Quantification of Vuggy Porosity in a Dolomite Reservoir from Borehole Images and Core, Dagger Draw Field, New Mexico

Abstract

Abstract Vugs, which are large irregular pores, are a key pore type in many carbonate reservoirs. Because of coarse sample rate and limited vertical resolution, conventional wireline logs commonly mask vuggy porosity. This becomes a major problem when logging tools combine high vuggy porosity with low matrix porosity to derive average porosity values that fall below arbitrary commercial cutoffs. Non-completion of such zones commonly results in bypassed pay. Borehole-imaging logs are high-resolution, oriented electronic "pictures" of the wellbore made by electrical or acoustic devices. Pixel-counting techniques, when applied to borehole images, can be used to detect and quantify vugs. The purpose of this study is to calibrate vugs quantified from borehole images to those quantified from digitally scanned core. Samples studied are vuggy dolomites of the Cisco and Canyon Formations (Pennsylvanian), Dagger Draw field, Eddy County, New Mexico. Results suggest that the neutron log is a good total-porosity device. However, this log suppresses the evidence for vuggy porosity which can lead to bypassed pay.