New pore space characterization method of shale matrix formation by considering organic and inorganic pores

• A superposition algorithm is used to combine inorganic pore digital core and organic pore digital core together.
• Multiple-point statistics method is used to construct the inorganic pore digital core.
• Markov chain Monte Carlo method is used to construct the organic pore digital core.
• Geometry and topology structure properties of shale matrix are obtained from pore network model.

A shale matrix is too tight to be described using conventional methods, and digital core technology is becoming an alternative method. Because both organic and inorganic pores exist in the shale matrix, a digital core and a pore network model that could describe these two types of pores at the same time are constructed in this paper. Firstly, the inorganic pore digital core is constructed based on the multiple-point statistics method, and the organic pore digital core is constructed based on the Markov chain Monte Carlo method. The two types of digital cores are superposed together according to a superposition algorithm, which includes information about the shale organic and inorganic pores. The pore network models of different constructed digital cores are extracted using the pore space medial axis method. Finally, based on these platforms, the geometry and topology structure properties, the pore size distribution and the coordination number of a shale sample are analyzed. The results show that the pore size distribution of the shale sample generally ranges from 2 nm to 100 nm, mainly distributing from 5 nm to 20 nm. The coordination number is almost always in the range of 2–3. The digital core results match well with the experimental results to some extent for our study case.