Methane Reservoirs Research Articles

In-situ geological conditions and their controls on permeability of coalbed methane reservoirs in the eastern Ordos Basin

In-situ geological conditions and their controls on permeability of coalbed methane reservoirs in the eastern Ordos Basin

Investigation of an Indian Site with Mafic Rock for Carbon Sequestration.

The increasing extent of greenhouse gas emissions has necessitated the development of techniques for atmospheric carbon dioxide removal and storage. Various techniques are being explored for carbon storage including geological sequestration. The geological sequestration has various avenues such as depleted oil and gas reservoirs, coal-bed methane reservoirs, and mafic and ultramafic rocks. Different trapping mechanisms are in play in these subsurface storage systems. In these sequestration sites, the mafic and ultramafic rocks are best suited for long-term and effective sequestration as they comprise minerals, conducive for chemical alteration, forming stable carbonates. However, these sites often suffer from distinct disadvantages of injectivity issues due to their low permeability and porosity. This study investigates the potential of sequestration in the rock samples obtained from one such site located in India. The rock samples are first characterized using various techniques including X-ray fluorescence, X-ray diffraction, Raman spectroscopy, and field emission scanning electron microscopy (FESEM). The mineralogical characterization shows that the rock sample contains approximately 10% of diopside. The samples were put in the reactor chamber comprising CO2, which were then investigated using FESEM analysis. Additionally, a reservoir block simulation using commercial software was conducted with the representative minerals in the sample to evaluate the CO2 sequestration potential. The simulation result suggests the formation of magnesite which corresponds to a major part of CO2 mineral trapping. The reduced injectivity due to low porosity and permeability in this rock can be addressed using hydraulic fracturing. The geomechanical behavior of the rock sample for hydraulic fracturing is studied using the Brazilian disc test. The Monte Carlo-based uncertainty analysis was conducted using the tensile strength data of the sample. Results suggest that the most likely fracturing pressure is 2100 psi for this rock sample.

Analysis of the Current Status and Hot Technologies of Carbon Dioxide Geological Storage

Carbon dioxide geological storage is one of the key measures to control and alleviate atmospheric carbon dioxide content. To better grasp the developmental dynamic and trend of carbon dioxide geological storage research over the world, promoting the research of CO2 storage theory and technology, 5052 related studies published in the past 22 years were collected from the Web Of Science database. The annual published articles on carbon dioxide geological storage research, partnerships, research hotspots, and frontiers were analyzed by using the knowledge map method of article analysis. The results show that the articles on the carbon dioxide geological storage are increasing yearly. The United States, China, and the United Kingdom are the most active countries; meanwhile, Tianfu Xu and Xiaochun Li from China are experts with the most achievements in the field of carbon dioxide geological storage. Although the theoretical and research frameworks for geological storage of CO2 are abundant, the field of enhanced gas formation recovery, shale gas extraction and subsurface storage, methane reservoirs, and methane adsorption are still challenging frontier science and technology topics.

Transient Pressure Behavior of CBM Wells during the Injection Fall-Off Test Considering the Quadratic Pressure Gradient.

Conventional coalbed methane (CBM) reservoir models for injection fall-off testing often disregard the quadratic pressure gradient's impact. This omission leads to discrepancies in simulating the transient behavior of formation fluids and extracting critical reservoir properties. Accurate determination of permeability, storability, and other properties is crucial for effective reservoir characterization and production forecasting. Inaccurate estimations can lead to suboptimal well placement, ineffective production strategies, and ultimately, missed economic opportunities. To address this shortcoming, we present a novel analytical model that explicitly incorporates the complexities of the quadratic pressure gradient and dual-permeability flow mechanisms, prevalent in many CBM formations where nanopores are rich, presenting a kind of natural nanomaterial. This model offers significant advantages over traditional approaches. By leveraging variable substitution, it facilitates the derivation of analytical solutions in the Laplace domain, subsequently converted to real-space solutions for practical application. These solutions empower reservoir engineers to generate novel type curves, a valuable tool for analyzing wellbore pressure responses during injection fall-off tests. By identifying distinct flow regimes within the reservoir based on these type curves, engineers gain valuable insights into the dynamic behavior of formation fluids. This model goes beyond traditional approaches by investigating the influence of the quadratic pressure gradient coefficient, inter-porosity flow coefficient, and storability ratio on the pressure response. A quantitative comparison with traditional models further elucidates the key discrepancies caused by neglecting the quadratic pressure gradient. The results demonstrate the proposed model's ability to accurately depict the non-linear flow behavior observed in CBM wells. This translates to more reliable pressure and pressure derivative curves that account for the impact of the quadratic pressure gradient.

