Laboratory Studies Of Oil Recovery From Tar Sands By Electrocarbonization
Authors: Schoeppel R.J. , Sarapuu E. 
Published: December 2007

The petroleum industry has long been interested in potential methods of increasing recovery from oil reservoirs. The energy necessary to produce a satisfactory increase in recovery has been supplied through use of a secondary fluid to displace, heat, and/or dilute the original reserve.

This paper describes a laboratory investigation into the application of electrical energy as a recovery agent in impermeable tar sands. The preliminary study presented has shown that flow continuity can be established and maintained in laboratory tar sand models solely by application of electrical energy. Formation of an electrically carbonized zone of 10 darcies permeability, high oil recovery, moderate thermal-productive requirements, and the production of qualitatively important proportions of electrocarbonization gas have been demonstrated with linear laboratory tar sand models. The size of the permeable channel created was found to be a function of the amount of electrical energy applied. Principal mechanisms responsible for these results have been identified as electrolytic and electronic conduction, electrical resistance heating, viscosity reduction, thermal expansion, and distillation with pyrolysis. Theoretical considerations on the effect of electrolyte content on the over-all resistivity of rock and electrode-earth contact resistance and heating rates arc discussed. Preliminary results of electrogasification and dielectric breakdown experiments with tar sands are mentioned.

Introduction

Application of thermal energy, as a means of increasing oil recovery from petroleum reservoirs, has received considerable industry interest during the past few years. The problem of producing highly viscous oils and tars presents an even greater challenge because of their tremendous reserve and because thermal recovery by fluid injection methods is not applicable for situations where sufficient flow continuity between wells cannot be established or maintained.

Thermal recovery techniques which have received greatest attention are the injection of air to support underground combustion, the injection of steam, the injection of-hot water, and detonation of thermonuclear devices within oil bearing formations. Use of electrical energy has recently been considered for bottom-hole heating within a single wellbore in order to initiate combustion, or to heat injected or produced fluids. Standard resistance heating elements lowered by conductor cable are usually selected for such purposes. An alternate technique is to utilize the natural earth resistance between two electrodes spaced a considerable distance apart. This technique has been successfully applied to electrocarbonization" experiments with coal and oil shale. However, no recent laboratory work has been reported in application of this technique to the recovery of crude oil from sands.

In the coal and oil shale investigations, the electrocarbonization treatment was found capable of creating a tortuous and permeable fixed-carbon channel, or "electrofracture", through the otherwise impervious strata. Somewhat similar results have been reported by Bill and Davis for oil sands and shales. In their experiments however, dielectric breakdown was used to create the permeable-conductive channel. They also found potential requirements for dielectric breakdown of an oil bearing formation was dependent on electrode spacing which precludes commercial application. On the other hand, electro-linkage - electrocarbonization processes have demonstrated their feasibility by successfully linking through 150 ft of coal with a maximum applied potential of 2,500 v. Total energy requirements for specific electro-thermal applications have been estimated for sands and commercially measured for oil shale.