Fault-Induced Bends on Schiehallion’s North Channel

De Miranda, Debora¹ (1) BP Exploration Operating Company Limited, Aberdeen, United Kingdom

Schiehallion, a BP-operated 1.9 billion barrel field 120km west of the Shetlands, produces from a series of stacked Tertiary turbidite sands. The reservoirs are trapped by a 3-way combination dip / fault closure and a stratigraphic onlap / pinch-out to the east, set against a pattern of East-West faulting.

3D seismic data are key to mapping the reservoirs as the 25-30% porosity sands are low-impedance bright amplitude anomalies when hydrocarbon bearing.

A confined channel, long recognised as one of largest undeveloped hydrocarbon pools on Schiehallion, is now under development.

This ‘North Channel' is a deep-cutting canyon feature. The scour is filled initially by a thick section of low-net reworked material followed by a series of 300-500m wide, 30m thick sand bodies. These internal channels shift around within the large canyon cut, reacting to subtle topographic changes caused by syn-depositional fault movement.

Seismic resolution is not high enough to give confidence in tracing individual bodies. One main concern has been the connectivity both between these internal channels and along the length of each one. Image logs indicate slumping / reworking at the base of each of these sands which appear to be extensive.

Multiple reservoir models were built to test reserves against alternative visions of sand geometry and connectivity.

Selection of a development concept was made recognising that channel boundaries and faults may seal but also that elsewhere in the field this was not always the case. In reverse of the normal arrangement, an up-dip injector and down-dip producer pair mitigate the risk of cross fault flow and horizontal producers and injectors are drilled across the constituent offset stacked channels that form the reservoir.