The fluid transport properties inside a nano-size conduit often deviate from those reported at unconfined conditions at an identical pressure and temperature. The deviation from the nominal value is well studied for a simple topology in nanofluidics. The observed peculiarities in synthetic nanofluidic systems seem relevant to shale formations because the characteristic pore size in the shale matrix is on the order of nanometers. What remains unclear, or overlooked, is how the deviations influence the fluid behavior at the 1-cm scale.
We originally used the tree-like pore model to simulate mercury injection capillary pressure measurements of the shale. The tree-like model is acyclic in a graph-theoretic sense, in which a cycle is a path that starts and ends at the same node without retracing any bond. The acyclic models are fundamentally different from cyclic models, such as the regular lattice and sphere-packing models, in which there are at least two paths between any two pores in their structures. The main feature of the tree-like pore model is that it accounts for the effective connectivity of the pore space at the core scale, as it can simulate the core-scale measurements.
Schematic of mercury injection in the tree-like model where the nonwetting phase is shown in red.
Our goal in this research is to determine the effective transport properties of a shale formation at the 1-cm scale by accounting not only for the pore-scale processes but also for the effective connectivity of the pore space at the core scale. We have already examined a variety of properties (effective viscosity, effective density, critical temperature, critical pressure, compressibility factor, slippage, permeability, and adsorption–desorption hysteresis). We have also collected an exhaustive database of the petrophysical measurements (porosity, permeability, mercury injection capillary pressure measurements, and nitrogen adsorption and desorption) of the shale formations (Bakken, Barnett, Eagle Ford, Haynesville, Marcellus, Monterey, New Albany, Niobrara, Utica, Wolfcamp, and Woodford).
Representative articles
- Yu, C., Tran, H., and Sakhaee-Pour, A. (2018). Pore size of shale based on acyclic pore model. Transport in Porous Media, 124(2), 345 – 368.
- Tran, H., Sakhaee-Pour, A., and Bryant, S. L. (2018). A simple relation for estimating shale permeability. Transport in Porous Media, 124(3), 883 – 901.