The use of freshwater, near freshwater, or treated water in hydraulic fracturing represents an ever-increasing cost in the Permian Basin. Environmental concerns add to the pressure to develop methods to use significantly higher volumes of produced water in hydraulic fracture fluids. To solve the challenge of viscosifying untreated, high total dissolved solids water a move was made away from organic-based viscosifiers to silica-based technology.

Fumed silica is highly effective as a viscosifier for high-density brines that has demonstrated excellent low-end rheology, exceptional suspending ability, and a nominal filter cake. However, the high cost of fumed silica and operational challenges have precluded commercial adoption. This paper describes thatsimilar rheology is achievable at a fraction of the cost using a silica gel.

The focus of the paper is on the field trials in West Texas where untreated produced water was viscosified with silica gel and run as alternatives to a standard 20 lb/Mgal crosslinked guar fluid made with fresh water. Low cost and operational efficiencies were obtained bypreparingthe silica gel on-location using standard and readily available hydraulic fracturing equipment. Procedures for making the silica gel-based frac fluid were similar to those of making a crosslinked guar fluid.

Field trials have demonstrated that silica-gel carries high loadings of 20/40 mesh sand even at low pump rates. Production data from the trials has varied from exceeding expectations to being similar to existing production results.On a chemical cost basis, silica gel is comparable to a borate-cross-linked guar frac fluid. The economics tip very much in favor of silica gel when factoring in the savings using untreated produced water.

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