Engineering topics

Busch, Andreas

Publications and source records attributed to Busch, Andreas.

3 records

DOE OSTI2023

Evolution of Pore Structure in Organic-Lean and Organic-Rich Mudrocks

The pore structure of mudrocks is a key characteristic to evaluate flow behavior through these rocks. Although significant advances have been made to resolve pore characteristics, porosity evolution, or pore connectivity, there is still insufficient knowledge linking porosity evolution to flow and transport in mudrocks. To better understand these links, we conducted very small-angle (VSANS) and small-angle neutron scattering (SANS) experiments on 13 sets of mudrocks from global locations, characterized by differences in composition, maturity, and depositional environment. Our results indicate that a homogeneous pore structure reflects a stable and low-energy depositional environment. Organic-lean mudrocks mainly contain pores <10 nm, which restricts flow and is beneficial for, e.g., caprock seal integrity. Increasing maturity as a result of increasing burial depth, and therefore, temperature leads to porosity evolution. In organic-rich mudrocks (ORMs), this happens through the generation of organic matter pores and pore preservation around diagenetically formed carbonates. ORMs mainly contain macropores (>50 nm), favoring production from, e.g., unconventional reservoirs. SANS-derived pore size distributions will help to better understand fluid imbibition and flow properties in mudrocks through comprehensive quantitative characterization of the nano- to micron scale pore network conduits and their relationships to burial diagenesis.

58 GEOSCIENCES↗

DOE OSTI2022

Molecular Structure of Adsorbed Water Phases in Silica Nanopores

The adsorption of water vapor in silica nanopores with different pore morphologies and surface hydrophilicities was studied to quantify the densities and thicknesses of the water sorption layers and deduce their molecular structures. Water adsorption to surface hydroxyls is described by a multilayer sorption model. At low pressure, the water adsorption isotherms are largely independent of pore size and the adsorbed amounts scale with the surface hydroxyl density. Adsorbed-phase densities corresponding to the adsorption of two water molecules per surface hydroxyl group are found in the first adsorbed water layer for a wide range of surface hydroxyl densities. The densities and layer thickness values found in narrow pores indicate that patchy adsorbed layers form if not enough water molecules exist for a full layer, which coexist with dry pore surface regions. This behavior indicates cooperative adsorption effects, i.e., a preference for the formation of hydrogen bonds between water molecules bound to surface hydroxyls. In narrow pores, pore condensation limits further growth of the sorption layer, and in larger pores and at the planar quartz surface, a second adsorbed water layer is formed, which can hold up to approximately 4 additional water molecules per surface hydroxyl group. The water molecules in these thicker adsorption layers arrange such that the sorption layer density is similar to the bulk water density. Pore confinement limitations on the sorption layers are observed in pores with radii of as large as 8 nm. Molecular dynamics modeling reveals two preferential orientations for water molecules adsorbing to surface hydroxyl groups and suggests an intralayer structuring in the adsorbed monolayer. Furthermore, adsorbed water molecules in the sorption layer are bonded to the surface hydroxyl group via the donation and acceptance of hydrogen bonds.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Predicting Fluid Flow Regime, Permeability, and Diffusivity in Mudrocks from Multiscale Pore Characterisation

In geoenergy applications, mudrocks prevent fluids to leak from temporary (H 2 , CH 4 ) or permanent (CO 2 , radioactive waste) storage/disposal sites and serve as a source and reservoir for unconventional oil and gas. Understanding transport properties integrated with dominant fluid flow mechanisms in mudrocks is essential to better predict the performance of mudrocks within these applications. In this study, small-angle neutron scattering (SANS) experiments were conducted on 71 samples from 13 different sets of mudrocks across the globe to capture the pore structure of nearly the full pore size spectrum (2 nm–5 μm). We develop fractal models to predict transport properties (permeability and diffusivity) based on the SANS-derived pore size distributions. The results indicate that transport phenomena in mudrocks are intrinsically pore size-dependent. Depending on hydrostatic pore pressures, transition flow develops in micropores, slip flow in meso- and macropores, and continuum flow in larger macropores. Fluid flow regimes progress towards larger pore sizes during reservoir depletion or smaller pore sizes during fluid storage, so when pressure is decreased or increased, respectively. Capturing the heterogeneity of mudrocks by considering fractal dimension and tortuosity fractal dimension for defined pore size ranges, fractal models integrate apparent permeability with slip flow, Darcy permeability with continuum flow, and gas diffusivity with diffusion flow in the matrix. This new model of pore size-dependent transport and integrated transport properties using fractal models yields a systematic approach that can also inform multiscale multi-physics models to better understand fluid flow and transport phenomena in mudrocks on the reservoir and basin scale.

36 MATERIALS SCIENCE↗