The response of existing transient triple-porosity models for fractured horizontal wells do not converge to that of linear dual-porosity model (DPM) in the absence of micro-fractures (MF). The reason is the assumption of sequential-depletion from matrix to MF, and from MF to hydraulic-fractures (HF). This can result in unreasonable estimates of MF and/or HF parameters. Hence, the authors proposed a quadrilinear flow model (QFM) in a previous paper which relaxes the sequential-depletion assumption to allow simultaneous matrix–MF and matrix–HF depletion. Also, it is proved that QFM simplifies to both DPM and linear sequential triple-porosity model (STPM).
This work considers the implications of applying QFM, STPM and DPM type-curves and analysis equations on production data from tight reservoirs. QFM, STPM and DPM are applied to two fractured horizontal wells completed in Bakken and Cardium Formations. A comparative study of the reservoir parameters estimated from the application of these models to the same production data set reveals two key results. Firstly, the application of DPM on production data from reservoirs with active MF could result in overestimation of HF half-length. This happens to compensate for the extra fluid depletion pathways/communication-interface provided by MF. Secondly, the application of STPM on production data from reservoirs with active matrix–HF communication could result in underestimation and overestimation of MF spacing and number respectively.
Results from this study are significant when selecting the appropriate model for interpreting production data from fractured horizontal wells completed in formations with or without active MF. DPM is appropriate if analog studies (e.g. outcrop, micro-seismic and image log analyses) reveal high spacing aspect ratio (negligible MF) in the reservoir. Spacing aspect ratio is MF spacing divided by HF spacing. STPM is appropriate if analog studies reveal low spacing aspect ratio (e.g. matrix–HF face damage or high MF density within a given HF spacing). QFM is appropriate for all spacing aspect ratios.