Development and Evaluation of an Alternative Fluid for Offshore Fracturing of Moderate to High Permeability Formations

Abstract For decades, borate crosslinked guars have been the workhorse for fracturing conventional and higher permeability formations particularly in offshore operations. The development of shales/unconventional reservoirs has led to many new learnings and innovations including new fracturing fluids. In shales, uncrosslinked polyacrylamides (PAs) at low gel concentrations (0.5-2.0 gpt) have become the dominant fluid because of their lower cost, greater friction reduction, and higher retained conductivity. The use of these fluids is commonly regarded to be limited to unconventional formations where permeabilities are in the nano-micro darcy range. Recently, some conventional low permeability (0.1-1 mD) reservoirs have been fractured using higher concentrations (4-12 gpt) of PA in place of crosslinked gels with encouraging results. The potential of these fluids for fracturing of even higher permeability formations (10-1000 md), as commonly found offshore, has not been investigated. This paper describes the identification and evaluation of a linear polyacrylamide (PA) fluid designed to meet the technical specifications for fracturing deepwater/offshore wells in higher permeability formations. Early evaluation identified that a very high polymer loading of 40 gallons per thousand(gpt) would be needed to meet the challenging requirements for offshore application. The evaluation of a 40 gpt polyacrylamides for use as a fracturing fluid has not been looked at by the industry. The qualification and testing program evaluated fluid compatibility, rheology, proppant conductivity, regain permeability, fluid loss, and fluid friction in comparison to a typical 35 pounds per 1000 gallons (lbm/Mgal) borate crosslinked (XL) gel. The practicality of pumping the PA system was also evaluated by an SIT test from an offshore stimulation vessel. The results show that the 40 gpt PA fluid appears to be an attractive alternative to borate crosslinked fluids for offshore fracturing. Its benefits include higher fracture conductivity for improved productivity, reduced formation damage, lower friction pressures, and simpler QC with fewer additives. In some cases, these fluids could replace high density XL-based fracturing fluids needed for fracturing over pressured reservoirs. The SIT test confirmed its feasibility for use in offshore fracture operations.