In situ coal permeability and favorable development methods for coalbed methane (CBM) extraction in China: From real data

Chen, Shida; Tao, Shu; Tang, Dazhen

doi:10.1016/j.coal.2024.104472

Cited by 9 publications

(6 citation statements)

References 79 publications

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“…The correlation between coal permeability and buried depth in the study area is, overall, low, but it was found that the coal permeability shows a decreasing trend with the increase in buried depth (Figure 9a). Previous studies have shown that present-day stress magnitude and orientation are important reasons for vertical variation in permeability [47][48][49]. Figure 9b illustrates that a negative relationship exists between coal permeability and minimum horizontal stress magnitude in the study area.…”

Section: Permeability Characteristicsmentioning

confidence: 73%

Geological Conditions Evaluation of Coalbed Methane of Dacun Block in the Guxu Mining Area, Southern Sichuan Coalfield

Zhu,

Zhang,

et al. 2024

Applied Sciences

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The geological conditions evaluation of coalbed methane (CBM) is of great significance to CBM exploration and development. The CBM resources in the Southern Sichuan Coalfield (SSC) of China are very abundant; however, the CBM investigation works in this area are only just beginning, and the basic geological research of CBM is seriously inadequate, restricting CBM exploration and development. Therefore, in this study, a representative CBM block (Dacun) in the SSC was selected, and the CBM geological conditions were evaluated based on field injection/fall-off well testing, gas content and composition measurements, and a series of laboratory experiments. The results show that the CH4 concentrations of coal seams in the Dacun Block, overall, take on an increasing trend as the depth increases, and the CH4 weathering zone depth is 310 m. Due to the coupled control of temperature and formation pressure, the gas content shows a “increase→decrease” trend as the depth increases, and the critical depth is around 700 m. The CBM is enriched in the hinge zone of the Dacun syncline. The moisture content shows a negative correlation with CBM gas content. The porosities of coal seams vary from 4.20% to 5.41% and increase with the Ro,max. The permeabilities of coal seams show a strong heterogeneity with values ranging from 0.001mD to 2.85 mD and present a decreasing trend with the increase in depth. Moreover, a negative relationship exists between coal permeability and minimum horizontal stress magnitude. The reservoir pressure coefficients are between 0.51 and 1.26 and show a fluctuation change trend (increase→decrease→increase) as the depth increases, reflecting that three sets of independent superposed gas-bearing systems possibly exist vertically in the Longtan Formation of the study area. The Langmuir volumes (VL) of coals range from 22.67 to 36.84 m3/t, indicating the coals have strong adsorptivity. The VL presents a parabolic change of first increasing and then decreasing with the increase in depth, and the turning depth is around 700 m, consistent with the critical depth of gas content. The gas saturations of coal seams are, overall, low, with values varying from 29.10% to 116.48% (avg. 68.45%). Both gas content and reservoir pressure show a positive correlation with gas saturation. The CBM development in the Dacun Block needs a large depressurization of reservoir pressure due to the low ratio (avg. 0.37) of critical desorption pressure to reservoir pressure.

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Section: Permeability Characteristicsmentioning

confidence: 73%

Geological Conditions Evaluation of Coalbed Methane of Dacun Block in the Guxu Mining Area, Southern Sichuan Coalfield

Zhu,

Zhang,

et al. 2024

Applied Sciences

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“…To address this, larger fracturing scales and increased sand addition are needed to improve permeability and reduce stress sensitivity. 14 Additionally, some deep CBM wells in the study area exhibit poor production continuity, attributed to inappropriate drainage and production technology. Thus, there is an urgent need to explore drainage and production technologies suitable for the production characteristics of a deep CBM.…”

Section: Production Characteristics Of Medium-production Wellsmentioning

confidence: 97%

“…Conversely, in regions characterized by horizontal compressive stress, natural fractures are underdeveloped, and the permeability and the fracturing effect are poor, resulting in relatively lower gas production and a less favorable stable production effect. To address this, larger fracturing scales and increased sand addition are needed to improve permeability and reduce stress sensitivity . Additionally, some deep CBM wells in the study area exhibit poor production continuity, attributed to inappropriate drainage and production technology.…”

Section: Differences In Production Characteristics Of Deep Cbm Wellsmentioning

confidence: 99%

“…It is found that the stress characteristics of the reservoir play an obvious role in controlling the production capacity of deep CBM wells. , The deep CBM production capacity is also affected by factors such as the degree of resource enrichment and the scale of fracturing. , In the site of tensile stress, the permeability of the reservoir is higher, the supply capacity of the CBM is better, and the gas production effect is better. On the contrary, the high extrusion stress within the reservoir reduces the conductivity of the fracture system, , which limits the transport of CBM.…”

Section: Introductionmentioning

confidence: 99%

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Dynamic Production Characteristics of Deep Coalbed Methane: A Case Study of Daning-Jixian Block

