Coal bed gasification method based on high-temperature desorption-pressure relief antifouling double drive

Abstract

The present application belongs to the technical field of coal seam gasification control, and specifically discloses a coal seam gasification method based on high-temperature desorption-pressure relief-transparency enhancement double driving. By synchronously collecting temperature fields, rock stress fields and gas pressure fields in coal seams and combustion empty areas, and delimiting high-temperature pyrolysis desorption zones, pressure relief-transparency enhancement zones and gas migration resistance zones in three-dimensional geological space, the geometric accuracy of boundary identification of key role areas is significantly improved. At the same time, on the basis of fine delimitation of high-temperature pyrolysis desorption zones, pressure relief-transparency enhancement zones and gas migration resistance zones, the spatial topological relationship between the high-temperature pyrolysis desorption zones and the pressure relief-transparency enhancement zones is further quantitatively identified, and different control strategies are implemented according to whether they are overlapped or separated or different coupling states, which can identify the imbalance of the dominant mechanism and carry out control optimization under non-coordinated working conditions such as no gas but road or no road but gas, thereby significantly reducing the disaster risk caused by gas accumulation and the waste of gasification channel resources.

Description

Technical Field

[0001] This invention belongs to the field of coalbed gasification control technology, and specifically discloses a coalbed gasification method based on high-temperature desorption-pressure relief and permeability enhancement dual drive. Background Technology

[0002] Coal, as a crucial component of the energy structure, contains abundant coalbed methane resources. However, in certain regions, low-permeability, high-gas coal seams, due to their extremely low permeability and strong gas adsorption capacity, render traditional underground extraction methods inefficient, resulting in poor gas pre-extraction. To address these challenges, underground in-situ coal gasification technology has emerged. This technology aims to directly convert underground coal into combustible gas and simultaneously extract the desorbed gas, achieving the goal of producing gaseous fuels without actual coal mining.

[0003] In this technical system, high-temperature thermal desorption and pressure relief and permeability enhancement in the combustion-ghost zone are considered two physical mechanisms for improving gas recovery. High-temperature thermal desorption refers to the transfer of heat generated during the gasification process to the surrounding coal seam, causing adsorbed gas molecules to gain energy and detach from the coal surface to become free. Pressure relief and permeability enhancement, on the other hand, refers to the redistribution of stress in the overlying strata as cavities are formed during coal combustion, resulting in numerous fractures that improve the permeability of the coal and rock mass and provide pathways for gas migration.

[0004] However, current gasification technologies are still in a relatively rudimentary and passive state in utilizing these two driving mechanisms. Specifically: First, in the geological environment, high-temperature thermal desorption and the pressure relief effect of the combustion air zone originate from the heat energy released by the gasification reaction and the redistribution of surrounding rock stress, respectively. Spatially, each induces the formation of action domains with specific physical response characteristics, providing conditions for gas release and migration. However, the spatial development morphology of the high-temperature thermal desorption zone and the pressure relief and permeability enhancement zone is extremely irregular. Existing technologies mainly rely on scattered point sensor data for empirical judgment, making it difficult to accurately define the three-dimensional boundaries of these two key action areas, thus restricting the refined control of the gasification process.

[0005] Furthermore, due to geological conditions, the development of these two areas is often asynchronous. Existing gasification operations mostly employ fixed injection parameters or extensive control strategies based on feedback from a single physical quantity, which easily induces two types of uncoordinated operating conditions: one is that the high-temperature thermal desorption zone develops too rapidly, resulting in a large amount of gas desorption, but due to the lag in the pressure relief and permeability enhancement zone, there is a lack of necessary seepage channels, causing gas retention and creating a high-pressure risk; the other situation is that the pressure relief and permeability enhancement zone expands preferentially, which improves permeability, but due to insufficient temperature, the amount of gas desorption is limited, failing to fully utilize the existing high-quality channels and resulting in resource waste. Summary of the Invention

[0006] To solve the above-mentioned technical problems, or at least partially solve them, the present invention provides a coalbed gasification method based on high-temperature desorption-pressure relief and permeability enhancement dual drive.

[0007] The objective of this invention can be achieved through the following technical solution: a coalbed gasification method based on high-temperature desorption-pressure relief and permeability enhancement, comprising the following steps: S1, synchronously collecting in-situ monitoring data of temperature field, rock mass stress field, micro-fracture events and gas pressure distribution from a sensor network deployed in the coal seam and surrounding rock of the combustion zone.

[0008] S2. In three-dimensional geological space, delineate the high-temperature thermal desorption zone based on temperature field data, delineate the pressure relief and permeability enhancement zone based on rock mass stress field data and micro-fracture events, and delineate the gas migration stagnation zone based on gas pressure distribution data and in combination with local geological structures.

[0009] S3. Determine the spatial relationship between the high-temperature thermal desorption zone and the pressure relief and permeability enhancement zone.

[0010] S31. When the two zones do not intersect in space, identify the relative positions of the high-temperature thermal desorption zone and the pressure relief and permeability enhancement zone in three-dimensional space, and output the dominant action mode in combination with the distribution of the gas migration stagnation zone.

[0011] S32. When there is spatial overlap between the two regions, identify the dominant region of thermo-pressure coupling within the overlap area.

[0012] S4. Trigger the corresponding regulatory action based on the dominant action mode or the type of dominant region.

[0013] Combining all the above technical solutions, the positive effects of this invention are as follows: 1. By simultaneously collecting temperature field, rock stress field and gas pressure field in the surrounding rock of coal seam and combustion zone, this invention delineates high-temperature thermal desorption zone, pressure relief and permeability enhancement zone and gas migration stagnation zone in three-dimensional geological space, breaking through the limitations of traditional point monitoring, significantly improving the geometric accuracy of boundary identification of key action areas, and providing refined and spatially explicit decision-making basis for coal gasification.

