Physicochemical Interactions of Source-Rocks with Injected Water-Based Fluids

Abstract

Water-based fracturing fluids contain polymers to function either as fluid viscosifiers or friction-reduction agents. Whereas much work has been done on optimizing these functions, little or no published work focuses on their chemical interactions with the rock they are targeting. Co-polymers of polyacrylamide are used in slick-water fracturing, while Guar gum or one of its derivatives is used as a base for linear or cross-linked gels. This thesis reports studies on the adsorption behavior of some, primarily, guar-based polymers onto the surface of source rock outcrop samples in order to provide a better picture of the interactions of polymers with these rocks. Outcrop samples from the Barnett, Eagle Ford, and Marcellus were collected, analyzed for mineralogy and total organic carbon, and then exposed to different polymer solutions under elevated temperature and moderately elevated pressure. Viscosities of these polymer solutions were measured before and after exposing them to the rock in order to establish a correlation between polymer adsorption and the rock mineralogy and organic content. Results indicate that there is a significant correlation between the adsorption behavior of the polymer and the rock mineralogy and its organic carbon. Polymer adsorption is in agreement with cation exchange mechanisms as described in earlier work. Cationic polymers are more prone to be adsorbed on the surface of the rock than non-ionic polymers. The importance of polymer adsorption has not yet been determined. It is speculated that due to viscosity reduction resulting from polymer adsorption, wellbore clean-up could be enhanced through the use of this property. It could also have detrimental impacts on hydrocarbon production. This work also shows that oxidizing breakers might be spent on removing the organic content of the rock rather than being spent on breaking cross-linked gels, especially in rocks with high organic content. The results from this work point out that fluid-rock interactions are significant, and that further research regarding source-rock polymer interactions and its effects on hydrocarbon production is needed.