Core-flood Effluent and Shale Surface Chemistries in Predicting Interaction between Shale, Brine, and Reactive Fluid

Journal Article · Mon Jul 26 00:00:00 EDT 2021 · Proceedings of the Unconventional Resources Technology Conference (URTeC)

DOI:https://doi.org/10.15530/urtec-2021-5640· OSTI ID:1886926

Gundogar, Asli S. ^[1]; Druhan, Jennifer L. ^[2]; Ross, Cynthia M. ^[3]; Jew, Adam D. ^[4]; Bargar, John R. ^[4]; Kovscek, Anthony R. ^[3]

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1. SLAC National Accelerator Lab., Menlo Park, CA (United States); SLAC
2. University of Illinois at Urbana-Champaign, IL (United States)
3. Stanford University, CA (United States)
4. SLAC National Accelerator Lab., Menlo Park, CA (United States)

We report field and laboratory observations to date indicate that the efficiency of hydraulic fracturing, as it relates to hydrocarbon recovery, depends significantly on geochemical alterations to rock surfaces that diminish accessibility by partial or total plugging of the pore and fracture networks. This is caused by mineral scale deposition such as coating of fracture surfaces with precipitates, particle migration, and/or crack closure due to dissolution under stress. In reactive flow-through experiments, mineral reactions in response to acidic fluid injection significantly reduced system porosity and core permeability. The present study focuses on changes to fluid chemistry and shale surfaces (inlet and fracture walls) resulting from shale-fluid interactions and integrating these findings for an improved estimate of transport-related consequences. The reacted shale surfaces were examined by spatially-resolved scanning electron microscopy - energy dispersive spectroscopy (SEM-EDS) analysis. Importantly, inductively coupled plasma - mass spectrometry/optical emission spectroscopy (ICP-MS/OES) was utilized to probe the chemical evolution of the core-flood effluents. The three study cores selected from the Marcellus formation represent different mineralogies and structural features. In flow-through experiments, lab-generated brine and HCl-based fracture fluid (pH=2) were injected sequentially under effective stress (up to 500 psi) at reservoir temperature (80°C). SEM-EDS results confirmed by the ICP concentration trends showed significant Fe hydroxide precipitates in clay- and pyrite-rich outcrop samples due to partial oxidation of Fe-bearing phases in the case of intrusion of low salinity water-based fluids. Porosity reduction in the MSEEL (Marcellus Shale Energy and Environmental Laboratory) carbonate-rich sample is related to compaction of cores under stress due to matrix softening with substantial dissolution, and pore-filling by hydroxides, as well as barite and salts. Despite the same fluid compositions and experimental conditions used for both MSEEL samples, barite precipitation was much more intense in the MSEEL clay-rich sample due to its greater sorption capacity and additional sulfate source as well as fissile nature with multiple lengthwise cracks. ICP tests revealed time-resolved concentration trends in produced brine and reactive fluids that in turn complemented the pre-/post-reaction SEM-EDS observations.

• Research Organization: SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)
• Sponsoring Organization: National Science Foundation; USDOE Office of Fossil Energy (FE)
• Grant/Contract Number: AC02-76SF00515
• OSTI ID: 1886926
• Journal Information: Proceedings of the Unconventional Resources Technology Conference (URTeC), Journal Name: Proceedings of the Unconventional Resources Technology Conference (URTeC) Vol. 5640; ISSN 2159-6832
• Publisher: Unconventional Resources Technology Conference
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
fluid
permeability
porosity
shale
unconventional