The primary objective of this project is to apply a number of geomechanical modelling tools to a specific poroelastic problem (fluid withdrawal and subsequent injection into a pinnacle reef), and to assess the strengths and weaknesses of these modelling tools. A secondary objective is to use the modelling results to assess: (i) the critical pore pressures at which the reservoir’s seal could be compromised, for the specific pinnacle reef problem being analysed; and (ii) the locations and types of rock failure processes that would negatively impact the seal’s integrity if these critical pressures were exceeded.

This paper summarizes semi-analytical and closed-form solutions that can be used to assess the poroelastic stress changes induced within a porous formation (reservoir) during a pore pressure change. Further, solutions are presented for the stress discontinuities at the interfaces between reservoirs and the rocks that surround them. When used in combination with rock failure criteria, these solutions enable relatively simple analyses of the potential for induced fracturing or fault reactivation within a reservoir or the rock immediately adjacent to it. The latter , in particular, is useful for assessing if the hydraulic integrity of the surrounding rock (i.e., the bounding seal) will be affected by a pore pressure change. The use of the approach presented in this paper is illustrated with an analysis of a pinnacle reef with dimensions and properties representative of reefs in the Zama oil field, northwestern Alberta, Canada. Scenarios of pore pressure decrease (during historical production operations) and pore pressure increase (during several years of acid gas injection operations) are analyzed, for three different idealizations of reservoir properties and geometry (two plane strain and one axisymmetric). These results suggest that that the potential for induced fracturing is not significant at any point within the reservoir or the surrounding rock for both the production and injection scenarios that were simulated. Similarly, fault reactivation was not predicted for the reservoir or any of the points that were analyzed in the surrounding rock. However, fault orientations having the greatest potential for reactivating during historical production operations were identified; thus, illustrating a means of using geomechanical models to focus geological characterization efforts on the features that are most critical to acid gas containment. (PDF) Poroelastic Modelling of Production and Injection-Induced Stress Changes in a Pinnacle Reef. Available from: https://www.researchgate.net/publication/313904468_Poroelastic_Modelling_of_Production_and_Injection-Induced_Stress_Changes_in_a_Pinnacle_Reef [accessed Sep 25 2018].