Performance evaluation of analytical methods in linear flow data for hydraulically-fractured gas wells

Hydraulically fractured wells drilled in unconventional gas reservoirs are often produced with significantly high fixed drawdown to increase production. However, such unconventional gas wells exhibit extended periods of linear flow regime which could last for several years. Linear flow regime results from the fluid flow throughout Infinite-Conductivity Hydraulic Fractures (ICHFs) and Finite-Conductivity Hydraulic Fractures (FCHFs). This makes the analysis of linear flow regime of great importance to estimate parameters like fracture half-length, fracture width, fracture permeability and other parameters. Since the fracture half-length is an essential parameter for history matching and forecasting, it should be properly estimated and predicted. In this study, two analytical methods for analyzing linear flow were used to estimate the fracture half-length in hydraulically fractured gas wells producing from ICHFs and FCHFs under constant pressure conditions (fixed drawdown). The analytical methods compared are square root time and inverse production method. The investigated two analytical methods were compared along with the use of five different correction methods. The correction methods applied on the analytical solutions are those proposed by Ibrahim and Wattenbarger (2006), Nobakht and Clarkson (2012), Behmanesh et al. (2017), Chen and Raghavan (2013) and mean pressure. The comparison was done by conducting sensitivity analysis in term of initial pressure, flowing bottom hole pressure, reservoir temperature, permeability and dimensionless fracture conductivity. The study demonstrated that for ICHFs, both analytical methods provide close estimates of fracture half-length with the best results coming from the use of correction techniques of Nobakht and Clarkson (2012) and Behmanesh et al. (2017). For FCHFs, the inverse production method performed better than the square root time technique with the use of Chen and Raghavan (2013) and Ibrahim and Wattenbarger (2006) corrections. However, the inverse production methodology seems to be more sensitive than square root time to the change level in initial pressure and permeability. Moreover, it is shown that the square root time methodology generally overestimates the value of fracture half-length for FCHFs except some of the cases where the mean pressure is used. The results of this study provide general guidelines on the most accurate methods with their correction ways that can help to better analyze linear flow data in fractured gas wells. Also, this research can serve as selection criteria to choose the best analytical production methods to evaluate the performance of hydraulic fractures according to the well and reservoir properties.

Automated summary

This study analyzed the linear flow data in unconventional gas wells and provided guidance on estimating parameters such as fracture half-length using analytical methods and correction techniques. The results showed that different methods and correction techniques have different accuracy in estimating fracture half-length under different conditions.