Parameter Determination Using 3D FIB-SEM Images for Development of Effective Model of Shale Gas Flow in Nanoscale Pore Clusters

Abstract

A large amount of nano-pores exists in pore clusters in shale gas reservoirs. In addition to the multiple transport regimes that occur on the nanoscale, the pore space is another major factor that significantly affects the shale gas recoverability. An investigation of the porescale shale gas flow is therefore important, and the results can be used to develop an effective cluster-scale pore network model for the convenient examination of the process efficiency. Focused ion beam scanning electron microscope imaging, which enables the acquisition of nanometre-resolution images that facilitate nano-pore identification, was used in conjunction with a high-precision pore network extraction algorithm to generate the equivalent pore network for the simulation of Darcy and shale gas flows through the pores. The characteristic parameters of the pores and the gas transport features were determined and analysed to obtain a deeper understanding of shale gas flow through nanoscale pore clusters, such as the importance of the throat flux-radius distribution and the variation of the tortuosity with pressure. The best parameter scheme for the proposed effective model of shale gas flow was selected out of three derived schemes based on the pore-scale prediction results. The model is applicable to pore-scale to cluster-scale shale gas flows and can be used to avoid the multiple-solution problems in the study of gas flows. It affords a foundation for further study to develop models for shale gas flows on larger scales.

A 3D coupled model of organic matter and inorganic matrix for calculating the permeability of shale

“…In order to guarantee the spatial correlation between pores and throats, a PNM based on the work of Blunt et al [25] in which large pores prefer to be connected with large throats is employed in this study. For real-shale networks, the AB (axis & ball) algorithm [26] is employed to extract the PNMs from FIB/SEM images.…”

“…In this study, the AB (axis & ball) algorithm [26,32] is employed to extract the kerogen blocks and get the corresponding PNMs, those PNMs are coupled to the inorganic matrix and subsequently the real-shale model is found. For the real shale in Fig.…”

“…Ravg is the arithmetic mean throat radius. For more details about AB extraction algorithm and the properties of those kerogens, one can refer to Jiang et al's work [26].…”

Rapid Evaluation of the Permeability of Organic-Rich Shale Using the 3D Intermingled-Fractal Model

“…where k is the equivalent tube diameter (for a square tube, k is the edge length); M is the molar mass of natural gas (in kg/kmol); l is the viscosity of natural gas (in PaÁs); R is the universal gas constant (in J/molÁK); T is temperature (in K); q avg is the average density of natural gas (in kg/m 3 ); P in and P out are inlet and outlet pressures (in Pa), respectively; p avg is the average gas pressure (in Pa); and a is the tangential-momentum-accommodation coefficient. The viscosity and density of natural gas change significantly with the average pressure; the equations for the viscosity and density of natural gas were tested by Lee et al (1966) in a laboratory experiment. A is cross-sectional area (in a single tube, A ¼ k 2 ) and L is the length of the tube.…”

“…The viscosity, density, and compressibility factor of gas changed with the average temperature and pressure. We used the experimental results of Lee et al (1966).…”