Multiphysics Investigation of Geochemical Alterations in Marcellus Shale Using Reactive Core-Floods

Date

2021-07-01

Author

Gündoğar, Satı Aslı
Ross, Cynthia M.
Jew, Adam D.
Bargar, John R.
Kovscek, Anthony R.

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The interaction of reactive fracture fluid with host shale and formation water plays an important role on fractured reservoir productivity. This study explores the prominent impacts of shale-fluid reactions on flow properties using representative core-flood experiments under confining stress. Alteration of shale is monitored using time-lapse X-ray computed tomography (CT), microCT (mu CT) of samples pre- and post-reaction, and scanning electron microscopy (SEM). The imaging approach is multiscale from nm's to cm's. The samples are clay-rich and partially fractured Marcellus outcrop and carbonate-rich MSEEL (Marcellus Shale Energy and Environmental Laboratory) downhole endmembers. Both samples have distinct microcracks for probing reactive transport in fractures communicating with matrices. A reduction in krypton-accessible CT porosity and liquid permeability was observed for both samples after fracture fluid exposure. Based on SEM-EDS surface analysis, an iron-bearing precipitate formed on and near fracture openings and in the shale matrix of the Marcellus outcrop indicating partial dissolution of pyrite and/or ferruginous dolomite followed by precipitation of iron (hydro)oxide. The compiled images reveal fracture filling with migrated and/or precipitated fine particles. Significant barite scale growth was detected on the reacted MSEEL surfaces together with halite and other (hydro)oxide precipitates resulting from geochemical reactions between the basin-specific injectants and shale minerals. The MSEEL sample experienced substantial calcite dissolution and a corresponding decrease in its bulk density and microcrack openings. Experimental results presented here indicate the significance of fracture fluid composition optimization based on intrinsic shale and resident brine chemistries.

URI

https://hdl.handle.net/11511/117657

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Department of Petroleum and Natural Gas Engineering, Article