Effect of Cage Occupancies on Molecular Vibrations of Methane in Structure H Clathrate Hydrate: Ab Initio Molecular Dynamics Simulation.

The structure H (sH) of methane hydrate, which has a distinctive structure with large (LL) cages capable of encapsulating multiple methane molecules, has been suggested as a methane reservoir in large icy bodies such as Titan, making it important in planetary science. This high-pressure phase, which exists in the GPa range, lends itself to the study of methane states and dynamics using powerful experimental techniques such as IR and Raman spectroscopy. However, the interpretation of the vibrational spectra of methane in the sH structure has been challenging because of the spectral complexities. The signals attributed to the methane molecules in the LL cage, as well as those of the other two cage types, overlap in the spectra. In this study, we investigated the microscopic origins of the shape of the C-H stretching vibration spectrum of methane in the LL cage using ab initio molecular dynamics (AIMD) simulations. For a single methane molecule in the LL cage, the ν3 band of the C-H stretching mode was observed at a higher frequency typical of isolated molecules in vacuum due to the large size of the LL cage. As the number of methane molecules in the LL cage increased beyond one, a tendency to blue-shift with increasing methane occupancy was observed, consistent with a loose-cage-tight-cage model. By characterizing the time correlation function of methane stretching vibrations based on the solvation number of methane and water molecules proximal to methane within the LL cage, we showed that the complicated spectral line shape observed in cases of higher methane occupancy in the LL cage resulted from the wider variation of the solvation shell states. Analysis of the solvation structures of the AIMD trajectories provided interpretations of the experimental spectral line shape, demonstrating the complementary nature of AIMD to the experiment and its effectiveness in analysis.

Gas-liquid permeability of propped fracture with retained coal fine particles in coalbed methane reservoirs

Coal fine particles are easily retained in the propped fractures during hydraulic fracturing and CBM (coalbed methane) extraction, which seriously affects the gas–liquid permeability. In this paper, gas–liquid permeability test experiments of propped fractures under different retained coal fine particles concentration were conducted. The results showed that the retained coal fines discharge rate (Rd) and gas/liquid effective permeability (Kge/Kwe) decreased with the increase of the closure stress. As the gas–liquid ratio increased, the Rd of the propped fractures with retained coal fine particles decreased. The Kwe decreased significantly while Kge increased slightly, yet the gas/liquid effective permeability loss rate (lw/lg) rose. As the retained coal fine particles concentration in the propped fractures increased, both the Rd and Kge/Kwe decreased monotonously. When the retained coal fine particles concentration reached 10%, changing the gas–liquid ratio and.closure stress exerted little effect on the gas/liquid effective permeability. In addition, the lg/lw was inversely proportional to Rd within the propped fractures with retained coal fine particles. The research results are of guiding significance for optimizing the CBM extraction system, solving the problem of low gas–liquid permeability caused by retained coal fine particles, and promoting the smooth drainage of CBM.

