Oil Production Response To In Situ Electrical Resistance Heating (Erh)
Authors: Wattenbarger R.A. , McDougal F.W. 
Published: March 2010

An oil well can be stimulated by applying AC current to the formation in a single well. This type of stimulation can be called electrical resistance heating (ERH). The viscosity reduction which results from a higher temperature around the wellbore increases the oil production rate. This process has been tested in the field and the performance successfully matched with reservoir simulation. This study was performed to find a simple method of estimating steady state stimulated production rate.

A two-dimensional simulator was developed and run for 52 cases which covered a variety of reservoir conditions. This sensitivity analysis showed that four parameters accounted for most of the variation in production rate. The parameters were initial oil viscosity, formation thickness, drainage radius and induced temperature change.

The predictive equation takes the form of steady-state radial Darcy's Law with a modified oil viscosity term. The modified oil viscosity is a weighted average between the initial oil viscosity and the minimum oil viscosity at the wellbore. The weighting factor was matched to the reservoir simulation results by regression analysis. The use of this simple predictive equation agrees well with simulation results for steady state flow.

Introduction

Oil production can be stimulated by applying electrical power in the formation. The electrical power causes a temperature increase which reduces oil viscosity and results in increased oil production rates.

Electrical energy is converted to heat in the formation by a combination of electrical resistance heating (ERR) and electromagnetic power absorption, depending on the electromagnetic power frequency. This study was- confirmed to electrical resistance heating (ERH), which is the major source of heating when low frequency (60 Hertz) AC electric power is used.

The literature reveals several papers dealing with the possibility of using the ERR process for stimulating oil recovery.(1,5). Pilot studies have also been initiated in Canada, United States, Mexico, and other countries with varying degrees of Success(1,3,6,7).

One of the earliest examples of electrically stimulating oil recovery was reported by World Oil in 1970(1). The method was designated as the "Electrothermic Heating Process". The process used an AC current applied around the wellbore. The heat was reported to improve production of low API gravity oils up to 300%. Single-phase AC electric power was used to avoid metal corrosion associated with DC electric power.

Flock and Tharin(2) mentioned multi-well ERH as a possible recovery method. They proposed using electrically heated water in secondary recovery projects to increase displacement efficiency. They also pointed out poor efficiency in electric power generation was a major drawback to the ERH method. As a result, Flock and Tharin considered ERR as a preheat for more conventional thermal processes rather than an independent recovery process.

Schumacher(3) reported on ERR using multi-well installations. Because of the high cost of electrical power it was primarily considered as a means of preheating a reservoir as noted in the Flock and Tharin paper. The problem of water flashing to steam near the wellbore was also noted.