Abstract The Volund Field lies in the Norwegian sector of the North Sea (Quad 24/9). This field produces from a ‘classic’ large-scale sandstone injection complex located in Lower Eocene strata. The sandstone reservoir has been injected into the lower permeability surrounding mudstones of the Sele and Balder formations and Hordaland Group to create an ‘intrusive trap’. The Volund Field consists of a deeper central unit of stacked sandstone sills, surrounded by shallower, steeper-dipping injected sandstone dykes, which make excellent reservoirs with consistently high porosity and permeability. Many of the steeply-dipping injected dykes appear to have excellent connectivity from the water leg through the oil leg and into the gas cap. The complex was identified on seismic data that exhibit a Class 3 amplitude versus offset (AVO) signature on the far-offset stack reflection seismic volume. The seismic data have been used to successfully locate horizontal production wells. Volund seismic geobodies have been extracted and incorporated into the reservoir geomodel to determine the geometry of the injectite features and to populate sands within the injection complex. Volund Field (estimated mean gross resource of 54 mmboe (million barrels oil equivalent)) is producing oil from four horizontal branches (end December 2012), with one water injector well, and has a common oil–water contact and gas–oil contact.

Abstract Mad Dog is a giant, subsalt, deep-water oil field that will be producing hydrocarbons for the co-owners BP, BHP Billiton Petroleum, and Chevron in the Gulf of Mexico for many years to come. The field was discovered in 1998 by the GC0826#1 well and sidetracks. Four appraisal wells proved up a material resource but also showed evidence of compartmentalization and imperfect subsalt seismic imaging. A spar development was selected and first oil was achieved in 2005. Further appraisal drilling continued from the spar rig and mobile offshore drilling units, ending with the Mad Dog North appraisal program in December 2011. The original spar rig was lost during Hurricane Ike in September, 2008, and a rig replacement project is currently underway. In 2009, the Mad Dog South appraisal well proved up large volumes of hydrocarbons beyond the drilling radius of the original spar rig, necessitating the construction of a second production facility. Mad Dog hydrocarbons are predominantly contained in deep-water turbidite sandstones of early Miocene age that can be correlated over hundreds of square miles. The turbidites are interpreted as a series of individual lobes in a submarine fan complex that was deposited in an unconfined basin floor environment. Deformation of the rocks commenced shortly after deposition and continued through the Plio-Pleistocene boundary. The reservoir is divided into several large compartments that are identified by differences in pressure, fluid composition, and oil-water contacts. These large compartments are interpreted to be bounded by seismically visible faults. Smaller seismically visible and subseismic faults act as baffles to fluid flow in the field, and have been identified through logs, dynamic data, and reservoir simulation. The phased development of the Mad Dog Field has enabled BP and co-owners to mitigate project risk during full-field development. By starting small, developing the known hydrocarbons, investing in technology to improve the imaging of the field, and continuing appraisal drilling, the team was able to evaluate the resources while simultaneously unlocking their value. The integration of dynamic production data with the improved seismic image and appraisal well results has allowed the second phase of the development to proceed with significantly reduced subsurface uncertainty. This has enabled the team to unleash the full potential of the Mad Dog field to be a large deep-water producer for the next 40 years.