The Use of Multilateral Well Designs for Improved Recovery in Heavy Oil Reservoirs

Abstract There are now a variety of ways to achieve higher recovery factors from heavy oil reservoirs, but most of them involve the injection of thermal energy or chemicals to reduce the oil viscosity. While these techniques have been highly successful, they can also be very expensive when the steam generation and/or chemical injection costs are accumulated throughout the productive life of the field. A lower cost solution, one that has been very successful in the Faja Del Orinoco of Eastern Venezuela, is to use multi-branched wells (multilaterals) to increase reservoir exposure and achieve an arguably higher recovery factor. These multilateral wells have been shown to produce more oil over a longer period of time than conventional horizontal wells without any additional operating costs. This paper will discuss the concept of using multilateral wells as an alternative to conventional Enhanced Oil Recovery (EOR) techniques in heavy oil reservoirs. It will argue that the oil recovery factor of a reservoir that is drilled with increased wellbore exposure can be comparable to thermal/chemical EOR under the right circumstances, and that the project will have a much lower operating cost. While steam injection has become the successful mainstay of most EOR projects, there are many drawbacks such as the costs of the steam generation and the emission of greenhouse gases. Multilateral wells can potentially offer an option to produce the same reservoir with lower costs while still recovering an increased percentage of the oil from the reservoir. This technique is especially applicable in inter-bedded or thin oil zones where steam injection would be costly and inefficient. Extensive background information will be presented from the Orinoco belt in Venezuela, where multilateral wells have proven to be an economical approach to develop a very challenging "extra-heavy" oil reservoir.