and unconventional gas reservoir engineering technology, and specifically relates to a method for hydrogen generation from olivine serpentinite. Background Technology

[0002] Serpentinization of iron- and magnesium-rich rock masses, such as peridotite, under water contact conditions is one of the main geological mechanisms for natural hydrogen generation. However, natural serpentinization for hydrogen generation usually occurs in deep tectonic zones or localized fracture zones. The reaction environment is controlled by multiple factors, including formation temperature and pressure, water-bearing conditions, and fracture connectivity. The spatial distribution is scattered, the reaction rate is low, and it is difficult to directly form stable and recoverable hydrogen reservoirs.

[0003] Existing methods for natural hydrogen exploration and development mainly include well drilling and hydraulic fracturing. Well drilling involves directly drilling to extract gas from natural hydrogen seepage points, connecting natural fractures through the wellbore, and intercepting the migrating hydrogen. However, the near-wellbore structure is uncontrollable, heavily reliant on natural fractures and seepage channels, with a dispersed water-rock interface and limited reaction space, making it impossible to form a hydrogen enrichment space on an engineering scale, resulting in poor hydrogen production stability. Hydraulic fracturing technology borrows from conventional oil and gas fracturing techniques to perform volumetric fracturing and water injection in fracture zones and peridotite masses. High-pressure fluids are used to initiate and expand fractures in the rock mass to increase the water-rock contact area and seepage capacity. However, fracture morphology is uncontrollable, easily forming complex fracture networks, causing hydrogen to dissipate along multiple channels, making it difficult to achieve directional convergence and retention in the near-wellbore area, and posing engineering risks such as large-scale water injection and the potential to induce formation instability. Summary of the Invention

[0004] To address the challenges of dispersed reaction interfaces, difficulty in hydrogen enrichment, large-scale water injection, and high engineering risks in existing natural hydrogen development technologies, this invention provides a method for hydrogen generation through serpentinization in peridotite. This invention constructs a controllable main fracture-cavity system near the wellbore and employs a staged water injection process. This allows for the simultaneous enhancement of the serpentinization hydrogen generation reaction, in-situ enrichment of generated hydrogen, and safe and controllable production within a limited and controllable stimulation range. Ultimately, this significantly improves hydrogen generation efficiency and recovery rate while reducing the risk of hydrogen escape and formation instability.

[0005] This invention utilizes downhole water jets to directionally cut and erode near the wellbore in the target olivine section, constructing a main fracture channel and expanding it near the wellbore to form a reaction cavity with a certain volume and geometric constraints, thus creating a main fracture-cavity structure. This main fracture-cavity structure serves the dual function of a high specific surface area water-rock reaction zone and a local hydrogen enrichment space. Based on this structure, combined with a staged water injection process of "high-pressure water jet fracture and cavity creation" and "medium-low pressure water injection for hydrogen enrichment," an integrated technical route of "near-well fracture and cavity creation + continuous hydrogen generation reaction + wellbore enrichment buffer + production through advantageous channels" is formed. This significantly improves the efficiency of serpentine hydrogen generation and hydrogen recovery rate, and reduces the risk of hydrogen escape and formation instability within a controllable water injection scale and limited modification range.

[0006] The purpose of this invention is to provide a method for generating hydrogen from olivine serpentinite, comprising the following steps: High-pressure water jet fracture and cavity creation treatment: A high-pressure water jet with an injection pressure of 20MPa–50MPa and an injection flow rate of 0.5L / min–2.0L / min is supplied to the target well section. The high-pressure water jet is used for directional cutting and erosion to construct a main fracture channel that matches the geostress field. Erosion and expansion are then carried out at the end of the main fracture channel and around the wellbore to form a geometrically constrained reaction cavity and fracture zone, resulting in a main fracture-cavity structure containing the main fracture channel, reaction cavity, and fracture zone. The length of the main fracture channel is 0.5m–10m, the width is 2mm–50mm, and the volume of the reaction cavity is 0.005m³. 3 ~2.0m 3 Medium and low pressure water injection hydrogen enrichment treatment: medium and low pressure water injection is carried out continuously or intermittently into the main fracture-cavity structure to generate hydrogen through serpentinization reaction, and the hydrogen is enriched in the reaction cavity; the injection pressure of medium and low pressure water injection is 30% to 70% of the formation fracture pressure, and the water injection flow rate is 0.1L / min to 30L / min.