Structure evolution law of coalbed methane reservoirs under different initial pressure CO2 phase change fracturing conditions

As a new coal bed fracturing technology, CO2 phase transition fracturing (CPTF) has received much attention due to its advantages of safety and high efficiency. However, little research has been conducted to investigate the fracture behavior of CPTF in coal seams under different CO2 release pressure conditions. To address this research gap, we performed fracture tests on coal rock under different initial pressure conditions using the developed CPTF experimental system. Then, scanning electron microscopy, low-pressure nitrogen adsorption, and mercury intrusion porosimetry testing techniques were used to investigate the fracture characteristics and microstructural evolution of coal rocks under different initial pressures of CPTF. The results show that with increasing initial pressure, the number of macroscopic fractures and the degree of fragmentation of the coal after CPTF fracturing increased significantly, the number of microscopic fractures and pores in the fractured coal samples increased, the N2 adsorption capacity and the amount of mercury intrusion of the coal samples increased to a greater extent, and the visible porosity increased from 52.47% of the raw coal to 63.88%, 64.31%, 68.48%, 63.64%, and 62.83%, and the proportion of macroporosity increased from 24.31% to 28.48%, 31.73%, 26.55%, and 34.38%. This research will contribute to a fuller understanding of the potential of CPTF as a technique for improving the pore and fracture structure of coalbed methane reservoirs.

Resource classification of coal bed methane and its contribution in energy transition and decarbonization path of oil and gas industry (A synopsis of CBM Life Cycle Analysis)

World economies are becoming increasingly more dependent on energy and countries have a voracious appetite for energy therefore, the need for an abundant clean energy is becoming a necessity. Energy companies are challenging environmental costs of coal bed methane as with advancement of new technology the impact from production of coal bed methane can reduce and to a certain extent avoided or offset. Production of coal bed methane results in changes to the land, to surface water and to ground water systems. Carbon quantification is required to understand, monitor and manage these changes. Previous life cycle analysis for this resource class has lack of process design details because of which there is a knowledge gap in understanding of emission profile of coal bed methane’s production. The objective of this study is to add value and reduce the scientific gap with respect to the production techniques of coal bed methane and its environmental impact. Removal of water continuously from coal seams depletes ground water and may eventually lower surface water flows (streams and rivers). It can also change the flow of groundwater drawing fresh water into the coal seams. To better understand this phenomenon the work establishes the Coal Bed Methane production foundation by in depth understanding of · Coal Bed Methane reservoir types; · Coal Bed Methane depositional environment, generation, and geological distributions; · Coal Bed Methane resource energy supply methods by understanding its construction, production and processing. The study then uses Life Cycle Assessment approach and understands previous emission numbers of Coal Bed Methane’s resource development. The work does systematic analysis and summarizes the previously published Life Cycle Analysis to understand further the potential environmental impacts of resource development of Coal Bed Methane. This will help energy companies to understand the field development, production, and operations of coal bed methane’s resource in terms of carbon numbers thereby optimizing the operations through carbon management thus reducing the potential impacts.

Experimental Analysis of the Mechanical Properties and Failure Behavior of Deep Coalbed Methane Reservoir Rocks

Experimental Analysis of the Mechanical Properties and Failure Behavior of Deep Coalbed Methane Reservoir Rocks

Laboratory Study of Liquid Nitrogen Cryo-Fracturing as an Environmentally Friendly Approach for Coalbed Methane (CBM) Reservoirs

This study evaluated two distinct cryo-fracturing techniques using liquid nitrogen (LN2). The evaluation included tests for peak compression strength, acoustic emission, and energy absorption. The experiments compared single-exposure freezing time (FT) and multiple-exposure freezing–thawing cycle (FTC) processes on dried specimens. The outcomes indicated that FTC experiments demonstrated lower uniaxial compression stress (UCS) values compared to FT experiments because, during the thawing phase, the ice inside the pores reverts to liquid as the temperature rises. The difference between average baseline experiments versus FT180 and FTC6 indicated a reduction in stress of 14.5% and 38.5%, respectively. The standard error of our experiments ranged from 0.58% for FT60 to 5.35% for FTC6. The damage factor follows a downward trend in both FT and FTC experiments as the time of LN2 treatment augments. The amount of energy that can be absorbed in elastic or plastic deformation before failure is less for FTC specimens with the same total LN2 exposure time. Samples undergoing the freezing time process demonstrate a greater and denser quantity of acoustic emissions in comparison to freezing–thawing cycle processes, suggesting a positive correlation with uniaxial compressive strength outcomes. The large network of fractures formed by the FTC and PFTC techniques indicated that they have the greatest potential as stimulation approaches. The engineering results were improved by adding the geological context, which is essential to apply these findings to coals that have comparable origins.

