Tectonic History, Basin Evaluation, and Petroleum Geology of Upper Jurassic Facies of South Iraq

M. W. Ibrahim

Callovian-Tithonian rocks of south Iraq are deposits of a major regressive sedimentary cycle. It began with the deposition of a basinal black bituminous shale and carbonates of the Naokelekan Formation, which graded southwestwardly into a neritic, oolitic carbonate of the Najmah Formation and finally terminated by a lagoonal-supratidal dolomite and anhydrite of the Gotnia-Barsarin Formations.

This sedimentary cycle is located on the same Tethyan shelf, at similar depth, deposited under the same paleoenvironments and is chronologically correlative with the Tuwaiq-Hith cycle of eastern Saudi Arabia.

In the study area, drill-stem tests have proved the Najmah as an oil producer and the Gotnia as a cap rock and have pointed out the basinal black shales and carbonates of the Naokelekan and the underlying Bathonian Sargelu Formations as potential sources of hydrocarbons. In this study, the Upper Jurassic lithofacies have been, structurally, geothermally, and hydrodynamically mapped and evaluated for source, reservoir, and cap rock potentials. Patterns, styles, and histories of structural growth of structural anomalies have been evaluated and clustered into areas with identical structural style and growth history.

Prospectivity was rated by projecting incipient structural growths, paleoextent of geothermal source rock maturation, and probable paleodirections of fluid migration on a series of paleostructural maps which illustrates the evolution of these variables against a background of Upper Jurassic facies maps.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.