Gas wells in low-permeability formations usually require hydraulic fracturing to be commercially viable. Pressure transient analysis in hydraulically fractured tight gas wells is commonly based on analysis of three flow regimes: bilinear, linear and pseudo-radial. With current well test analysis techniques, a reliable estimation of hydraulic fracture and reservoir properties relies on occurrence of all these three flow regimes. Without the presence of pseudo-radial flow, neither reservoir permeability nor fracture half length can be independently estimated. In other words, to reliably estimate fracture half length, reservoir permeability has to be known. Since pseudo-radial flow is often absent, the estimation is uncertain and unreliable. On the other hand, elliptical flow, which exists between linear flow and pseudo-radial flow, is of long duration (typically months to years). We can acquire much rate and pressure data during this flow regime but no practical well test analysis technique is currently available to interpret these data.

This paper presents a new approach to reliably estimate reservoir and hydraulic fracture properties from analysis of constant-rate drawdown pressure data obtained during the elliptical flow period. The method is based on equations modeling the elliptical flow regime and is applicable to estimate effective fracture half length, formation permeability and skin factor independently for both infinite- and finite-conductivity fractures. The method is iterative and features rapid convergence. It can estimate formation permeability when pseudo-radial flow does not exist. It can also be coupled with stable deconvolution technology, which convert variable production-rate and pressure measurements into an equivalent constant-rate pressure drawdown test, and thus provide property estimates from readily available, noisy production data. We present synthetic and field examples to illustrate the procedures and demonstrate the validity and applicability of the proposed approach.

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