Synthetic fractures with varying roughness and mineralogy

• https://www.onepetro.org/conference-paper/URTEC-2902986-MS?sort=&start=0&q=determining+fractures+javier+santos&from_year=&peer_reviewed=&published_between=&fromSearchResults=true&to_year=&rows=25#
• 10.15530/urtec-2018-2902986

Abstract — Hydraulic fracturing techniques aim to create high conductivity channels through low permeability rocks, enhancing hydrocarbon flow to the wellbore. However, characterizing the reduction of mobility in fractures as a result of surface heterogeneities, has received limited attention. In this work, we study the effect of the heterogeneity in composition and roughness in flow through hydraulically induced fractures. Since analytical solutions are restricted to simple domains, a 3D direct simulation approach was selected. To assess these effects, domains exhibiting geometrical mineral arrangements, and self-affine fractures were created to carry out drainage and imbibition simulations. The relations of different wetting/non-wetting patterns and surface roughness, with interfacial areas, capillary pressure, and residual fluid saturation were quantified. We show that there is an effective mineral feature size related to the fracture dimensions that modifies the capillary pressure behavior. Similarly, the correlation range of the surface apertures determines the effect of the shape of a non-wetting front. Correspondingly, we found that for increasingly rough surfaces, there is a linear relation between the residual non-wetting saturation and capillary pressure with the aperture distribution. Thus, the shape, mineral size ratio, and surface roughness can have a significant effect on flow patterns. The results of this work can be used to improve macroscopic simulations, having a priori knowledge of the microscopic characteristics.

• https://www.pge.utexas.edu/images/pdfs/theses18/EstradaSantosThesis18.pdf

Abstract — Fractures are widely present in the subsurface, often representing primary channels for fluid flow in low permeability rocks. While fracture surfaces are composed bydifferent minerals and are rough by nature, mathematical models to predict flow proper-ties rarely take in account these heterogeneities. Therefore, the pore-scale mechanisms offlow through fractures are not well understood. Because characterizing multiphase flowphenomena in these geometries has received limited attention, this thesis aims to addressthis issue, by studying the effect of surface roughness and heterogeneous wettability inimmiscible displacement through single fractures.Since analytical solutions are restricted to simple domains and obtaining data fromlaboratory experiments is unpractical, a 3D direct simulation approach via the lattice Boltz-mann method was selected. This was chosen based on its rigorous kinetic derivation, itsability to simulate immiscible displacement, and its versatile boundary conditions.To study the effects of surface heterogeneities, synthetic domains exhibiting geo-metrical mineral arrangements, and self-affine fractures were created to carry out drainage and imbibition simulations with different input parameters. The relationships of differentwetting/non-wetting patterns and surface roughness, with interfacial areas, capillary pres-sure, and residual fluid saturation were quantified.It has been shown that there is an effective heterogeneous feature size related tothe fracture dimensions that modifies the capillary pressure behavior, and the shape ofan invasive fluid front. We further found that for increasingly rough surfaces, there is alinear relation between the residual non-wetting saturation and capillary pressure with theaperture distribution. Thus, the shape, mineral size ratio, and surface roughness can have asignificant effect on flow behavior.The results of this work can be used to better inform field simulations, by providingphysically-accurate input parameters to characterize fracture network models, enhanced flow rate predictions for naturally fractured reservoirs can be obtained.