Effect of Temperature On Ultrasonic Velocities of Unconsolidated Sandstones Reservoirs During the SAGD Recovery Process

Doan, D.H. (Institut Francais du Petrole) | Nauroy, J.F. (Institut Francais du Petrole, ) | Baroni, A. (Institut Francais du Petrole) | Delage, P. (Ecole des Ponts ParisTech) | Mainguy, M. (TOTAL)

OnePetro 

ABSTRACT:

The steam assisted gravity drainage (SAGD) has been successfully used to enhance the recovery of heavy oil in Western Canada and Eastern Venezuela basins. Pressure and temperature variations during SAGD operations induce complex changes in the elastic properties of the reservoir rock. To study these changes, measurements of ultrasonic wave velocities were performed on both reconstituted samples and natural oil sands samples. Reconstituted samples were made of Fontainebleau sand with a slight cementation formed by a silicate solution. They have a high porosity (about 37 % to 40 %) and a high permeability (about 10-12 m²). Natural oil sands samples are unconsolidated sandstones extracted from the fluvio-estuarine McMurray Formation in Alberta (Canada). The saturating fluids were heavy oil and glycerol with a strongly temperature dependent viscosity. Tests were carried out at different temperatures (in the range -30°C and 80°C) and at different effective pressures (from 1.2 MPa up to 8 MPa). Experimental results showed that the elastic wave velocities measured are strongly dependent on temperature (mainly through the viscosity) whereas little effect of effective pressure was observed. Velocities decrease with increasing temperature and increase with increasing effective pressure. These effects are mainly due to the variations of the saturating fluids properties. The experimental results were afterwards compared with the Ciz and Shapiro [1] approach, a extension of the poroelastic theory of Biot-Gassmann [2, 3], applied for rock filled with the hightly viscous fluids.



1. INTRODUCTION

Vast quantities of heavy oils, estimated to 56.1011 barrels [4] are mainly trapped in unconsolidated sandstone reservoirs in Western Canada and Eastern Venezuela basins. The world's largest deposits are almost entirely located in the province of Alberta, Canada with three major oil sands deposits defined as Athabasca, Cold Lake and Peace River. The SAGD technique combined with horizontal wells has been developed as one of the most effective in-situ process to produce heavy oils. SAGD heats the oil and reduces its viscosity making it mobile and capable to flow towards horizontal lower well by gravity drainage. Steam injection produces changes in the reservoirs, namely changes in temperature, pressures, reservoir porosity, and pore fluid content. These changes obviously affect elastic properties of the rock layers and generate consequently differences on seismic velocities and amplitudes. 4D seismic and other seismic technology can be used to monitor the impact of the changes enumerated above. By comparing maps of seismic attributes at different times the spatial distribution of the heated reservoir zones can be approximately located. Over the past two decades, several measurements of elastic properties of unconsolidated rock reservoir have been published [5, 6, 7, 8, 9, 10, 11]. However, there is still a lack of clear understanding of the effect of the thermal process on the reservoir behavior. Measurements were carried out in natural core samples from some Canadian oil sands reservoirs and also in reconstituted samples saturated with various viscous fluids (heavy oil and glycerol) so as to investigate the effect of changes in viscosity on the elastic properties of saturated rock.