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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