[0007] This invention utilizes high-pressure water jets to directionally construct a "main fracture-cavity" structure, including a main fracture channel, a reaction cavity, and a fracture zone, in the near-wellbore zone of the target peridotite section. This structure not only serves as a concentrated area of ​​the high specific surface area water-rock reaction interface but also as a local buffer and enrichment space for hydrogen. Subsequently, switching to a medium-low pressure water injection mode continuously induces serpentinization reactions to generate hydrogen, which is then enriched within the reaction cavity and finally extracted in a controlled manner. Through the synergy of the two stages of "high-pressure water jet fracture and cavity creation" and "medium-low pressure water injection for hydrogen generation and enrichment," as well as the closed loop of "monitoring-feedback-local re-modification," integrated development with enhanced reaction, controllable enrichment, and reduced risk is achieved.

[0008] Preferably, in the high-pressure water jet fracture and cavity creation process, the length, width, and volume of the main fracture channel and the reaction cavity are controlled by adjusting the injection pressure, flow rate, and trajectory of the high-pressure water jet, thereby forming a near-wellbore space that meets the requirements of serpentinization reaction and hydrogen enrichment near the wellbore. The near-wellbore space refers to the locally modified volume centered on the wellbore, extending radially from the main fracture channel, and including the reaction cavity and surrounding fracture zone. Its boundary is jointly defined by the effective extension distance of the main fracture channel, the equivalent aperture of the fracture, and the volume of the reaction cavity. Specifically, the length of the main fracture channel is the effective radial extension distance from the wellbore wall to the fracture end, the width is the equivalent aperture of the fracture, and the volume of the reaction cavity is the cavity volume formed by erosion and expansion near the wellbore. This invention utilizes high-pressure water jets to directionally cut, erode, and expand the iron-magnesium mineral-rich rock mass such as olivine near the wellbore, forming a main fracture channel matching the direction of the principal geostress, and constructing a reaction cavity with a certain volume and an irregular inner surface and a surrounding fracture zone at the end of the main fracture and around the wellbore. The main fracture serves as a guide and connector, the cavity serves as a local buffer and enrichment function, and the fractured zone provides a high specific surface area reaction interface. Together, these three elements constitute a near-wellbore concentrated, geometrically designable serpentinization reaction and hydrogen generation unit.

[0009] Preferably, the injection pressure of the high-pressure water jet is 30 MPa, and the injection flow rate is 0.8 L / min. The expansion of the reaction interface is mainly controlled by the injection pressure and injection flow rate of the high-pressure water jet; higher injection pressure and larger injection flow rate can ensure stronger water jet cutting force, making the formation of cracks and reaction cavities more uniform, further increasing the area of ​​the reaction interface, thereby increasing the hydrogen generation rate.

[0010] Preferably, in the high-pressure water jet fracture and cavity creation process, the high-pressure water jet's trajectory adopts a combined trajectory of "directional injection + rotational scanning + axial stepping." The trajectory of the high-pressure water jet is as follows: the deflection angle of the high-pressure water jet relative to the wellbore axis is 30° to 60°, the rotational speed is 0.2 rpm to 5 rpm, the single-point residence time is 1 min to 30 min, and the axial stepping distance is 1 mm to 20 mm. This combined trajectory is used to form a main fracture channel near the wellbore that matches the direction of the principal geostress, and to construct a reaction cavity and a periphery fracture zone with a certain volume at the end of the main fracture and around the wellbore.

[0011] Preferably, in the high-pressure water jet fracture and cavity creation process, a segmented setting and segmented injection method is adopted to construct multiple independent or interconnected main fracture-cavity systems within the same well section.

[0012] Preferably, the injection pressure for medium-low pressure water injection is 40% of the formation fracturing pressure, and the injection flow rate is 0.5 L / min to 10 L / min. More preferably, it is 0.5 to 3 L / min, used to enhance enrichment and avoid hydrogen carryover and escape due to excessive injection flow rate. Hydrogen enrichment and migration are mainly affected by injection pressure and injection flow rate. Higher injection pressure can ensure effective penetration of the water jet and fracture formation, increasing the efficiency of hydrogen accumulation; at the same time, appropriate adjustment of the injection flow rate can effectively control the rate of hydrogen enrichment and avoid hydrogen escape caused by excessively fast injection flow rate. Under medium-low pressure continuous water supply or periodic water injection soaking conditions, the injected water preferentially infiltrates along the main fracture-cavity-fractured zone system, undergoing serpentinization reaction with iron-magnesium rich minerals such as peridotite, generating hydrogen and secondary minerals such as serpentine and iron oxides. Hydrogen gradually accumulates within the main fractures and cavities, forming a near-wellbore "hydrogen enrichment zone," which migrates towards the upper wellbore space under the influence of buoyancy and pressure difference. Secondary minerals are deposited on the fracture and cavity walls, continuously renewing the reaction interface and roughening the local structure. By adjusting the wellhead backpressure and controlling the flowback rhythm, an in-situ hydrogen generation and migration model can be achieved without relying on the natural fracture network, consisting of "near-wellbore fracture and cavity creation - continuous reaction-generated hydrogen - hydrogen enrichment and preservation - production through the dominant channel."

