Abstract
Apparent gas permeability (AGP) is a significantly important parameter for productivity prediction and reservoir simulation. However, the influence of multiscale effect and irreducible water distribution on gas transport is neglected in most of the existing AGP models, which will overestimate gas transport capacity. Therefore, an AGP model coupling multiple mechanisms is established to investigate gas transport in multiscale shale matrix. First, AGP models of organic matrix (ORM) and inorganic matrix (IOM) have been developed respectively, and the AGP model for shale matrix is derived by coupling AGP models for two types of matrix. Multiple effects such as real gas effect, multiscale effect, porous deformation, irreducible water saturation and gas ab-/de-sorption are considered in the proposed model. Second, sensitive analysis indicates that pore size, pressure, porous deformation and irreducible water have significant impact on AGP. Finally, effective pore size distribution (PSD) and AGP under different water saturation of Balic shale sample are obtained based on proposed AGP model. Under comprehensive impact of multiple mechanisms, AGP of shale matrix exhibits shape of approximate “V” as pressure decrease. The presence of irreducible water leads to decrease of AGP. At low water saturation, irreducible water occupies small inorganic pores preferentially, and AGP decreases with small amplitude. The proposed model considers the impact of multiple mechanisms comprehensively, which is more suitable to the actual shale reservoir.
Highlights
With the gradual depletion of conventional energy, unconventional resource such as shale gas, methane hydrate and geothermal energy has drawn extensive attention [1,2]
The ultimate production is determined by the long-term stage of low production, which indicates the importance of gas flow behavior in shale matrix [6]
Shale matrix is composed of organic matrix (ORM) and inorganic matrix (IOM), and gas storage and transport mechanisms are distinctly different in two types of matrixes (Figure 1)
Summary
With the gradual depletion of conventional energy, unconventional resource such as shale gas, methane hydrate and geothermal energy has drawn extensive attention [1,2]. Considering phase behavior change and multiple gas transport mechanisms, Song et al [20] proposed AGP models for ORM and IOM. Considering the influence of stress effect, real gas and of water film on gas flow, Sun et al [21] improved B&K model to describe gas transport in organic and inorganic pore. The accuracy of slip boundary model depends on empirical coefficients, so more experimental or molecular simulation data is needed due to complex composition of shale matrix [23] Another type of analytical model is using weighting coefficient to couple multiple transport mechanisms. The proposed model reveals the impact of irreducible water saturation on the gas features of AGP and relative permeability calculated by effective hydraulic aperture and PSD are transport characteristics in multiscale shale matrix and provides reference for engineering discussed at last. Transport characteristics in multiscale shale matrix and provides reference for engineering application
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
