Improving the Success of Morrow Stimulations the Old-Fashioned Way

摘要

The Morrow gas sand reservoirs in southeast New Mexicohave permeability values that can range across three orders ofmagnitude. The best wells are completed naturally; the poorerquality rock usually needs to be fracture stimulated to producecommercially. Early attempts to fracture stimulate the Morrowwith water-base systems were only marginally successful.Previous studies have suggested that the poor fracturingresponse to water-base systems was due to a combination ofwater-sensitive clays and capillary pressure effects. Earlytheories were that the Morrow experienced reducedpermeability as a result of clay swelling and high watersaturations in the zones invaded by fracture fluid filtrate.These issues were addressed by using energized fracturetreatments that included high quantities of CO2 and methanolin the fracture fluid. Stimulation success with foams has notbeen consistent. Successful fracturing response to smallerhydraulic fracture jobs using foams has been observed inhigher permeability wells where near-wellbore damage hasbeen successfully bypassed. However, in lower permeabilitywells where fracture length is critical to stimulation success,foams have not provided economic stimulation results.Although foams were used to address water-sensitivityissues, undesirable side effects countered the foam benefits.Low viscosities, high friction pressures and high chemical costresulted in increased screenout frequency and increasedtreatment cost. Early screenouts with low proppantconcentrations have left many Morrow reservoirs producing atrates well below their potential. To achieve optimum inflowpotential, a fluid system is required that is capable ofdeveloping adequate hydraulic width and transporting largervolumes and concentrations of proppant.Water-base fracturing fluid technology has come a long waysince the early days of Morrow fracture stimulation. Advancesin both fluid selection and fracture design now make itpossible to use a water-base system to achieve successfulstimulation results in the Morrow in southeast New Mexico.The net result of this engineering approach is improvedstimulation results with lower treatment cost.Two examples of successful applications of modernfracturing techniques demonstrate that operators in theMorrow of southeast New Mexico have a choice of fracturingfluids other than CO2 foams.