Persistence in EOR - Design of a Field Trial in a Carbonate Reservoir using Solvent-based Water-Flood Process

Abstract

Abstract Primary and secondary recovery processes produce about one third of oil in place, leaving significant volumes behind. For low permeability and highly saline carbonate reservoirs, exploiting these resources is often challenging and unfeasible either technically and/or commercially. In this paper we discuss the application of an emerging EOR technique that has shown promising results in the lab. Di-Methyl Ether (DME) enhanced waterflood (DEW) is a process in which DME is added to injection water, which upon injection into the reservoir, it preferentially partitions into the remaining oil. As a result, it swells the oil and reduces its viscosity which significantly improves oil mobility in the reservoir. Several core-flood experiments conducted in tight carbonate plugs have shown incremental recoveries of up-to 20% post waterflood. Additionally, the process provides significant acceleration to oil production, which would otherwise take several pore volume of water injection. After successful PVT and core flood experiments, a field trial has been designed to de-risk this technology which if successful would add significant reserves. The pilot will be implemented in a tight carbonate reservoir that has been under waterflood. Some key uncertainties this pilot will address include solvent utilisation, oil incremental recovery, solvent back production and impact of geology on the process. This paper discusses the key physical mechanisms of the process, pilot design and challenges of full field considerations. In addition, it also highlights key considerations when designing solvent-based EOR applications. The paper also highlights the need of lab work to mitigate operational issues prior to implementation. Calibrated numerical models were used to generate full field profiles, which show the need for a well optimised pattern design to make such processes feasible