Shale Wettability: Data Sets, Challenges, and Outlook

The wetting characteristics of shale rocks at representative subsurface conditions remain an area of active debate. A precise characterization of shale wettability is essential for enhanced oil and gas recovery, containment security during CO2 geo-storage, and flow back efficiency during hydraulic fracturing. While several methods were utilized in the literature to evaluate shale wettability (e.g., contact angle measurements, spontaneous imbibition method,and NMR method), we here review the recently published data sets on shale contact angle measurements. The objectives of this review are to (a) develop a repository of the recent shale wettability data sets using contact angle measurements at high pressure and temperature (HPHT) conditions, (b) explore the factors influencing shale wettability, (c) identify potential limitations associated with contact angle methods, and (d) provide a research outlook for this area. On the basis of the data reviewed here, we conclude the following: (1) Shale/oil/brine systems demonstrate water-wet to strongly oil-wet wetting behaviors. (2) Shale/CO2/brine systems are usually weakly water-wet to CO2-wet. (3) Shale/CH4/brine systems are weakly water-wet. The key contributing factors that underpin this high shale wettability variability include, but are not limited to, operating pressure and temperature conditions, total organic content (TOC), mineral matter, and thermal maturity conditions. Thus, this review provides a succinct analysis of the shale wettability contact angle data sets and affords an overview of the current state of the art technology and possible future developments in this area to enhance the understanding of shale wettability.

Automated summary

This review examines recent data sets on shale wettability using contact angle measurements, identifying influencing factors and limitations associated with contact angle methods. The study concludes that shale/oil/brine systems demonstrate water-wet to strongly oil-wet behaviors, while shale/CO2/brine systems are weakly water-wet to CO2-wet, and shale/CH4/brine systems are weakly water-wet. Factors contributing to the variability in shale wettability include operating conditions, organic content, mineral matter, and thermal maturity. This review provides a concise analysis of shale wettability data and offers insights into current technology and future developments in this field.