Application Of Numerical Modelling To The Simulation Of The Electric-Preheat Steam-Drive (Epsd) Process In Athabasca Oil Sands
Authors: Hiebert A.D. , Vermeulen F.E. , Chute F.S. 
Published: March 2010

An implicit three-dimensional electrothermal simulator has been developed to numerically model multi-phase electric-preheat steam-drive (EPSD) processes in the Athabasca deposit. Two versions of the model are discussed. In the first version (Model 1), the electric preheat phase of process is modelled assuming that fluid expansion and flow can be neglected. The second model (Model 2) accounts for the flow of oil, water, and steam, as well as heat transfer due to conduction and convection during both the electric preheat and steam-drive phases of the recovery process.

Data from two simple two-dimensional reservoir simulations using both models are presented and compared. The results suggest that in most circumstances the expansion and flow of fluids during the electric preheat may have negligible effect on the temperature distributions established in the reservoir, and hence, that the computationally less complex Model 1 is generally adequate for simulating EPSD processes in the Athabasca deposit.

Finally, an EPSD process in a representative reservoir is simulated using a 1 ha repeated 5-spot pattern with an electric preheat of 365 days. The preheat is followed by a combination of steam and hot waterflooding extending for a period of approximately eight years. Cumulative recovery is shown to be about 60% original-oil-in-place (OOIP) at an OSR of 0.42.

Introduction

Large portions of the Athabasca oil sand deposits of Alberta have porosities, oil saturations and pay thicknesses that should make them excellent candidates for economical steamflooding. However, to inject steam and produce bitumen continuously at practical rates it is necessary to have some initial fluid communication between injector and producer wells. Under in situ conditions the reservoir fluids in these formations are virtually immobile.

In an electric-preheat steam-drive (EPSD) process the reservoir is first selectively heated electrically so as to lower the viscosity of the oil along predetermined paths between wells. Fluid mobilities along these heated interwell channels are generally several hundred times greater than in the original reservoir, and steam can be injected at satisfactory rates, at pressures well below fracture pressure.

Electrode wells (which may also be required to serve as injectors or producers), excited at power frequency), are located with due consideration given to reservoir lithology and electrical properties so as to cause current to pass through the regions that are desired to be heated. Electric current flows primarily through the interconnected water paths in the oil sand and the electrical power dissipated along these filamentary paths is rapidly transferred to the surrounding bitumen and to the sand matrix. Detailed considerations for the selection and placement of electrode wells for various reservoir lithologies have been previously reported(1–3). As well, a considerable literature relating to the numerical and physical modelling of electric-preheat processes has developed(1–16). Recently the economics of such processes have been examined by the Alberta Oil Sands Technology and Research Authority(17) and by Petrotec Systems Inc. of Denver(18).

Few of the referenced articles consider the problem of fluid flow during electrical preheating(4, 6, 7, 12, 15, 16, 17). Only three of these(12, 15, 17) specifically address modelling of the electric-preheat steam-drive process.