Investigation of coal pore and fracture distributions and their contributions to coal reservoir permeability in the Changzhi block, middle-southern Qinshui Basin, North China

Du, Zhigang; Xiao-dong, Zhang; Huang, Qiang; Zhang, Shuo; Wang, Chenlin

doi:10.1007/s12517-019-4665-9

Cited by 15 publications

(13 citation statements)

References 26 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…76 The Changzhi block (Figure 24b), as a successive block for CBM development nowadays, is in a transition area between the east margin of Qinshui Basin synclinorium and the west edge of Taihangshan anticlinorium. 79 It belongs to a west-dipping monocline, whose orientation is NNE-NEE with an about 4°dip angle. Due to tectonic movements, major transtensional faults that are oriented at NE and NNE and minor crumples that consist of gentle folds with the orientation of NE and closed folds with the orientation of NNE and NNW develop widely in the southeast Changzhi block.…”

Section: Discussionmentioning

confidence: 99%

Analysis of the Key Factors Affecting the Productivity of Coalbed Methane Wells: A Case Study of a High-Rank Coal Reservoir in the Central and Southern Qinshui Basin, China

Xiao-dong

et al. 2020

ACS Omega

Self Cite

View full text Add to dashboard Cite

In the present study, three CBM blocks in the central and southern Qinshui Basin, China, including Fanzhuang, Zhengzhuang, and Changzhi blocks, were selected. Combined with the data, such as the physical properties of coal reservoirs, logging, hydrofracture operation, injection/drawdown well testing, microseismic fracture monitoring technology, and over 2000 days gas production rate, the key factors affecting the gas production rate of CBM wells were analyzed comprehensively and systematically. Unimodal and bimodal models can be identified according to the long-term gas production rate data. The unimodal model corresponds to a declining pump pressure curve, meaning that caprock integrity is destroyed during hydrofracture operations, commonly causing poor gas production performance. The bimodal model is associated with fluctuating-rising and stable pump pressure curves, indicating good hydrofracture consequences. On the premise of the relatively high gas content, the gas saturation/critical-reservoir pressure ratio, permeability, and coal deformation are the major geological factors that affect the long-term gas production performance of CBM wells. Engineering factors, including pollution by the drilling fluid and cement paste, the type of the fracturing fluid, tonstein intercalation, coal deformation, and in situ stress, affect gas production performances via the following four mechanisms: the effect of hydrofracture operations on caprock integrity, the effect of fluids pumped on the pore-fracture system, the initiation and propagation of artificially induced fractures, and the performances of proppants pumped. This work can provide guidelines for the optimization and development of high-rank CBM blocks.

show abstract

Section: Discussionmentioning

confidence: 99%

Analysis of the Key Factors Affecting the Productivity of Coalbed Methane Wells: A Case Study of a High-Rank Coal Reservoir in the Central and Southern Qinshui Basin, China

Xiao-dong

et al. 2020

ACS Omega

Self Cite

View full text Add to dashboard Cite

show abstract

“…The pores are the main location for gas accumulation, whereas coal-rock fractures are the main channels for gas flow. 13 (2) When drilling hole drainage is implemented in the working face, the drilled hole is relatively shallow and located in the pressure relief zone of coal seam. 14 − 16 (3) The failure of borehole seal leads to low extraction efficiency.…”

Section: Introductionmentioning

confidence: 99%

Development and Application of Water Sealing Technology for Gas Drainage Boreholes

Hai-jin

Gao

et al. 2021

ACS Omega

View full text Add to dashboard Cite

The poor sealing effect of gas extraction boreholes causes low efficiency of gas extraction. As a consequence, the requirements of coal mine safety production are often not attained. The sealing effect of boreholes depends not only on the sealing material itself but also on the combination degree between the material and the hole wall and the structural change characteristics of the material during operation. Our theoretical analysis shows that the amount of liquid leakage increases with the gap width Δ h in a cubic law, decreases with the sealing hole viscosity in a hyperbolic form, increases linearly with the diameter of the borehole, and increases with the eccentricity in a quadratic function. We have developed a PD sealing material that has good compactness and sealing effects, excellent water retention performance, and an expansion rate of 1.29. The material can generate secondary expansion through microscopic development, which is beneficial to improve the quality of the sealing hole. HV-CMC has good stability in plugging mucus. In addition, the manual pump has been redeveloped to be portable and also to overcome the blockage of the suction valve of the original device. In addition, the auxiliary device for drilling and sealing has been invented. The field application demonstrates that the gas concentration and flow pressure difference of the new sealing borehole can be maintained at a high level in a short period of time and then decrease slowly with time. The resulting improved sealing effect demonstrates that our new approach has important theoretical and practical significance for mine gas drainage.

show abstract

“…The Qinshui Basin of China is presently a fast-growing target block for CBM exploration and exploitation of high-rank coal in the world (Du et al, 2019; Ye et al, 2007; Zhou et al, 2016). After experiencing four-stage tectonic movements, the Qinshui Basin deformed into a synclinorium structure (Figure 1).…”

Section: Methodsmentioning

confidence: 99%

CBM exploration: Permeability of coal owing to cleat and connected fracture

Tao

Xiao-dong

et al. 2021

Energy Exploration & Exploitation

Self Cite

View full text Add to dashboard Cite

Coalbed methane (CBM) resources cannot be efficiently explored and exploited without a robust understanding of the permeability of fracture-size heterogeneities in coal. In this study, two sister coal samples were imparted with pre-developed cleat and connected fractures, and the permeability of the coal samples was measured under different conditions of controlled confining and gas pressures. Furthermore, the implications of the results for CBM exploration and exploitation were discussed. The permeability of coal with cleat development ranged from 0.001–0.01 mD, indicating ultra-low permeability coal. The gas migration in this coal changed from a linear flow to a non-linear flow, with the increase in gas pressure (>1 MPa). Thus, the permeability of the coal initially increased and then decreased. However, the Klinkenberg effect does not exist in this ultralow-permeability coal. For the coal sample with connected fracture, permeability ranged from 0.1–10 mD, which is larger by hundred orders of magnitude than that of the sample with cleat. For this coal, with a decrease in gas pressure (<1 MPa), the Klinkenberg effect significantly increased the permeability of the coal. With an increase in the applied confining pressure, both the Klinkenberg coefficient and permeability of the coal presented a decreasing trend. It is suggested that field fracture investigation is a prerequisite and indispensable step for successful CBM production. The coal beds that cleat network is well conductive to the connected fracture can be an improved target area for CBM production. During CBM production, a variety of flow regimes are available owing to the decrease in CBM reservoir pressure. In particular, under the low CBM reservoir pressure and low in situ geo-stress conditions, the gas migration in the CBM reservoir with connected facture development exhibits remarkable free-molecular flow. Thus, the reservoir permeability and predicted CBM production will be enhanced.

show abstract

Investigation of coal pore and fracture distributions and their contributions to coal reservoir permeability in the Changzhi block, middle-southern Qinshui Basin, North China

Cited by 15 publications

References 26 publications

Analysis of the Key Factors Affecting the Productivity of Coalbed Methane Wells: A Case Study of a High-Rank Coal Reservoir in the Central and Southern Qinshui Basin, China

Analysis of the Key Factors Affecting the Productivity of Coalbed Methane Wells: A Case Study of a High-Rank Coal Reservoir in the Central and Southern Qinshui Basin, China

Development and Application of Water Sealing Technology for Gas Drainage Boreholes

CBM exploration: Permeability of coal owing to cleat and connected fracture

Contact Info

Product

Resources

About