[0013] Preferably, in the medium-low pressure water injection hydrogen enrichment treatment, the mass ratio of the injected water to the peridotite sample is 6:1.

[0014] Preferably, the process of high-pressure water jet fracturing and cavity creation treatment and medium- and low-pressure water injection hydrogen enrichment treatment also includes a monitoring and feedback step: real-time monitoring of injection pressure, return fluid flow rate and hydrogen concentration; based on the monitoring results, when the conductivity or hydrogen generation efficiency of the main fracture-cavity structure decreases, switching to high-pressure water jet fracturing and cavity creation treatment to locally compensate for erosion and expand the cavity of the main fracture-cavity structure, destroying the deposition and sealing on the reaction interface; and then carrying out medium- and low-pressure water injection hydrogen enrichment treatment.

[0015] Preferably, based on monitoring results, when the injection pressure increases by more than 15% compared to the previous stable stage and the hydrogen generation rate decreases by more than 20% compared to the previous stable stage for 6 hours, a high-pressure water jet cracking and cavity-creating treatment step is performed to locally compensate for erosion and expand the cavity of the main crack-cavity structure, destroy the deposited shell on the reaction interface, and then a medium-low pressure water injection hydrogen enrichment treatment step is performed.

[0016] This invention accelerates the formation of the main fracture and reaction cavity by increasing the injection pressure and jetting time of the high-pressure water jet, thereby increasing the exposed area of ​​the reaction interface and enhancing the intensity of the hydrogen generation reaction. During the reaction process, when the reaction slows down, the reaction interface can be stimulated by local pressure pulses and small pressure increases to restore the stability of hydrogen production. This invention deploys pressure, flow rate, and gas composition monitoring units near the wellbore to continuously record parameters such as injection pressure, flowback rate, and hydrogen concentration, tracking the evolution of the conductivity and hydrogen generation efficiency of the main fracture-cavity-fractured zone structure. When monitoring results show an increase in injection pressure, a decrease in flowback rate, or a decrease in hydrogen concentration, it can be determined that the conductivity structure is sealed, passivated, or partially blocked. A short-term pressure pulse or small pressure increase is then used to reactivate the water jet to compensate for erosion and locally expand the cavity, destroying the sedimentary layer and restoring the rough interface, before switching back to medium-low pressure water injection for hydrogen enrichment. This forms a cyclical development model of "high-pressure water jet forcing and cavity creation - medium and low-pressure water injection for hydrogen enrichment - monitoring, evaluation and feedback - local re-modification", which enables the same well section to maintain stable hydrogen generation and production capacity over a longer time scale.

[0017] Compared with the prior art, the present invention has the following technical effects: 1. This invention utilizes water jets to construct a main fracture channel in the near-wellbore zone of the target peridotite well section, and expands it near the wellbore to form a reaction cavity, creating a "main fracture-cavity" structure. The rough surface of the main fracture channel, the inner wall of the reaction cavity, and the surface of the fractured particles collectively provide a fresh peridotite exposure interface with a high specific surface area, significantly increasing the effective water-rock contact area per unit well section. This concentrates and efficiently carries out the serpentinization reaction around the well, significantly improving the hydrogen generation rate per unit well section. Simultaneously, the reaction cavity, as a geometrically constrained local space, effectively buffers and enriches the generated hydrogen, altering the pattern of rapid hydrogen escape along natural fractures. Furthermore, it reduces the risk of hydrogen escape and formation instability within a controllable water injection scale and limited modification range.

[0018] 2. This invention utilizes the main fracture channel to provide a low-resistance advantage, and the reaction cavity to provide a geometrically constrained buffer and enrichment space, allowing generated hydrogen to preferentially accumulate within the peri-wellbore main fracture-cavity system. Combined with wellhead backpressure management and periodic gas production strategies, a "concentrated enrichment followed by smooth production" migration pattern can be formed within the main fracture-cavity system, achieving phased enrichment and controllable release of hydrogen in time and space, significantly improving near-wellbore hydrogen recovery rate and production stability.

[0019] 3. This invention limits the modification scope to the near-wellbore zone, optimizing the near-wellbore reaction interface and conductivity through localized water jet fracturing and cavity creation. Furthermore, high-pressure operation is limited to the brief fracturing and cavity creation phase, while the hydrogen generation phase employs medium-to-low pressure water injection, significantly lower than the fracturing pressure. This "localized fine-tuning + gentle, continuous reaction" approach, compared to large-scale volumetric fracturing, significantly reduces disturbance to the far-field stress field, decreases the risk of induced earthquakes and surrounding rock instability, and makes the water injection scale and energy consumption more controllable.

