Arous Al-Bahar Gas Discovery, Area 54, Offshore Libya
Michael Quinn, Andrew Hughes, Geoffrey Bent, Scott Pluim, and Yohan Kusumanegara
The Area 54 exploration licence, in Libya’s offshore Sirte Basin, was awarded to Hess in mid-2005 following Libya’s EPSA IV Exploration Licence Round. Area 54 is 10,530 square kilometres in area, and is centred off the coast of Libya 100 kilometres due north of Ras Lanuf. Hess is currently operator and sole IOC contractor for Area 54. In December of 2008, Hess drilled the Arous Al-Bahar prospect and encountered approximately 120 metres of net gas pay in the initial exploratory well. Drilling operations concluded on the A1-54/01 well in January of 2009.
Later in 2009, the A1-54/01 well was re-entered and a 90-metre carbonate reservoir interval was perforated and a drill stem test was performed. The well flowed at a rate of 27 mmscf of gas and 533 bbls of condensate per day on a 52/64 inch choke. Immediately following the well test, the A2-54/01 appraisal well was drilled, located approximately 7 kilometres to the NW of A1-54/01. The A2-54/01 well discovered approximately 11 metres of net gas pay. The A2- 54/01 well was also tested and flowed at a rate of 24 mmscf of gas and 1010 bbls of condensate per day on a 52/64 inch choke.
The Arous Al-Bahar gas discovery is hosted in Upper Cretaceous carbonate reservoirs that lie beneath a Base Tertiary Unconformity (BTU). Across the Arous Al-Bahar structural high, Eocene marls and limestones lie unconfomably above a dipping subcrop of Cenomanian and Turonian carbonate rocks. Upper Cretaceous reservoirs are variably dolomitised and the dolomitisation appears to be the key determinant on reservoir quality. In contrast to A1-54/01, the dolomitisation at the A2-54/01 location was much reduced and net gas pay was about 10% of that seen at A1-54/01. The favoured model for dolomitisation involves prolonged period of (sustained or episodic) subaerial exposures during development of the BTU. Additionally, depositional facies variations appear to have also controlled the degree of dolomitisation.
Quantifying the discovered hydrocarbon resource at Arous Al Bahar is complicated due to difficulties in predicting reservoir properties away from well control. In addition, as yet unexplored sections of Lower Eocene elsewhere onlap the structure and are regionally known to have reservoir potential. As currently understood, Hess believes Arous Al- Bahar carries resource potential anywhere between 1 and 4 TCF. Future appraisal of Arous Al-Bahar will be focused toward strategic data gathering in order to narrow the remaining reservoir and resource uncertainties.
AAPG Search and Discovery Article #90161©2013 AAPG European Regional Conference, Barcelona, Spain, 8-10 April 2013