Estimation for Representative Element Area of a Coquinas Analogue Using Statistical and Numerical Methods

Abstract

The Itapema formation consists fairly of a limestone reservoir section with coquinas (shell fragments) deposited under high salinity lacustrine conditions. The environment in which this deposits accumulated along with the diagenetic processes subsequently undertaken created reservoir rocks with high heterogeneity in several scales of investigation. The representative elementary length plays a major role to characterize such reservoirs. The present work describes a quantitative approach to determine the size of a representative elementary area (REA) using both numerical and statistical methods defined for a Coquinas analogue. Two effective properties are determined for the REA: Porosity and Permeability. The porosity is defined here as the visible porosity from a micro tomography slice and the permeability estimated from a virtual Darcy's experiment using a finite element implementation of Brinkman's equation. Brinkman's equation is deemed necessary to properly model the flow within the vugs and porous matrix. The REA is subject to periodic boundary conditions with a pressure gradient on each boundary face. The variance is estimated and used as a statistical instrument to guide the REA size and later compared to the results obtained from the porosity and permeability estimations. The laboratory routine core analysis (RCA) provides a bulk measurement for porosity and permeability of the whole Coquinas sample. The RCA is used to constraint the obtained results for the simulations and statistical estimation and delineate the asymptotic behavior.

Microscopy and image analysis of the micro-fabric and composition of saline rocks under different phaseCO2-Brine states

“…The concept of REA was proposed in an attempt to present a systematic method for evaluating spatial variability in measured properties as functions of scale (Fan & Bras, 1995). It has been used in several fields of research for property evaluation (Cosenza et al, 2019;Garbrecht, 1991;Peter Indelman, 1993;Indelman & Dagan, 1993a, 1993bOliveira et al, 2014). Like representative element volume (REV), REA can be found for an entire rock type or for a phase of the rock where a phase is a mineral or fabric component of the rock (Mehmani et al, 2020).…”