Abstract

Conventional reservoir simulation may not fully characterize the recovery mechanism of the SAGD process in the uncemented oil sands reservoirs. The uncemented oil sands exhibit significantly different geomechanical behaviour from that of their cemented counterpart. Therefore, to fully explore the SAGD recovery process, the coupled reservoir geomechanical simulations are required. This simulation technique can characterize both the multiphase fluid flow and reservoir parameter variations based on certain stress-strain relationships of oil sands in the SAGD process. In this paper, sequentially coupled reservoir geomechanical simulations are conducted. It is based on both the reservoir simulator, EXOTHERM, developed by T.T. &Associates Inc. and the geotechnical simulator, FLAC, developed by Itasca Consulting Group Inc. This paper discusses the strategies and methodology of the coupled reservoir geomechanical simulations for the SAGD process based on these two simulators. Meanwhile, the results of the conventional reservoir simulations and the coupled reservoir geomechanical simulations are compared. These comparisons are conducted based on initial stress conditions of Ko=1.0. The simulation results show that differences exist between coupled reservoir geomechanical simulations and conventional reservoir simulations under certain SAGD operation conditions.

Introduction

Canada has huge oil sand resources. The total volume of oil sand resources is 269,371 × 106 m3, which are distributed in three major areas in Alberta: Athabasca (212,886x 106 m3), Cold Lake (31,906?106 m3), and Peace River (24,579 × 106 m3) [1]. Its current production is 0.222x 106 bbl per year. Development technologies of oil sand resources include world-class surface mining, SAGD, Vapex, and cold production. The SAGD process has proven to be a promising technology and will play a critical role in the development of oil sand resources. In addition to reliable reservoir characterization and production facilities, realistic predictions of production performance are an important component in the design of commercial scale SAGD projects.

The realistic prediction of the SAGD performance by numerical simulation is an integral component in the design and management of a SAGD project. Conventional reservoir numerical simulation emphasizes multiphase flow in the porous media but generally does not take the interactions between fluid and solid into account. Unfortunately, this treatment is not correct for oil sand material. Oil sands are locked sands [2] which have very high rates of dilation at failure. In Athabasca deposits, McMurray Formation oil sands display a high incidence of tangential contacts as well as common straight and interpenetrative contacts [3]. Owing to the grain-to-grain contacts observed in locked oil sands, it shows the following characteristics: absence of cohesion, highly quartzose mineralogy, high strength, steeply curved failure envelopes, low porosities, lack of interstitial cement, brittle behaviour, and exceptionally large dilation rates at failure [4]. These properties are the basis of large variations of reservoir parameters and processes in the SAGD processes.

In the SAGD process, continuous steam injection and fluid flow can change reservoir pore pressure and temperature, which can increase or decrease the effective stress in the reservoir. Thus, deformations can occur in some regions. Likewise, the deformations of the oil sand material (skeleton and pores) changes the fluid flow related reservoir parameters [5].

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