|REDEFINING A GIANT TURBIDITE FIELD IN THE CNS: THE NEW NELSON FFM|
|Field Developments and Case Studies|
1Shell UK Limited
The Nelson Field is a complex, channelized reservoir that has been in production for over 14 years and is at the mid-mature stage of field life. The current management strategy has focused on identifying infill well locations with the aim of recovering bypassed oil.
A number of generations of reservoir models have failed to history match. The causes of this are poorly understood. New insights into both the static and dynamic behaviour of the field have led to an improved understanding of the reservoir. There are three key areas of change: a new structural framework, a new macrofacies model and its associated petrophysical property subdivision.
The Nelson intra-reservoir horizons are poorly imaged and historically difficult to interpret. New biostratigraphic data integrated with production, well log correlation, pressure and bridge plug performance data has resulted in a complete remapping of the intra-reservoir boundaries. This has modified the structural envelope (locally up to 200ft), and changed reservoir zones assigned to many perforated intervals. This in turn had a major impact on assumed reservoir connectivity and fluid flow.
The Nelson reservoir has long been subdivided into 3 sedimentological elements; Channel axis, margins and inter-channels. These elements, or macrofacies are used: 1) to populate petrophysical properties in the static model, 2) as compartments for screening of remaining oil, 3) as an indication of well productivity (oil, water and sand!) 4) to plan and design infill wells. At the core scale, additional facies types with distinct reservoir properties had previously been recognized: turbidite fans, areas of slumps and abandoned channels with a fine-grained sediment plug. The use of multi-attribute sculpting and seismic facies extraction has now allowed to consistently incorporating these additional macrofacies into the 3D static model.
The primary objective of this study was to build Full Field Model that (for the first time) would achieve a good history match and provide the Greater Nelson subsurface team with a high confidence production forecasting capability. The new model will be used to identify areas of bypassed oil, scope for production optimisation of the existing wells, test further infill/sidetrack targets, and evaluate the benefits of water injection, to optimise water off-take and gas lift provision on Nelson.