Pilot Main, Pilot South & Harbour Fields, Licence P2244

Block 21/27a

Licence P2244 highlighted in pink

Licence P2244 highlighted in pink

Pharis Energy Ltd is operator of, and holds a 100% interest in, Seaward Production Licence P2244, block 21/27a, which covers the Pilot Main, Pilot South and Harbour fields.

These three discovered fields have about 240 mmbbls of proven plus probable oil in place and have been very well appraised, with modern 3D seismic, and six successful wells plus a deviated sidetrack and a horizontal sidetrack.

The oil is heavy with API gravities ranging from 12º to 17º and reservoir viscosities which range from approximately 100 cP to 1200 cP,  a horizontal appraisal well in the most viscous region produced nearly 2,000 bopd.

Parameter Steam Criteria Pilot Result
Depth 400' to 3000' 2700' ✔︎
Thickness >30' 30' to 75' ✔︎
Porosity >30% 35% ✔︎
Permeability >1 Darcy 2-8 Darcies ✔︎
Oil Satn. >40% 92.5% ✔︎
Oil Gravity 8º to 25º API 12º to 18º API ✔︎
Oil Viscosity 200 to 15,000 cP 160 to 900 cP ✔︎
Pattern size <10 acre ≣ 5 acre ✔︎

Screening criteria for a sucessful steam flood; derived from a combination of the five references used in Table 15.1 of the Petroleum Engineering Handbook.

At a depth of less than 3000’ subsea, Pilot is one of the few heavy oilfields in the UKCS which passes all the conventional screening criteria for Steam Flooding. Depth is considered a key criteria for steam flooding success for two main reasons: firstly, the deeper the well the more energy is lost as the steam flows down the wellbore, though this is less critical for highly productive wells; and secondly, as reservoir pressure increases with depth, steam temperature also increases and the enthalpy of condensation (which is the main way that the thermal energy is delivered to the reservoir) reduces. At about 7000' the pressure is normally such that the phase boundary between steam and water disappears and there is no enthalpy of condensation at all. The conventional limit for steam flooding is around 3000', at a reservoir depth of 2700' Pilot is well within the necessary limit.

Whilst the oil is viscous at reservoir temperatures, the reservoir itself has very good porosity and is very permeable,  which enables the production and injection wells to be highly productive. The core photographs below are from the 21/27a-5 well and show the quality of the unconsolidated sandstones in the gas cap; the oil staining in the oil zone and, below that, cores from the water leg.

© British Geological Society

© British Geological Society

The Pilot Main reservoir architecture also favours a steam flood. The reservoir is dip closed to the East and North, bounded by a facies change to the South and there is a stratigraphic pinch out to the West; all this means that over half of the oil in place is not underlain by water. The conventional approach to steam flooding is less effective in fields with bottom water, so limited bottom water is a great advantage.

Pilot Cross Section.png
Map showing the depth of the Top Tay sandstone, with wells and oil gravities noted.

Map showing the depth of the Top Tay sandstone, with wells and oil gravities noted.

There is a significant variation in oil properties across the reservoir. Indeed a previous operator had hoped to develop a portion of the oil in place by focussing on the lower viscosity, higher gravity parts of the field. However, when appraisal drilling failed to confirm their model of how viscosity varied across the field, and with a low oil price prevailing at the time, they could not proceed with the project. Steam flooding is much less sensitive to this variation, so we expect that the recovery factor will not be much affected by the change in oil quality across the field, though we do expect to see higher initial well productivities in the wells with better quality oil.

Based upon the reservoir engineering and geological evaluation that we have done so far we believe that a steam flood will recover about 113 mmbbls from a development of these reservoirs, we expect that a hot water flood would recover approximately 60 mmbbls.