[0020] 4. The hydrogen generation method of this invention can be directly implemented using existing drilling and completion structures and mature water jet operation equipment, without the need for fundamental modifications to the wellbore structure and surface processes. It features high technical integration, strong field operability, and is suitable for both natural hydrogen exploration and development wells, as well as for testing and application in existing oil and gas wells or geothermal wells, resulting in relatively low promotion costs.

[0021] 5. This invention integrates near-wellbore monitoring and feedback control mechanisms to perceive the coupled evolution of "reaction-seepage-structure" in real time. When the reaction interface becomes passivated due to mineral deposition, local re-modification can be initiated in a timely manner to restore system performance. This closed-loop "construction-production-maintenance" model is conducive to achieving long-term, steady-state or quasi-steady-state hydrogen production, extending the effective development life of a single well. Attached Figure Description

[0022] Figure 1 This is a schematic diagram illustrating the construction of the main fracture channel and reaction cavity in the peridotite well section according to an embodiment of the present invention. Detailed Implementation

[0023] The method of this invention uses a single well as the basic implementation unit, preferably in a wellbore in a target peridotite or other iron-magnesium mineral-rich rock mass where drilling and basic completion operations have been completed. On-site construction revolves around two stages: "near-well directional fracture and cavity creation" and "continuous water supply for hydrogen generation – production through the dominant channel," and closed-loop control is achieved through monitoring and regulation during operation.

[0024] like Figure 1 As shown in the specific implementation plan, the first stage is the identification of target peridotite strata and the selection of optimal well sections. Through comprehensive interpretation of logging curves, wellbore imaging, core and geochemical test results, the well sections with developed iron-magnesium mineral-rich rocks such as peridotite within the wellbore formation are determined. In conjunction with the principal stress direction and wellbore trajectory, suitable stimulation windows for the initiation and propagation of the main fracture are selected.

[0025] Subsequently, the waterjet tool is lowered into the wellbore for near-wellbore directional fracture and cavity creation. The waterjet tool string, equipped with a high-pressure nozzle assembly and a packer, is lowered into the wellbore, positioning the nozzle near the center of the target well section. The packer is then set, isolating the target well section from the upstream and downstream non-working sections, creating an independent working space for fracture and cavity creation and reaction. After tool positioning, the high-pressure waterjet fracture and cavity creation stage begins. The surface high-pressure pump is activated to supply water to the downhole nozzle at the designed injection pressure and flow rate, causing the high-energy water jet to impact the wellbore and the subsequent formation along a predetermined azimuth. By controlling the nozzle azimuth, injection duration, and axial / azimuth movement of the tool, shear failure and erosion cutting are caused in localized areas of the well casing, cement sheath, and outer peridotite mass, forming a main fracture channel that matches the geostress field. After the main fracture is initially connected, high-pressure jets can be maintained to conduct targeted and intensified erosion of the fracture ends and adjacent rock masses, causing rock fragments to loosen, peel off, and be carried out of the wellbore with the flowback fluid. This creates a cavity with a certain volume and irregular inner surface near the wellbore, and a fractured zone with smaller particle size and well-developed fractures forms around the cavity. By adjusting the injection pressure, time, and trajectory of the high-pressure water jet, the length and width of the main fracture and the volume of the reaction cavity can be controlled, ensuring that the near-wellbore space formed by the main fracture-cavity-fractured zone meets the design requirements for hydrogen generation in serpentine chemical reactions. If necessary, a segmented setting and segmented injection method can be adopted, that is, multiple main fracture-cavity structural units can be arranged within the same well section.

[0026] After the fracture and cavity creation stage, the water supply system is smoothly switched from high-pressure to medium-low-pressure operation, entering the medium-low-pressure continuous water supply and serpentinization hydrogen generation reaction stage. At this time, while keeping the water jet tool string position basically unchanged, the high-pressure pump is shut down, and the medium-low-pressure injection pump is activated to continuously / intermittently inject clean water or prepared water into the main fracture-cavity system at an injection pressure far lower than the fracture pressure. The injected water diffuses along the wellbore axially and radially within the main fracture, preferentially wetting the fresh peridotite fracture surfaces in the cavity inner surface and surrounding fractured zones, undergoing serpentinization reactions with iron-magnesium-rich minerals, gradually generating hydrogen and secondary minerals such as serpentine and magnetite. Because the main fracture-cavity structure significantly increases the specific surface area of ​​the near-wellbore region, the serpentinization reaction is concentrated within this system, and the near-wellbore zone becomes the main hydrogen generation reaction zone.

