Structural and stratigraphical significance of reservoirin heglig field (Sudan)‎

Abstract EN

The Greater Heglig area encompasses some 380 sq.km.

The area forms part of the Cretaceous-Tertiary Muglad Basin in south-central Sudan.

The basin was initiated as an extensional graben to the immediate south of the Central African Shear Zone.

An early phase of extensional tectonics led to rapid subsidence and lacustrine basin fills comprising the rich source rocks of the Lower Cretaceous Barremian-Neocomian Sharaf Formation and Albian-Aptian Abu Gabra Formation.

The reservoir section in the Late Albian to Cenomanian Bentiu Formation accumulated as widespread sheet sandstones in response to a cessation of active extension and during a period of regional sag marks a fundamental change from an internally draining lake basin to larger scale sediment dispersal patterns transporting sediment out of the basin in the north and south.

A sudden change from the sandstone-dominated successions of the Bentiu Formation to the shale-dominated interval of the Aradeiba Formation marks the onset of a second phase of extension and increases subsidence during the early Turonian.

The Bentiu Formation comprises the main reservoir interval in the study area and is characterized by stacked successions of thick, amalgamated cross-bedded sandstones and intervening extensive laterally, thinner mudrock intervals.

Sandstones of the overlying Aradeiba Formation are characteristically isolated within an otherwise mudrock-dominated succession.

No significant thickening of stratigraphic units across faults is evident in the study area.

It is likely that subtle difference in subsidence due to differential compaction across buried grabens and halfgrabens will have influence on sediment dispersal patterns during Bentiu and Aradeiba times.