Investigation of water imbibition and fracture formation in tight sandstones usingX‐ray computed tomography

Abstract:

Rapidly increasing energy demand and corresponding exhaustion of conventional resources have shifted the research and industry focus to unconventional hydrocarbon resources. In addition, constant advances in new technologies, including horizontal drilling and multi-stage hydraulic fracturing, have led to more economical extraction of hydrocarbons from unconventional reservoirs. Despite the promising future of unconventional hydrocarbons as an energy resource, fundamental issues related to the coupled hydro-mechanical phenomena in low permeability rocks still lack understanding. Different, constantly changing mechanical and environmental conditions alter tight sandstone properties over a range of spatial and temporal scales and are difficult to predict.

To date, several methodologies have been developed to study liquid imbibition and fracture development in porous media, such as Amott-Harvey Method, US Bureau of Mines method, spontaneous imbibition, to name a few. These macroscopic methods are efficient for evaluating different influencing factors on the imbibition process. However, the examination of the underlying microscopic mechanics governing the imbibition phenomena and fracture formation is missing. Full-field X-ray imaging has emerged as an indispensable tool for capturing and analyzing the structural and chemical composition of the inhomogeneous porous media. Therefore, it is pivotal to use this imaging technique to obtain complete information and gain an enhanced understanding of the rock structure and composition.

This paper presents an experimental study into the mechanisms of water imbibtion in small, unconfined specimens of tight sandstone. Water imbibtion, fracture formation, and porosity change were monitored using both x-ray tomography. The subsequent analysis of the resulting images showed that the clay mineralogy is the major controlling factor in water imbibition and physical alteration of low permeability clay-rich rocks. Immediately after the low permeability, low porosity clay-rich sandstone came into contact with water, clay minerals started to swell which induced microcracking at the water-rock interface. Continuous clay swelling further enlarged microcracks resulting in the accelerated adsorption of water in the early stage of water imbibition.