Simplified scaling relations for the depth-dependence and IFT reduction of fluid imbibition in gas-saturated reservoir rocks

Imbibition of water into fractured unconventional reservoirs is a significant factor contributing to the large volumes of permanently lost water by hydraulic fracturing. The lost water partitions at the fracture-matrix interface thereby restricting gas flow into the fractures. Thus, minimizing the large water footprint during the fracturing process is very attractive for water conservation and gas production. A key step towards achieving this goal is quantifying uncertainties needed to reliably predict water imbibition and to evaluate the success of efforts aimed at minimizing it. In this contribution, we present new scaling relations for water imbibition in gas-saturated rocks that account for the depth-dependence of fluid properties and chemical alteration of IFT through the use of a surfactant. We then propose a new method for quantifying uncertainties relating to rock properties, two-phase fluid properties, and the driving force for imbibition. We applied the proposed approach to analyze glass-bead pack and shale experiments involving water imbibition into air-filled pores, and validated our model predictions against published values from X-ray CT images and transient permeability measurements. Our work provides a methodology for quantifying the uncertainties pertaining to water imbibition, thereby enabling optimization of post-fracturing interventions aimed at minimizing water loss in deep unconventional shale gas reservoirs.

Automated summary

The imbibition of water into fractured unconventional reservoirs leads to significant water loss and restricts gas flow. Minimizing water usage during fracturing process is important for water conservation and gas production. This study proposes new scaling relations and a method for quantifying uncertainties in water imbibition. The approach was validated using experiments and provides a methodology for optimizing interventions in deep unconventional shale gas reservoirs to minimize water loss.