[0014] 2. Based on the precise delineation of the high-temperature thermal desorption zone, the pressure relief and permeability enhancement zone, and the gas migration stagnation zone, this invention further quantitatively identifies the spatial topological relationship between the high-temperature thermal desorption zone and the pressure relief and permeability enhancement zone. Based on different coupling states such as whether they overlap or separate, differentiated gas injection and extraction control strategies are implemented. This mechanism can identify the imbalance of the dominant mechanism and optimize its control under non-coordinated working conditions such as gas without a path or a path without gas, thereby significantly reducing the risk of gas accumulation and disaster and the waste of gasification channel resources. Attached Figure Description

[0015] The present invention will be further described with reference to the accompanying drawings, but the embodiments in the drawings do not constitute any limitation on the present invention. For those skilled in the art, other drawings can be obtained based on the following drawings without creative effort.

[0016] Figure 1 This is a diagram illustrating the implementation steps of the method of the present invention.

[0017] Figure 2 This is a flowchart illustrating the delineation of the gas migration stagnation zone in this invention.

[0018] Figure 3 This is a flowchart for determining the dominant action mode when two regions do not overlap in space in this invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] See Figure 1 As shown, the present invention proposes a coalbed gasification method based on high-temperature desorption-pressure relief and permeability enhancement dual drive, including the following steps: S1, synchronously collecting in-situ monitoring data of temperature field, rock mass stress field, micro-fracture events and gas pressure distribution from the sensor network deployed in the coal seam and surrounding rock of the combustion zone.

[0021] During the in-situ underground gasification of coal, the coal body continuously releases a large amount of heat energy due to the pyrolysis reaction, causing the local temperature to rise rapidly and diffuse to the surrounding coal seams through heat conduction, forming a dynamically evolving temperature field. Under the action of this thermal field, the gas molecules adsorbed on the surface of the micropores of the coal matrix gain sufficient energy to overcome the adsorption barrier, undergo significant desorption, and transform into free gas.

[0022] The physical state of this gas undergoing a large-scale transformation from an adsorbed state to a free state is precisely the essential characteristic and identification basis of the high-temperature thermal desorption zone. Therefore, the temperature field of the coal seam constitutes a prerequisite for the formation of the high-temperature thermal desorption zone.

[0023] Furthermore, considering that during the in-situ underground gasification of coal, the coal undergoes a controlled combustion reaction under the injection of oxidizing gases, continuously consuming coal and forming a combustion goaf. As the combustion goaf expands, the overlying and lateral surrounding rocks become mechanically unstable due to the loss of the original coal support, leading to a redistribution of the original geostress field. This stress adjustment process induces compressive deformation and even tensile-shear fracturing in the surrounding rocks, thereby forming numerous fissures in the rock mass and improving the permeability of the coal-rock mass.

[0024] This state of rock mass damage and increased permeability driven by stress unloading is the physical characteristic of the stress-relief and permeability-enhancing zone. Therefore, the rock mass stress field and its accompanying micro-fracture activity together constitute the prerequisite and identifying condition for the formation of the stress-relief and permeability-enhancing zone.

[0025] Furthermore, during coalbed gasification, the heat released by the pyrolysis reaction of the coal body causes a large amount of adsorbed gas to desorb, while the pressure relief effect induces the expansion of coal and rock fractures. Both factors jointly drive the accumulation of free gas in the pores. However, due to factors such as the local structural closure and insufficient channel connectivity, gas migration is obstructed in some areas, causing gas to stagnate in a limited space, thus resulting in temporal and spatial variations in gas pressure.

[0026] This abnormally high gas pressure and the lack of pressure equilibrium with the surrounding area are key characteristics of gas migration stagnation zones. Therefore, gas pressure distribution data constitute the direct basis and foundation for identifying gas migration stagnation zones.

[0027] This stagnation zone does not directly correspond to the high-temperature thermal desorption zone or the pressure relief and permeability enhancement zone, but rather truly reflects the physical state of the actual obstruction of gas migration in the coal seam. Its value lies in providing direct observational evidence of gas seepage behavior, effectively compensating for the blind spots and lags that exist when relying solely on the high-temperature thermal desorption zone and the pressure relief and permeability enhancement zone for gasification extraction control, and improving the accuracy and adaptability of the control strategy to the actual gas flow response.

[0028] As a preferred implementation of the above scheme, the specific data acquisition process for in-situ monitoring is as follows: a distributed temperature measurement fiber optic network is embedded along the pre-set gasification channel and the surrounding rock of the combustion zone to acquire continuous spatial temperature field data.

[0029] It can be explained that the spatial temperature field reflects the temperature distribution data at various locations in the three-dimensional space of the coal seam and the surrounding rock of the combustion zone.

[0030] In the coal seam and the roof and floor strata, stress sensors and microseismic monitoring probe arrays are deployed in a three-dimensional grid to capture rock mass stress field data and micro-fracture event signals.

[0031] It can be explained that the rock mass stress field reflects the stress state data of the coal seam and its roof and floor surrounding rock in three-dimensional space.

[0032] In one embodiment, the process of capturing micro-fracture event signals using a microseismic monitoring probe array is as follows: First, microseismic monitoring probes are deployed in a three-dimensional spatial grid pattern in the coal seam and the surrounding rock of the roof and floor.

