Advanced and Integrated Petrophysical Evaluation for Reservoir Characterization of Complex Carbonate Reservoir - Case Study
Authors: Gibrata Muhammad A. , Ghedan Shawket G. , Rouis Lamia , Yanfidra Djanuar 
Published: October 2019

Reservoir characterization and quantification of initial oil in place in carbonate reservoirs are challenging steps, where reliability of the produced data and its uncertainty level will be critical for reservoir development. The field, under study, is a complex carbonate reservoir, with variations in its fluid contacts and stratigraphic settings. This carbonate reservoir requires an integrated petrophysical evaluation study that involves geology, geophysics, openhole logs, special core analysis (SCAL), reservoir rock typing (RRT), saturation height model (SHM) and detailed reservoir/fluid analysis, that would result in reliable reservoir characterization, fluid contacts, and fluids in place estimation with least levels of uncertainty.

An innovative integrated petrophysical evaluation has been conducted for reservoir characterization. Using core data, reservoir quality index (RQI) bins have been imposed over porosity-permeability cross-plots to define the reservoir rock types, RRTs, in this carbonate reservoir. An advanced permeability log has been developed from porosity, clay/bound water, pore size, core, diagenetic and mobility data, have derived for each rock type. The Saturation Height Model (SHM) was based on SCAL data of Mercury Injection Capillary Pressure (MICP), capillary pressures-water saturation from Porous plate/Centrifuge and Relative Permeability for every RRT for reservoir subunits. The free water level (FWL) derived from formation pressure has been used to identify an initial oil water contact, and thus it has provided good comparison of SW_Log & SW_SHM for reservoir modeling. An initial water saturation, relative permeability and residual oil saturation from SCAL data have been used in evaluation. The log data of water saturation from resistivity, core saturation height model and reservoir pressure depletion in production wells have been evaluated for an improving reservoir characterization.

The advanced and integrated evaluation approach of subsurface and well test data has been used to provide reliable carbonate reservoir properties and results on porosity, permeability, fluid contacts, reservoir rock typing, initial water saturation, and initial oil in place. It has provided reliable reservoir characterization, reservoir modeling approach for this complex carbonate reservoir. Hence, this approach has provided reliable assurance and important benefits for reservoir characterization, optimization and reservoir management.

The integrated petrophysical approach of this paper presents an integrated reservoir petrophysical approach for carbonate reservoirs. It is an integrated approach that used the available log, core, dynamic pressure data, to derive reservoir rock types, assignment of permeability as a function of porosity, pore size, clay/bound water, diagenetic and mobility data. Integration of available petrophysical, pressure, and SCAL data to derive the reservoir fluid contacts, and develop SHMs for oil in place estimation and reservoir modeling purposes.