Does the Chow Pressure Group Analysis Provide Any New Information in the RTA of Unconventional Reservoirs?

Abstract

Abstract This study presents a thorough mathematical analysis of Chow Pressure Group (CPG) for unconventional reservoirs exhibiting characteristic power-law behavior and demonstrates that the CPG analysis yields the same results that traditional rate transient analysis (RTA) provides using the log-log plot between rate-normalized pressure (RNP) vs. material balance time (MBT) and Cartesian plot between RNP and timen, where n is the flow exponent. CPG analysis was proposed for flow regime identification, power-law decline-curve analysis, predicting long-term well performance from choked-back wells, and evaluating long term performance changes associated with offset frac hits. Our work shows that the presence of fracture skin may impair the CPG analysis results, while in absence of fracture skin, CPG analysis leads to the computation of the same model parameters as a standard RTA. Our study examined the expression used to calculate CPG and shows that its formulation is closely related to β −derivative (d log(RNP)/ d log(time)). We show that the power-law model does not take fracture damage into account, and this could disguise the actual start of a flow regime resulting in a poor estimation of b−value and other model parameters using CPG. We demonstrate that the Bourdet derivative is not affected by fracture damage and leads to a more definitive flow regime identification. We further explain the CPG analysis model parameters in terms of the Wattenbarger type curve parameters for a simpler and more meaningful interpretation of the reservoir and fracture properties. We validate our hypothesis using field production data from an unconventional reservoir. Our work presents a thorough mathematical analysis of the CPG and shows that it computes the same model parameters as standard RTA in absence of fracture damage. In presence of fracture damage, CPG could show a significant delay in identifying a unique flow regime and may result in poor estimation of b-value and other model parameters. We found that the Bourdet derivative is less sensitive to fracture damage and should be used for a more definitive flow regime identification. We recommend using CPG analysis as a complementary tool to traditional methods such as Arps decline-curve analysis for RTA of production data.