[0033] When a coal and rock mass undergoes micro-fractures under the coupling of high temperature and stress, it will release elastic strain energy instantaneously, exciting high-frequency elastic waves propagating in the form of P-waves and S-waves, i.e., microseismic signals.

[0034] These signals propagate through the rock mass and are received by nearby microseismic monitoring probes.

[0035] Next, the micro-vibration monitoring probe collects continuous waveform data and makes an initial judgment on the waveform by setting an amplitude threshold, such as the absolute amplitude exceeding the background noise level by several times.

[0036] If multiple microseismic monitoring probes simultaneously record amplitude responses higher than the amplitude threshold within a short period of time, it is determined that a micro-fracture event has been captured.

[0037] Clusters of gas pressure and concentration sensors are installed at intervals inside the gas extraction channels to monitor the pressure distribution data of the gas.

[0038] It can be seen that the pressure distribution of gas reflects the gas pressure data at various spatial locations in the coal seam pores.

[0039] Temperature field data, rock mass stress field data, and gas pressure distribution data are spatiotemporally aligned to generate an in-situ monitoring dataset.

[0040] In in-situ data acquisition, due to differences in the acquisition frequencies and triggering sequences of various sensors, time alignment processing is required to unify different physical quantities into the same time window. Simultaneously, spatial registration integrates heterogeneous monitoring data into a unified three-dimensional geological spatial framework. This spatiotemporal collaborative alignment mechanism provides a geometrically consistent, temporally synchronized, and physically comparable multi-field coupled data foundation for delineating high-temperature thermal desorption zones, depressurization and permeability enhancement zones, and gas migration stagnation zones.

[0041] S2. In three-dimensional geological space, delineate the high-temperature thermal desorption zone based on temperature field data, delineate the pressure relief and permeability enhancement zone based on rock mass stress field data and micro-fracture events, and delineate the gas migration stagnation zone based on gas pressure distribution data and in combination with local geological structures.

[0042] In an optional embodiment of the present invention, the process of delineating the high-temperature thermal desorption zone is as follows: the acquired spatial temperature field data is divided into grids to form several spatial units.

[0043] Understandably, the raw temperature field data exists in linear or discrete point form. Through three-dimensional meshing, temperature information can be interpolated or mapped to each spatial unit, constructing a structured temperature field covering the entire monitoring area. Furthermore, given that the high-temperature thermal desorption zone is essentially a spatially continuous physical domain, its identification depends on the adjacency relationships between high-temperature units. Only after meshing can it be determined which high-temperature units are connected to each other; therefore, the mesh units constitute the basic geometric units delineating the high-temperature thermal desorption zone.

[0044] The temperature values ​​of each spatial unit are compared with the critical desorption temperature of coal gas. Continuous spatial units with temperatures higher than the critical desorption temperature of coal gas are selected and topologically connected to construct the framework of the high-temperature region.

[0045] It is important to understand that the critical desorption temperature of coal gas refers to the lowest temperature threshold at which adsorbed gas in coal begins to desorb rapidly and in large quantities due to thermal energy input under specific pressure conditions. In engineering practice, this temperature is usually between 150°C and 200°C. Below this temperature, the thermal desorption effect is weak; above this temperature, the thermal desorption effect increases, causing the adsorbed gas to rapidly convert into free gas.

[0046] The high-temperature thermal desorption zone is defined as an active zone for gas desorption dominated by thermal drive. The critical desorption temperature is the turning point from negligible to significant thermal desorption. Only when the coal temperature reaches or exceeds this critical value can adsorbed gas undergo significant and continuous thermal desorption and be converted into mobile free gas.

[0047] The high-temperature region framework constructed based on this ensures that the delineated region has actual thermal desorption capacity.

[0048] For each spatial unit in the high-temperature region skeleton, temperature time series data is extracted, the temperature change rate between adjacent time steps is calculated, and compared with the preset transient disturbance criterion threshold. For spatial units whose temperature change rate does not reach the transient disturbance criterion threshold, the duration of high temperature is further statistically analyzed.

[0049] If a spatial cell meets any of the following conditions, it is determined to be a transient high-temperature cell: (1) The temperature change rate of adjacent time steps is higher than the transient disturbance criterion threshold.

[0050] (2) The duration of high temperature is shorter than the duration of effective heat effect.

[0051] Given that the high-temperature thermal desorption zone not only needs to have sufficient thermal desorption capacity to trigger significant gas desorption, but also must have good thermal stability to ensure that the continuous effect of thermal energy on the coal body can effectively drive gas desorption and maintain stable gas production, the preliminary high-temperature zone framework cannot be directly equated with the final high-temperature thermal desorption zone. Further thermal stability assessment is required.

[0052] In thermal stability assessment, the rate of temperature change between adjacent time steps is defined as the ratio of the absolute value of the temperature difference between two moments to the time interval, used to quantify the intensity of local temperature fluctuations. A larger rate of change indicates a more unstable thermal field, potentially stemming from transient combustion disturbances. Therefore, a transient disturbance criterion threshold is introduced as an upper limit for stability assessment. This threshold can be determined based on background thermal fluctuations, which are the natural temperature fluctuation levels under undisturbed conditions. The specific determination process is as follows: In the early stages of the gasification process, a sufficiently long time window, typically greater than 1 hour, with no known significant external disturbances, is selected as the background reference period.

[0053] For each spatial cell, continuous temperature time series data is extracted within the selected background reference period, and the rate of temperature change of adjacent time steps is calculated for the series.

[0054] Calculate the mean and standard deviation of the temperature change rate series.

[0055] Since the rate of temperature change under background conditions is usually small and its distribution is approximately normal, the standard deviation can characterize the degree of dispersion of background thermal fluctuations.

