--> Abstract: Shelf to Deep-Water Transition – Analogues and Their Application to Offshore Labrador, by Stephen O'Connor; #90177 (2013)

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Shelf to Deep-Water Transition – Analogues and Their Application to Offshore Labrador

Stephen O'Connor

The Labrador Shelf extends from the Saglek Basin in the north to the Hopedale Basin in the south, along the NE margin of East CA. Mud-weights in many of the Labrador wells are low; however, there are occurrences in wells such as Pothurst P-19 of very high kicks taken, implying under-balanced drilling and mis-understanding of the pore pressure regime on the Shelf. This uncertainty will be even greater as exploration moves into the deeper-water where there is no well calibration. This moved is suggested as a result of the recent large-scale multi-client 2D seismic survey of offshore Newfoundland and Labrador. The Scotian Shelf provides a suggestion on some of the problems of moving into the deeper-water; between 2002 and 2004 industry drilled seven deep-water wells on the Scotian Slope with one gas discovery (Annapolis), one gas show (Newburn) and four dry wells (Balvenie, Crimson, Weymouth and Torbrook). The seventh well, Annapolis B-24, was a precursor to the discovery well that was abandoned due to a shallow gas kick. Clearly the geopressure regime has impacted of the safe drilling of wells in this area. Therefore, as there is no well calibration in the Saglek and Hopedale Basins in the deep water, this paper presents results from the drilling of other worldwide deep-water areas that form useful analogues. One of these analogue areas is Mid-NO. Here, recent exploration has re-located to the Voring Basin, with water depths of up to 1.5km. The Upper Cretaceous Nise Formation consists of deep-se fan deposits; these fans are locally amalgamated such that the overpressures in the aquifer are the same or similar, and are considered to form part of a hydrodynamic system, despite their deep burial depth. In more stratigraphically isolated parts of the fans, overpressures can be similar to the encasing shale pressures. These differential pressures enhanced seal capacity and establish the opportunity for hydrodynamic trapping; similar deep-water fan complexes are observed in the recently shot seismic in the Labrador area. Stratigraphically younger but similar in terms of facies, the Base Tertiary Ormen Lange Field reservoir is hydrodynamic, with a tilted contact, affecting estimates of reserves and field development. Similar deep-sea fan complexes have already been recognised on the recently shot seismic data offshore Labrador. This paper will demonstrate that using analogues such as the Mid-NO shelf to deep-water transition can not only aid safe drilling in Labrador – an example is the kick taken in the Pothurst P-19 well; calculating the rate of sedimentation for the overburden above the Paleocene Cartwright Formation in which the kick was taken and utilizing the relationship in Swarbrick et al (2002) linking pore pressure profiles and this rate, provides a first order approximation of the kick pressure. Analogues can also be used to provide insight into the petroleum system, in terms of seals, migration and fluid flow.

AAPG Search and Discovery Article #90177©3P Arctic, Polar Petroleum Potential Conference & Exhibition, Stavanger, Norway, October 15-18, 2013