[0027] The process involves hydrogen enrichment and production, as well as wellhead gas-liquid separation. As the reaction proceeds, the generated hydrogen continuously accumulates in the main fracture and reaction cavity, rising upwards to the reaction cavity and upper wellbore space under the influence of buoyancy and formation pressure differential. With appropriate back pressure maintained at the wellhead and in conjunction with the gas-liquid separation device, the gas-liquid two-phase flow in the reaction cavity and main fracture can be introduced into the surface separation system at a set cycle by controlling the flowback rhythm, achieving phased hydrogen production. Specifically, a cyclical operation mode of "water injection-soaking-venting / gas production" can be used. This involves maintaining continuous water injection or soaking for a period within a cycle to enhance the serpentinization reaction rate and increase hydrogen generation efficiency. Then, the wellhead back pressure is reduced or the gas production channel is opened in a short time to release the hydrogen enriched in the near-wellbore cavity and main fracture to the surface. Alternatively, a "continuous low-pressure water injection-synchronous gas production" method can be used at lower injection intensities to bring the hydrogen generation reaction and gas production process close to a steady state.

[0028] During the continuous water supply hydrogen generation-dominant channel production phase, the near-wellbore pressure and component monitoring unit continuously records changes in pressure inside and outside the wellbore, flowback flow rate, and concentration changes of components such as hydrogen. The data acquisition and parameter optimization unit analyzes this information. When a significant increase in injection pressure, a continuous decrease in flowback flow rate, and a decrease or intensification of hydrogen concentration fluctuations are detected, it can be determined that the conductivity of the main fracture-cavity system has decreased or that there is localized sealing or an increase in sedimentary minerals. At this time, short-duration pressure pulses or slight increases in injection pressure can be used to compensate for erosion and expand the cavity in the local area, destroying part of the sedimentary and passivation layers and restoring the rough reaction interface. After the compensation and modification are completed, the system is switched back to the medium-low pressure continuous water supply condition to ensure that the hydrogen generation reaction intensity and hydrogen enrichment capacity are maintained within the target range. Through the periodic combination of "fracture and cavity creation - continuous water supply - monitoring and evaluation - local modification", the main fracture-cavity system can achieve cyclical production within the same well section, supporting steady-state or quasi-steady-state hydrogen generation development over a longer timescale.

[0029] In addition, when there are multiple peridotite sub-layers or multiple sets of structural fracture zones in the same well section, a multi-segment separation method can be adopted to sequentially carry out water jet fracture and cavity creation on each sub-layer, and water supply system and production rhythm can be set for each segment. By combining the opening and closing of segmented valves, the rotation or coordinated operation of different main fracture-cavity systems can be realized to improve the overall hydrogen generation flux and recovery rate of the entire well section.

[0030] It should be noted that this invention relies on an integrated near-wellbore structural unit consisting of "main fracture-cavity-fractured zone" constructed near the wellbore to organically couple the water-rock reaction, hydrogen migration, enrichment, and storage during the hydrogen generation process of olivine serpentinization within the same controlled space. Its synergistic working mechanism is as follows: During the high-pressure water jet fracture and cavity creation stage, a main fracture channel matching the stress field is formed under the influence of the principal geostress direction. Erosion and expansion occur at the main fracture tip and in the adjacent wellbore area, constructing cavities with irregular inner surfaces and surrounding fracture zones. The rough fracture surface of the main fracture, the inner wall of the cavity, and the surface of the fracture zone particles together form a near-wellbore concentrated high specific surface area water-rock reaction interface. Compared to the original scattered fracture system of the formation rocks, this significantly increases the exposed area of ​​fresh peridotite per unit well section, causing serpentinization reactions to occur concentrated within the main fracture-cavity-fracture zone system.

[0031] The main fracture provides a low-resistance, advantageous channel for hydrogen, while the cavity, with its geometric constraints, forms a local buffer and enrichment space. The generated hydrogen preferentially accumulates at the top of the cavity and the end of the main fracture, rather than diffusing widely along natural fractures far from the wellbore. By adjusting the wellhead backpressure and controlling the flowback rhythm, hydrogen is enriched in stages within the main fracture-cavity system before being introduced into the wellbore, achieving a migration mode of "wellbore enrichment and storage - advantageous channel production".

