Impacts of Mineralogy on Petrophysical Properties

Abstract

Because of their extreme heterogeneity at multiple scales, carbonate rocks present a great challenge for studying and managing oil reservoirs. Depositional processes and diagenetic alterations of carbonates may have produced very complex pore structures and, consequently, variable fluid storage and flow properties of hydrocarbon reservoirs. To understand the impact of mineralogy on the pore system, we analyzed four carbonate rock samples (coquinas) from the Morro do Chaves Formation in Brazil. For this study, we used thin sections and XRD for their mineralogical characterization, together with routine core analysis, NMR, MICP and microCT for the petrophysical characterizations. The samples revealed very similar porosity values but considerably different permeabilities. Samples with a relatively high quartz content (terrigenous material) generally had lower permeabilities, mostly caused by more mineral fragmentation. Samples with little or no quartz in turn exhibited high permeabilities due to less fragmentation and more diagenetic actions (e.g., dissolution of shells). Results confirm that carbonate minerals are very susceptible to diagenesis, leading to modifications in their pore body and pore throat sizes, and creating pores classified as moldic and vug pores, or even clogging them. For one of the samples, we acquired detailed pore skeleton information based on microCT images to obtain a more complete understanding of its structural characteristics.

Multiscale pore‐network reconstruction of a fine‐textured heterogeneous soil

“…Pore network modeling was carried out using the new PoreStudio software (Lima et al., 2022; PoreStudio, 2023), which comprises a cross‐platform pore network code and associated solver. The software allows simulations of a full range of flow and transport processes based on several modules.…”

“…Pore network modeling was carried out using the new PoreStudio software(Lima et al, 2022;PoreStudio, 2023),T A B L E 1…”

Effects of pore size and pore connectivity on trapped gas saturation

“…Investigations of pore structures at scales ranging from micrometers to a few millimeters are possible using microCT scanners that provide non-destructive 3D images of the internal structure of materials (Lima et al, 2022). Image acquisitions were performed using CoreTOM equipment (Tescan/XRE) with a 25 µm voxel size, while the images were reconstructed using the Acquila reconstruction software (Tescan/XRE).…”

“…Understanding and quantifying the effects of trapped gas in oil reservoirs is a challenge, particularly for carbonate rocks which have an unusually complex multiscale heterogeneous pore structure causing unique fluid retention and flow properties (Godoy et al, 2019;Sun et al, 2017). Carbonate hydrocarbon reservoirs, including the Brazilian Pre-Salt, are the subject of several scientific investigations due to their geological complexity and economic value (Herlinger et al, 2017;Lima et al, 2022).…”

Modeling sub‐resolution porosity of a heterogeneous carbonate rock sample

“…Carbonate rocks often exhibit multi‐modal pore size distributions (PSDs), involving a wide range of pore throat sizes from nanometers to macropores spanning several centimeters in diameter (Drexler et al., 2022; Silveira et al., 2022). For typical core samples with diameters around 5 cm, the µCT resolution is confined to a few micrometers (Ferreira et al., 2023; Lima et al., 2022). Achieving higher resolutions necessitates either focusing on a smaller sample area (thus reducing the VOI) or physically segmenting the sample for multiple scanning processes (Drexler et al., 2022; Lima et al., 2022).…”