Novel optimization method for production strategy of coal-bed methane well: Implication from gas-water two-phase version productivity equations

Coal seam gas (CSG), as a type of unconventional gas resource, is playing an increasingly important role in energy generation and transition to renewables, as the world takes action to meet the climate change challenge. To produce CSG, the reservoir first needs to be dewatered, but unreasonable dewatering rates can lead to various unfavorable outcomes, such as a reduction in productivity, capillary trapping, borehole instability, excessive coal fines generation, and frequent production well workovers due to particle-induced damage to pumps. Determining the optimum dewatering strategy is currently in a very primitive stage of development, and CSG operators rely on empirical and instinctive approaches to deal with this problem. This paper conducts a comprehensive literature review to (i) explain why dewatering rate optimization remains a great challenge for the CSG industry, (ii) illustrate the complexity and nature of the issue through a conceptual model, and (iii) investigate four key factors that dominate the dewatering optimization design, borehole stability, stress-dependent permeability, gas–water two-phase flow, and generation of coal fines. A detailed summary of current dewatering optimization practices in CSG reservoirs is then presented, focusing on the employed theories, methodology, key learnings, and limitations of each practice. Finally, the remaining knowledge gaps are highlighted, and recommendations for further future work are provided.

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Section: Current Practices In Dewatering Rate Optimizationmentioning

confidence: 99%

“…Besides, Sun et al proposed to optimize the dewatering strategy using gas–water pseudopressure equations, as shown below …”

Section: Current Practices In Dewatering Rate Optimizationmentioning

confidence: 99%

Dewatering Optimization of Coal Seam Gas Production Wells: A Review and Future Perspectives

et al. 2022

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“…The depressurization scheme has a great influence on the production of CBM wells. 54 The greater the depressurization rate, the easier it is for hydraulic fracturing to close. 55,56 Based on this, we argue that the depressurization rate is correlated with the stress sensitivity of hydraulic fracturing area.…”

Section: Potential Research Topicsmentioning

confidence: 99%

Two-Phase Flow Model of Coalbed Methane Extraction with Different Permeability Evolutions for Hydraulic Fractures and Coal Reservoirs

et al. 2021

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Fluid flow modeling of coalbed methane (CBM) wells is effective in predicting gas production and designing appropriate depressurization schemes. Moreover, hydraulic fracturing is an important measure for improving the permeability of CBM reservoirs. In this work, we assumed the hydraulic fracture area near the main fracture to be rectangular. We developed a gas–water two-phase flow model considering the difference in stress sensitivity between the hydraulic fracturing area and the original coal reservoir. The numerical simulation results indicate that our model can accurately predict the production of CBM wells. In the early stage of CBM extraction, gas production increased with the increase of gas relative permeability. When the water saturation was below 0.7, the relative permeability of the gas phase was difficult to increase. At this time, the absolute permeability of the hydraulic fracturing area continued to decrease, leading to a decrease in gas production. Thus, if the difference of permeability evolution between the two areas is not considered, the production of CBM wells will be overestimated. In the process of CBM extraction, both reservoir pressure and water saturation decreased, but the distribution was inconsistent. The variation in reservoir pressure was mainly affected by absolute permeability and gas desorption, while the variation of water saturation was further affected by the distribution of relative permeability and initial water saturation. Therefore, the evolution of water saturation is generally more complex than that of reservoir pressure. In the hydraulic fracturing area, the effect of fracture compressibility on gas production was greater than the initial permeability. In the original coal reservoir, the larger initial permeability was more beneficial than the fracture compressibility for improving the production of CBM wells.

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“…Research on the characteristics of fracture cavity filling (Hu et al 2014), the physical properties of fracture cavity filling materials, the degree of this map and its origin and distribution (Wang 2017;Kangxun 2014b;Jin et al 2015d) act as indispensable parts of the research on fracture cavity characteristics. Reservoir connectivity (Song et al 2013;Li et al 2014b;Hu and Yang 2005;Yang 2004;Sun et al 2019e;Yi et al 2011), fracture cavity separation (Rong et al 2015), and reservoir separation (Li 2016) reflect the distribution characteristics of fracture cavity reservoir space from different perspectives. Reservoir modeling (Yan et al 2013;Zhang et al 2007b) and numerical simulation (Hu et al 2013) give the results of fracture cavity distribution in the sense of mathematical modeling.…”

Section: Progressmentioning

confidence: 99%

Research progress and prospect of Ordovician carbonate rocks in Tahe oilfield: karst feature

Chen

Yinguo

et al. 2021

J Petrol Explor Prod Technol

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Inspired by structural geology, karstology, geomorphology, as well as petroleum geology, coupling excellent documented research works and the field investigation, the status and prospect for the studies on karst feature of Tahe oilfield are discussed comprehensively. Results indicate: (a) the majority of research works have appeared since 2000 and can be classified as three categories and 12 subclasses, in which caves, fracture cave systems and fault-karst reservoirs are considered as the main research topics, (b) existed studies can be divided into four stages, and fault-karst reservoir analysis is a hot spot recently, focusing on the scale of the formed reservoir. It is the common sense that faults control both fractures and caves. Originally, there exist close relationships among karst phenomena whether they're on the ground or underground. Revealing these relationships mentioned above is the important direction for the studies of Tahe oilfield in the future. As for the areas where faults are widely distributed in karst, there exist hierarchical properties in karstology: (1) fault controls topography and landform, (2) fault, topography and landform control the water system and (3) fault, topography, landform and water system control karst. These hierarchical properties are the basic connotation of the laws for karst evolution, and the vital goals of the karst study of Tahe oilfield as well. Applications of methods and techniques and field-karst investigation are the solid guarantees to achieve these goals.

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Novel optimization method for production strategy of coal-bed methane well: Implication from gas-water two-phase version productivity equations

Cited by 7 publications

References 50 publications

Dewatering Optimization of Coal Seam Gas Production Wells: A Review and Future Perspectives

Dewatering Optimization of Coal Seam Gas Production Wells: A Review and Future Perspectives

Two-Phase Flow Model of Coalbed Methane Extraction with Different Permeability Evolutions for Hydraulic Fractures and Coal Reservoirs

Research progress and prospect of Ordovician carbonate rocks in Tahe oilfield: karst feature

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