The rock typing of complex clastic formation by means of computed tomography and nuclear magnetic resonance

Abstract

This study provides a new rock-typing approach for low-resistive and low-permeable clastic rocks. The approach includes integrated interpretation of routine core analysis data with microstructural characteristics, acquired from computed tomography (CT) and nuclear-magnetic resonance (NMR) data. The studied formation comprises siltstones in its bottom, which are replaced by sandstones in its top. Sandstones form the main part of the oil reservoir, whereas siltstones were originally considered as water-saturated. The reserves calculation was performed based on a single Archie equation for the whole formation. Despite on apparent water saturation and low permeability of the siltstones, incidental perforation showed considerable oil inflow from them as well. In order to delineate missed productive intervals within the low-resistive siltstones, we had to develop a new rock-typing approach, acknowledging rock multimineral composition, diversity of microstructures, a wide range of porosity, permeability, and residual water saturation values. Designed laboratory program included porosity, permeability, electrical resistivity measurements, capillary, NMR and CT tests. The experiments were performed on the same core samples that enabled reliable correlation between measured parameters. The joint interpretation of flow zone indicator, calculated as a function of porosity and residual water saturation, together with the results of petrophysical and microstructural measurements allowed reliable rock-typing of the clastic formation. It will serve as a petrophysical basis for identification of the missed productive intervals. The developed laboratory program and rock-typing algorithm can be implemented in other oilfields.

Geophysical Subsurface Mapping Using the Electrical Resistivity Technique: A Comprehensive Study of the Petroleum Training Institute Main Campus in Effurun

“…These layers exhibit distinct resistivity patterns indicative of their unique geological characteristics. For instance, areas with low resistivity values may signify conductive fracture zones, clay-rich materials, and subterranean sandstone formations (Tchistiakov et al, 2022). The concordance between VES analysis and dipole-dipole methodologies lends credibility to the geological model, offering insights into subterranean movements and structures.…”