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Orienting the Unoriented: Paleocurrent Determination from Unoriented Deepwater Gulf of Mexico Wilcox Conventional Cores Using Helical Computed Tomography (CT) Scans

Larry Zarra¹ and Allison Jackson²
¹Chevron, Houston, TX, USA
²University of Utah, Salt Lake City, UT, USA

Abstract

Conventional cores from deepwater turbidite reservoirs commonly contain paleocurrent structures, but these have been of limited utility because the cores are not oriented. We present a novel approach to orienting conventional cores by leveraging helical computed tomography (CT) scan data in a 3D volume visualization format. This methodology also requires formation dip and strike derived from seismic and/or wellbore datasets, a moderate dip differential between the formation map horizon and the wellbore, and beds or laminae that were deposited as flat beds on the sea floor. With these givens, the flat beds can be oriented to compass coordinates at time of deposition. Rotational corrections can be determined using either vector calculations or stereonets. The correction is then applied to a flattened core CT volume to determine an oriented paleocurrent vector.

A proof of concept study was conducted using 460' of conventional core from the Moccasin discovery, a GoM deepwater Wilcox well in Keathley Canyon (KC 736). Turbidite sandstone intervals in the cores were deposited as either channel elements or unconfined lobe elements. Paleocurrent measurements in channels were mostly from trough cross-stratified sandstone (Tt) beds; measurements from lobes were mostly from ripple cross-laminated sandstone (Tc) beds. Other sedimentary features investigated include flame structures, scours, and imbricated clasts.

More than 100 paleocurrent vectors were compiled and evaluated within a context of discrete depositional elements. The resulting sets of paleocurrent vectors are well constrained, are compatible with the regional stratigraphic context, and are consistent with interpreted depositional processes. Primary impacts of this methodology include accurate orientation of geobodies in reservoir models, predicting sweet spots, and developing more effective enhanced recovery strategies.

AAPG Search and Discovery Article #90206 © AAPG Hedberg Conference, Interpretation Visualization in the Petroleum Industry, Houston, Texas, June 1-4, 2014