--> Abstract: Structural Characterization of the Cenozoic-Mesozoic at Balad Field, Iraq, with Emphasis on Superposed Structures, by Kirk W. Schafer and Richard P. George; #90077 (2008)

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Structural Characterization of the Cenozoic-Mesozoic at Balad Field, Iraq, with Emphasis on Superposed Structures

Kirk W. Schafer* and Richard P. George
ExxonMobil, USA
*[email protected]

Balad field is located 60 km north of Baghdad on the western flank of the Mesopotamian foreland basin. Primary reservoirs are the Upper Cretaceous limestones of the Hartha, Sa’di, and Khasib formations. Interpretation of available seismic data over Balad reveals a superposition of structures that we use to constrain the structural evolution of central Iraq. Structures interpreted from 2-D and 3-D seismic data include: (1) sub-parallel, right-stepping, en-echelon faults that offset Upper Cretaceous reservoirs and that define two grabens (each about 4.0 km wide) oriented NW-SE; (2) a roll-over anticline within each graben affecting the Lower Cretaceous; (3) a fault-bounded anticline (half-wavelength of about 3.0 km) affecting the Triassic-Jurassic, with the long axis sub-parallel to the directly-overlying graben axis; (4) subtle anticlines (half-wavelength of about 1.0 km) affecting the Tertiary through Cretaceous, with long axes approximately perpendicular to the graben axes.

Interpreted syn-kinematic deposition of the Sa’di and Hartha constrains graben development to the Santonian and Late Campanian. Graben faults do not offset the Tertiary. Interpretation of several 2-D lines indicates that the Jurassic- and Triassic-level anticline may have developed as early as the Jurassic or as late as the Neogene. Importantly, the Triassic does not appear to be offset, in a normal-fault sense, by the overlying (Upper Cretaceous) graben faults. Hence, it is difficult to explain graben development by a continuous, upward-propagating, basement normal-fault.

The following conceptual models of structural evolution are considered both individually and in tandem: (1) extension and folding associated with left-lateral reactivation/inversion of an inferred basement fault; (2) contraction during the Jurassic followed by Late Cretaceous decoupled extension along inferred Triassic or Jurassic detachment(s). Subsequent loading from the Zagros during the Neogene induced regional tilting and subtle contraction.

 

AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain