The Morrow gas sand reservoirs in southeast New Mexico have permeability values that can range across three orders of magnitude. The best wells are completed naturally; the poorer quality rock usually needs to be fracture stimulated to produce commercially. Early attempts to fracture stimulate the Morrow with water-base systems were only marginally successful. Previous studies have suggested that the poor fracturing response to water-base systems was due to a combination of water-sensitive clays and capillary pressure effects. Early theories were that the Morrow experienced reduced permeability as a result of clay swelling and high water saturations in the zones invaded by fracture fluid filtrate. These issues were addressed by using energized fracture treatments that included high quantities of CO2 and methanol in the fracture fluid. Stimulation success with foams has not been consistent. Successful fracturing response to smaller hydraulic fracture jobs using foams has been observed in higher permeability wells where near-wellbore damage has been successfully bypassed. However, in lower permeability wells where fracture length is critical to stimulation success, foams have not provided economic stimulation results.

Although foams were used to address water-sensitivity issues, undesirable side effects countered the foam benefits. Low viscosities, high friction pressures and high chemical cost resulted in increased screenout frequency and increased treatment cost. Early screenouts with low proppant concentrations have left many Morrow reservoirs producing at rates well below their potential. To achieve optimum inflow potential, a fluid system is required that is capable of developing adequate hydraulic width and transporting larger volumes and concentrations of proppant.

Water-base fracturing fluid technology has come a long way since the early days of Morrow fracture stimulation. Advances in both fluid selection and fracture design now make it possible to use a water-base system to achieve successful stimulation results in the Morrow in southeast New Mexico. The net result of this engineering approach is improved stimulation results with lower treatment cost.

Two examples of successful applications of modern fracturing techniques demonstrate that operators in the Morrow of southeast New Mexico have a choice of fracturing fluids other than CO2 foams.

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