Graben hydrocarbon plays and structural styles

Abstract

Hydrocarbon occurrences, types of traps, and structural styles have been synthesized from the Sirte, Suez, and Viking grabens. Hydrocarbons occur in a stacked succession of one or more basins: pregraben, graben and interior sag. Preservation of pregraben reservoirs depends on late initiation of crustal arching and limitation of uplift to the graben shoulders. Trap closure in pregraben and graben-fill deposits is primarily dependent on the multidirectional orientation of normal faults, tilting of fault blocks, and flexing or erosion parallel to block edges. Fault patterns include dominant longitudinal faults parallel to the graben axis and oblique faults. Block rotation is influenced by fault profile, amount of extension, fault pattern, downwarping of the sag basin, and isostatic adjustments between large blocks. Fold closures result from the upward termination of faults into forced folds that are subsequently accentuated by fault drag. Folds extend to shallower depths and into the interior-sag base by passive drape and differential compaction. Traps above this level are dependent on factors other than graben tectonics.