Work Flow Screens Surfactants for EOR Through Wettability Alteration

Abstract

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper URTeC 3866246, “A Systematic Laboratory and Model-Based Surfactant Screening Work Flow for Enhanced Recovery Through Wettability Alteration in the Eagle Ford,” by Jason Jweda, SPE, Russ Bone, SPE, and Hesham El-Sobky, ConocoPhillips, et al. The paper has not been peer reviewed. _ Previous experimental studies and published field trials have shown that injected surfactants can be an effective means of improving recovery. Most experiments, however, have been conducted at ambient rather than reservoir conditions. The complete paper presents a novel approach to screen thermally stable surfactants at high pressures and high temperatures for the explicit purpose of wettability alteration in the operator’s Eagle Ford acreage. Early Internal Efforts Surfactant usage was initiated at the inception of the play. The use of these surfactants was discontinued after approximately 5 years of field development. Fieldwide performance analysis confirmed that off-the-shelf surfactants, on average, did not improve long-term performance statistically. Initial laboratory screening of bespoke surfactant chemistries commenced a few years later. To test surfactant properties near Eagle Ford reservoir conditions, a novel microfluidics experiment was conducted using synthetic microchips designed with reservoir specifications. Twenty-six flowback tests with Eagle Ford crude oil were conducted at 300°F and up to 3,800 psi with six different commercial surfactant chemistries. Imbibition results with the six commercial surfactants were compared with a control case with make-up brine water. Testing performed at 2 gal/thousand increased overall performance for the oil-wet conditions but decreased performance for mixed-wet conditions when compared with 1 gal/thousand. The surfactants tested in this series were temperature-dependent and had clogging tendencies of varying degrees within the microfluidics chips. Methods and Work Flow Promising results from the Amott cell imbibition and other experiments encouraged the authors to evaluate surfactants more holistically, with an emphasis on testing at Eagle Ford reservoir conditions. The first set of experiments involved fluid-stability tests, contact-angle measurements, interfacial-tension (IFT) measurements, static spontaneous-imbibition experiments, and completion-fluid-compatibility tests. An extensive set of commercially available surfactants was screened. The highest potential cationic and nonionic cosurfactant blends that passed through fluid stability, contact-angle, and static spontaneous-imbibition experiments were selected for hydraulic stimulation-fluid compatibility tests. After the compatibility tests, the two best-graded cationic and nonionic cosurfactant blends were used in a novel flowback experiment coupled with multistage nuclear magnetic resonance (NMR) measurements. Mechanistic reservoir simulation models were used to evaluate the production effect of wettability change caused by surfactant injection. The combination of laboratory-based experimentation and reservoir simulations provided strong confidence in holistically evaluating the potential of cosurfactant blends in the Eagle Ford.