New Rock-Typing Index Based on Hydraulic and Electric Tortuosity Data for Multi-Scale Dynamic Characterization of Complex Carbonate Reservoirs

Abstract

Rock-pore-space geometry and network topology have a great impact on dynamic reservoir characteristics, in particular on capillary pressure and relative permeability curves. Hydraulic tortuosity is a key independent measurement relating the pore-space geometry and topology to the rock's effective porosity and absolute permeability. Therefore, hydraulic tortuosity can be an important concept for dynamic reservoir characterization and reservoir simulation. Our objectives are to recommend a new dynamic rock-typing process and to assess the corresponding improvement on reservoir simulation processes. We introduce an innovative dynamic reservoir-rock-typing (DRRT) index, using absolute permeability, porosity and hydraulic tortuosity data, derived from mercury-injection capillary pressure (MICP) experiments. For correlation purposes, we also derived electric tortuosity data from formation-resistivity experiments. We used the experimental data from the Worldwide Rock Catalog (WWRC) provided by a joint-industry project (Core Lab, 2014), for both carbonate and clastic rocks. Based on the new proposed DRRT index and on corresponding dynamic reservoir properties, we prepared a comprehensive sensitivity study on the impact of hydraulic tortuosity heterogeneity on oil recovery results. This sensitivity study was done by incorporating the concept of hydraulic tortuosity in a synthetic carbonate- reservoir simulation model. The analysis of the MICP and formation-resistivity data showed both greater average tortuosity and greater tortuosity variability for carbonates, when compared with clastic rocks. It also showed good correlation between hydraulic and electric tortuosity values. The sensitivity study results showed a significant impact of hydraulic tortuosity heterogeneity on oil in place and reserves estimates for improved oil recovery (IOR) / enhanced oil recovery (EOR) processes in typical complex carbonate reservoirs, such as the ones found in the Brazilian Pre-Salt. It also showed the importance of applying proper corrections while deriving dynamic reservoir properties from capillary pressure and relative permeability experiments. The new DRRT index shows a much stronger correlation with pore-space geometry when compared with traditional reservoir-quality (RQI) and flow-zone (FZI) indexes. Therefore, it has clear potential to enhance the dynamic rock-typing process for reservoir simulation of IOR / EOR in complex carbonate rocks. We also discuss the importance of an integrated laboratory test and well log program to enable the proper characterization, population, and upscaling of dynamic rock properties. In complex carbonate reservoirs under IOR / EOR, overlooking the rock-pore-space geometry and network topology may result in significant errors in reservoir characterization and simulation processes. In this context, proper DRRT in carbonates, including tortuosity, is therefore crucial for reservoir simulation; enabling correspondence between core, well log and reservoir-scale dynamic properties. The presented correlation between hydraulic and electric tortuosity significantly increases the potential of dielectric measurements for dynamic reservoir characterization of complex carbonates on both core and well log scales.

Truncated Multi-Gaussian Pore-Throat-Size Decomposition and a New Universal J-Function for Rock Characterization of Complex Carbonate Reservoirs

“…This paper is a further development of the study presented by Ferreira et al (2015), where they have shown the importance of hydraulic tortuosity and corresponding pore-throat-size heterogeneity to the dynamic characterization of complex carbonate reservoirs. The main corresponding capillary effects are wettability; capillary pressure and relative permeability curves; end-point saturations; and hysteresis.…”

“…(2) Ferreira et al (2015) showed that RQI* has a much stronger correlation with pore-space geometry when compared with Winland R35, reservoir-quality (RQI) and flow-zone (FZI) indexes. Therefore, RQI* may significantly improve dynamic reservoir characterization, property population and upscaling of capillary effects for reservoir simulation of IOR / EOR in complex carbonate rocks.…”

“…Ferreira et al (2015) have further modified the J*-function to obtain: Ferreira et al (2015) have further modified the J*-function to obtain:…”

“…However, Ferreira et al (2015) recently showed that dielectric measurements in both core and well log scales have a significant potential for deriving electrical and hydraulic tortuosity properties. However, Ferreira et al (2015) recently showed that dielectric measurements in both core and well log scales have a significant potential for deriving electrical and hydraulic tortuosity properties.…”

“…NMR T2 distributions are routinely used as a proxy for MICP and are hence useful for porosity partitioning (Hassal et al, 2004). New developments in dielectric log interpretation and 2D-NMR analysis are leading to improved (Souza et al, 2013) textural analysis in carbonates for determining electric tortuosity properties, which may correlate with hydraulic tortuosity and the average pore-throat squared radius ͗r 2 throat ͘ of the multimodal rock (Ferreira et al, 2015). Acoustic borehole image logs are similarly analyzed by thresh-holding amplitude histograms .…”