흡착-보정 디컨벌루션 방법을 이용한 셰일가스 생산자료 분석 연구

Abstract

In analyzing the production data obtained from shale gas reservoir, the rate-normalized pressure (RNP) method has been widely used in shale gas industry due to its simplicity. However, for sharply varying production data such as inclusion of production and shut-in, and also for pressure-interfered production data, RNP method gives erroneous results in reservoir characteristics. Meanwhile, deconvolution method can overcome the limit of RNP method for sharply varying production data. Since the deconvolution method is only applicable to linear relationship in pressure-rate data, it is not possible to perform production data analysis for coal seam or shale gas reservoir containing sorption characteristics. This production data shows nonlinear relationship in pressure-rate data due to the compressibility of desorbed gas which is strong function of pressure. In this study, the deconvolution method implemented with the sorption-corrected pseudopressure was proposed for being able to analyze not only sharply varying production data but also pressure-interfered data containing sorption characteristics. In this aspect, the sorption-corrected pseudopressure was derived from material balance equation for linearizing the pressure-rate relationship through a variable substitution method. By implementing the sorption-corrected pseudopressure into shale gas reservoir modeling study, the results showed that a linear relationship of pressure-rate was generated so that pressure transient analysis could be conducted. As results of sorption-corrected deconvolution method, the effective permeability including fracture permeability was obtained differently whether the sorption-corrected pseudopressure was implemented in deconvolution method, its discrepancy was almost 24%. For the production data acquired from multiple shale gas wells having pressure interference effect, RNP method as currently used in shale gas industry yielded different results of effective permeability and estimated ultimate recovery (EUR) depending on the level of pressure interference effect, even though production data was obtained from the same reservoir. Meanwhile, the sorption-corrected deconvolution method proposed in this study resulted unique values in effective permeability and estimated ultimate recovery by being able to remove the pressure interference effect.