Thermal stability of brine foams for shale gas drilling
Abstract Producing gas from shale gas reservoirs is challenging because of the non-darcy permeability of the pay rock. Gas well productivity is reduced by formation damage due to the shaly nature of the producing zone. Brine foams have been used as drilling fluids in shale gas drilling to improve well performance. While the thermal stability of foam is a big concern in deep well drilling, this issue has not been investigated for brine foams. This paper presents the result of our investigations on thermal stability of foams made from two brines and compared with foam from fresh water. Thermal stabilities of three foam systems were investigated in laboratory conditions at a temperature of 170 °F. They are fresh-water-based foams, KCl-solution-based foams, and CaCl 2 -solution-based foams. AQF-2 and HC-2 were used as foaming agents. Guar-gum, Xanthan-gum, and HEC were used as foam viscosifiers. We found that the stability of brine foams are more significantly influenced by viscosifiers than fresh water foams. Guar-gum can generate foam from KCl-solution that is as stable as that from fresh-water. Xanthan-gum can generate foam from CaCl 2 -solution that is as stable as that from fresh-water. This paper provides engineers with basic data necessary for formulating the most stable foams for shale gas drilling.