Gas Loss Compensation Method for Prolonged Exposure Samples from Deep Boreholes: Experiment, Theory, and Numerical...

Area of Science:

• Geosciences and Environmental Science
• Mining Engineering
• Petroleum Engineering

Background:

• Accurate coal seam gas content is vital for mine safety and coalbed methane reserve assessment.
• Extended borehole depths for gas determination limit sampling times, challenging existing gas loss compensation methods.
• Current methods inadequately estimate long-duration gas loss due to reliance on initial desorption data.

Purpose of the Study:

• To develop a transient gas diffusion model incorporating adsorption effects for long-term gas loss estimation.
• To propose novel gas loss compensation methods suitable for prolonged coal sample exposure.
• To provide accurate gas loss estimation for deep borehole drilling and sampling.

Main Methods:

• Established a transient gas diffusion equation with gas adsorption effects.
• Analyzed the relationship between dimensionless time (T) and dimensionless desorption quantity (Y).
• Developed and compared the Initial Measurement Point Tangent Method (CQSB) and the Dynamic Point Tangent Method (DQSB).

Main Results:

• The developed diffusion model accurately characterizes long-term gas diffusion.
• The T-Y relationship follows a power-law function, with exponent variability causing errors if fixed.
• CQSB is accurate for short exposure times (<2 min), while DQSB accurately estimates gas loss for prolonged exposure (3-30 min).

Conclusions:

• The Dynamic Point Tangent Method (DQSB) offers a significant improvement for estimating gas loss under extended exposure conditions.
• This research provides a new approach for gas loss estimation in deep drilling and sampling processes.
• Further research is needed to theoretically determine the dynamic point location and validate the method for fractured coal samples.