[0056] The transient disturbance criterion threshold is set as a multiple of the mean temperature change rate during the background reference period plus the standard deviation. For example, the transient disturbance criterion threshold is set as the mean temperature change rate plus twice the standard deviation.

[0057] However, even if the rate of temperature change is below the transient disturbance criterion threshold, it is still insufficient to fully demonstrate that the region is under effective thermal action. Therefore, the duration of high temperature is further introduced as a second criterion, which reflects the cumulative effect of thermal action. If the duration of high temperature is too short, even if the temperature fluctuation is small during the duration, it is insufficient to complete the entire process of gas from adsorption to full desorption and diffusion into the seepage channel, making it difficult to form an effective contribution to gas production.

[0058] Therefore, the effective thermal action time is set as the lower limit requirement for thermal stability. This time can be set to 3 to 5 times the gas desorption time constant to ensure that the continuous action of the thermal field is sufficient to drive the effective release of most of the adsorbed gas. The gas desorption time constant is the time required for the coal sample to desorb 63.2% of the adsorbed gas at a constant temperature, and this value is usually between 1 and 5 hours.

[0059] In summary, by using the dual constraints of temperature change rate and high temperature duration, spatial units that possess both thermal intensity and thermal stability can be effectively identified, thereby extracting high-temperature thermal desorption regions based on the high-temperature regional framework.

[0060] In the constructed high-temperature region skeleton, all identified transient high-temperature units are removed, and the remaining spatial units are reconstructed in three dimensions and fitted with an equivalent breadth to generate a high-temperature thermal desorption region.

[0061] Since the retained spatial units are still discretely distributed, in order to ensure the spatial continuity and topological integrity of the high-temperature thermal desorption zone, these units are reconstructed into continuous geometric entities in a unified three-dimensional geological coordinate system through three-dimensional spatial reconstruction.

[0062] Based on this reconstruction, an equivalent breadth fitting is further performed to fit a smooth, closed, and completely enclosing outer boundary surface that covers all effective elements. This process can effectively eliminate jagged edges, local holes, or isolated fragments caused by mesh discretization.

[0063] Ultimately, the resulting three-dimensional closed entity with geometric shape and continuous boundaries is the high-temperature thermal desorption zone.

[0064] In a further optional embodiment of the present invention, the delineation process for the pressure relief and transparency enhancement zone is as follows: the location of micro-fracture events captured by the microseismic monitoring array is determined, and a microseismic event point cloud is formed.

[0065] By applying three-dimensional spatial density clustering to the point cloud of microseismic events, the regions where the spatial distribution of microseismic events is concentrated are delineated, namely, the dense zone of micro-rupture events.

[0066] It should be noted that the high-density clustering of microseismic events indicates that the local coal and rock have undergone brittle fracture or shear slip, marking a concentrated area of ​​damage and fractures. The interconnection of numerous microfractures in this area can increase local permeability, thus this dense zone serves as an indicative area of ​​potential permeability enhancement.

[0067] The rock stress field data collected by the stress sensor is mapped to a spatial grid consistent with the temperature field.

[0068] For each spatial element, the stress value at the corresponding location is obtained, and the adjacent region is constructed by combining the adjacent elements.

[0069] In the specific implementation of the above scheme, the adjacent region of each spatial unit is composed of spatial units that are directly adjacent to it in the three-dimensional mesh, reflecting the background field characteristics of the local stress environment in which the unit is located.

[0070] By comparing the stress value of each spatial unit with the initial stress state, if the stress value is lower than the initial stress state, it is determined that there is a stress reduction.

[0071] It should be added that the initial stress state refers to the distribution of the in-situ stress field of the coal and rock mass under natural equilibrium conditions before the implementation of the underground in-situ coal gasification project.

[0072] The stress value of each spatial unit is compared with the average stress level of its adjacent region. If the stress value is lower than the average stress level, it is determined that a local stress gradient exists.

[0073] The aforementioned stress reduction amplitude reflects the degree of unloading of the rock mass relative to its initial geostress state under the influence of gasification disturbance in the temporal dimension, satisfying the absolute stress relief condition. The local stress gradient, in the spatial dimension, characterizes the stress difference between this unit and its neighboring areas, reflecting the spatial concentration and directionality of the stress relief effect. These two factors, from the perspectives of temporal evolution and spatial distribution respectively, together constitute the dual criteria for identifying stress reduction units.

[0074] If a spatial element simultaneously exhibits stress reduction and local stress gradient, then the element is determined to be a stress-reducing element.

[0075] Three-dimensional connectivity clustering is performed on all elements identified as having reduced stress, and these clusters are merged to form stress-reduced regions.

[0076] In the stress-reduced region, the spatial boundary of the dense micro-fracture event zone is modified and smoothed to form a pressure-relief and permeability-enhancing zone.

[0077] Since microfracture events only characterize the occurrence of fracture damage in rock mass, although they can serve as an indicator signal of potential permeability enhancement, their causes are multifaceted. Not all microseismic activity is induced by effective pressure relief. Pressure relief is a prerequisite for increased coal and rock permeability. Without stress reduction support, even with microseismic activity, fractures may close rapidly and fail to form a continuous flow channel. Therefore, true pressure relief and permeability enhancement must simultaneously satisfy two physical conditions: stress reduction and effective fracture connectivity.

[0078] Based on this, after identifying the dense zone of micro-fracture events, it is still necessary to further determine the stress reduction area. By limiting the dense zone of micro-fracture events to the stress reduction area, it is equivalent to conducting a mechanical rationality screening of the micro-seismic events, ensuring that the delineated area truly reflects the synergistic effect of pressure relief and transparency enhancement.

