Experiments Examine Shear-Enhanced Two-Phase Flow in Athabasca Sands

Abstract

This article, written by Editorial Manager Adam Wilson, contains highlights of paper SPE 160092, ’Shear-Enhanced Two-Phase-Flow Properties in Athabasca Sands,’ by Syed M. Farrukh Hamza, SPE, Jon E. Olson, SPE, and Jon Holder, The University of Texas at Austin, prepared for the 2012 SPE Annual Technical Conference and Exhibition, San Antonio, Texas, 8-10 October. The paper has not been peer reviewed. Field results in steam assisted gravity drainage (SAGD) heavy-oil operations suggest formation permeability changes during production operations. This process was investigated using samples constructed from loose Athabasca sand. Results indicate that permeability changes and endpoint oil- and water-saturation variation are a function of loading boundary conditions. Overall, laboratory experiment results support increased permeability from steam injection in heavy oil; and, more importantly, the observed reduction in residual oil saturation implies that SAGD-induced deformation should improve recovery factors. Introduction Athabasca Oil Sands Properties. The Athabasca oil sands are relatively shallow deposits containing quartz sand, silt, clay, water, and bitumen. Most of the oil-rich sands are fine-to-medium grained with some silt- and clay-sized material. The quartz grains are water-wet. The porosity estimates range from 32 to 46%. Oil sands are loose sands, held together by bitumen. However, bitumen does not act as a cementing agent because it is a Newtonian fluid and, hence, provides no shear resistance at a zero shear rate. As a consequence, it cannot contribute to the static mechanical strength of the material, provided that the deformation does not proceed very rapidly. SAGD. During SAGD, steam is injected into the Athabasca oil sands reservoir at high temperature and pressure. The changes in pressure and temperature cause changes in stress and deformations, which result in formation shearing and permeability changes. The deformation response of Athabasca oil sands is stress-path dependent. The thermal expansion of the reservoir from the injected steam causes thermal stresses in the horizontal direction because the reservoir is bounded laterally by the surrounding rock formations. The vertical stress from the over-burden remains constant because, at shallow depths, the Earth’s surface is a free surface. Study Objective. The aim of this work was to study the deformation and associated multiphase-flow properties of the Athabasca oil sands using stress paths representative of the SAGD process. Experimental results document permeability and endpoint saturation change from SAGD stress paths that can lead to a better understanding of coupled geomechanical and fluid-flow processes, the implementation of which could lead to improved recovery from heavy-oil reservoirs.