Block 9/11a Mariner (Licence P0335)

Operated by Statoil Hydro ASA and located on the East Shetland Platform, west of the Viking Graben, the Mariner oil accumulation, discovered in 1981 and with 15 subsequent well penetrations, is the largest, most highly appraised undeveloped discovery in the UKCS. These wells have tested oil at 1,000 to 1,595 bopd from both the Palaeocene Maureen Sandstone and the shallower Heimdal Sandstone. Both sands have excellent reservoir characteristics and during an extended well test (EWT) in 1997 a single horizontal well in the Maureen Sandstone produced 662,000 barrels of oil over 63 days at a maximum rate of 14,991 bopd (14.5 API)

During the period the joint ventures’ resources were focused on characterising and defining the areal distribution of the shallower Heimdal Sandstone reservoir and enhancing our already detailed knowledge of the deeper Maureen sandstone. Statoil have applied the proven geophysical techniques used in their successful Grane heavy oil field by acquiring two further seismic surveys. Firstly in June 2008, a high resolution 3D seismic survey was acquired to enhance the interpretation of the Maureen reservoir. In August 2008 Statoil added a 3D ocean bottom cable (OBC) survey over the core of the Heimdal reservoir to record shear wave seismic data which is beneficial to the interpretation of the low impedance contrasts typical of the oil filled sands. These mark the first operational activities over the discovery since the EWT.

The new 3D seismic has been successful in defining the top of the Maureen sand which now appears to be shallower than previously mapped in some areas which will increase the hydrocarbon column and volume. As anticipated, the OBC data has imaged the main Heimdal channels and other sand bodies higher in the sequence. Both the improved Maureen and Heimdal reservoir models will be input into reservoir simulations by end 2009. Production profiles for both reservoirs are expected to be generated in early 2010.

Since successfully passing through a major decision gate in October 2008 Statoil has been identifying development options and will shortlist and propose the preferred development concept before the next major decision gate at the end of 2010.

Following on from site surveys acquired in the summer of 2009 over three considered platform locations, geotechnical and environmental studies will be conducted to aid platform design and development.

Considerable operator effort has been guided towards evaluation of polymer injection to improve oil recovery factor and simplifying well design to reduce costs. Furthermore the use of autonomous valves in the completion assemblies to control water influx has shown encouraging test results. In addition blending tests to both decrease viscosity and increase marketability is yielding positive outcomes. Prior to the performance of the above work programme the operator reported best estimate contingent resources of 369mmbo gross (90mmbo net) for both the Maureen and Heimdal reservoirs.

Mariner is a large, economically robust development which will pass through the next decision gate at the end of 2010 before commencing Front End Engineering and Design (FEED) and completing an Environmental Impact Assessment in 2011. This will lead to project sanction by the joint venture followed by FDP submission during 2011 and first oil in 2015 or earlier if Maureen wells are pre-drilled.