Semi-analytical model for characterization of anomalous linear-flow behavior in partially-propped fractured wells

Abstract

This paper introduces an anomalous linear-flow behavior, which has been observed when analyzing pressure transient data from wells with partially-propped fractures. Unlocking underlying characteristics of partially-propped fractures using transient-pressure responses will enable analysts to better understand well performance. This study focuses on the anomalous behavior and provides a solution to the problems this issue raises. This work utilized time-normalized fracture conductivity concept and formulated governing diffusivity equations for propped fractures and dynamically-closed unpropped fractures. Resulting log-log plot of bottom-hole pressure versus time shows non-linear-flow characteristics following bilinear flow; we named this flow period “anomalous linear flow”. Pressure and derivative type curves during the anomalous linear flow exhibit straight lines with slope less than one-half. Sensitivity analysis was performed to determine the effect of key model parameters on transient-pressure responses, indicating that the anomalous behavior is caused by unpropped fracture characteristics. Based on the resulting observations, we highlighted pitfalls that usually arise when traditional methods are employed to estimate fracture properties. Finally, case studies demonstrate the practicality of our work, and show pitfalls identification and an associate workflow; the results indicate that fracture properties estimated using our model can improve the reliability of analyses.