A novel workflow for water flowback RTA analysis to rank the shale quality and estimate fracture geometry

Abstract

Recently, flowback data analysis enabled us to evaluate important fracture parameters including fracture conductivity and volume in unconventional reservoirs. To perform the analysis, diagnostic plots, straight-line techniques, and history-matching techniques have been used. Immediate water and gas production usually occurs on flowback in shale gas wells. In this paper, a novel workflow is developed for the analysis of water flowback data and the early-time production of shale gas wells. This analysis then helps to define the movable water and the applicability of the soaking process on these wells.Rate transient analysis (RTA) combined with decline curve analysis (DCA) were used to analyze different shale gas wells. Effective fracture volume and geometry were calculated from the RTA analysis. The estimated ultimate water recovery (EURw) was calculated from DCA. The calculated original water-in-place (OWIP) and the EURw were compared to the injected fracturing fluid. The impact of the soaking process on the well performance was studied.Results showed that in high-quality shale wells, with no movable formation water, gas kicked off early. OWIP was equal to the total injected water volume, and boundary dominated flow (BDF) regime was observed with no transient period. The performance of these wells improved with soaking.On the other hand, in low-quality shale wells, initial formation water saturation was higher than the connate water, and water production was from both the frac fluid and formation water. Consequently, gas kicked off later and transient flow regimes were observed. Transient flow regimes were used to estimate the fracture stimulated area. In this case, however, soaking had a negative impact on the performance as the movable water saturation was high.Honoring the flowback data can be used to estimate the fracture geometry and judge the quality of the shale formation and its validity for the soaking process.