Modelling Silica Transport In Large-Scale Laboratory Experiments
Authors: Stone T. , Boon J. , Bird G.W. 
Published: March 2010

A number of experiments involving steam and steam-C02 cyclic drives in Athabasca oil sands have been carried out in a 150 cm diameter pressure vessel at reservoir conditions. Four different experiments are discussed from which aqueous silica concentrations were measured at the production well. The first is a steam only injection experiment, the second is a CO2 pre-soak followed by steam-Dilly injection, the third is a steam-CO2 co-injection experiment, and the last is a steam-only injection with CO2 slugs introduced at the end of the drawdowns.

An extensive experimental program has determined the kinetics of silica dissolution and precipitation for sands from the McMurray Formation, From this study, a model describing the kinetics was derived. This experimental study has been reported elsewhere. The present paper describes how all equation governing conservation of silica was then added to a thermal numerical reservoir model that conseres energy, water, heavy oil, two additives and a tracer. This model has no adjustable parameters and contains only experimentally measured constants. It was used to simulate silica transport in the experiments described above.

This simulation study was generally successful in predicting the average behaviour of the measured silica concentrations at the production well. Discrepancies between the model and experiment are discussed. Also discussed are other possible future geochemical applications of the numerical model.

Introduction

Many experiments have been carried out at the Alberta Research Council since 1975 to test the effectiveness of additives on recovery of Athabasca and Cold Lake bitumen. A series of experiments that utilized a 150 cm diameter pressure vessel involved steam, steam in combination with CO2, or pure CO2 as injected fluids. The carbon dioxide was also used to pre-soak one experiment after which steam injection was initiated. The experiments discussed in this paper had their production fluids analyzed for silica concentration.

Using a simple silica kinetics model with transport constants determined as part of an experimental program using Athabasca sand, a numerical reservoir model in conjunction with a silica conservation equation was used to predict the experiments and the silica concentrations in the production fluids.

This study was undertaken to better understand the physical mechanisms raking place within the pressure vessel that lead to oil production. Analyzing and predicting the silica transport dynamics gives additional data at the production well that can possibly be used to understand these mechanisms in field conditions.

As well, there have been reported cases in the literature of gravel pack disintegration and well collapse (Reed, 1979), Thus, a second motivation in developing a model of silica transport was ro be able to predict the dissolution and precipitation of silica under field conditions.

Description of Experiment

The 150 cm diameter simulator system (Fig. 1) consists of a large pressure vessel (150 cm ID by 270 cm high) designed to allow steam and gas to be injected simultaneously into the test bed under controlled flow rates. Oil sand is packed into this vessel and maintained at field overburden conditions.