An Integrated Model with Reconstructed Full-Scale Shale Matrix and Fractures

Abstract

Four types of voids exist in shale, including inorganic pores, organic pores, natural fractures, and hydraulic fractures, where the gas flow within is affected by voids sizes, shapes, and the mineral composition surrounding them. It is still a challenge to build an effective multi-scale model for shale by now. A model classifying organic pores and inorganic pores with and without clay was proposed in our previous work by incorporating various testing methods. However, some improvements can be made, including wider the pore size of the model to full-scale and adding the fractures without being considered previously. Therefore, a new model is proposed by integrating an improved full-scale matrix pore network model (PNM) with fractures. That is, the effects of four types of voids, including organic pores, inorganic pores containing clay, inorganic pores without clay, and fractures, on gas flow are all considered in the model. Then, the factors affecting the permeability of the matrix (i.e., without fractures) and the whole model (i.e., with fractures) were analyzed. The results show that connectivity both in small- and large-scale PNM and total organic content facilitate the flow, while clay content and water film thickness hinder the flow, especially within small pores. Fractures along the pressure drop accelerate gas flow, and the fractures perpendicular to the pressure drop only channel the pressure when the fractures along the pressure drop both exist. The model can be applied to other mudstones and shales and studies the fluid migration within them through proper parameters adjustment.