Roles of Surfactants during Soaking and Post Leak-Off Production Stages of Hydraulic Fracturing Operation in Tight Oil-Wet Rocks

Srikanth Tangirala, James J. Sheng

Research output: Contribution to journalArticlepeer-review

10 Scopus citations

Abstract

Many experimental studies have been conducted in the recent past to assess the inclusion of different types of surfactant in a frac fluid in hydraulic fracturing of low-permeable formations. These lab studies either corresponded to spontaneous imbibition testing using Amott cells or dynamic core-flooding tests to assess the hydrocarbon permeability after the invasion of the frac fluid. Both these tests have been considered independently by different authors but have not been analyzed as one holistic approach to assess the oil recovery potential of a surfactant. It is prudent to understand the superiority of the specific interfacial mechanism of the surfactant that correlates to the best-case scenario of oil recovery by considering both the tests that lead to leak-off and follow the leak-off of frac fluid into the matrix. In this experimental study, two tests related to soaking and production processes are conducted simultaneously using surfactants with different interfacial properties of interfacial tension (IFT) reduction and wettability alteration for both low-permeable and high permeable core samples. The oil recovery from soaking tests are compared to the oil productivity of dynamic production tests assessed from the calculated parameters of effective permeability of oil recovered and flowback efficiencies. The results obtained in this study indicate that the surfactant which simultaneously reduces the IFT and alters the wettability of the low-permeable rock from oil-wet to water-wet is not conducive for oil productivity during dynamic production process despite it being very effective in oil recovery during the soaking process. Rather, a neutral-wetting surfactant seems to produce optimal results when the whole process of oil recovery from hydraulic fracturing is considered. The trend in the results for flowback efficiency and effective permeability of oil post leak-off observed in this study across the high and low-permeable rocks could be extended to unconventional shale rocks to safely infer that with regards to oil productivity, it would be beneficial to avoid any leak-off of the surfactant fluid, which showcases both IFT reduction and wettability alteration. The insights provided in this study motivate the reader to analyze beyond the common experimental methods of static imbibition testing in labs to embrace the methods that consider a complete hydraulic fracturing process for assessing enhanced oil recovery of low-permeable formations.

Original languageEnglish
Pages (from-to)8363-8373
Number of pages11
JournalEnergy and Fuels
Volume33
Issue number9
DOIs
StatePublished - Sep 19 2019

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