Water-Wet or Oil-Wet: is it Really That Simple in Shales?
- Ishank Gupta (University of Oklahoma) | Jeremy Jernigen (University of Oklahoma) | Mark Curtis (University of Oklahoma) | Chandra Rai (University of Oklahoma) | Carl Sondergeld (University of Oklahoma)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- Publication Date
- June 2018
- Document Type
- Journal Paper
- 308 - 317
- 2018. Society of Petrophysicists & Well Log Analysts
- 15 in the last 30 days
- 288 since 2007
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In this study, experiments were done on samples from the Marcellus, Woodford, and Eagle Ford shales. The experiments showed that samples from these formations were grossly water-wet, mixed-wet and oil-wet, respectively. The correlation of average wettability index with total organic carbon (TOC) showed that 5 wt% is the critical TOC content required to achieve connectivity and generate oil-wet pathways. Similarly, correlation of average wettability index with clay content showed that <10 wt% clay, samples are oil-wet and >65 wt%, they are predominantly water-wet, and between 10 and 65 wt% clay content, samples exhibited mixed wettability. The threshold values of 5 wt% TOC and 10 wt% clays represent the same volumetric fraction (~10%) of the rock. The figure of 10% can be thought of as percolation threshold for connectivity in shale rocks.
Scanning electron microscope (SEM) imaging done on representative samples (one per formation) was used to quantitatively assess the fraction of different pore types. The fractions of different pore types were in agreement with the observations from the macroscopic imbibition experiments. For instance, oil-wet Eagle Ford samples had a higher fraction of organic pores (22.5%) while water-wet Marcellus samples had a higher fraction of inorganic pores (40%). The samples from all the three shales had a high fraction of mixed-wet pores (Marcellus 57%, Eagle Ford 69%, and Woodford 68%). This knowledge of fractions of different pore types can be instrumental in modeling connectivity pathways.
|File Size||2 MB||Number of Pages||10|