[0079] Furthermore, in the process of identifying stress reduction areas, by introducing dual criteria of time and space dimensions, it is possible to more accurately distinguish between effective pressure relief areas and non-pressure relief disturbance areas, thereby improving the physical rigor of area identification.

[0080] Furthermore, after delineating the stress reduction region, considering the influence of noise such as positioning errors on the original microseismic point cloud, its cluster boundaries are often jagged, fragmented, or contain isolated points. Under the physical constraint of the stress reduction region, boundary correction and smoothing, such as surface fitting and morphological closing operations, can generate a continuous and closed spatial envelope, which is more suitable for subsequent spatial relationship analysis with the high-temperature thermal desorption zone.

[0081] See Figure 2 As shown, in a further optional embodiment of the present invention, the gas migration stagnation zone is defined by the following process: based on the collected gas pressure distribution data, a set of spatial points in three-dimensional space where the gas pressure is higher than the critical pressure is located.

[0082] The aforementioned intermediate critical pressure refers to the threshold pressure level that characterizes the risk of obstructed gas migration. Its physical meaning is that when the local gas pressure exceeds this threshold, it indicates significant gas accumulation in the area, meeting the preconditions for the formation of migration barriers. Only when this fundamental characteristic of abnormal gas accumulation is met can geological conditions be further considered to delineate the gas migration obstruction zone.

[0083] The critical pressure can be determined based on historical monitoring data, taking the percentile value of the gas pressure distribution during normal extraction or gasification, such as the 95th percentile, as the critical value.

[0084] Based on the local geological structural characteristics of the spatial point set, high-pressure areas located at structural turning points or without a connecting path to known high-permeability channels are identified as gas migration stagnation zones.

[0085] In one embodiment, structural turning points such as the top of an anticline, the core of a syncline, or a fault-locked segment typically exhibit geometric closure. When the high-pressure spatial point set is located in such structural locations, it indicates that it is situated within a naturally closed geological unit, satisfying structural closure.

[0086] High-permeability channels are known, such as natural fracture zones, hydraulically fractured networks, or historical main extraction channels.

[0087] Although high-pressure areas with gas pressures above the critical pressure constitute a necessary prerequisite for identifying gas migration stagnation zones, they only reflect the state of gas accumulation and are not sufficient to confirm the existence of migration obstruction. If the high-pressure zone is in an open structural environment, the gas can still be effectively discharged and may not form a stagnation zone.

[0088] Therefore, it is necessary to further consider the local geological structure characteristics of the high-pressure area. Only when the high-pressure area simultaneously meets the requirements of structural sealing or lacks an effective seepage path can it be identified as a gas migration stagnation zone.

[0089] It should be added that the delineation of the high-temperature thermal desorption zone and the pressure relief and permeability enhancement zone must be based on a synchronous time period to ensure the consistency of the two in terms of spatiotemporal reference, and to avoid incorrect superposition due to time misalignment when determining the spatial relationship, which would lead to incorrect conclusions of coordination or mismatch.

[0090] S3. Determine the spatial relationship between the high-temperature thermal desorption zone and the pressure relief and permeability enhancement zone: S31. When the two zones do not intersect in space, identify the relative positions of the high-temperature thermal desorption zone and the pressure relief and permeability enhancement zone in three-dimensional space, and output the dominant action mode in combination with the distribution of the gas migration stagnation zone.

[0091] The purpose of determining the spatial relationship after delineating the high-temperature thermal desorption zone and the depressurization and permeability enhancement zone is to assess the degree of synergy driven by thermodynamic coupling, thereby identifying whether the gas desorption and migration channels are matched during the gasification process, and providing a basis for dynamic regulation.

[0092] When the two zones do not overlap in space, it indicates that the thermal desorption and pressure relief permeability enhancement processes are not synchronized. Although the high-temperature thermal desorption zone has promoted the desorption of a large amount of gas, the zone lacks a high-permeability fracture network formed by stress unloading; or although the pressure relief permeability enhancement zone has good seepage conditions, the temperature has not reached the effective desorption threshold, and the amount of gas released is limited.

[0093] This type of state corresponds precisely to two uncoordinated operating conditions: having air but no way to pass through and having a way to pass through but no air.

[0094] In response to the aforementioned uncoordinated operating conditions, it is necessary to identify the dominant mode of action in order to take targeted regulatory actions. Blindly regulating without identifying the dominant mode may exacerbate the imbalance.

[0095] See Figure 3 As shown, the specific output dominant mode includes the following: using the advancing direction of the gasification working face as a spatial reference, the leading edge of the high-temperature thermal desorption zone and the leading edge of the pressure relief and permeability enhancement zone are identified.

[0096] The leading edge mentioned above refers to the boundary closest to the gasification working face.

[0097] The projected distance between the leading edge of the high-temperature thermal desorption zone and the leading edge of the pressure relief and permeability enhancement zone in the advancing direction of the gasification working face is calculated and defined as the leading distance.

[0098] When the leading distance is greater than zero and there is an intersection between the gas migration stagnation zone and the high-temperature thermal desorption zone, or when the gas migration stagnation zone is completely surrounded by the high-temperature thermal desorption zone, the output heat-driven-pressure relief-gas retention mode is adopted.

