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Midrikah Field: A Major Paleozoic Gas Discovery
in a Fault-Bound Play in
Al-Shammery, Hafiz J., Ali Y. Al-Hauwaj,
Saudi Aramco,
The Midrikah area is the southern nose of the Ghawar anticline, which is formed largely due to compressional tectonics. This stress regime formed the
gently dipping eastern flank and the steeply dipping and reverse faulted
western flank in Midrikah. The Midrikah
field flowed gas from the down thrown block of the reverse fault. This fault is
a major feature which originates from the basement and extends up to the
Triassic section. The fault, also, merges with the major reverse fault system
present in west of the Ghawar field and extends more
than 70 km north of the prospect. The Midrikah
prospect was mapped using high quality 480 fold 3-D seismic data. Due to the
heterogeneity of the Unayzah Reservoir the data was
processed to preserve relative amplitude to enable stratigraphic
interpretation of the seismic events in the target time level. Depth migration
was deemed necessary for proper lateral positioning of the bounding faults of
the prospect due to the high dip exhibited by the overburden formations. In
addition to depthing of the key geological markers,
fault mapping was vital for defining this prospect since fault trapping was proposed
as the lateral sealing mechanism. Coherence and dip attributes were
instrumental in defining faults and fracture zones in the area. Hydrodynamic
data was used to assess the sealing potential of the bounding fault in Midrikah. Seismic attributes such as acoustic impedance,
frequency and trace classes were utilized to investigate the presence of the Unayzah reservoirs in the prospect. Interpretation of these
attributes gave consistent results and aided in delineating areas of favorable
reservoir development. The accurate startigraphic and
structural models developed from the interpretation of the 3-D seismic data
contributed significantly to the success of this wildcat.