Solid phase speciation controls copper mobilisation from marine sediments by methanobactin

Although marine environments represent huge reservoirs of the potent greenhouse gas methane, they currently contribute little to global net methane emissions. Most of the methane is oxidized by methanotrophs, minimizing escape to the atmosphere. Aerobic methanotrophs oxidize methane mostly via the copper (Cu)-bearing enzyme particulate methane monooxygenase (pMMO). Therefore, aerobic methane oxidation depends on sufficient Cu acquisition by methanotrophs. Because they require both oxygen and methane, aerobic methanotrophs reside at oxic-anoxic interfaces, often close to sulphidic zones where Cu bioavailability can be limited by poorly soluble Cu sulphide mineral phases. Under Cu-limiting conditions, certain aerobic methanotrophs exude Cu-binding ligands termed chalkophores, such as methanobactin (mb) exuded by Methylosinus trichosporium OB3b. Our main objective was to establish whether chalkophores can mobilise Cu from Cu sulphide-bearing marine sediments to enhance Cu bioavailability.Through a series of kinetic batch experiments, we investigated Cu mobilisation by mb from a set of well-characterized sulphidic marine sediments differing in sediment properties, including Cu content and phase distribution. Characterization of solid-phase Cu speciation included X-ray absorption spectroscopy and a targeted sequential extraction. Furthermore, in batch experiments, we investigated to what extent adsorption of metal-free mb and Cu-mb complexes to marine sediments constrains Cu mobilisation.Our results are the first to show that both solid phase Cu speciation and chalkophore adsorption can constrain methanotrophic Cu acquisition from marine sediments. Only for certain sediments did mb addition enhance dissolved Cu concentrations. Cu mobilisation by mb was not correlated to the total Cu content of the sediment, but was controlled by solid-phase Cu speciation. Cu was only mobilised from sediments containing a mono-Cu-sulphide (CuSx) phase. We also show that mb adsorption to sediments limits Cu acquisition by mb to less compact (surface) sediments. Therefore, in sulphidic sediments, mb-mediated Cu acquisition is presumably constrained to surface-sediment interfaces containing mono-Cu-sulphide phases.

An anisotropic rock physics modeling for the coalbed methane reservoirs and its applications in anisotropy parameter prediction

The elastic properties and anisotropy of coalbed methane reservoirs are still poorly understood due to the complicated pore structure and the existing state of the coalbed methane. Therefore, an anisotropic rock physics model for the coalbed methane reservoirs is proposed based on the related effective medium theories, which focuses on the equivalent calculation of the elastic properties for adsorbed coalbed methane and the characterization of the multiple pore structure. Many factors related to the elastic properties of coal are considered, including the composition, pore structure, adsorbed gas content and pore fluid. The measured ultrasonic and well-logging data demonstrate that the proposed physics model is effective in predicting the elastic constants and velocity anisotropy parameters. The results suggest that the elastic constants increase with the increase of adsorbed gas content to some extent, and the effect of porosity on the elastic constants is much more obvious than that of adsorbed gas content. The velocity anisotropy parameters increase with the aligned fracture porosity and the fracture aspect ratio, and the P-wave anisotropy is more sensitive to these two factors. With increasing organic matter and clay content and porosity, Young's modulus and brittleness index decrease while the Poisson's ratio increases, and the impact of the porosity on the brittleness index is more significant than that of organic matter and clay content. The results are helpful in establishing the relationship between reservoir physics parameters and seismic response and can provide a basis for coalbed methane reservoir prediction and hydraulic fracturing.

