The existing transient models for multistage fractured horizontal wells assume single-phase flow. This assumption is violated in early times, when hydraulic fractures are filled with both water and gas/oil. Hence, the need for a model that can capture the transient 2-phase (water + gas/oil) flow in fractures during flowback. This paper proposes a flowback analysis model (FAM) which accounts for transient 2-phase flow in hydraulic fractures by extending the existing linear dual-porosity model (DPM).

FAM expresses hydrocarbon relative-permeability as a non-linear function of time to account for rapid watersaturation drop in the HF network. This function is obtained by combining the cumulative water + gas/oil data measured during flowback operations with drainage relative-permeability curves from existing literature. The resulting relative-permeability function of time is then incorporated into the existing DPM static-framework toobtain FAM flow equations. The FAM equations capture the fluid physics from flowback until hydrocarbon production in the life of a multifractured well. They are solved with Laplace transforms. Type-curves are then generated by numerically inverting the resulting Laplace space solutions to time-space using the Gaver-Stefhest algorithm. FAM converges to DPM at the limit of single-phase flow.

This paper develops an integrated workflow for analyzing transient 2-phase flowback data. It applies the workflow to history-match flowback data from a multifractured shale-gas well completed in the Horn River Basin. This match

  • estimates effective half-length, pore-volume of active secondary fractures interconnected with HF, percentage of injected fluid left in the HF, and

  • forecasts gas production.

Results from this study show how short-period flowback data analysis (FDA) can provide quick estimates of reservoir parameters (before full production data becomes available) and forecast long-term gas recovery. Also, the outputs from FDA could be used as inputs during post-flowback production data analysis to

  • reduce uncertainty in reservoir parameter estimates and

  • improve fracture characterization.

This study encourages the industry to start careful measurement of rate and pressure immediately after putting wells on flowback.

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