A Field Trial in a Carbonate Reservoir Using a Solvent-Based Waterflood Process

Abstract

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 179838, “Persistence in EOR—Design of a Field Trial in a Carbonate Reservoir Using a Solvent-Based Waterflood Process,” by Abdullah Alkindi, SPE, Nasser al-Azri, Dhiya Said, and Khalid AlShuaili, Petroleum Development Oman, and Paul te Riele, SPE, Shell Development Oman, prepared for the 2016 SPE Enhanced Oil Recovery Conference at Oil and Gas West Asia, Muscat, Oman, 21–23 March. The paper has not been peer reviewed. Dimethyl-ether (DME) -enhanced which waterflood (DEW) is a process in DME is added to injection water and, upon injection, preferentially partitions into the remaining oil. As a result, it swells the oil and reduces the oil viscosity, significantly improving oil mobility. Several coreflood experiments conducted in tight-carbonate plugs have shown incremental recoveries of up to 20% post-waterflood. A field trial has been designed to derisk this technology, which, if successful, would add significant reserves. Introduction Enhancing oil recovery from low- permeability formations has been challenging. DEW presents the advantages of a miscible flood without the negative effects of density differences. DME is a slightly polar hydrocarbon that is miscible with most known crude oils. As a result, upon contact with crude oil, the DME will swell the oil and reduce its viscosity, after which the oil will be effectively displaced. DME is soluble in water and, therefore, can be injected with any existing waterflood. Because the molecule is small, there are no limitations on formation type or permeability. Its water solubility enables efficient recovery of the DME with a clean-brine chase. Because it does not interact with the formation, recovery efficiencies of DME are found to be close to 100% in laboratory core experiments. Depending on the injected-slug size and the crude-oil composition, oil recovery could be enhanced by 10 to 25% in field application. In a DEW, DME is dissolved in the injection brine and injected into the formation. The DME solubility is dependent on salinity and temperature but can be up to 38 wt% for fresh water. Upon contact with the oil in the reservoir, the DME will partition to the oleic phase, where it will swell the oil, reduce its viscosity, and mobilize the oil to the producer wells. The process is schematically presented in Fig. 1. In light-oil reservoirs, additional oil is primarily produced by oil swelling. After injection of the DME-containing brine slug, a chase phase will be used to dis-place the mobilized oil further and recover the DME from the remaining oleic phase. During this chase, DME will partition back into the initially DME-free water phase. Recovery efficiencies are found to be very high. There is no residual DME because of its solubility in the mobile phase. DME does not adsorb to the rock/fluid interface, and DME recovery occurs microscopically in a shock.