Piloting Chemical EOR in a Mature Field: Pushing the Envelope in a Challenging Case

Abstract Despite the push towards the energy transition, the latest forecast for energy consumption calls for the oil demand to plateau or slightly decrease until 2035, and mature fields still have their place in the landscape of energy supply. The challenge for these fields, however, is recovering as much of the oil left as economically feasible. The Velasquez field in Colombia is one of these fields and increasing recovery there comes with a specific set of challenges. The field, which started production in 1947, produces from a complex, multilayered, heterogeneous and faulted reservoir bordered by an active edge aquifer. It contains a medium gravity oil with variable properties. The water has a high salinity as well as extreme hardness and reservoir temperature is approximate ly 150°F. Due to the very active aquifer there has been no need for any water injection, but the recovery factor is only 25% with a water-cut over 80%. The operator therefore felt that EOR would be needed to increase recovery and polymer injection was selected as the best option by a screening study. The design of a pilot was then undertaken by a multi-disciplinary team. The paper describes the workflow used to prepare a polymer flood pilot in the field, which include a laboratory study to select polymers suitable to the extreme hardness of the formation water as well as reservoir simulations and the design of the pilot itself. Due to the limited water injection experience in the field, polymer injectivity is an unknown which will have to be addressed by the pilot. A polymer capable of resisting the extreme hardness has been identified and a preliminary pilot design has been conducted. The pilot is expected to be sanctioned and then construction will proceed. The pilot has been designed to address the challenges specific to the field and to provide all the information required to expand the polymer injection to the whole field. Although it is still early to talk about expansion, this should always be at the forefront of any project as a pilot is only the means to an end. This paper will be of interest to operators which are faced with similar issues of rejuvenating mature fields which still have relatively low recovery factors through the application of chemical EOR. Although the field has some peculiar characteristics, the workflow and philosophy are applicable to any mature field.