[0099] Understandably, when the leading distance between the high-temperature thermal desorption zone and the pressure relief and permeability enhancement zone is greater than zero, it indicates that thermal desorption is spatially ahead of the system, and the system is in a state of thermal drive dominance and pressure relief lag. At this point, it is still necessary to further determine the spatial topological relationship between the gas migration stagnation zone and the high-temperature thermal desorption zone. The purpose is to verify whether the accumulation of high-pressure gas directly stems from the inability to effectively discharge the free gas generated by thermal desorption. If there is significant overlap or an envelope relationship between the two, it indicates that a large amount of gas has desorbed under high temperature but remains trapped in the coal seam due to the lack of effective seepage channels. This confirms the existence of a non-coordinated working condition with gas but no path, providing a clear basis for subsequent enhanced pressure relief control.

[0100] When the leading distance is less than zero and the total volume of the gas migration stagnation zone is less than the sum of the combined volumes of the high-temperature thermal desorption zone and the depressurization and permeability enhancement zone, the output depressurization-dominant-thermal-driven hysteresis mode is adopted.

[0101] The threshold set above is used to quantify the overall smoothness of gas migration under the pressure relief-dominant-heat-driven lag condition. Specifically, it can be based on the data set of the proportion of gas migration stagnation zone volume under the statistical dominant-heat-driven lag condition in the extraction test, and the percentile of its statistical distribution, such as the 90th percentile, can be taken as the set threshold.

[0102] Understandably, when the leading distance is less than zero, it indicates that the pressure relief and permeability enhancement zone expands ahead of the high-temperature thermal desorption zone in terms of spatial expansion, and the system exhibits characteristics of pressure relief dominance and thermal drive lag. At this point, it is still necessary to introduce the volume ratio criterion for the gas migration stagnation zone. This step aims to eliminate local high-pressure interference and confirm whether the overall gas migration status is unobstructed: if the stagnation zone ratio is small, it indicates that although thermal desorption is insufficient, the already formed high-permeability network is not blocked by gas, and the channels are in an vacant and usable state, confirming the mismatch of having a channel but no gas, thus supporting the adoption of a control strategy to enhance the supply of the thermal field, rather than blindly expanding the pressure relief range.

[0103] Therefore, the relative positions of the high-temperature thermal desorption zone and the pressure relief and permeability enhancement zone alone are insufficient to fully characterize the operating state of the gasification system. It is necessary to couple the spatial distribution and volumetric characteristics of the gas migration stagnation zone in order to accurately diagnose the essential causes of the imbalance of the dominant mechanism and achieve precise and systematic control decisions.

[0104] S32. When there is spatial overlap between the two regions, identify the dominant region of thermo-pressure coupling within the overlap area.

[0105] It should be noted that when the two zones spatially overlap, it indicates that the thermal desorption and depressurization-enhancing processes are basically synchronized in time and space in that region, initially meeting the basic conditions for efficient gas desorption-migration synergy. However, even if the two zones spatially overlap, the temperature intensity and stress unloading degree at different locations within them often differ. If the dominant mechanism is not distinguished and the entire overlapping zone is regarded as an ideal synergistic zone, it may mask local performance bottlenecks.

[0106] In a preferred embodiment of the present invention, the implementation process of the dominant region is as follows: within the spatial overlap region, several spatial units are obtained by dividing according to the spatial grid, and the dominant index of temperature change and the dominant index of stress change in each spatial unit are calculated one by one.

[0107] The calculation process applied to the above scheme is as follows: For each spatial unit in the overlapping area, extract the time-series monitoring data of itself and its adjacent areas within a set time window, including temperature sequence and stress sequence.

[0108] For the obtained temperature and stress sequences, temperature-time curves and stress-time curves are plotted respectively.

[0109] Using the observed values ​​corresponding to the start and end times of the time window as a benchmark, the difference between the first and last nodes of the curve is calculated to obtain the temperature rise and stress fall.

[0110] In the above operation, the temperature-time curve shows a monotonically increasing trend over time because the gasification reaction continuously transfers heat energy to the surrounding coal. Therefore, within the set time window, the observed temperature at the end is usually higher than the observed temperature at the beginning. Based on this physical characteristic, the temperature increase is obtained by calculating the difference between the temperatures at the end and the beginning.

[0111] In the stress-time curve, as the combustion zone expands and causes unloading of the surrounding rock, the effective stress borne by the rock mass generally decreases over time. Therefore, within the same time window, the stress observation value at the end time is usually lower than the stress observation value at the beginning time. Based on this, the stress decrease can be obtained by calculating the difference between the stress at the beginning and end times.

[0112] Similarly, by plotting the average temperature-time curve and the average stress-time curve of the adjacent region corresponding to each spatial unit, the average temperature rise and the average stress fall can be obtained.

[0113] The ratio of the temperature rise of each spatial unit to the average temperature rise of its adjacent regions is used as the dominant index of temperature change for that unit.

[0114] The ratio of the stress decrease of each spatial element to the average stress decrease of its adjacent region is used as the dominant index of stress change for that element.

[0115] Given the significant spatial heterogeneity of thermo-coupling processes, the absolute temperature rise or stress decrease of a single spatial unit cannot accurately reflect its relative dominance in a local region. Therefore, the ratio to the average response of the adjacent region is introduced as a normalization index to eliminate the influence of regional background trends and highlight the relative activity of the unit in the local microenvironment.

[0116] By comparing the two indices, spatial units are divided into thermodynamically dominant units dominated by thermal effects and stress-dominated units dominated by stress effects.

[0117] Specifically, when the dominant index of temperature change is greater than the dominant index of stress change in a certain space unit, the space unit is regarded as a thermally dominant unit; when the dominant index of temperature change is less than the dominant index of stress change, the space unit is regarded as a stress dominant unit.

[0118] In three-dimensional space, units with the same properties and spatially adjacent units are aggregated to form continuous thermal dominance zones and stress dominance zones.

