Petroleum System Study of the Humma Marrat Reservoir in the Partitioned Neutral Zone (PNZ)

Stewart Griest¹, W. Scott Meddaugh², and David L. Barge^3
1 ChevronTexaco Exploration and Production Technology Company, Bellaire, TX
² ChevronTexaco Energy Technology Company, Bellaire, TX
³ ChevronTexaco Joint Operations, Wafra, PNZ, Kuwait

The Jurassic-age Humma Marrat Limestone reservoir in the southwest Partitioned Neutral Zone (PNZ) was discovered in 1998. The structure setting of the western PNZ is dominated by the Humma-Fuwaris-Wafra-Burgan trend that extends over 250 miles from the South in Saudi Arabia to Burgan Field in the north. The Jurassic Marrat Limestone is interpreted to be folded over deeper-seated horst blocks present in the Paleozoic and basement intervals. Multiple tectonic events periodically reactivated the structure and resulted in folding and fracturing of the Marrat Limestone reservoir.

Thermally mature Paleozoic source rocks are stratigraphically adjacent to and/or beneath the Marrat. Though immature on structures in the PNZ the source sequences are thermally mature in the adjacent basinal areas. Lateral migration of hydrocarbons could come from the Arabian Gulf basin to the north and east and from the Dibdibah trough to the west. Additional migration pathways may be present through vertical and short-distance migration from source rocks at and beneath the reservoir.

Middle and Lower Jurassic Marrat deposition occurred in a shallow carbonate ramp setting within a transgressive systems tract. Multiple porous intervals throughout the Middle and Lower Marrat are capped by intra-formational seals consisting of tight carbonates or shale-rich carbonates. Porosity and permeability in the Marrat Limestone is variable. Porosity within productive zones is 6-20% and permeability is generally less than 20 md. The lowermost Marrat “E” interval is the most porous and permeable zone and is dolomitized. Fractures may be important in the uppermost limestone Marrat “A” zone.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005