A Comprehensive Coal Reservoir Classification Method Base on Permeability Dynamic Change and Its Application

Abstract

Due to the unique adsorption and desorption characteristics of coal, coal reservoir permeability changes dynamically during coalbed methane (CBM) development. Coal reservoirs can be classified using a permeability dynamic characterization in different production stages. In the single-phase water flow stage, four demarcating pressures are defined based on the damage from the effective stress on reservoir permeability. Coal reservoirs are classified into vulnerable, alleviative, and invulnerable reservoirs. In the gas desorption stage, two demarcating pressures are used to quantitatively characterize the recovery properties of permeability based on the recovery effect of the matrix shrinkage on permeability, namely the rebound pressure (the pressure corresponding to the lowest permeability) and recovery pressure (the pressure when permeability returns to initial permeability). Coal reservoirs are further classified into recoverable and unrecoverable reservoirs. The physical properties and influencing factors of these demarcating pressures are analyzed. Twenty-six wells from the Shizhuangnan Block in the southern Qinshui Basin of China were examined as a case study, showing that there is a significant correspondence between coal reservoir types and CBM well gas production. This study is helpful for identifying geological conditions of coal reservoirs as well as the productivity potential of CBM wells.

Quantitative optimization of drainage strategy of coalbed methane well based on the dynamic behavior of coal reservoir permeability

“…The slippage effect is ignored as its effect on permeability is only one-tenth of the matrix shrinkage effect [25][26][27] . Therefore, permeability induced by the effective stress effect and the matrix shrinkage effect can be expressed as follow: Substituting Eqs.…”

“…When the permeability damage induced by effective stress is equal to the permeability recovery induced by matrix shrinkage, reservoir permeability decreases to a minimum level ( k rb ) and the corresponding reservoir pressure is the rebound pressure ( P rb ), which is provided by the solution to k ′ =0 as described in Eqs. (10) and (11) 25,27 . www.nature.com/scientificreports/…”

Dynamic Characterization during Gas Initial Desorption of Coal Particles and Its Influence on the Initiation of Coal and Gas Outbursts

“…The law of gas desorption in coal particles has always been the one breakthrough point to explore the issues of efficient coal-bed methane recovery and gas dynamic disaster prevention [1][2][3][4][5]. For the mechanism of gas dynamic disasters such as outburst, as an outburst process only takes a few ~tens of seconds with an average time of 20 s [6], the law of gas initial desorption in coal particles is a key point that needs to be explored.…”

A new desorption-induced permeability dynamic model and its application in primary coalbed methane recovery

“…During the depletion of CBM reservoir, a reduction in permeability will occur due to the increasing effective stress imposed to the coal seam (Lin et al 2020). However, this reduction will be opposed or even offset by the permeability enhancement resulting from the matrix shrinkage associated with methane desorption (Yan et al 2020).…”