Advances in Special-Core-Analysis Data Interpretations of Multiscale Measurements

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 164140, ’Advances in SCAL Data Interpretations of Multiscale Measurements From Different Carbonate Rock Types in a Giant Oil Field in Abu Dhabi,’ by Moustafa R. Dernaika, Ingrain Inc.-Abu Dhabi; Samy Serag El Din and Zubair Kalam, ADCO; and Loay Hannon, Weatherford Laboratories, prepared for the 2013 SPE Middle East Oil and Gas Show and Exhibition, Manama, Bahrain, 10-13 March. The paper has not been peer reviewed. The evaluation of complex carbonate reservoirs is a challenging task, and a detailed understanding of reservoir heterogeneity is still lacking. In this study, the effect of static rock type and sample size was investigated on special-core-analysis laboratory (SCAL) data derived from capillary pressure and resistivity-index experiments at reservoir temperature and net confining stress. Whole cores were generally found to yield different capillary pressure and saturation exponents that may not be possible to derive from average plug data. Introduction Most carbonate reservoirs are characterized by multiple-porosity systems that impart petrophysical heterogeneity to the gross reservoir interval. Reservoir heterogeneity is dependent upon the depositional environments and subsequent events in the history of the reservoir. In previous work, the effect of multiscale measurements (whole cores down to small trims) was studied on porosity/permeability and cementation factor. The whole-core samples were taken from a single well in a carbonate reservoir in Abu Dhabi, where 1.5-in. core plugs were drilled adjacent to the whole cores. Small trims were cut from the plugs for mercury-injection capillary pressure (MICP) determination. The main findings were that whole-core porosity matched log data very well and the plug porosities, when compared with the whole-core data, were systematically higher. The degree of heterogeneity played a major role in comparing whole-core to plug permeability: In the low- permeability range (less than 10 md), whole cores could enhance 3D connection pathways and yield higher permeability values, whereas, in the high-permeability range, permeability can be overestimated in plugs through relatively larger porosity channels. The cementation factor was systematically reported to be lower in the measured whole-core samples. X-ray computed-tomography (CT) scanning was essential in explaining most of the variability seen in the measured rock properties at different scales. In another investigation on four different wells in the same reservoir, these earlier observations were confirmed on hundreds of multiscale samples.