Prediction of
Sub-Seismic Sealing Faults Using Simple Numerical Simulation Models
Bain, Richard C.1, Kirk H.
MacIvor1, Brooke E. Holt1, D. Scott Beaty1 (1)
Chevron
In order to justify development drilling
in partly-depleted, highly faulted gas reservoirs in which untapped
higher-pressure compartments may exist, convincing evidence for fault
separation from existing wells must be provided, either by obvious fault breaks
on 3-D seismic or by missing section due to faults encountered in a well.
Lacking such evidence, it is uncertain that prospect reserves will be
incremental, as opposed to acceleration, even when volumetric analysis suggests
that existing wells will not capture all of a reservoir's producible reserves.
Two examples from the Lobo Trend of Webb
County,
In the first example, a simple simulation
predicted the presence of sub-seismic faulting that provided a seal for the
objective reservoir. The proposed location was in a syncline between two wells
that had produced large volumes of gas and were producing at very low
bottom-hole pressures. An iterative approach involving the seismic interpreter
and reservoir engineer resulted in a geologic model that was supported by
seismic data and agreed with history matching efforts. The well, which would
not have been drilled without the model's support, encountered near-virgin
reservoir conditions.
The second example provides a lesson
learned, demonstrating a reservoir in which the simulation and history match
correctly predicted the presence of a sealing fault, but incorrectly predicted
which of several faults was sealing. The wellbore
penetrated the sealing fault and the seal was ruptured during fracture
stimulation.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California