Pore-fracture network of high-rank coal based on the three-dimensional digitalization modeling

Description

Unlike other nations, the exploitation of coal bed methane (CBM) in China firstly obtained the success in Anthracite of the Qinshui Basin. At present, Chinese CBM is mainly produced in Anthracite reservoir. Anthracite is the tight rocks with more complex and changing pore-fracture structure and totally lower permeability. Therefore, the exploitation of CBM in Anthracite is difficult. The level of awareness of the structure and desorption-diffusion-seepage networks of anthracite reservoir is one of the key factors restricting the scientificalness of geologic evaluation and effectiveness of development technology of CBM in China. The application of Computed Tomography (CT) Images, Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM) and other new techniques make it possible for the digital characterization and three-dimensional (3D) modeling of coal reservoir pore-fracture structure in the scale of macropore and mesopores. In order to study the interconnecting characteristics of pores and fractures in high-rank coal, the study focuses on the #3 anthracite reservoir in Qinshui basin. Based on the 3D digitized modeling method of coal reservoir structure, 3D digital network model of coal bed multi-scale pore-fracture structure was established, pore-fracture parameters were extracted. Further, combined with scanning electron microscope observation, connected relations between pores and fracture and contributions of different genetic types of pores and fractures to the connectivity of coal were discussed. The results show that pore throat diameters in high-rank coal are small. Pore volume gives priority to mesopores whose diameters smaller than 50 nm. The tortuosity of pore throat is small, and pore cross-sections give priority to square and regular triangle. These mean that pore throat has small capillary pressure to gas. Pores in coal have poor connectivity. Mesopores whose diameters smaller than 50 nm are significant to the pore connectivity. There are 2 types of pores in #3 coal bed: primary pores mainly including biological structure pores and intergranular pores, and secondary pores usually including secondary gas pores, differential shrinkage pores, mineral pores and macromolecular structure pores. #3 coal bed gives priority to secondary pores. Differential shrinkage pores are the most important nanoscale interconnected pores in #3 coal bed. Due to the development of differential shrinkage pores among quartz and clay minerals of different physiochemical properties, fluid flow network structure with network topological features was formed in #3 coal bed. 3D digital network model of coal bed pore-fracture structure characterizes the distribution characteristics and topological relations of pores and fractures. It’s the digital and visual characterization of the internal spatial structure of coal. Reconstruction of multi-scale and complex coal bed pore-fracture network will greatly promote the research of CBM output process and mechanism of liquid flow in coal reservoir.

Period	9 May 2017
Event title	9th International Conference on Porous Media and Annual Meeting
Event type	Conference
Conference number	9th
Location	Rotterdam, NetherlandsShow on map
Degree of Recognition	International