Aberdeen Evening Lecture: January 2019

The Beryl Field area in the South Viking Graben is undergoing a rejuvenation driven by development drilling and near-field exploration, providing an excellent example of how the life of a mature giant oil field can be extended. Historical production derives from Jurassic and Triassic-aged stacked sandstone reservoirs trapped within faulted structural closures formed within a large relay ramp along the Viking Graben normal fault. After discovery in 1972, Mobil commenced production on the Beryl Field in 1976 achieving a maximum rate in excess of 200,000 barrels of oil equivalent per day. Several additional subsea satellite fields were brought online from 1987 and overall production rates were maintained until the field entered into a steady decline. By 2012, some 1.6 billion barrels of oil equivalent had been produced. It was originally expected production at the Beryl Field would last 25 years. However, Beryl celebrated its 40th anniversary in 2016 and based on recent infill and exploration success, the end of field life is now projected to extend beyond 2030.

The Beryl field area has recently benefited from the acquisition of a new 3D broadband seismic data and subsequent drilling of new exploration targets spanning multiple play types. This has led to an arrest in production decline and a forecast of increased production over the next 5-10 years. The new widespread broadband 3D seismic dataset acquired in 2012/13 has been key in better integrating the greater Beryl area in terms of structural interpretation and reservoir geology. Advanced processing efforts have provided multiple volumes for use in defining and assessing prospects. These volumes include several PSDM’s using different algorithms and several different Inversions. The interpretation of a single survey, with multiple derivative volumes, has led to an enhanced prospect portfolio, part of which became the near-field exploration drilling campaign starting in 2015. This drilling campaign has a 66% success rate with 4 commercial discoveries in 2 years, including Callater, Storr, Corona, and Garten. First production in mid 2017 from the Callater field was achieved only 23 months after discovery. This short cycle time to production, benefiting from tying into nearby existing infrastructure with ullage significantly improved the economics of these new projects.

As in any mature area, prospects near to the Beryl infrastructure were increasingly complex in terms of structural and reservoir geology. Key to determining commercial success in these more complex exploration prospects was to plan geologic sidetracks from the beginning to fully evaluate multiple compartments of the overall traps. At Callater, for example, 3 penetrations were drilled in succession with the 3rd well encountering over a 2000 ft Triassic oil column height, second only in thickness to the original Beryl field column. This 3rd well was suspended and production began 23 months later. This was in contrast to past experience. For example, and for many different reasons, the Buckland field took 21 years and 3 wells to come on line, and the Skene field 17 years and 7 wells to come on line.

The exploration phase drilling program of the Jurassic/Triassic Callater and Storr discoveries, as well as the Corona Tertiary discovery, illustrate the need to persevere by drilling multiple compartments of a complex trap in order to confidently assess enough in-place volume to justify proceeding to development. Importantly, with only one well at each, none of these prospects would have transitioned to a development stage just after the exploration drilling but would need further appraisal, delaying first production by many years. If the first wells on each prospect had been considered uncommercial to develop, and no further wells had been drilled, then significant reserves would have been left behind. The Garten discovery followed on from an evolving knowledge of the area. The drilling results at Callater and Storr re-emphasised the importance of pressure cell boundaries, new source rock intervals and resulting migration routes. Success of the deep low-side fault trap at Garten, in turn, gives encouragement to the testing of further downthrown fault closures in the Beryl embayment.
This presentation will walk through the well results at each field to illustrate the benefit of drilling multiple exploratory well bores at each prospect and the sometimes surprising results that were encountered.