Electrofacies and Geological Facies for Petrophysical Rock Typing: Khuff C
Authors: Clerke E. A. 
Published: May 2009

For integrated reservoir characterization a translation scheme must be established to link subsurface data across the disciplines, from the seismic and geological through the petrophysical to the reservoir dynamic properties. This translation process requires data sets that cross discipline boundaries and that establish robust mathematical and statistical relationships. Such information does not readily arise from single discipline based workflows, especially considering the various discipline specifics in the treatment of uncertainty. A process has been started to establish these cross disciplinary data sets for the Khuff gas reservoir and to develop the cross disciplinary translation process. In this work, we show important first results from the first well studied and establish some important links between well log electrofacies and the geological facies described by Tawil and Eid.

In this well, Khuff C cores have been described geologically by Dr. Aus Al Tawil and Ghazi Al Eid. A fairly complete set of conventional well logs was acquired. In addition, the cores had a thin slice taken along their entire length (veneer) and this material was carefully ground and homogenized on a foot by foot basis. This powdered veneer material was submitted for XRay Diffraction analysis. The veneer mineralogy data represents a very complete analysis of the bulk mineralogy of the interval. Today, new well logging technology makes similar mineralogy data available from well logs albeit with reduced accuracy and precision and for a reduced suite of minerals. In this sense, this core-log integration study explores the additional capabilities that mineralogy data enables in integrated characterization at a level more accurate than our current best well logs. An early important result from the mineralogy data is the distinguishing of exposed aerial influenced sediments from purely aqueous sediments.

With this well log and mineralogy data, electrofacies are developed in good agreement with a combination of the Tawil-Eid depositional facies and the Grain Type and Grain Size data. All of these results are being used to guide selective core resampling for petrophysical rock types. Key findings regarding the important data types are the result of this work and are reported here with preliminary electrofacies - geological facies results. Determination of the amount of anhydrite and the amount of total aluminosilicate (QIFM - Quartz, Illite, Feldspars, Mica) are paramount.The calculated water saturation which is quite probably the irreducible water saturation is strongly correlated to the total amount of QIFM material.Mineralogy is highly variable and if poorly defined limits the ability to accurately define the porosity.The compressional sonic velocity, when used in conjunction with an accurate, mineralogy independent well log porosity, can greatly aid characterization of carbonate texture variations, facies and permeability modeling.Pore system variations of facies represent themselves in the flushed to deep zone saturation behavior in this well which is above a water contact and where gas is present.Core material described with the Archie rock typing scheme showed rapid variation and thin bedding styles throughout the core and high vertical resolution data acquisition is required.Appropriate petrographic data was developed for support of the petrophysical rock typing.