[0032] As the serpentinization reaction progresses, the mineral composition, pore structure, and permeability of the peridotite continuously evolve over time: the reaction and microfracture expansion continuously activate new reaction interfaces, enhancing hydrogen generation intensity in the short term; simultaneously, secondary minerals such as serpentine, carbonates, and iron oxides deposit on the surface of the main fractures and cavities, gradually forming a sealing and passivation layer, reducing conductivity and water-rock contact efficiency. This invention continuously monitors injection pressure, flowback flow, and hydrogen concentration through a near-wellbore pressure and composition monitoring unit. Once a decrease in conductivity or enhanced sealing is identified, local compensation erosion and cavity expansion are implemented using short-term pressure pulses or small pressure increases to destroy part of the sedimentary and passivation layers, restore the rough reaction interface, and then switch back to medium-low pressure continuous water supply conditions. This constitutes a cyclical development mechanism of "fracture and cavity creation - continuous water supply - monitoring and evaluation - local re-modification," ensuring stable and efficient hydrogen extraction over a longer timescale.

[0033] This invention incorporates a gas-liquid separation and safety control unit at the wellhead. Through hydrogen concentration detection, a combustible gas lower explosive limit concentration early warning device, and interlocking valves, it establishes an early warning and automatic shutdown mechanism for hydrogen leakage around the wellhead and surface equipment. Simultaneously, it sets injection pressure and wellhead pressure boundaries for high-pressure fracturing and medium-to-low-pressure water supply conditions, respectively, and coordinates with blowout preventers and choke / kill manifolds to achieve pressure constraint and safety protection throughout the entire process. This enhances near-wellbore stimulation and hydrogen generation while ensuring the operation remains within controllable safety boundaries.

[0034] This embodiment simulates the process of hydrogen generation from serpentinization in peridotite strata using the method of this invention under actual underground conditions. The specific experiment used water jet equipment similar to that used in actual construction sites, including a high-pressure water jet tool, a gas monitoring device, flow and pressure regulating valves, and a data acquisition system.

[0035] High-pressure water jet tools include a high-pressure nozzle assembly (rotary nozzle, intermediate tube), a rotary controller, a packer, and associated tubing or continuous tubing. For example... Figure 1 As shown, a high-pressure pump pressurizes surface water and delivers it through tubing to a downhole nozzle. The nozzle then directs a high-energy water jet onto the wellbore and peridotite layer, cutting, eroding, fracturing, and locally expanding the wellbore to create a main fracture and near-wellbore cavity structure. A packer is installed to isolate non-working sections, ensuring the water jet energy is concentrated on the target layer. This process is implemented within a wellbore where drilling and basic completion have been completed in the target peridotite and other iron-magnesium mineral-rich rock mass.

[0036] Example 1 A method for generating hydrogen from olivine serpentinite includes the following steps: Step 1: Preparation of peridotite samples: Peridotite samples were obtained from the mining area, where the peridotite strata are located at depths of approximately 3000m–3500m and are primarily composed of iron- and magnesium-rich minerals. Analysis of seismic data, well logging curves, and core samples confirmed that the peridotite in this area exhibits well-developed and relatively uniformly distributed structural fractures, making it suitable as a target area for hydrogen generation reactions. After cleaning and drying, the peridotite samples were cut into 100mm × 100mm × 100mm cubes according to experimental requirements. Experimental equipment included: a high-pressure reactor (simulating the wellbore and formation environment), a high-pressure water pump and pipeline (simulating a surface pump unit), a miniature high-pressure water jet nozzle (simulating downhole tools), pressure and temperature sensors, an online gas chromatograph (for monitoring gas components), a data acquisition system, and a gas-liquid separation and collection device.

[0037] Step 2, Water jet cavity creation stage: A simulated wellbore hole with a diameter of 10 mm and a depth of 60 mm was machined axially into a 100 mm × 100 mm × 100 mm peridotite sample. The peridotite sample was placed in a reactor simulating a wellbore and sealed. The internal temperature of the reactor was raised to 160°C and the pressure was raised to 15 MPa, and kept constant for 2 hours to simulate the temperature and pressure conditions of the target formation and stabilize the system.

[0038] The high-pressure water pump was started, and the water jet injection pressure was set to 30 MPa and the nozzle flow rate was set to 0.8 L / min. The nozzle was sprayed at a 45° angle and rotated at a speed of 1 rpm. After spraying for 10 minutes at each predetermined position, it was advanced 5 mm axially to form macroscopic fractures (simulating the main fracture) and expansion areas at the fracture ends (simulating reaction cavities) in the periphery of the wellbore, and a certain range of fracture zone was formed.

