Dissolution-driven permeability reduction of a fractured carbonate caprock

Brian R. Ellis, Jeffrey P. Fitts, Grant S. Bromhal, Dustin L. McIntyre, Ryan Tappero, Catherine Anne Peters

Research output: Contribution to journalArticle

74 Scopus citations

Abstract

Geochemical reactions may alter the permeability of leakage pathways in caprocks, which serve a critical role in confining CO2 in geologic carbon sequestration. A caprock specimen from a carbonate formation in the Michigan sedimentary Basin was fractured and studied in a high-pressure core flow experiment. Inflowing brine was saturated with CO2 at 40 C and 10 MPa, resulting in an initial pH of 4.6, and had a calcite saturation index of-0.8. Fracture permeability decreased during the experiment, but subsequent analyses did not reveal calcite precipitation. Instead, experimental observations indicate that calcite dissolution along the fracture pathway led to mobilization of less soluble mineral particles that clogged the flow path. Analyses of core sections via electron microscopy, synchrotron-based X-ray diffraction imaging, and the first application of microbeam Ca K-edge X-ray absorption near edge structure, provided evidence that these occlusions were fragments from the host rock rather than secondary precipitates. X-ray computed tomography showed a significant loss of rock mass within preferential flow paths, suggesting that dissolution also removed critical asperities and caused mechanical closure of the fracture. The decrease in fracture permeability despite a net removal of material along the fracture pathway demonstrates a nonintuitive, inverse relationship between dissolution and permeability evolution in a fractured carbonate caprock.

Original languageEnglish (US)
Pages (from-to)187-193
Number of pages7
JournalEnvironmental Engineering Science
Volume30
Issue number4
DOIs
StatePublished - 2013

All Science Journal Classification (ASJC) codes

  • Environmental Chemistry
  • Waste Management and Disposal
  • Pollution

Keywords

  • CO sequestration
  • calcite dissolution
  • caprock integrity
  • fines migration
  • fracture flow
  • leakage

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