Multiscale Pore Structure Evolution of Different Rank Coals Induced by Chelating Agent Intrusion

Summary China’s coalbed methane (CBM) reservoirs are characterized by low permeability (<1 md). Stimulation with conventional acids is facing the problems of secondary precipitation, high corrosion rates, and fines migration. Chelating agent intrusion was proposed as a promising alternative for conventional acids, while the pore structure evolution induced by it needs to be further clarified. In this study, coal samples with three different ranks were selected and treated with L-glutamic acid N, N-diacetic acid (GLDA). Low-temperature Ar and N2 adsorption tests, mercury intrusion porosimetry (MIP), and scanning electron microscope (SEM) analyses were applied to investigate nanoscale to macroscale pore structure changes. X-ray fluorescence (XRF) spectroscopy tests were conducted to determine the mineralogical change of coal. The results show that chelating agent intrusion can widen fracture width, connect micropores, and create void space in macropores by dissolving carbonate minerals, while the nanoscale pore volumes (PVs) showed a slight decrease due to clay minerals collapse. The fractal dimensions Dm calculated by the MIP results of lignite, bituminous coal, and anthracite coal decreased by 0.2735, 0.1734, and 0.1444, respectively. It is indicated that a pore structure with a diameter of >100 nm of the coal became more unified, which favors the seepage of gas/water. The chelating agent intrusion shows a significant effect on lignite, followed by bituminous and anthracite coal. However, the metal element reduction rate of anthracite coal presents the highest, followed by bituminous coal and lignite. There can be a risk that a long intrusion time would loosen the skeleton of lignite, leading to further reservoir damage. Therefore, bituminous and anthracite coal samples are preferred, as the skeletons of higher-rank coals are more compact. These research findings introduced a potential stimulation method for enhancing CBM recovery and provided references for field application.

Investigation on the Nanopore Heterogeneity in Coals and its Influence on Methane Adsorption: A Multifractal Theory Study.

Coalbed methane (CBM) reservoirs constitute a distinct class of dense organic rocks characterized by extremely low porosity and permeability. Conducting an in-depth investigation into pore heterogeneity assumes paramount importance for the exploration and development of CBM. This study focuses on the multifractal analysis of the pores with diameters below 300 nm in six coal samples sourced from the Junggar Basin and the Qinshui Basin in China. The analysis is based on a series of experiments involving CO2 adsorption, low-temperature N2 adsorption/desorption, and CH4 isothermal adsorption. This work delves into the influence of pore heterogeneity on gas adsorption capacity by linking the structural parameters to CH4 adsorption properties. The results indicate that both the micropores, as assessed through CO2 adsorption, and mesopores to macropores, measured via N2 adsorption, exhibit multifractal behavior. In contrast to micropores, the mesopores and macropores display stronger heterogeneity and lower connectivity. Generally, uniform and well-connected nanopores are anticipated to positively contribute to gas adsorption. However, there is a positive correlation between the Langmuir volume and the heterogeneity degree of micropores. This phenomenon is ascribed to the fact that the greater surface complexity in micropores involves a larger specific surface area and a higher abundance of adsorption sites. This research contributes to a more profound and precise comprehension of the heterogeneous pore structure within CBM reservoirs, thereby establishing a theoretical foundation for the sustainable exploitation of CBM.

