Interpretation of Closure Pressure in the Unconventional Montney using PTA Techniques

摘要

The Montney formation In NE British Columbia and NW Alberta is one of the largest economically feasible resource plays in North America. It contains both gas and liquids rich light ends. Horizontal multi-staged fracturing is the method for developing this vast resource. Prior to hydraulically fracturing the wellbore, the toe stage is frequently mini-fraced to obtain reservoir and geomechanical properties. Interpreting these mini-fracs, commonly referred to as DFIT’s (Diagnostic Fracture Injection Tests), has proved to be a challenge using traditional combination G Function and square root plots. It is always important to ensure that all data being analyzed is associated with a reservoir response and not wellbore behavior, surface operational interruptions or data quality issues. Some of these challenges can be overcome when using some new techniques for mini-frac Fall-off analysis, which will be discussed in this paper. Various pressure transient analyses (PTA) based interpretation techniques have been introduced to the industry over the last couple of years for the determination of closure pressure (Bachman et al. 2012, Mohamed et al. 2011 and Marongiu-Porcu et al. 2011). From a theoretical viewpoint, unification of the fields of traditional PTA and mini-frac interpretation has been achieved. We recommend that the standard PTA based log-log derivative plot using equivalent time is included in the analysis of mini- frac / fall-off tests. This plot is rarely, if ever, used in current interpretations. For mini-frac interpretation, the starting point should now be the standard PTA based log-log derivative plot. The primary pressure derivative (dp/dt) curve should also be added to the log-log derivative plot as an independent flow regime identification technique. This now gives two independent flow regime identification techniques in one plot. The power of the primary pressure derivative to enhance the interpretation of closure and flow regime identification will be illustrated. Subsequently, flow regime specific plots can be constructed to enhance the interpretation. A number of field examples from the Montney formation in the Farrell Creek area of NE British Columbia are illustrated using a systematic PTA interpretation methodology demonstrating multiple closure events, high fracture extension pressure gradients of 34.0 kPa/m, non-Darcy pressure derivative diagnostics and observation of complex fracture orientation.