Critical depth prediction based on in-situ stress and gas content model of deep coalbed methane in Liupanshui Coalfield in China

Fang Lv ¹, Ruidong Yang ^2,3, Wei Gao ^2,4

¹School of Petroleum Engineering, Chongqing University of Science and Technology, Chongqing, 401331, China. haoganga@hotmail.com.
²College of Resources and Environmental Engineering, Guizhou University, Guiyang, 550025, China.
³Key Laboratory of Karst Geological Resources and Environment, Ministry of Education, Guiyang, 550025, China.
⁴Guizhou Coalfield Geology Bureau, Guizhou, 550016, China.
⁵Guizhou Engineering Research Institute of Oil&Gas Exploration and Development, Guiyang, 550081, China.
⁶College of Mining Engineering, Guizhou University, Guiyang, 550025, China.
⁷School of Mechanics and Engineering, China University of Mining and Technology, Xuzhou, 221116, China.
⁸Guizhou Coalbed Methane Shale Gas Engineering Technology Research Center, Guiyang, 550016, China.
⁹Key Laboratory of Unconventional Natural Gas Evaluation and Development in Complex Tectonic Areas, Ministry of Natural Resources, Guizhou, 550081, China.
¹⁰Key Laboratory of Tectonics and Petroleum Resources, Ministry of Education, University of Geosciences, 430074, Wuhan, China.
¹¹SINOPEC Exploration Company, 610041, Chengdu, China.
¹²Bureau of Geology and Mineral Exploration and Development Guizhou Province, 114 Brigade, 563000, Zunyi, China.
¹³Guizhou Coalfield Geology Bureau, Guizhou, 550016, China. gzsmtdzyts@vip.163.com.
¹⁴Guizhou Provincial Key Laboratory of Coal Fluidized Mining, 550014, Guizhou, China. gzsmtdzyts@vip.163.com.

⁰School of Petroleum Engineering, Chongqing University of Science and Technology, Chongqing, 401331, China. haoganga@hotmail.com.

Scientific Reports +

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January 2, 2025

View abstract on PubMed

Summary

This study reveals how in-situ stress impacts coalbed methane content in China

Area Of Science

Geosciences and Petroleum Engineering
Focus on coalbed methane (CBM) reservoir characterization and stress analysis.

Background

In-situ stress is crucial for coalbed methane (CBM) desorption, adsorption, and transport.
Reservoir gas content is a key parameter for CBM enrichment capacity and laws.
Understanding stress-gas content relationships is vital for CBM exploration and development.

Purpose Of The Study

To analyze the longitudinal stress development and gas content characteristics in Liupanshui coalfield.
To establish relationships between geostress field parameters and CBM reservoir gas content.
To develop a simplified model for vertical in-situ stress and analyze the lateral pressure coefficient.

Main Methods

Data collation and computation of stress parameters (pore pressure, breakdown pressure, closure pressure, triaxial principal stress) and gas content.
Linear regression for vertical in-situ stress model based on burial depth.
Hyperbolic regression algorithm to derive lateral pressure coefficient (k value) formulas.
Analysis of fault mechanisms (reverse, strike-slip, normal) with depth.

Main Results

The study area exhibits middle-high stress zones with evolving fault mechanisms from shallow to deep.
A simplified vertical in-situ stress model and median/envelope formulas for lateral pressure coefficient (k) were derived.
The lateral pressure coefficient stabilizes around 0.65 at greater depths.
Mean gas content is 11.89 m³/t, generally increasing with depth before decreasing; pore pressure positively correlates with gas content.
Critical depths for lateral pressure coefficient conversion (450-500 m), in-situ stress conversion (670 m), and gas content conversion (700-800 m) were identified.

Conclusions

The developed simplified in-situ stress model and lateral pressure coefficient analysis provide insights into stress field evolution.
The study establishes a vertical 'in-situ stress-gas content mode' relationship model for CBM development.
Identified critical depths aid in understanding CBM enrichment and development potential in the Liupanshui coalfield, with deep CBM potential around 800 m.

Keywords:

Coalbed methane Conversion critical depth Deep effect Gas content In-situ stress Liupanshui coalfield