[0119] S4. Trigger the corresponding regulatory action based on the dominant action mode or the type of dominant region.

[0120] In the first preferred implementation of the above steps, the corresponding control action is triggered according to the dominant action mode as follows: when the output is the heat-driven dominant-depressurization hysteresis-gas retention mode, the depressurization expansion action of the combustion air zone towards the gas migration stagnation zone is triggered.

[0121] It is important to understand that the above model indicates that high temperatures have induced the desorption of a large amount of gas, but insufficient pressure relief has prevented the effective formation or connection of the fracture network, leading to gas accumulation in the stagnant zone and creating a high-pressure risk. At this point, the core problem is the lack of seepage channels. By guiding the combustion zone towards the stagnant zone, the stress redistribution and thermally induced fracturing effect of the surrounding rock caused by pyrolysis can be utilized to actively induce pressure relief and fracture expansion, opening up gas migration paths and achieving both risk mitigation and coordinated gas release.

[0122] When the output is in the depressurization-dominant-heat-driven hysteresis mode, it triggers the action of directional migration of the thermal field to the depressurization zone.

[0123] It is important to understand that the above model reflects the formation of high-permeability channels in the depressurized and permeable zone, but the temperature has not reached the effective desorption threshold, resulting in low gas release and wasting valuable channel resources. By adjusting the gas injection parameters, such as increasing the oxygen concentration, changing the gas injection point, or introducing an auxiliary heat source, the high-temperature reaction zone can be directed to the depressurized area, allowing heat energy to act on the high-permeability coal body and activate the efficient desorption of adsorbed gas.

[0124] In the second preferred implementation of the above steps, the corresponding control action is triggered according to the type of dominant zone as follows: For the thermal dominant zone, the enhanced gas extraction and diversion action is triggered.

[0125] It is important to understand that while areas dominated by thermal advantages possess strong thermal desorption capabilities, insufficient extraction can lead to the accumulation of desorbed free gas in the pores, inhibiting subsequent desorption and even inducing localized high pressure. By enhancing negative pressure extraction, desorbed gas can be rapidly extracted, reducing pore pressure, maintaining high desorption driving force, and preventing the risk of gas retention.

[0126] In the stress-dominant zone, targeted heat source replenishment and enhanced gas desorption are triggered.

[0127] It is important to understand that although the stress-dominant zone has well-developed fractures and good permeability, insufficient heat input leads to low gas desorption flux and the channels are in an empty state. By locally injecting oxygen-enriched gas, adjusting the gasifying agent ratio, or introducing auxiliary heat sources such as microwave / electric heating, the temperature in this area can be specifically increased to above the critical desorption threshold, activating the release of adsorbed gas and making the high-permeability channels effectively utilized.

[0128] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented using software, the above embodiments can be implemented, in whole or in part, in the form of a computer program product.

[0129] Those skilled in the art will recognize that the modules and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0130] In addition, the functional modules in the various embodiments of this application can be integrated into one processing module, or each module can exist physically separately, or two or more modules can be integrated into one module.

[0131] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0132] Finally, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A coalbed gasification method based on a dual-drive approach of high-temperature desorption and pressure relief enhancement, characterized in that, Includes the following steps: S1. Simultaneously collect in-situ monitoring data of temperature field, rock mass stress field, micro-fracture events and gas pressure distribution from the sensor network deployed in the coal seam and surrounding rock of the combustion zone. S2. Delineate the high-temperature thermal desorption zone based on temperature field data in three-dimensional geological space: The acquired temperature field data is meshed to form several spatial units; The temperature values ​​of each spatial unit are compared with the critical desorption temperature of coal gas. Continuous spatial units with temperatures higher than the critical desorption temperature of coal gas are selected and topologically connected to construct the framework of the high-temperature region. For each spatial unit in the high-temperature region skeleton, temperature time series data is extracted, the temperature change rate between adjacent time steps is calculated, and it is compared with the preset transient disturbance criterion threshold. For spatial units whose temperature change rate does not reach the transient disturbance criterion threshold, the duration of high temperature is further statistically analyzed. A spatial unit is classified as a transient high-temperature unit if it meets any of the following conditions; (1) The rate of temperature change in adjacent time steps is higher than the threshold of the transient disturbance criterion; (2) The duration of high temperature is shorter than the duration of effective heat effect; In the constructed high-temperature region skeleton, all identified transient high-temperature units are removed, and the remaining spatial units are reconstructed in three dimensions and fitted with an equivalent breadth to generate a high-temperature thermal desorption region. Based on rock mass stress field data and micro-fracture events, delineate the pressure relief and permeability enhancement zone; based on gas pressure distribution data and combined with local geological structures, delineate the gas migration stagnation zone. S3. Determine the spatial relationship between the high-temperature thermal desorption zone and the pressure relief and transparency enhancement zone: S31. When the two zones do not intersect in space, identify the relative positions of the high-temperature thermal desorption zone and the pressure relief and permeability enhancement zone in three-dimensional space, and output the dominant action mode in combination with the distribution of the gas migration stagnation zone. S32. When there is spatial overlap between the two regions, identify the dominant region of thermo-pressure coupling within the overlapping area. S4. Trigger the corresponding regulatory action based on the dominant action mode or the type of dominant region.

