Impact of Concurrent Solubilization and Fines Migration on Fracture Aperture Growth in Shales during Acidized Brine Injection

Journal Article · Sat May 14 00:00:00 EDT 2022 · Energy and Fuels

DOI:https://doi.org/10.1021/acs.energyfuels.2c00611· OSTI ID:2345051

Khan, Hasan Javed ^[1]; Ross, Cynthia M. ^[2]; Druhan, Jennifer L. ^[3]

---

1. Univ. of Illinois at Urbana-Champaign, IL (United States); King Fahd University of Petroleum and Minerals, Dhahran (Saudi Arabia); Stanford University
2. Stanford Univ., CA (United States)
3. Univ. of Illinois at Urbana-Champaign, IL (United States)

Acidic hydraulic fracturing fluid chemically and physically alters shale rock fabric during injection and shut-in, creating a “reaction-altered zone” along the fracture faces. To better characterize the variable thickness and composition of this reaction-altered zone under advective flow, we take a coupled experimental and modeling approach. A fluidic cell, with six fiducial markers, is first fabricated to keep the rock sample in place during the core floods and to allow image alignment of acquired images. Then, we conduct a series of reactive core floods in a clay-rich siliceous Wolfcamp shale sample with 10 wt % carbonate, using a synthetic fracturing fluid under no confining stress and at room temperature. High-resolution computed tomography (CT) scans are periodically conducted to observe the spatial alteration of the fracture network. We then perform scanning electron microscopy (SEM-EDS) on the two orthogonal surfaces (fracture surface and freshly cut profile face) to generate high-resolution elemental maps that show the change in mineralogy, both with distance along a given flow path along a fracture surface and with depth from the fracture surface into the shale matrix. These results are contrasted against a two-dimensional (2D) advection-diffusion reaction model developed previously for batch reactions between shale and synthetic fracturing fluids. The model simulates the geochemical interaction occurring at the fracture/matrix interface and penetrating into the shale matrix during the reactive core flood. Both model and experimental results show that the acidic brine is neutralized during the core flood, corresponding to an increase in fracture aperture as a function of fluid volume injected with the greatest change near the inlet. SEM-EDS scans reveal significant dissolution of carbonates on the fracture surface without pyrite oxidation. The reactive transport model indicates that carbonate depletion into the shale interior should be observable, yet SEM-EDS shows no discernible loss of carbonate in the orthogonal profile face. The combination of these observations suggests an additional fracture evolution mechanism in the reactive system, i.e., fines migration. We show that fines migration enhances the access of fracturing fluid to the matrix resulting in a more pronounced fracture widening. Finally, we conclude that coupled mineral dissolution and fines migration govern fracture aperture growth during acidized brine injection. In this work, we effectively show the underlying risk of relying solely on models that do not include an important (transport) process that can alter the system significantly and propose a combined chemomechanical mechanism for fracture evolution appropriate for this shale mineralogy.

• Research Organization: Energy Frontier Research Centers (EFRC) (United States). Center for Mechanistic Control of Unconventional Formations (CMC-UF); Stanford Univ., CA (United States)
• Sponsoring Organization: National Science Foundation (NSF); USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: SC0019165
• OSTI ID: 2345051
• Alternate ID(s): OSTI ID: 1977824
• Journal Information: Energy and Fuels, Journal Name: Energy and Fuels Journal Issue: 11 Vol. 36; ISSN 0887-0624
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
deformation
fluids
inorganic carbon compounds
minerals
shale