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Methods for simultaneously evaluating reserve and permeability of undersaturated coalbed methane reservoirs using production data during the dewatering stage

Authors :
Juntai Shi
Zhihua Xiao
Cheng Liu
Jiayi Wu
Zheng Sun
Kamy Sepehrnoori
Source :
Petroleum Science. 17:1067-1086
Publication Year :
2020
Publisher :
Elsevier BV, 2020.

Abstract

In this work, a flowing material balance equation (FMBE) is established for undersaturated coalbed methane (CBM) reservoirs, which considers immobile free gas expansion effect at the dewatering stage. Based on the established FMBE, five straight-line methods are proposed to determine the control area, initial water reserve, initial free gas reserve, initial adsorbed gas reserve, original gas in place, as well as permeability at the same time. Subsequently, the proposed FMBE methods for undersaturated CBM reservoirs are validated against a reservoir simulation software with and without considering free gas expansion. Finally, the proposed methods are applied in a field case when considering free gas expansion effect. Validation cases show that the straight-line relationships for the proposed five FMBE methods are excellent, and good agreements are obtained among the actual reserves and permeabilities and those evaluated by the proposed five FMBE methods, indicating the proposed five FMBE methods are effective and rational for CBM reservoirs. Results show that a small amount of free gas will result in a great deviation in reserve evaluation; hence, the immobile free gas expansion effect should be considered when establishing the material balance equation of undersaturated CBM reservoirs at the dewatering stage.

Details

ISSN :
19958226 and 16725107
Volume :
17
Database :
OpenAIRE
Journal :
Petroleum Science
Accession number :
edsair.doi...........6b7a86434c3c81e35f4412cf919f4001
Full Text :
https://doi.org/10.1007/s12182-019-00410-3