Examining the Effects of Stress Dependent Reservoir Permeability on Stimulated Horizontal Montney Gas Wells

Abstract

Abstract The Montney gas play in NE British Columbia and NW Alberta is undergoing intense development utilizing multi-stage fracturing of horizontal wells. Problems persist in determining an optimal development strategy for each area within the Montney. For the Groundbirch area, operators are in the early stages of development. As a consequence they have invested significantly in well monitoring including microseismic, pressure build-ups, real time rate and pressure measurements and offsetting pressure observation wells. Conventional core analysis indicates that reservoir rocks have permeability in the micro-Darcy range. Lab experiments indicate permeability is also a function of the changing effective stress. Effective stress increases and permeability decreases as production occurs. A coupled geomechanical/reservoir study was performed after 400 days of production history in order to match behavior and determine the sensitivity of conventional production forecasts to the changing stresses within the reservoir. This paper focuses on the performance analysis of a single Upper Montney well in the Groundbirch area. The approach is staged, with the analysis proceeding from the simple to the more complex. The first step involved an improved version of production analysis. After the identification of linear flow, the utility of a long neglected plot, dm/q versus superposition linear time is illustrated. The ability of this plot to accurately split production well performance into reservoir properties and skin effects introduced by the fracture treatments is shown. This has wide ranging implications for the industry. Finally a simple practical method has been found to compare performance of various types of horizontal multi-stage fracture treatments where the impact of reservoir properties has been removed. In the second step of the study various descriptions of the study well were developed for all the processes the well encountered. These reservoir simulation models successfully matched treatment placement, an early build-up test distorted by clean-up effects and long term production behavior. Models types ranged from constant reservoir permeability through stress dependent permeability variation. Techniques were developed that eliminated the need to perform the time consuming geomechanical calculations. This allows the use of conventional reservoir models with pressure dependent permeability functions of a special form, to be used in day to day analysis. Sensitivity of the predicted production response with these models was then quantified.