[0039] After the fracture and cavity were created, the equivalent length of the main fracture was measured to be approximately 40 mm, and the average equivalent aperture was approximately 1.2 mm; the volume of the cavity was approximately 2.8 cm³. 3 The interface of the joint formation zone was characterized, and the roughness increased from 6.1 μm to 8.1 μm (an increase of approximately 33%), while the specific surface area increased from 0.52 m² / s². 2 / g increased to 0.73m 2 / g (increases by approximately 40%).

[0040] Step 3, Continuous Hydrogen Generation and Monitoring Phase: The high-pressure water jet pump was stopped and switched to a medium-low pressure water injection pump. Water was continuously injected into the system at 5 MPa (40% of the simulated fracture pressure) at a flow rate of 2.0 L / min, maintaining a water-to-rock ratio of 6:1. The water-to-rock ratio is the ratio of the mass of injected water to the mass of the peridotite sample; the mass of the injected water was measured using the injection flow rate and time.

[0041] The online gas chromatograph was turned on to continuously monitor the volume fractions of hydrogen, methane, nitrogen, and other components in the exhaust gas. Injection pressure, water flow rate, temperature, and cumulative water injection volume were recorded to ensure stable reaction conditions. The hydrogen production rate per unit time was used as the indicator, and the hydrogen production process was statistically analyzed over a continuous 48-hour period.

[0042] Step 4, Hydrogen enrichment and extraction: A back pressure of 1.5 MPa is applied by adjusting the opening of the reactor outlet valve, causing the generated gas to preferentially reside and accumulate in the "reaction cavity" region. A periodic gas sampling strategy is adopted: every 12 hours, the outlet valve is briefly opened for 5 minutes to introduce the enriched gas into a gas-liquid separator for collection and analysis.

[0043] Statistics show that under periodic gas extraction conditions, the volume fraction of hydrogen in the exhaust gas remains stable at 35%–40%. The stability is evaluated using the coefficient of variation (CV) of the hydrogen integral fraction; the CV for Example 1 is 0.15.

[0044] Step 5, Performance Degradation and Remodeling: If, under constant water injection flow, the injection pressure rises by more than 15% and continues for 6 hours during a relatively stable phase, while the hydrogen generation rate decreases by more than 20% compared to the previous stable phase and continues for 6 hours, then it is determined that the reaction interface has undergone deposition and sealing, leading to passivation.

[0045] Triggering Re-modification: The high-pressure water pump (30MPa) was restarted, and targeted spraying was performed near the inner wall of the cavity for 2 minutes to disrupt the deposited layer; then, the reaction was switched back to the medium-low pressure water injection mode of step 3 to continue. After re-modification, the hydrogen generation rate recovered to approximately 92% of its pre-decay level, and the hydrogen gas integral recovered to 33%–38%, indicating that the closed-loop operation of "build-produce-maintain" can restore the reaction interface and conduction capacity and extend the effective hydrogen generation stage.

[0046] Comparative Example 1 The difference from Example 1 is as follows: No water jet cavitation or back pressure was applied for enrichment.

[0047] Test 1.

[0048] Gas was collected using the same gas chromatography monitoring and 12-hour sampling intervals. Statistical results showed that under periodic gas production conditions, the hydrogen volume fraction in the gas discharged from Comparative Example 1 within 48 hours ranged from 18% to 26%, with significant fluctuations and a coefficient of variation of 0.34. In Example 1, the hydrogen volume fraction in the gas discharged within 48 hours remained stable at 35% to 40%, with a coefficient of variation of 0.15; and the cumulative hydrogen production over 48 hours was 1.52 times that of Comparative Example 1. Stability was evaluated using the coefficient of variation (CV) of the hydrogen volume fraction. Example 1 showed a significantly lower coefficient of variation than Comparative Example 1, indicating higher hydrogen production stability. Compared to Comparative Example 1, Example 1, without increasing the medium-low pressure water injection, significantly increased the effective water-rock contact interface through the "main fracture-cavity system," and improved hydrogen enrichment and production stability through cavity geometric constraints and back pressure management, thus verifying the beneficial effects described in this invention.

[0049] Example 1 and Comparative Example 1 were compared and verified under the same temperature and pressure conditions and the same medium-low pressure water supply conditions. After the water jet fracture and cavity were created in Example 1, the roughness and specific surface area of ​​the fracture / cavity interface were tested. The results showed that the surface roughness of the fracture increased by about 33% compared with Comparative Example 1, and the specific surface area of ​​the fracture / fracture zone increased by about 40% compared with Comparative Example 1. This indicates that the water jet treatment significantly increased the fresh peridotite exposed interface and the effective water-rock contact area.

