Whole Core Versus Plugs: Integrating Log and Core Data to Decrease Uncertainty in Petrophysical Interpretation and STOIP Calculations

Abstract

Abstract Most carbonate reservoirs are commonly characterized by multiple-porosity systems that impart petrophysical heterogeneity to the gross of reservoir interval. Hence, the specific types and relative percentages of pores present, and their distribution within the rocks, exert strong control on the production and stimulation characteristics of carbonate reservoirs. The impact of heterogeneity on core and log measurements is assessed. The challenge is to determine the reliability of relatively small scale properties measured by a log or core to the large scale reservoir property. A related question is one of reconciling the variability seen in high resolution (small volume of investigation) measurements (e.g. core plugs), with the variability in relatively low resolution (large volume of investigation) measurements (e.g. wireline log). Routine and SCAL laboratory measurements on carbonate core samples from prolific reservoir in Abu Dhabi. The measurements were conducted on different scale samples ranging from small trims to full diameter whole core samples. Porosity and permeability obtained from small trims, plugs and whole core samples were compared with log data to study the impact of the measured volume on the results. Electrical property measurements were performed on 1.5" diameter plugs and 4" diameter whole core samples to evaluate the impact of heterogeneity and volume scale on cementation factors which are essential for proper petrophysical interpretation and saturation calculations. Different scale measurements showed variations in both Routine and SCAL data and emphasized the importance of the whole core measurements in representing reservoir heterogeneity which could be used to better evaluate resistivity logs. Plug scale Poroperm data; however, were important in capturing higher degree of reservoir heterogeneity. The better integration between core and log data and the use of the right electrical parameters in petrophysical interpretation tends to minimize the uncertainty in STOIP calculations.