Smartwater-Based Synergistic Technologies Offer Potential in Enhanced Oil Recovery

Abstract

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 209360, “Smartwater-Based Synergistic Technologies: A Next-Recovery Frontier for Enhanced Oil Recovery,” by Subhash C. Ayirala, SPE, Abdulkareem M. Alsofi, SPE, and Zuhair A. Al-Yousef, SPE, Saudi Aramco, et al. The paper has not been peer reviewed. _ In the complete paper, the authors explore the synergistic effects of smartwater in polymerflooding, surfactant polymer (SP) flooding, carbonated waterflooding, and foam-assisted gas-injection processes. A suite of multiscale experimental data is analyzed to demonstrate and quantify the benefits of water-chemistry synergies in these enhanced oil recovery methods. Smartwater increased oil recoveries by 5–7% in addition to reducing polymer-concentration requirements by one-third in polymerflooding. Experimental Materials, Methods, and Procedures _ Materials Brines. High-salinity water (HSW) as well as two low-salinity smartwater brines, SW1 and SW2, were used. HSW had a salinity of 57,670 ppm total dissolved solids (TDS). The two smartwaters had roughly the same salinity but different individual ions. SW1 was represented by a 10-times dilution of HSW, while SW2 was of the same salinity but enriched with mainly sulfate ions. Crude Oil. Two crude oils were used. The crude oil used for polymerflooding oil-displacement experiments had a viscosity of 2.0 cp, while the crude oil with a viscosity of approximately 4.4 cp at reservoir temperature (90–100°C) is used for SP-flooding experiments. Both the crude oils had an asphaltene content of approximately 6.0 wt%. Polymer. A sulfonated polyacrylamide polymer having a sulfonation degree of 25 mol% and a molecular weight of 12 million Dalton was used. Polymer concentrations within the range of 1,000–2,000 ppm were chosen for polymerflooding and SP-flooding experiments. Surfactants. A betaine-type amphoteric surfactant was used for SP-flooding experiments. The gases used to generate the foam were nitrogen gas and carbon dioxide gas (CO2) with a purity of approximately 99.99 and 99.50%, respectively. Core Samples. Carbonate core plug samples were obtained from carbonate reservoirs. One sample was used to conduct the displacement experiment with polymerflooding, while six preserved plugs were used for evaluating SP-flooding synergy with smartwater. The ambient porosity ranged from 22.1 to 29.3%, and air permeability ranged from 123 to 1,978 md. A single plug was used for polymerflooding oil-displacement tests, while two-plug composite core samples were used for SP-flooding experiments.