The Contradiction in the Lower Tertiary Deepwater GoM

Abstract

Exploration in the Gulf has progressively moved farther and farther offshore. Initially oil companies concentrated on the shelf and then moved into the deep water and the Miocene trend. The Miocene is a well established trend with a considerable amount of producing acreage. With the acquisition and processing of data farther offshore, attention has switched to a new trend in the Lower Tertiary. The Lower Tertiary sits beneath the Miocene and is older. The Tertiary time period includes Pliocene, Miocene, Eocene and Paleocene. We tend to lump everything below the Miocene into what we call the Lower Tertiary because our Wilcox sands are Paleocene and Eocene in age. Most of the cumulative GOM production has been Miocene in age. This is an emerging play in the deepwater Gulf of Mexico, to date there have been 12 announced discoveries out of 19 wells drilled (Figure 1). This trend data is only for Alaminos Canyon, Keathley Canyon and Walker Ridge. There are additional penetrations along trend to the northeast. There is a contradiction between traditional interpretation and NMR data in the Lower Tertiary. An NMR log (CMR) was run with the aim of identifying the best reservoir intervals of Porosity, Swir, and Permeability. The NMR log has many responses depending on the borehole fluid, free fluid and viscosity. These results will be discussed.Oil bearing interval with Swir higher than SwCMR porosity undercalled in oil-bearing intervalLittle free fluid in oil-bearing intervalCalibration of Klog permeability to core Traditional logs indicate the presence and quantity of oil, but provide no information on its quality. NMR is sensitive to oil viscosity. NMR can be misleading in the presence of viscous oil as the oil signal can overlie the bound fluid volumes, resulting in the incorrect evaluation of the reservoir in an oil base mud system. The NMR must be used with caution in an oil base mud system (OBM).