Understanding poromechanical response of a biogenic coalbed methane reservoir

Biogenic coalbed methane (BCBM) reservoirs aim to produce methane from in situ coal deposits following microbial conversion of coal. Success of BCBM reservoirs requires economic methane production within an acceptable timeframe. The work reported here quantifies the findings of previously published qualitative work, where it was found that bioconversion induces strains in the pore, matrix and bulk scales. Using imaging and dynamic strain monitoring techniques, the bioconversion induced strain is quantified here. To understand the effect of these strains from a reservoir geomechanics perspective, a corresponding poromechanical model is developed. Furthermore, findings of imaging experiments are validated using core-flooding flow experiments. Finally, expected field-scale behavior of the permeability response of a BCBM operation is modeled and analyzed. The results of the study indicated that, for Illinois coals, bioconversion induced strains result in a decrease in fracture porosity, resulting in a detrimental permeability drop in excess of 60% during bioconversion, which festers itself exponentially throughout its producing life. Results indicate that reservoirs with high initial permeability that will support higher Darcian flowrates, would be better suited for coal bioconversion, thereby providing a site-selection criteria for BCBM operations.

Identification of Interwell Interference Based on Hydrogeochemical Characteristics of Produced Water from Coalbed Methane Wells: A Case Study in the Southern Qinshui Basin, China

Summary Interwell interference is the superposition effect of coalbed methane (CBM) reservoir pressure. This study aims to provide a new direction for the quantitative analysis of interwell interference from the hydrogeochemical characteristics of produced water from CBM wells. A total of 24 produced water samples collected from the Panhe (PH) group, Shizhuangnan (SZN)-1 group, and SZN-2 group in Qinshui Basin were selected for the comparative analysis. The water type of all water samples is characterized by Na-HCO3, with Na+ being the main total dissolved solids (TDS) provider. The self-similar major ionic characteristics of the PH and SZN-2 groups are prone to the occurrence of interwell interference. The δD and δ18O show that the main source of produced water is atmospheric circulating water. The similar isotope characteristics of produced water in the PH and SZN-2 groups represent that there is remarkable interwell interference. Sr, As, Cu, Ga, Li, Rb, Sn, Mo, and V are selected as indicator elements. In the cluster analysis, all CBM wells form a single cluster in the PH and SZN-2 groups in the first three iterations, indicating interwell interference. According to the established fuzzy discriminative model, interwell interference is divided into two types—strong interwell interference and weak interwell interference. Most CBM wells in the PH and SZN-2 groups show strong interwell interference. This study can provide theoretical foundations for the dynamic pressure regulation and well pattern infilling of CBM wells.

Fluid Spontaneous Imbibition Under the Influence of Osmotic Pressure in Deep Coalbed Methane Reservoir in the Ordos Basin, China

Summary The flowback rate of a hydraulic fracturing fluid is related to coalbed methane (CBM) production in gas wells. The deep (>2000 m) CBM reservoir in the Ordos Basin has an extremely high salinity (>200 000 mg/L), which results in a very low flowback rate of fracturing fluid. The mechanism underlying the extremely low flowback rate of the fracturing fluid remains unclear. This study experimentally simulated two patterns of osmotic pressure variation that exist at a hydraulic fracturing site: the processes of injection of a low-salinity fracturing fluid into a high-salinity reservoir and a high-salinity fracturing fluid into a low-salinity reservoir. Low-field nuclear magnetic resonance (NMR) technology was used to monitor dynamic fluid migration and fluid distribution in the coals. Results showed that osmotic pressure is a driving force for spontaneous imbibition when the salinity of the fracturing fluid is lower than that of the reservoir water, and more fluid enters the coal as the osmotic pressure increases. This causes the displacement of the high-salinity fluid already present in the micropores by the low-salinity fracturing fluid. In high-salinity deep coal seams, both osmotic pressure and capillary forces cause the spontaneous imbibition of the fracturing fluid from fractures into pores, promoting CH4 desorption, alleviating the water-blocking effect, and enhancing the filtration loss of the fracturing fluid. In contrast, the injection of a high-salinity fluid into the reservoir with a low-salinity brine (LSB) creates an osmotic pressure difference that prevents fluid imbibition. In shallow, low-salinity coal seams, the injection of high-salinity fracturing fluids can result in high flowback rates. Therefore, these two injection schemes are significant for an understanding of the role of osmotic pressure in deep CBM extraction and serve as valuable guides for optimizing the selection of the fracturing fluid and improving its effective flowback.

