Ultra-Deep Resistivity Boosts Geosteering for Reservoir Targeting

Abstract

The oil industry is constantly seeking new ways to improve the estimation of hydrocarbons in place, maximize recovery, and identify new frontiers for future development. Resistivity based logging while drilling (LWD) has always been a key geosteering tool because it has deeper depth of investigation (DOI) and exhibits sensitivity to resistivity boundaries, which are usually an indication of formation changes or difference in saturating fluids. Directional deep resistivity measurements have been, for many years, among the most important geosteering tools. The deep resistivity tool is single collar with lower frequency than conventional resistivity tools and with a directional sensitivity; the frequency used is 100 KHz or more. Technology development has enabled the use of even much lower frequencies and increased the spacing between the transmitter and the multiple receivers. The development of such ultra-deep resistivity tools has been a game changer in the quest for multilayer mapping, achieving different DOI based on lower and different frequencies and variable transmitter-to-receiver spacing. LWD tools are classically deployed to map and evaluate well trajectory and identify nearby boundaries; while this is the primary scope, with deeper DOI, it is now possible to map potential additional layers that could be targeted at a future stage, as well as evaluate individual layers characterized by different resistivity signatures and reservoir thickness. Fluid contact uncertainty, potential tilting of the boundaries, and fluid level changes in time, following production and reservoir depletion, are key factors to asses and monitor hydrocarbon column thickness and understand the driving mechanisms, including water-coning, if any. Fluvial and alluvial channeled reservoirs are the most challenging reservoirs in clastic environments, characterized by sand lenses and high angle cross bedding. Geosteering in such reservoirs requires proficient tools capable of deeply exploring the encountered rock formations, detecting potential reservoir sweet spots and selectively targeting them. In conclusion, this work illustrates how ultra-deep resistivity LWD tools have multiple applications, ranging from geosteering to reservoir mapping, and finally fluid mapping, with the potential to minimize the need for pilot holes because of deeper DOI with the added benefit of cost savings and reserve maximization.

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018