Fault Seal; an Exploration Perspective
Sirat, Manhal *1; Morad, Sadoon 2; Van Laer, Pierre 1; Vahrenkamp, Volker C.1
(1) EUFR, Abu Dhabi Company for Onshore Operations, Abu Dhabi, United Arab Emirates. (2) Geosciences, Petroleum Institute, Abu Dhabi, United Arab Emirates.
Up-dip lateral seals play a significant role in defining traps of 3-way closure in SE Abu Dhabi Prospects. Several leads are bounded by well recognized seismic faults (N75°W & N45°W) together with other, less prominent, sub-seismic fault sets (e.g. N15°W, NNE, N30°E & N60°E). The main risk associated with these leads is that the faults, which have been developed and reactivated in different modes throughout the tectonic evolution of the region, should have been held closed (sealed) after migration and entrapment.
We introduce here a sealing potential risk chart of each individual fault set that varies with geological time. The sealing potential depends mainly on the maximum principal horizontal stress σH (= σ1) orientation and magnitude, the host-rock alteration/cementation associated with fault damage zones associated with these seismic faults, and the geomechanical behavior of different rock units. The latter parameter is sensitive to the HC (Hydrocarbon Column) height, which together with the pore-fluid pressure (Pp), determines the sealing capacity of a fault that can sustain before breaching due to increase in the effective stress.
The main results indicate that the sealing potential of the two major fault sets (N75°W & N45°W) has been optimum versus hydrocarbon maturation and migration (upper Cretaceous), and entrapment (Miocene to present). Other minor and sub-seismic faults, which have also gone through similar reactivation of openness and closeness in different modes over geological time owing to the continuous shift of the σH towards the north, have higher risk for sealing potential. Such a risk would, in turn, has limited the leads occurrence. We conclude that the Hydrocarbon Column Height should be at maximum of 300 ft in order to sustain the cap rock/fault seal integrity without breaching due to effective stress.
AAPG Search and Discovery Article #90141©2012, GEO-2012, 10th Middle East Geosciences Conference and Exhibition, 4-7 March 2012, Manama, Bahrain