Pressure-retarded osmosis for enhanced oil recovery

Abstract

Pressure-retarded osmosis (PRO) is a membrane-based process that has been used historically to harness the osmotic energy of saline feed solutions. While conventional PRO applications target seawater (SW) /freshwater solution pairings, this paper focuses on an innovative high salinity gradient PRO application for waterflooding (WF) in the petroleum industry. WF is an industry-wide practice wherein produced water (PW) or SW is injected into the geological formation to displace hydrocarbons and increase oil production at the wellhead. PW represents the largest volume waste stream in oil production and harnessing its osmotic energy in a PRO application converts that waste stream into an asset leading to higher oil production while simultaneously reducing pumping energy requirements and enhancing injectivity.In this application, hypersaline PW at 28% total dissolved solids (TDS) is the draw solution and SW at 3.5% TDS is the feed. In contrast with hydroturbine (HT) & reverse osmosis (RO) applications where the economic benefit is energy, in WF, the primary benefit is additional oil production and a secondary benefit is energy savings. With the PW/SW solution pairing, PRO economics were compared for the WF, HT, and RO applications. The key economic metric is the “dollars of economic benefit derived per module per year” and for WF, that benefit is estimated at $71,700/module-year while the HT and RO configurations were found to return <$500/module-yr. Based on these findings, it is recommended that the application of PRO for WF be investigated further, to better define pretreatment requirements, commercial membrane performance limits and other environmental considerations.