An Analytical Method for Timely Predicting of Coal Seam Pressure during Gas Production for Undersaturated Coalbed Methane Reservoirs

Coal seam pressure is an important parameter for production performance evaluation and prediction of coalbed methane (CBM). CBM production from undersaturated CBM reservoirs can be divided into two stages according to critical desorption pressure. At present, few prediction models of coal seam pressure performance consider the comprehensive influence of critical desorption pressure, dissolved gas, matrix shrinkage, and stress sensitivity. For the purpose of accurately predicting coal seam pressure during gas production for an undersaturated coalbed methane reservoir, the material balance principle is used to establish the analytical method for predicting coal seam pressure, considering the comprehensive influence of the critical desorption pressure, dissolved gas, matrix shrinkage, and stress sensitivity. Then, the proposed method is verified against a numerical simulation case using a computer modelling group (CMG) and two actual coalbed methane wells. Finally, the sensitivities of influencing factors on the coal seam pressure are analyzed. The results show that good agreements were obtained between the calculated coal seam pressures using the proposed method and those from the CMG-GEM simulation case and actual CBM wells, with the relative errors all being less than 1%. When ignoring the influence of critical desorption pressure and mistaking pd for pi as well as ignoring Cs, the relative error can reach as high as 31.3%. The main factors affecting the coal seam pressure are the critical desorption pressure and free gas saturation. The proposed method is simple to use, and without shutting-in the well, it can provide an important basis for production performance evaluation and development strategies.

Research on Fracturing Optimization of Coalbed Methane Wells Aiming at Economic Benefit—A Case Study of Liulin Block

Hydraulic fracturing is an essential technology in the development of coalbed methane reservoirs. Hydraulic fracturing can create a highly conductive fracture in the reservoir and increase its permeability. At present, the focus of coalbed methane reservoir fracturing optimization is gradually shifting to the fracturing scale. In the current development process, more and more coalbed methane blocks try to increase the fracturing scale to increase the gas production of coalbed methane wells. Field tests show that gas production of coalbed methane wells will increase to a certain extent with the increase of fracturing scale. However, the increase in the scale of fracturing also increases its cost. Therefore, the most economical fracturing scale is not necessarily the optimal fracturing scale for gas production. The field test usually pays more attention to the gas production effect, but the development of a coalbed methane field should pay more attention to the economic benefit, and the optimization of fracturing should take the economic benefit as the goal. Taking economic benefits as the starting point, this paper uses fracturing simulation to calculate the fracture extension under different geological conditions and different fracturing scales. It also uses numerical simulation to calculate the gas well productivity under different fracture extension conditions. The economic evaluation model was established to calculate the economic benefits under different fracturing scales, and the optimal fracturing scale was obtained. Finally, the typical maps of fracturing optimization under different geological conditions are formed. The optimization method of fracturing scale integrating economy, fracturing, and gas reservoir is realized. The research results have been successfully applied to the optimization scheme of Liulin block development, and very good results have been achieved. Because this method is targeted at different geological conditions, it can be used to guide the fracturing optimization of other coalbed methane blocks and has very important significance for the development and optimization of coalbed methane reservoirs.

Study on Seepage of Coalbed Methane in Pore-fracture Double - porosity Medium

The study of coalbed methane (CBM) seepage within dual-porosity medium constitutes a significant research endeavor in the field of geology and coalbed methane reservoir engineering. This research delves into the complex dynamics governing CBM flow through porous coal matrices within dual-porosity systems. Employing advanced methodologies including numerical simulation and experimental analysis, this investigation aims to elucidate the mechanisms underlying CBM migration, encompassing diffusion and adsorption phenomena within the coal matrix, as well as interactions with adjacent strata. The outcomes of this study carry substantial implications for optimizing CBM extraction techniques and promoting the sustainable utilization of this invaluable natural resource.