Fault
Seal Analysis Applied to the Erawan Gas Condensate Field in the
Gulf of Thailand
Tokio Kachi1, Hideki Yamada1, Kiyoshi
Yasuhara1, Masamichi Fujimoto2, Shutaro
Hasegawa3, Shoji Iwanaga4, and Rasoul Sorkhabi5
1 Mitsui Oil Exploration Company, Tokyo, Japan
2 INPEX Company, Tokyo, Japan
3 Idemitsu Oil and Gas Company, Tokyo, Japan
4 Geoscience Research Laboratory, Kanagawa, Japan
5 Energy and Geosciences Institute, Salt Lake City, UT
The Erawan field in the Gulf of Thailand is characterized by a series of
east- and west-dipping normal faults displacing the Miocene clastic reservoirs.
The fault
seal capacity of these faults was assessed using sand-shale
juxtaposition diagrams, clay smear parameters, and
fault
seal failure
probability (based on in-situ stress conditions). For this study, five
east-dipping faults in the Erawan North Platform area were selected (faults
E-16, E-17, E-18, E-20, and E-27). Several deviated wells have been drilled
through the footwall blocks of these faults. Low values of Shale Smear Factor
(SSF<6) and high values of Clay Content Ratio (CCR>30%) of four of the
faults suggest that
fault
seal along their planes. In contrast to these four
faults,
fault
E-27 appears to act as an across-
fault
conduit for some intervals
and seal in others. Intervals without trapped hydrocarbons have higher SSF
values suggesting that the
fault
leaks locally. These five faults trap 15 gas
pay zones. Eight of the pay zones have sand-shale juxtaposition across the
faults which may explain 8 of the 15 accumulations. Clay smear parameters can
account for all 15 accumulations.
Fault
seal failure probability (FSFP) was
derived fro one of these faults (E-16) by integrating the CCR values and the
probability of
fault
slip tendency and
fault
dilation tendency under the current
stress regime in the Erawan field. Low FSFP values indicate that the
fault
seals
do not appear to have been breached given the in-situ stress field acting upon
the normal
fault
.
AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005