1999 Abstract: Slatt et al.
Behind-Outcrop Borehole Imaging for Improved Characterization of Turbidite Reservoirs
R.
M. Slatt, N.
F. Hurley, E. M.Witton
Colorado School of Mines
Department of Geology and Geological Engineering
Golden, CO 80401-1887
G.
R. Clemenceau
Amoco
Exploration and Production Co.
Houston,
Texas 77253-3092
H. Homann
Baker
Atlas
Houston,
Texas 77042
R.
J. Davis
Schlumberger
Wireline and Testing, Inc.
Jakarta
12560
Indonesia
G.H.
Browne
New
Zealand Institute of Geological and Nuclear Sciences
Lower
Hutt
New
Zealand
Abstract
To bridge the sometimes large conceptual gap between what is observed in outcrop and what occurs in the subsurface, outcrop information ideally should be placed into the more familiar format used for exploration and development, that is, well logs, seismic, cross sections, and 3-D models. Borehole imaging logs from behind an outcrop, when calibrated to the outcrop (and core), can be particularly useful for identifying image log criteria that can be used for predicting stratigraphic (and structural) features away from the borehole, and sometimes for predicting well performance.
Since the mid-1990’s, there have been a number of behind-outcrop borehole imaging projects. In this paper we discuss two such projects involving turbidite and related strata, one in the Miocene Mount Messenger Formation of New Zealand, and the other in the Cretaceous Lewis Shale of Wyoming.
In the Mount Messenger Formation, two boreholes were drilled 450 ft (150 m) apart and 360 ft (100 m) back from a well-exposed coastal cliff face. One borehole cored 140 ft (47 m) of strata, and the other borehole cored 315 ft (105 m). Both boreholes were logged using Schlumberger’s FMITM and Platform ExpressTM log suites. By comparing the borehole images to the cores and outcrops, we were able to develop borehole-image criteria for a variety of sedimentary structures and stratification styles, and from these, to identify depositional facies. These recognition criteria were applied to the Ram-Powell "L" Sand reservoir in the offshore Gulf of Mexico and were found to be useful for identifying the character of the producing interval.
In the Lewis Shale, a development well drilled 8 mi (13 km) west of Lewis Shale outcrops was logged through the same stratigraphic interval using Baker Atlas’ STARTM acoustic and electrical borehole images, as well as conventional log suites using the ECLIPSTM acquisition and processing system. Again, a variety of sedimentologic features and bedding styles observed in the outcrop were identified on the image logs. In particular, laterally continuous and discontinuous sandstones could be differentiated from borehole image attributes, which allowed prediction of attributes away from the wellbore. Behind-outcrop borehole images from these two turbidite outcrops demonstrate their value for interpreting individual sedimentologic features, facies, and attributes away from the wellbore. These interpretations could not be made using conventional gamma-ray logs. Such observations and interpretations provided by borehole images are critical for improved volumetric calculations, well placement, and prediction of well performance.