Analyzing Discrepancies in PTA and RTA for Accurate Flow Regime Identification and Fracture Geometry Estimation – An Example from a Highly Heterogeneous Unconventional Sandstone Reservoir

Abstract

This paper analyses a clear example of how results from Pressure Transient Analysis (PTA) and Rate Transient Analysis (RTA) in heterogenous reservoirs can yield different results, and proposes a methodology that capitalizes on these discrepancies to provide a logical and accurate identification of flow regimes periods, and estimation of key fracture geometry parameters. Due to formation heterogeneity, natural fractures and multi-frac stimulation along the lateral, it was clearly observed that early responses of studied wells were masked by a type of complicated flow which was a by-product of different flow regimes. This was first identified when PTA was completed, necessitating the need for additional tools to be integrated to unlock the mystery of that complicated flow. Next, RTA was analyzed by focusing on the log-log plot of pressure derivative with time. It was noticed that the log-log plot in some instances was able to clarify the uncertainties in early pressure response, and in other instances, it wasn't as clear. In the latter, the normal pressure derivative plot was utilized to identify flow regimes, confirming the feasibility of the adapted integrated workflow. the integration of PTA and RTA in cases where initial fracture signatures are uncertain, provides a practical tool that accurately and precisely estimates fracture geometry parameters that are key in the overall performance evaluation of the well. This paper illustrates the results of adapting this integrated novel workflow on an example from a highly heterogeneous unconventional horizontal well within a sandstone reservoir.