Insights from high-speed in-situ imaging of wormhole growth in limestone cores.

Positive feedback between permeability and dissolution during the flow of a matrix-dissolving fluid through porous media can create diverse, evolving structures [1]. The dynamics of this hydrochemical instability depend on both flow rate and the geometric properties of the pore space, leading to a wide range of structures: from intricate, cave-like wormholes to simple surface dissolution patterns. 

A variety of petroleum engineering applications led to a significant number of industry-oriented studies, and the effects of flow and reaction rates on wormhole formation are well established [2], however mechanisms governing their propagation dynamics remain poorly understood.

This study investigates the dominant wormhole regime, which has applications in various industrial and natural contexts, including carbon capture and storage. Understanding the dynamics of fluid interaction with the porous matrix requires high-resolution temporal and spatial data. We have recently conducted in-situ X-ray microCT imaging of developing wormholes in dissolving limestone cores flooded with hydrochloric acid, achieving high temporal frequencies (50–100 frames per experiment) [3]. To further improve temporal and spatial resolution, we utilized the ID-19 beamline at the European Synchrotron Radiation Facility. A limestone core was confined in a Hassler cell and flooded with hydrochloric acid, while high-frequency 4D tomographic data tracked the evolving 3D shape of the growing wormhole. The time evolution of the wormhole profile has been compared with an analytical model of the growth of the tube-like dissolution structure [4]. As we show, such data, when properly interpreted, allow for a measurement of the mineral dissolution rate constant and the assessment of the impact of diffusive transport on the dissolution process.

[1] Hoefner, M.L. and Fogler, H.S., 1988. Pore evolution and channel formation during flow and reaction in porous media. AIChE J., 34, pp.45-54

[2] Golfier, F., Zarcone, C., Bazin, B., Lenormand, R., Lasseux, D. and Quintard, M., 2002. On the ability of a Darcy-scale model to capture wormhole formation during the dissolution of a porous medium. J. Fluid Mech., 457, pp.213-254

[3] Cooper, M.P., Sharma, R.P., Magni, S., Blach, T.P., Radlinski, A.P., Drabik, K., Tengattini, A. and Szymczak, P., 2023. 4D tomography reveals a complex relationship between wormhole advancement and permeability variation in dissolving rocks. Advances in Water Resources, 175, p.104407

[4] Budek, A. and Szymczak, P., 2012. Network models of dissolution of porous media. Phys. Rev. E 86, 056318.