Assessing shale gas reservoir potential using multi-scaled SEM pore network characterizations and quantifications: The Ciñera-Matallana pull-apart basin, NW Spain

Abstract

In recent years, unconventional hydrocarbon reservoirs (UHRs), specifically shale gas plays, have become a vast source of economically viable hydrocarbons, in response to better drilling and stimulation techniques. To further improve recovery, more detailed pore network modeling needs to be conducted by means of detailed pore network characterizations, based upon predefined pore size and pore type classification schemes. Through the quantification of the nano/microporous properties of the pore network, a better understanding on how hydrocarbon storage and migration phenomena operate within UHRs and how well they might respond to stimulation can be developed. Kasimovian-Gzhelian (Late Carboniferous) lacustrine sediments from the Upper Pastora Formation of the Ciñera-Matallana coalfield, NW Spain, were investigated to identify the potential for shale gas, by conducting a detailed pore network analysis using SEM-based porosity data, alongside traditional methods of formation evaluation. Here we show that the Upper Pastora Formation demonstrates shale gas potential and that the nanoporous network is a complex multifaceted and multi-scaled system composed of various pore types and sizes, each with specific dynamic properties and varying contributions toward total porosity. The present contribution provides a full pore network characterization and quantification, based on pore type and size, followed by a quantification of the porosity percentage held within each pore type and size. This work will provide an insight into the need for pore network characterizations alongside pore property quantifications with regard to computational fluid flow models and as such the need to carry out this work in conjunction with more traditional methods of shale gas exploration.