2. The coalbed gasification method based on high-temperature desorption-pressure relief and permeability enhancement as described in claim 1, characterized in that: The specific process for collecting the in-situ monitoring data is as follows: A distributed temperature measurement fiber optic network is embedded along the pre-set gasification channel and the surrounding rock of the combustion zone to acquire continuous spatial temperature field data. In the coal seam and the roof and floor strata, stress sensors and microseismic monitoring probe arrays are deployed in a three-dimensional grid to capture rock stress field data and micro-fracture event signals. A cluster of gas pressure and concentration sensors is installed at intervals inside the gas extraction channel to monitor the pressure distribution data of the gas. Temperature field data, rock mass stress field data, and gas pressure distribution data are spatiotemporally aligned to generate an in-situ monitoring dataset.

3. The coalbed gasification method based on high-temperature desorption-pressure relief and permeability enhancement as described in claim 2, characterized in that: The delineation process for the pressure relief and enhanced transparency zone is as follows: The location of micro-fracture events captured by the microseismic monitoring array is determined, and a microseismic event point cloud is formed. By applying three-dimensional spatial density clustering to the point cloud of microseismic events, the regions where the spatial distribution of microseismic events is concentrated are delineated, namely, the dense zone of micro-rupture events. The rock stress field data collected by the stress sensor is mapped onto a spatial grid consistent with the temperature field; For each spatial element, obtain the stress value at the corresponding location, and construct the adjacent region by combining the adjacent elements; The stress value of each spatial unit is compared with the initial stress state. If the stress value is lower than the initial stress state, it is determined that there is a stress reduction. The stress value of each spatial unit is compared with the average stress level of its adjacent region. If the stress value is lower than the average stress level, it is determined that there is a local stress gradient. If a spatial element has both stress reduction amplitude and local stress gradient, then the element is determined to be a stress reduction element. Three-dimensional connectivity clustering is performed on all stress reduction units, and they are merged to form stress reduction regions; In the stress-reduced region, the spatial boundary of the dense micro-fracture event zone is modified and smoothed to form a pressure-relief and permeability-enhancing zone.

4. The coal seam gasification method based on high-temperature desorption-pressure relief and permeability enhancement as described in claim 1, characterized in that: The gas migration stagnation zone is defined as follows: Based on the collected gas pressure distribution data, locate the set of spatial points in three-dimensional space where the gas pressure is higher than the critical pressure; Based on the local geological structural characteristics of the spatial point set, high-pressure areas located at structural turning points or without a connecting path to known high-permeability channels are identified as gas migration stagnation zones.

5. The coalbed gasification method based on high-temperature desorption-pressure relief and permeability enhancement as described in claim 1, characterized in that: The output-dominant mode includes the following: Using the advancing direction of the gasification working face as a spatial reference benchmark, the leading edge of the high-temperature thermal desorption zone and the leading edge of the pressure relief and permeability enhancement zone are identified; The projected distance between the leading edge of the high-temperature thermal desorption zone and the leading edge of the pressure relief and permeability enhancement zone in the advancing direction of the gasification working face is calculated and defined as the leading distance; When the leading distance is greater than zero, and there is an intersection between the gas migration stagnation zone and the high-temperature thermal desorption zone, or the gas migration stagnation zone is completely surrounded by the high-temperature thermal desorption zone, the output heat drive-dominated-pressure relief lag-gas retention mode is used. When the leading distance is less than zero, and the total volume of the gas migration stagnation zone is less than the sum of the combined volumes of the high-temperature thermal desorption zone and the depressurization and permeability enhancement zone, the output depressurization-dominant-thermal-driven hysteresis mode is adopted.

6. The coalbed gasification method based on high-temperature desorption-pressure relief and permeability enhancement as described in claim 1, characterized in that: The process of identifying the dominant region of thermo-pressure coupling within the overlapping area is as follows: Within the spatial overlap region, several spatial units are obtained by dividing the space according to the spatial grid, and the dominant index of temperature change and the dominant index of stress change are calculated for each spatial unit. By comparing the two indices, spatial units are divided into thermodynamically dominant units dominated by thermal effects and stress-dominated units dominated by stress effects. In three-dimensional geological space, units with the same properties and spatially adjacent units are aggregated to form continuous thermal dominance zones and stress dominance zones.

7. The coalbed gasification method based on high-temperature desorption-pressure relief and permeability enhancement as described in claim 6, characterized in that: The specific calculation process for the dominant index of temperature change and the dominant index of stress change is as follows: For each spatial unit within the overlapping area, extract its own and its adjacent areas' time-series monitoring data within a set time window, including temperature and stress sequences; For the obtained temperature and stress sequences, temperature-time curves and stress-time curves were plotted respectively. Based on the observed values ​​corresponding to the start and end times of the time window in the curve, the difference between the first and last nodes of the curve is calculated to obtain the temperature rise and stress fall. Similarly, calculate the average temperature rise and average stress drop of the adjacent regions corresponding to each spatial unit; The ratio of the temperature rise of each spatial unit to the average temperature rise of its adjacent areas is used as the dominant index of temperature change in that unit. The ratio of the stress decrease of each spatial element to the average stress decrease of its adjacent region is used as the dominant index of stress change for that element.

8. The coalbed gasification method based on high-temperature desorption-pressure relief and permeability enhancement as described in claim 5, characterized in that: S4 includes the following: When the output is in the mode of heat drive-depressurization hysteresis-gas retention, it triggers the action of depressurization expansion from the combustion air zone to the gas migration stagnation zone. When the output is in the depressurization-dominant-heat-driven hysteresis mode, it triggers the action of directional migration of the thermal field to the depressurization zone.

9. The coalbed gasification method based on high-temperature desorption-pressure relief and permeability enhancement as described in claim 6, characterized in that: S4 also includes the following: In areas dominated by thermal advantages, enhanced gas extraction and diversion actions are triggered. In the stress-dominant zone, targeted heat source replenishment and enhanced gas desorption are triggered.

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