[0050] Regarding hydrogen production capacity, online gas chromatography was used to continuously monitor the components of the emitted gas and the hydrogen production rate was calculated by combining the gas production rate measurement. Using the average hydrogen production rate during the stable phase as a comparative indicator, the hydrogen production rate of Example 1 was approximately 1.52 times that of Comparative Example 1; characterized by the relative increase before and after the stable phase, the improvement in Example 1 was approximately 39% (all the above rate statistics are based on the same sampling interval and the same measurement caliber).

[0051] Regarding the enrichment effect, by adjusting the outlet valve opening to create back pressure and adopting a periodic gas production strategy, the hydrogen gas fraction in Example 1 remained stable at 35%–40% during the experiment, while in Comparative Example 1 it was 18%–26%. This indicates that the "main fracture-cavity system" can improve the enrichment degree of hydrogen in the near-wellbore space under the action of geometric constraints and back pressure management. To evaluate the enrichment stability, the coefficient of variation (CV) of the H2 volume fraction sequence was used, calculated as CV = σ / μ, where μ is the mean of the volume fraction sequence and σ is the standard deviation. The CV of Example 1 was 0.15, lower than that of Comparative Example 1 (0.34), indicating that Example 1 has higher enrichment stability and controllable production characteristics.

[0052] In summary, laboratory application examples have verified the effectiveness of the method of this invention in enhancing water-rock reactions in the near-wellbore region, and its ability to successfully enrich and extract hydrogen on a certain scale. By precisely controlling fractures and reaction space through water jet technology, this method significantly improves the efficiency of hydrogen generation from serpentinization in peridotite, demonstrating good engineering feasibility and providing a theoretical basis and technical support for subsequent large-scale practical applications.

[0053] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range, as well as any value between the two endpoints, can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of this invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended scope of protection is intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of this invention.

[0054] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of protection of this invention and its equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for hydrogen generation by serpentinization of peridotite, characterized in that, Includes the following steps: High-pressure water jet fracture and cavity creation treatment: A high-pressure water jet with an injection pressure of 20MPa–50MPa and an injection flow rate of 0.5L / min–2.0L / min is supplied to the target well section. The high-pressure water jet is used for directional cutting and erosion to construct a main fracture channel that matches the geostress field. Erosion and expansion are then carried out at the end of the main fracture channel and around the wellbore to form a geometrically constrained reaction cavity and fracture zone, resulting in a main fracture-cavity structure containing the main fracture channel, reaction cavity, and fracture zone. The length of the main fracture channel is 0.5m–10m, the width is 2mm–50mm, and the volume of the reaction cavity is 0.005m³. 3 ~2.0m 3 ; Medium and low pressure water injection hydrogen enrichment treatment: medium and low pressure water injection is continuously or intermittently carried out into the main fracture-cavity structure to generate hydrogen through serpentinization reaction, and the hydrogen is enriched in the reaction cavity. The injection pressure for medium and low pressure water injection is 30% to 70% of the formation fracturing pressure, and the injection flow rate is 0.1 L / min to 30 L / min.

2. The method for hydrogen generation from olivine serpentinization according to claim 1, characterized in that, The injection pressure of the high-pressure water jet is 30 MPa, and the water flow rate is 0.8 L / min.

3. The method for hydrogen generation from olivine serpentinization according to claim 1, characterized in that, The trajectory of the high-pressure water jet is as follows: the deflection angle of the high-pressure water jet relative to the well shaft axis is 30° to 60°, the rotation speed is 0.2 rpm to 5 rpm, the single-point residence time is 1 min to 30 min, and the axial step distance is 1 mm to 20 mm.

4. The method for hydrogen generation from olivine serpentinization according to claim 1, characterized in that, The injection pressure for medium and low pressure water injection is 40% of the formation fracturing pressure, and the injection flow rate is 0.5L / min to 10L / min.

5. The method for hydrogen generation from olivine serpentinization according to claim 1, characterized in that, In the medium- and low-pressure water injection hydrogen enrichment treatment, the mass ratio of the injected water to the peridotite sample was 6:

1.

6. The method for hydrogen generation from olivine serpentinization according to claim 1, characterized in that, The process of high-pressure water jet cavitation and medium-low pressure water injection for hydrogen enrichment also includes: Monitoring and feedback processing steps: Real-time monitoring of injection pressure, return fluid flow rate, and hydrogen concentration; Based on the monitoring results, under the condition of constant water injection flow, when the injection pressure increases by more than 15% and the hydrogen generation rate decreases by more than 20% compared with the previous stable stage for 6 hours, a high-pressure water jet crack and cavity creation treatment step is carried out to locally compensate for erosion and expand the cavity of the main crack-cavity structure, destroy the deposited shell on the reaction interface, and then a medium-low pressure water injection hydrogen enrichment treatment step is carried out.

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