An Evaluation of Digital Rock Physics Technology for the Prediction of Relative Permeability and Capillary Pressure for a Middle Eastern Carbonate Reservoir
Authors: Guice Kyle , Lun Lisa , Gao Bo , Gupta Robin , Gupta Gaurav , Kralik James G. , Glotzbach Rodney , Kinney Elizabeth , Leitzel Greg , Rainey Jennifer , Kudva Ryan Ashok , Al Jawhari Mohammed Omar 
Published: March 2015

Abstract
Digital rock physics (DRP) has received considerable attention in recent years as an alternative to laboratory measurement, especially for the prediction of reservoir properties for which the right laboratory measurements are difficult to perform or require long measurement times such as the special core analysis (SCAL) properties relative permeability and capillary pressure. While measurement of these reservoir properties can certainly be challenging to execute, there is a long history of successful, high-quality laboratory SCAL measurements. Before adoption of a DRP approach to generate reservoir properties that have significant impact on expected reservoir performance, it is important that the uncertainties introduced by use of DRP are better understood.
To this end, we have utilized samples from a large Middle Eastern carbonate reservoir to benchmark vendor DRP predictions of water-oil imbibition relative permeability and capillary pressure against high-quality SCAL results that were measured using consistent laboratory methods. Considerable scatter are observed in the DRP predictions that do not exist in the measured SCAL data and cannot clearly be attributed to sample heterogeneity. Wettability, which is an important input into digital rock predictions but is especially challenging to quantify in the laboratory, is shown to have a significant impact on DRP predictions of relative permeability and capillary pressure. Nevertheless, the dependence of the DRP results on wettability is inconsistent with the SCAL data. Given the additional scatter and inherent uncertainties associated with use of the DRP approach, we find that a high-quality laboratory program employing consistent test methods remains the best approach to obtain SCAL data to support reservoir definition development, and depletion objectives.

Introduction
Accurate, high-quality special core analysis (SCAL) data (e.g., relative permeability and capillary pressure) are integral to reservoir performance prediction and effective reservoir management. Achieving high-quality SCAL measurements in the laboratory is by no means an easy task, but can be accomplished provided that four key requirements are met:measurements must be on rock samples representative of the reservoir (the right samples),measurements must be made under conditions representative of displacement processes in the reservoir (the right conditions),measurements must be made using the appropriate test methodologies and using precision equipment and techniques (the right equipment), andtrained and experienced technologists are needed to ensure that appropriate samples are selected, to conduct the measurements, and to model the data (the right people).
Several prior publications elaborate on the four key requirements (Braun 1981, Gomes 2008, Hassler 1945, Honarpour 2006, Honarpour 2005, Honarpour 2004, Johnson 1959, Wang 2008). It is important to note that both relative permeability and capillary pressure data are necessary to define displacement processes in reservoir simulation, and methods to measure and to integrate SCAL data should consider both types of data (Bhatti 2012, Kralik 2010, Meissner 2009).