Improved
Fractured Reservoir Models Using Borehole Images and Cores from Horizontal
Wells:
Campbell, Tania C.1, Michael
R. Gross2, Jon R. Schwalbach3 (1) Occidental Oil and Gas,
Tupman, CA (2) Florida International University, Miami, FL (3) Aera Energy LLC,
Bakersfield, CA
A prerequisite for accurately modeling
fractured reservoirs is high quality data that captures the nature and
distribution of fractures and faults. Because fractures are discrete features,
often with irregular spacing and dimensions, it is difficult to capture valid
statistical data describing the fracture network from vertically-oriented data
sets. Unfortunately, most reservoir models rely on limited or extensive
vertical coring, borehole image logs, and analog comparisons from allegedly
similar outcrops. The data base for the Miocene Monterey Formation siliceous
shale reservoirs at Elk Hills is unique because it contains an extensive number
of electrical image logs from horizontal wells, and a core-image log pair from
a horizontal well that provides valuable calibration.
The core-image log data set reveals at
least two scales of fracture features. The bed-bounded fractures are typically
restricted to one or a small number of cm-thick stratigraphic layers (beds or
bed-sets). Bed-bounded fractures are most common in the brittle rocks, and
clearly reflect the fine-scale mechanical stratigraphy in the reservoir. Image
logs from horizontal wells provide excellent measurements of the spacing of these
features, and comparison with the core reveals lower limits of detection that
can be extrapolated when building reservoir models. The greatest benefit from
image logs coupled with cores from horizontal wells, however, is derived from
characterizing larger-scale features of the fracture network, sometimes
referred to as backbone- or mega-fractures. The image-core comparison reveals
the nature of these features. The cores provide information about apparent
aperture and mode of deformation. The image logs complement the core data with
information delineating the spacing and orientation of the feature. Calibrating
the core and images from horizontal wells significantly improves our confidence
for populating fractures in the reservoir model.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California