New Techniques in Interpretation of Closure Pressure in the Montney Formation

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 163825, ’Interpretation of Closure Pressure in the Unconventional Montney Using PTA Techniques,’ by Robert V. Hawkes, Pure Energy Services; Irene Anderson, Talisman Energy; R.C. Bachman, Taurus Reservoir Solutions; and A. Settari, SPE, University of Calgary, prepared for the 2013 SPE Hydraulic Fracturing Technology Conference, The Woodlands, Texas, USA, 4-6 February. The paper has not been peer reviewed. The Montney formation in Canada is one of the largest resource plays in North America. Horizontal multistaged fracturing is the best method for developing this vast resource. Before hydraulic fracturing of the wellbore, the toe stage is frequently minifractured to obtain reservoir and geomechanical properties. Various pressure-transient-analysis (PTA) -based interpretation techniques have been introduced to the industry over the last few years for the determination of closure pressure. From a theoretical viewpoint, unification of the fields of traditional PTA and minifracture interpretation has been achieved. Introduction Despite low natural-gas prices, the Montney- play region of northeast British Columbia remains one of the most active of such plays in North America. Operators continue to push drilling activity in the Montney, with increased liquids production within many portions of the trend. Characterization techniques and stimulation and production mechanisms continue to make economics favorable. Prefracture diagnostic testing is an approach that regulators and operators are now more commonly using in unconventional and tight formations. Industry’s current use of minifracture analysis for the determination of fracture closure and after-closure reservoir properties, however, still presents several challenges. The conventional approach to all minifracture analysis is the 1D Carter leakoff model, which leads directly to the concept of G time. For more than 30 years, G time (or the G-function) has played the dominant role for the determination of closure stress, but there remains ambiguity in performing minifracture analysis. Part of the problem is that the recommended plots do not rigorously identify the various flow regimes that occur during a minifracture/falloff. Minifracture analysis requires a general theory that accounts for all of the actual observed flow regimes (both before and after closure). The objective of this paper is to create and perform a consistent workflow process of four Montney diagnostic injection tests (one vertical and three horizontal wells) on the same pad, with a systematic approach highlighting the characteristic flow-regime slopes when using the Bourdet log-log derivative plot. In brief, the Bourdet derivative function used in the PTA-based log-log derivative approach accounts for rate variation before the analyzed shut-in period. The workflow we present is also dependent upon plotting the primary-pressure derivative (PPD) in combination with the Bourdet log-log derivative plot.