SmartWater Flooding Mechanisms and Water Chemistry Guidelines for Carbonates
Subhash Ayirala (Saudi Aramco)
SmartWater flooding (SWF) through tuning of injection water salinity and ionic compositions is becoming attractive for improved/enhanced oil recovery in carbonate reservoirs. However, the pore scale mechanisms responsible for oil recovery in SmartWater flooding are not completely understood yet and furthermore there are no clear guidelines available to design injection water chemistries for field applications. This lecture unravels these existing mysteries by presenting the data acquired from a series of multiscale experiments (nano-micro-macroscopic-core scales) to explore the interactions of salinity and aqueous ions at oil/brine and carbonate-oil/brine interfaces. The systematic analyses of multiscale aqueous-ion interactions at the two interfaces showed that SmartWater effect in carbonates is a combination of two effects, one being related to the release of oil attached on rock surfaces (wettability change) and the other being related to improved oil-phase connectivity and better oil mobilization (enhanced coalescence of oil ganglia). The results obtained from several case studies are also discussed to demonstrate the efficiency of SWF technology to mobilize residual oil at well scale in addition to providing some economic estimates. This talk highlights two important takeaway points: (1) Not every low salinity water can become a SmartWater for carbonates, and (2) SmartWater is nothing but a tailored water chemistry containing certain salinity and selective composition of three key ions including sulfates, magnesium, and calcium. These new learnings and major findings will provide useful practical guidelines on how to efficiently design injection water compositions and obtain higher oil recoveries from waterflooding projects in carbonate reservoirs.
Subhash Ayirala is the Champion of SmartWater flooding at Saudi Aramco’s Exploration and Petroleum Engineering Center—Advanced Research Center, Dhahran, Saudi Arabia. He holds MS and PhD degrees in petroleum engineering from Louisiana State University, Baton Rouge, USA. He has written over 75 technical papers, 50+ journal publications, and holds 20 granted patents. He is SPE distinguished member and currently serves as co-executive editor of SPE Reservoir Evaluation & Engineering. Ayirala received SPE Outstanding Technical Editor recognition 9-times (most recent one in 2020) and is also a recipient of the 2017 SPE A Peer Apart Award.