A Pore Scale Study Describing the Dynamics of Slickwater Distribution in Shale Gas Formations Following Hydraulic Fracturing

摘要

Hydraulic fracturing with slickwater to stimulate shale gas wells is routinely employed to enable increased contact with larger reservoir volumes and has the advantages of lower cost, the ability to create larger and more complex fractures, less formation damage and easier cleanup. However, a common observation is that during flow back only 10 to 20% of the frac water is recovered, even though a typical stimulation job requires several million gallons of water. Although there have been some attempts to address this phenomenon, the associated theories are lacking in scientific rigor. Due to the nanoporous nature of shales where pore proximity effects and strong inter-molecular interactions may dominate, a fundamental pore-level analysis is employed in this work to better understand and leverage the dynamics of the physiochemical processes during and after fracturing. By varying pore size in organic and inorganic pores in shales, we study the dynamics of water and gas molecules, as well as that of ions. The results of our study demonstrate that the mechanics of water entrapment and the water and ions distribution are strongly linked to the pore-surface mineralogy. Understanding the placement and distribution of frac water in both organic and inorganic pores in shales will potentially help in improved forecasting of well performance and address concerns related to the contamination of groundwater resources.