ABSTRACT: Utilization of High-Resolution Geologic, Geophysical and Borehole Data to
Quantify Fault
Seal Attributes in Major Oil Fields, Central Sumatra Basin
Heidrick, Tom L.1, Kenneth D. Kelsch1, Asyari
Ibrahim1, and David A. Castillo2
(1) PT Caltex Pacific Indonesia,
Pekanbaru, Indonesia
(2) GeoMechanics International Australia, Magill, Australia
Miocene siliciclastic reservoirs within the Central Sumatra Basin (CSB) experienced
penetrative syndepositional N-S oriented dextral strike-slip tectonism (25.5-12.5 Ma),
passive differential uplift/subsidence (12.5-3.5 Ma) and accelerated compressional
inversion and trap
formation during the Plio-Pleistocene. The Miocene wrench tectonic
stress state changed dramatically in the Early Pliocene to major Barisan compressional
tectonism.
Systematic analysis of numerous borehole images containing natural and drilling-induced
fractures, borehole breakouts, rock strength and pressure measurements in existing wells
help to define a complete stress tensor. Results indicate the CSB, is in a strike slip
stress regime
(SHmax > Sv > Shmin) with SHmax stress orientation varies NWN to NE.
Fifty fault
planes were constructed and analyzed using high-resolution 3D seismic data
from the Kulin and Duri fields CSB. This information was integrated with the local stress
tensor to calculate the shear and normal stresses resolved on the
fault
plane, in order to
assess whether a
fault
is critically stressed and prone for shear failure. This is
somewhat complicated due to SHmax stress orientations are non-uniform and appear perturbed
by adjacent major reactivated Miocene strike-slip faults.
Variability in fault
plane orientation and geometry is crucial in quantifying the
sealing character and their effectiveness in compartmentalizing reservoir production.
Other salient physical mechanisms contributing to
fault
seal failure or
fault
zone
permeability include shear failure on critically stressed faults, formation juxtaposition,
Shale Gouge Ratios (SGR), displacement field and stratigraphy. This analysis demonstrates
a given
fault
element can be successfully assigned to attributes describing the likelihood
of
fault
seal failure.
AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia