Characterization of gas transport behaviors in shale gas and tight gas reservoirs by digital rock analysis. (January 2017)

• Record Type: Journal Article
• Authors: Sun, Hai; Yao, Jun; Cao, Ying-chang; Fan, Dong-yan; Zhang, Lei
• Is Part Of: International journal of heat and mass transfer. Volume 104(2017:Jan.)
• Page Start: 227
• Page End: 239
• Publication Date: 2017-01
• Subjects: Knudsen diffusion -- Viscous flow -- Surface diffusion -- Shale gas -- Tight gas reservoir -- Apparent permeability -- Digital rock -- Lattice Boltzmann method; Heat -- Transmission -- Periodicals; Mass transfer -- Periodicals; Chaleur -- Transmission -- Périodiques; Transfert de masse -- Périodiques; Electronic journals; 621.4022
• DOI: 10.1016/j.ijheatmasstransfer.2016.07.083
• Languages: English
• ISSNs: 0017-9310

Abstract

Highlights: A new apparent permeability calculation method of porous media is proposed. Viscous flow, Knudsen diffusion, adsorbed layer and surface diffusion is considered. The micro/nano digital rock constructed method is introduced. Gas transport pattern of shale samples in Silurian Longmaxi Formation is analyzed. A new permeability and porosity relationship equation of shale samples is obtained. Abstract: Due to the extremely tiny pore size of tight gas and shale gas reservoir, the modified Darcy's law in which the intrinsic permeability is replaced by the apparent permeability that can be obtained by a function of three transport parameters (intrinsic permeability, porosity and tortuosity), is used to describe the combined mechanisms of viscous flow, Knudsen diffusion, the effect of the adsorbed layer thickness and surface diffusion through the adsorbed layer. A new apparent permeability estimation method based on digital rock was proposed in this paper. The digital rock with nanopores could be constructed by 3D pore structure images obtained from micro/nano CT and FIB-SEM images directly or reconstructed with Markov Chain Monte Carlo (MCMC) method from the 2D SEM images of pore structure; then Lattice Boltzmann method can be applied to calculate the intrinsic permeability, porosity and tortuosity of 3D digital rock. These parameters are used to calculate the apparent permeability under consideration of different combined gas transport mechanisms. This method is applied to samples from the shale gas reservoir in Silurian Longmaxi Formation of Sichuan Basin and from the tight gas reservoir in the Wenchang Formation of Huizhou Sag. The results show that all considered transport mechanisms greatly impact the shale apparent permeability and cannot be ignored in shale samples. In tight gas reservoirs, Knudsen diffusion is an important mechanism at low pressures of less than 1 MPa. However, Knudsen diffusion could be ignored when pressure is greater than 1 MPa due to its smaller impact.