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.

Interpretation and integration of the subsurface seismic and geological data has enabled a detailed sedimentological model to be used to define both a robust geomodel and a simulation model for the Maureen reservoir. This is expected to produce a better understanding of fluid flow, optimise the placement of producer wells and determine the hydrocarbon resources to optimally size the facilities. A parallel process is well advanced for the shallower Heimdal reservoir, whose areal and vertical distribution has been
imaged by combining the original 3D with recently acquired and processed Ocean Bottom Cable (OBC) seismic data.

Nautical has been instrumental in modifying the Heimdal sedimentological model by utilising its detailed regional knowledge to identify additional remobilised sands in the Lista Section. Since these sands have been derived from the original slope channel sands (penetrated by wells) improved connectivity through the Heimdal section can be implied. Both reservoir simulations will be completed by mid year when we aim to report
updated resources.

As a result of extensive processing and marketing studies it was concluded that the Mariner crude could be blended with lighter hydrocarbons both aiding crude processing (improved water separation and salt removal) and increasing the sale value of the blend.

The operator is screening a variety of development concepts including a fixed platform and floating systems. The studies are on schedule for concept selection at the end of the third quarter with Decision Gate 2 (Project Pre-Sanction) at year-end. After passing through Decision Gate 2, the Joint Venture intends to sanction the development and submit an FDP in 2011, anticipating first oil in 2015.