In our industry’s never-ending search to cut cost, there has been an alarming trend in the design of hydraulic fractures. This trend is the shift to lower fracture conductivity, which is being achieved through reduced proppant concentrations and the selection of less expensive, inferior proppants. This change is most evident in tight gas completions where even very low fracture conductivities are assumed to achieve infinite-acting fractures. Obviously, these changes can reduce the overall cost of the fracture treatment, but at what cost to well performance? This presentaion will review the production and economic impact of altering fracture conductivity in 18 low permeability wells in a mature East Texas gas field.
Most traditional conductivity calculations are problematic because they are based on laboratory-generated numbers and ignore the effects of non-Darcy and multi-phase flow. While most frac design engineers routinely and correctly include > 50% damage introduced to the proppant pack by polymers, they continue to dismiss the additional >90% conductivity reductions that can be induced by non-Darcy and multi-phase flow. This leads to a drastic underestimation of the pressure drop within the proppant pack, and consequently, production results that fail to meet expectations.
These rate-induced conductivity reductions are real and field results show that production improvements can be achieved through increased conductivity, although conventional "Darcy" analysis may erroneously indicate otherwise. In this case study, production results from eighteen wells located in a mature gas field in East Texas will be presented. Nine wells were completed with designs based on traditional Darcy flow models and nine offset wells utilized a new design to incorporate non-Darcy and multi-phase flow effects. In addition to production results, economic analyses are provided to show that the increased job cost is quickly recovered with improved production. Estimated ultimate recovery for each well is presented in an attempt to quantify the long term effects of increased conductivity. These analyses demonstrate that reducing fracture conductivity, as a cost savings measure, can significantly reduce both cash flow and net present value of the well. Production results to date indicate that the wells receiving the higher conductivity fractures will produce an average of 2 BCF/well incremental reserves for an additional investment of less than $50,000/well.