Fault-seal Analysis Applied to the Erawan Gas-condensate Field in the Gulf of Thailand

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, shale smear parameters, and fault-seal failure probability (FSFP) (based on in-situ stress conditions). For this study, five east-dipping faults in the Erawan N 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 the shale smear factor (SSF 6) and high values of the clay content ratio (CCR 30%) of four of the faults suggest that faults 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. Shale smear parameters can account for all 15 accumulations. Fault-seal failure probability was derived for 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 on the normal fault.