Zhang,

Lai,

Meng

et al. 2024

Energy Fuels

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The Daning-Jixian block, located in the eastern margin of the Ordos Basin, is abundant in deep coalbed methane (CBM) resources and serves as a pilot test block for deep CBM development in China. Currently, the exploration and development of a deep CBM are in the early stages. The production characteristics and development laws across different production stages are not fully elucidated, leading to uncertainties in discharge and production control measures as well as the optimization of the production system. This study addresses these challenges by analyzing actual production data from deep CBM wells. It establishes a classification standard for deep CBM wells and a production stage model diagram. Based on this, it compares and analyzes the production characteristics of deep CBM wells with middle and shallow CBM wells as well as the variations among different types of deep CBM wells. The findings reveal the following key points: (1) gas wells are categorized as low-, medium-and high-production wells based on average daily gas production of 1500 and 3000 m 3 /d, respectively; (2) deep CBM production is delineated into four stages: gas production rise, gas production decline, stable gas production, and gas production depletion; (3) in contrast to middle and shallow CBM wells, deep CBM wells predominantly produce free gas in the early stage, characterized by rapid and high gas production; and (4) the production capacity of deep CBM wells is mainly influenced by reservoir stress characteristics, the effectiveness of fracturing, and the continuity of production. This study provides a valuable reference for the formulation of deep CBM drainage and production systems and development strategies.

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“…Coalbed methane (CBM) is a highly sought-after unconventional natural gas resource that is stored within coal seams and attracts significant global attention. According to the International Energy Agency (IEA), the estimated worldwide CBM resources tally up to 260 × 10 12 m 3 , with abundance in major coal-producing countries such as China, Australia, USA, and Canada. , Given the intrinsic low porosity and permeability of CBM reservoirs, hydraulic fracturing often becomes imperative to stimulate CBM wells for economic production. , However, during hydraulic fracturing and subsequent drainage operations, due to the brittle nature and diminished strength of coal rock, substantial amount of coal fines is generated. − Large quantities of coal fines may infiltrate propped fractures (proppant packs) alongside gas and/or water flow. Some of these coal fines may become trapped within the proppant packs, leading to the clogging of pores and a reduction in conductivity, which ultimately impede the production of CBM. − The challenge posed by coal fines persists throughout the CBM production stages, including single-phase water flow, gas–water two-phase flow, and single-phase gas flow stages, with the two-phase flow stage experiencing particularly pronounced impacts. , For example, in a CBM well within the South Yanchuan Block, China, the rate of recovery of gas decreased from 2.0 × 10 4 to 0.6 × 10 4 m 3 /d within a short time period due to the retention of coal fines within proppant packs .…”

Section: Introductionmentioning

confidence: 99%

Transport and Retention of Coal Fines in Proppant Packs during Gas–Water Two-Phase Flow: Insights from Interface, Pore, to Laboratory Scales

Huang,

Wang,

Chen

et al. 2024

Energy Fuels

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The transport and retention of coal fines within proppant packs play a critical role in the recovery of coalbed methane (CBM). Their accumulation can lead to serious pore clogging and reduced pack conductivity. While previous research has primarily focused on the behavior of coal fines during single-phase water flow, there is a lack of understanding of their behavior during gas−water two-phase flow. The current study utilized visualization observations and theoretical analysis to investigate the multiscale behavior of coal fines within unsaturated proppant packs. A series of experiments were conducted to examine the transport and retention of coal fines within proppant packs under different gas-to-water flow rate ratios. The experiments involved visualizing the transport process of coal fines, as well as monitoring the displacement pressure and effluent concentration. The results showed that, during gas−water two-phase flow, gas−water interfaces (GWIs) frequently expanded and contracted, leading to the remobilization of coal fines retained on the solid−water interfaces (SWIs). The significant attachment of coal fines to GWIs hindered their mobilization and induced the formation of isolated gas bubbles, whereas the coal fines adhered to these bubbles and were retained within the proppant packs. At the laboratory scale, the distribution of retained coal fines was highly nonuniform, constructing preferential pathways for the smooth passage of gas, water, and coal fines. Furthermore, as the gas-to-water flow rate ratio increased, the amount of retained coal fines decreased and the area of preferential pathways increased. The interface-scale mechanisms governing the transport and retention of coal fines were analyzed using the force analysis. It was found that the attachment of coal fines to GWIs was chemically unfavorable, occurring passively during the removal of coal fines from SWIs by GWIs. The capillary force exerted by GWIs was identified as the primary driving force for the mobilization of coal fines, with coal fines being removed only during the contraction (advancement) of GWIs. Theoretical results were consistent with visualization observations. Overall, the findings from this study provide significant insights for effectively managing coal fines within proppant packs during gas−water two-phase flow, with implications for enhanced CBM recovery.

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In situ coal permeability and favorable development methods for coalbed methane (CBM) extraction in China: From real data

Cited by 9 publications

References 79 publications

Geological Conditions Evaluation of Coalbed Methane of Dacun Block in the Guxu Mining Area, Southern Sichuan Coalfield

Geological Conditions Evaluation of Coalbed Methane of Dacun Block in the Guxu Mining Area, Southern Sichuan Coalfield

Dynamic Production Characteristics of Deep Coalbed Methane: A Case Study of Daning-Jixian Block

Transport and Retention of Coal Fines in Proppant Packs during Gas–Water Two-Phase Flow: Insights from Interface, Pore, to Laboratory Scales

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