Laggan; a mature understanding of an undeveloped discovery, more than 20 years old

Abstract

Abstract Laggan, located in the west of Shetland, was discovered in 1986. There is now an improved understanding of Laggan, thanks to innovative and fully integrated geoscience studies and a successful appraisal campaign. Development studies are well advanced, with the discovery of Tormore in 2007 providing the potential for a combined development project. Laggan and Tormore are Paleocene gas condensate discoveries in approximately 600 m water depth. The traps are both mixed, stratigraphic with updip closure against bounding faults. The reservoir comprises sand-rich turbidite channelized lobes and lobes. Reservoir properties are good (permeability range 30–300 mD) due to the presence of chlorite and pre-sorting on the shelf. The geoscience evaluation of Laggan has matured over the last four years with the help of fully integrated studies using 3D seismic and well data. The depositional model has been defined on the basis of an evaluation of cores and seismic and supported by analogue studies. Seismic inversion studies have also helped constrain the reservoir architecture. Of particular value has been the application of AVO to quantify net gas sand, recognized as the principal static uncertainty. The main dynamic uncertainty is the risk of compartmentalization. This risk has been reduced through an improved definition of the fault configuration by re-processing the seismic and detailed seismic attribute analysis. The potential of Tormore was recognized by applying the geoscience understanding of Laggan to help de-risk the prospect. In particular, it was recognized that Laggan could be used as an analogue for the Tormore trapping configuration and reservoir potential and that AVO could be used to help define the Gas–Water Contact. The exploration well, drilled in 2007, was successful in finding a similar reservoir to that encountered in Laggan. The fluid encountered was a gas condensate, approximately three times richer than Laggan.