326 / 2024-03-15 16:39:35

A semi-analytical flow regime diagnosis model for a multi-fractured horizontal well in deep coal methane reservoirs

deep coalbed methane; multi-fractured horizontal well; semi-analytical model; flow regime

1、资源开发与利用 > 6、非常规能源与减碳路径

The exploration and development of deep coal methane using multi-fractured horizontal wells(MFHW) in reservoirs have emerged as a prominent area of interest within the industry. This study aims to investigate the intricate mechanisms governing transient pressure behavior. A novel semi-analytical flow regime diagnosis model is proposed, leveraging concepts of discrete elements and point-source functions. By employing Laplace transformation and the Gaver-Stehfest numerical inversion technique, a semi-analytical solution was obtained, providing insights into the dynamics of deep coal methane extraction. Six distinct flow regimes have been identified as the pressure response under constant rate conditions for a MFHW in deep coal reservoirs. Those include: wellbore storage flow(Ⅰ) , early pseudo-radial flow(Ⅱ), elliptical flow(Ⅲ), transitional flow(Ⅳ), desorptive gas dominated flow(Ⅴ), late pseudo-radial flow(Ⅵ). A phenomenon termed "desorptive concave" has been observed, serving as a signature of wells in reservoirs relying on desorption. This phenomenon becomes apparent in the desorptive gas dominated flow regime(Ⅴ) on the logarithmic derivative pseudo-pressure curve. Notably, tight gas reservoirs typically exhibit no "desorptive concave", while shallow coal seam during gas extraction often demonstrates a sharp one on log-log plots. These findings offer valuable insights to optimize coal gas well production through horizontal drilling and multi-fracturing techniques.