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F-O Gas Field, Offshore South Previous HitAfricaNext Hit — From Integrated Approach to Field Development

Kathleen Mudaly, Jim R. Turner, Florangel Escorcia, and Roger Higgs
New Ventures : Southern Previous HitAfricaNext Hit, PetroSA, Cape Town, South Previous HitAfricaNext Hit

The F-O tract is located in the eastern part of Block 9 on the northeastern flank of the Bredasdorp Basin, a sub-basin of the Outeniqua Basin on the southern continental shelf, offshore South Previous HitAfricaNext Hit. The F-O field is situated 110km from the nearest landfall and 40km SE of the F-A platform, which supplies gas and condensate to the PetroSA GTL plant located in Mossel Bay.
The principal reservoirs are tight, overpressured, highly faulted Valanginian shallow marine sandstones beneath the drift onset unconformity, 1At1. These were deposited as an extensive sandstone “sheet” within a tidal dunefield setting. The top and base of the reservoir is defined by the TUSM (Top Upper Shallow Marine) and BUSM (Base Upper Shallow marine) seismic events respectively. Four wells have been drilled in the F-O field, two of which are classified as gas discoveries with potentially commercial production rates. This heterogenous reservoir has low porosity (2-18%) and low permeability (<0.1 to 10 mD). The field has some good permeability streaks that reach values of 250 md. The field is on a well-defined structural high at the level of the regional drift onset unconformity, 1At1.

The proposed development of this field followed an integrated approach, incorporating geology, geophysics, sedimentology, reservoir engineering, petrophysics and rock mechanics. The aim was to understand reservoir distribution and quality to optimally locate the proposed three development wells. One of the options considered that can increase production is fracturing the reservoir. The study with Schlumberger integrates geomechanical analysis (single well geomechanical analysis, lab core analysis and hydraulic fracture designs), 3D static geological modelling, dynamic modelling and 3D mechanical earth modelling.

AAPG International Conference and Exhibition, Cape Town, South Previous HitAfricaTop 2008 © AAPG Search and Discovery