Multiphase Flowback Rate Transient Analysis of Multi-Fractured Horizontal Wells in Gas Condensate Shales

Abstract Flowback rate transient analysis (RTA) of multi-fractured horizontal wells (MFHWs) in shale gas has historically focused on single-phase or two-phase water and gas flow, ignoring the presence of condensate. We introduce a multiphase flowback RTA for MFHWs in gas condensate shales, accounting for condensate dropout when the pressure in hydraulic fractures (HFs) falls below the dewpoint. We develop a semi-analytical multiphase flowback model to analyze flowback data during HF depletion. Three flow regimes are considered: a two-phase water and gas infinite-acting linear flow (IALF), a two-phase boundary-dominated flow (BDF), and a three-phase water, gas, and oil BDF. We derive pressure diffusivity equations for water-, gas-, and oil-phase flows and employ the material balance approach to determine the average HF pressure. Defined pseudo-variables facilitate the construction of diagnostic plots for flow regime identification and specialty plots for characterizing HF properties. We obtain diagnostic plots for each phase using the developed semi-analytical solution. During the early flowback period, the water- and gas-phase diagnostic plots display a half-slope straight line, indicating the IALF regime. This is followed by a unit-slope line, signaling the transition to the BDF regime. For the oil phase, a unit-slope line denoting BDF is observed once the HF pressure drops below the dewpoint. Additionally, we validate the developed models against numerical simulations. The results show that the estimated HF permeability and fracture half-length from the models closely match the set values in the numerical model, with relative errors below 10%. Finally, we examine the applicability of the developed multiphase flowback model on an MFHW drilled in the Horn River Shale. The proposed multiphase flowback model significantly improves our understanding of the HF stimulation jobs and HF dynamics and characteristics.