Decameter-Scale Flow-Unit Classification in Brazilian Presalt Carbonates

Abstract

Summary Rock typing into flow units (FUs) plays a pivotal role in constructing static and dynamic models of petroleum reservoirs. Decisions made by asset teams mostly depend on predictions of how fluids will percolate through the subsurface during the reservoir life cycle. In carbonate settings, dealing with rock typing is complex and can generate a large quantity of units because of diagenetic processes such as dissolution, cementation, and silicification. Most rock-typing methods in carbonates successfully classify small-scale flow heterogeneity in well resolution but fail when interpolating those facies further away from the 1D domain, because of the lack of correlation between FUs and spatial data. Seismic data can be used to detect large-scale FUs and assist the interpolation of small-scale FUs in 3D reservoir volume, thus producing more-realistic static and dynamic models. We propose a modification of the classical rock-typing methods that use permeability (k) vs. porosity (ϕ) plots and electrical properties, with a data set from the Mero Field, part of the giant Libra Field of presalt carbonate reservoirs in offshore Brazil. From the permeability cumulative S-curve analysis, we established major large-scale FUs that maintain part of the carbonate flow heterogeneity and correlate them with the elastic attributes: P-impedance (PI) and S-impedance (SI). In addition, we established a priori PI and SI correlations with the formation-factor (FF) (F) parameter to categorize large-scale FUs using the F vs. k methodology. With the large-scale FUs mapped in seismic data sets, core-plug-scale FUs can be populated into the 3D static and dynamic models using geostatistics tools, thus creating more-realistic reservoir models and assisting asset teams in the decision-making process.

3D Seismic Flow Units, Porosity and Permeability Modelling in Brazilian Presalt Reservoirs: An Overview

“…Given the amount of core porosity and permeability analysis available (500m of core analysis, 1700 conventional porosity and permeability measurements), we performed the FU discretization mostly based on k versus ϕ related methods, like Gunter et al (1997) stratigraphic modified Lorenz plot (SMLP) and flow zone indicator (FZI; Amaefule and Altunbay, 1993), who approximates a given pore-throat size radius for each FU. Other Flow Units discretization using the Lorenz S-curve and Formation Factor attributes were also performed in the 1D domain, as discussed by Penna and Lupinacci (2020). We used the SMLP as a qualitative display to analyze the variation of flow units and fluid movement in the reservoir at different scales of observation, like stratigraphy sequence studies are made separating high order events from low order events.…”

“…1). We calculated a small and significant number of flow units that correlates with seismic elastic attributes and respond for the large-scale flow characteristics in the reservoir, maintaining part of the local flow complexity (Penna and Lupinacci, 2020). Within each FU, we establish petrophysical relations that calculates more accurate seismic derived 3D volumes of porosity and permeability and compared to volumes calculated using sedimentological k-ϕ relations.…”

Understanding the relationship between acoustic impedance and porosity in a presalt carbonate reservoir of the Santos Basin

“…This is because lithologies with different porosities present, in many cases, similar values of acoustic impedance. Several works address this problem and discuss alternatives to get around it (Teixeira et al, 2017;Castro e Lupinacci, 2019;Dias et al, 2019;Mello, 2020;Penna and Lupinacci, 2020;Penna and Lupinacci, 2021). This work aims to correlate the values of acoustic impedance with the values of effective porosity from well logs, in a scale compatible with the acoustic impedance volume, to evaluate the feasibility for future modeling of reservoir properties, and to evaluate the types of electrofacies that can be distinguished in a future classification of multi-attribute seismic facies.…”