Abstract
This paper presents an improved flowing material balance method for unconventional gas reservoirs. The flowing material balance method is widely used to estimate geological reserves. However, in the case of the unconventional gas reservoirs, such as coalbed methane reservoirs and shale gas reservoirs, the conventional method is inapplicable due to the gas adsorption on the organic pore surface. In this study, a material balance equation considering adsorption phase volume is presented and a new total compressibility is defined. A pseudo-gas reservoir is simulated and the results were compared with the existing formulations. The results show that the proposed formulation can accurately get the geological reserves of adsorbed gas reservoirs. Furthermore, the results also show that the volume of the adsorbed phase has a significant influence on the analysis, and it can only be ignored when the Langmuir volume is negligible.
Highlights
The flowing material balance method uses daily production data to estimate geological reserves by linear regressions
The traditionally used flowing material balance method cannot be applied in unconventional gas reservoirs, such as gas shale and coalbed methane, due to the gas adsorption on the organic pore surface (Shen et al, 2018, 2019)
An improved flowing material balance for unconventional gas reservoirs was presented in this study to estimate their storage
Summary
The flowing material balance method uses daily production data to estimate geological reserves by linear regressions. Williams-Kovacs et al (2012) established an MBE considering adsorbed phase volume Their studies indicate that the adsorbed phase volume has significant influences on the evaluation results of geological reserves (Zhang et al, 2017)
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