Resistivity zone index: A new approach in rock typing to enhance reservoir characterization using well log data

Abstract

Rock typing of reservoirs is a vital step for successful field development plans to improve oil and gas recovery. In this context, the current study addresses a new approach for reservoir rocks characterization based on their electrical properties obtained from mathematical processing of well logs. That is modifying the conventional Kozeny–Carman model is achieved by taking into consideration the True Formation Resistivity (RT) obtained from deep well logs. A log–log correlation between RTand square of normalized porosity (ΦN2) yields parallel straight lines (each represents a distinct Electrical Flow Unit (EFU)) the intercept of which (at ΦN2=1) gives a unique parameter specified as ”Resistivity Zone Index” (RZI). The validity of the proposed model is tested on log data obtained from 21 logged wells and 1135 core samples. RZI values (calculated for each EFU) show a marked accuracy for representing reservoir. Additionally, permeability is calculated by core analysis for different intervals, and the Flow Zone Indicator (FZI) concept is applied to characterize reservoirs by Amaefule technique. Moreover, irreducible water saturation (Swr)can be calculated for each rock type as well.

Keywords

• Well logs
• Resistivity Zone Index
• Rock characteristics
• Modified K–C model
• True formation resistivity