Present address: ExxonMobil Production Deutschland GmbH, Riethorst 12, 30659 Hannover, Germany.
Halite cementation and carbonate diagenesis of intra-salt reservoirs from the Late Neoproterozoic to Early Cambrian Ara Group (South Oman Salt Basin)
Article first published online: 24 JUL 2008
© 2008 The Authors. Journal compilation © 2008 International Association of Sedimentologists
Volume 56, Issue 2, pages 567–589, February 2009
How to Cite
SCHOENHERR, J., REUNING, L., KUKLA, P. A., LITTKE, R., URAI, J. L., SIEMANN, M. and RAWAHI, Z. (2009), Halite cementation and carbonate diagenesis of intra-salt reservoirs from the Late Neoproterozoic to Early Cambrian Ara Group (South Oman Salt Basin). Sedimentology, 56: 567–589. doi: 10.1111/j.1365-3091.2008.00986.x
- Issue published online: 8 JAN 2009
- Article first published online: 24 JUL 2008
- Manuscript received 22 November 2007; revision accepted 15 May 2008
- Bromine geochemistry;
- carbonate diagenesis;
- halite cementation;
- solid bitumen
Late Neoproterozoic to Early Cambrian carbonates of the Ara Group form important intra-salt ‘stringer’ reservoirs in the South Oman Salt Basin. Differential loading of thick continental clastics above the six carbonate to evaporite cycles of the Ara Group led to the formation of salt diapirs, encasing a predominantly self-charging hydrocarbon system within partly highly overpressured carbonate bodies (‘stringers’). These carbonates underwent a complex diagenetic evolution, with one stage of halite cementation in a shallow (early) and another in a deep (late) burial environment. Early and late halite cements are defined by their microstructural relationship with solid bitumen. The early phase of halite cementation is post-dated by solid reservoir bitumen. This phase is most pervasive towards the top of carbonate stringers, where it plugs nearly all available porosity in facies with initially favourable poroperm characteristics. Bromine geochemistry revealed significantly higher bromine contents (up to 280 p.p.m.) in the early halite compared with the late halite (173 p.p.m.). The distribution patterns and the (high) bromine contents of early halite are consistent with precipitation caused by seepage reflux of highly saturated brines during deposition of the overlying rock salt interval. Later in burial history, relatively small quantities of early halite were dissolved locally and re-precipitated as indicated by inclusions of streaky solid bitumen within the late halite cements. Late halite cement also seals fractures which show evidence for repeated reopening. Initially, these fractures formed during a period of hydrothermal activity and were later reopened by a crack-seal mechanism caused by high fluid overpressures. Porosity plugging by early halite cements affects the poroperm characteristics of the Ara carbonates much more than the volumetrically less important late halite cement. The formation mechanisms and distribution patterns of halite cementation processes in the South Oman Salt Basin can be generalized to other petroliferous evaporite basins.