The Effects of Unbroken Fracture Fluid on Gas Well Performance

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Abstract
Research sponsored by the Gas Research Institute indicates unbroken fracture· fluids can lower gas reserves by 30%, reduce initial gas rates by 80%, and delay fracture fluid clean-up by weeks or months. The unbroken fracture fluids slow fracture fluid cleanup and flatten the production profile. In extreme cases, gas production slowly increases for weeks or months despite constant flowing pressures. The fracture fluids must break to a viscosity of 50 cp or less to ensure that gas reserves are maximized. INTRODUCTION Many tight gas wells do not respond to hydraulic fracturing as expected. Following stimulation, a typical tight gas well achieves a high initial gas rate within a few days after stimulation and then experiences a steep hyperbolic production decline. Some tight gas wells, however, do not achieve an obvious production peak but instead sustain a flat production profile or exhibit a slowly increasing production rate for several weeks or months. Fig. 1 illustrates this type of performance for several wells completed in the Frontier formation.1 As shown by Fig. 1, the production can increase for up to three months before reaching a peak rate and then decline slowly. The peak rates shown in Fig. 1 are less than the peak rates expected from these wells. The production behavior shown in Fig. 1 is attributed to slow fracture fluid cleanup.1 Multiphase flow and fracture face damage contribute to this type of productive behavior,2 however, one mechanism that has not been directly evaluated in the past is the effect of the viscous gel in the proppant pack. A viscous, unbroken fracture fluid inhibits the flow of gas, water, and broken fracture fluid through the fracture, compounding the effects of fracture face damage and proppant pack conductivity reduction due to gel residue.

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