And then there is the IOW exploration licence,Dor has 5%of this and it is the IOW that was the source of the information that lead to the wytch farm discovery and the rest is history,but here a little of that fantastic story
The discovery of commercial oil in the Wessex Basin was important not only for the opening of a new basin but because at the time of discovery the UK government was keener than ever to reduce dependency on overseas oil producers. Late in 1973, the doubling of crude oil prices by OPEC and a shortage of coal, caused by industrial action, resulted in the introduction of the ‘Three-Day Week’ electricity consumption reduction measure.
It was against this backdrop that the Gas Council (GC) – the E&P part of British Gas – was drilling exploration wells in the Wessex Basin. Natural oil seeps, earlier drilling and the Kimmeridge discovery in 1959 had provided evidence that the basin had a working petroleum system and that hydrocarbons may be trapped in seismically mapped faults, but the belief that the area was unlikely to be sourced by marine kerogens had slowed down exploration efforts.
However, following the identification of marine kerogens in a well on the Isle of Wight, the Wareham-1 well was drilled to test (Jurassic) Inferior Oolite and Bridport Sand targets. Initial interpretations of the well suggested that no significant reservoir sands were present. Geologist Vic Colter at the GC disagreed and argued that the log responses resulted from thick permeable intervals punctuated with hardbands, similar to those seen in the nearby Bridport Cliffs. It was this interpretation that led the GC to drill the discovery well at Wytch Farm.
Good Husbandry Produces Bountiful Fruits
The first phase of development targeted the Bridport Sands and, to a lesser extent, the Inferior Oolite. Production was based on four well sites and ~6,000 bopd were extracted during the 1970s and early 1980s. The Bridport reservoir is a lower Jurassic structure at a depth of ~900m and is being depleted with conventional wells drilled from onshore drill sites. The Inferior Oolite contains small amounts of oil but in general acts with the Fuller’s Earth to seal the reservoir.
Simplified north–south cross section showing the main stratigraphic and structural elements at the discovery wellsite (based on Colter and Havard, modified after West).BP took over as operator in 1984 and, after upgrading the existing wellsites and constructing five new sites, saw extraction from the Bridport and recently discovered Sherwood reservoirs rise to approximately 60,000 bopd. It quickly became apparent that the main resources were trapped in the deeper Triassic Sherwood Sandstone formation, increasing the reserve base from around 30 MMbo to 378 MMbo, and a new phase of development began.
The Sherwood formation consists of a variable sequence of floodplain deposits, including lacustrine, sheetflood, channel-fill and aeolian facies, at a depth of 1,600m, and lies under Poole Harbour and out into the nearshore area. The reservoir is sealed by the Mercia mudstone. The next phase of development involved extended reach drilling from the mainland under Poole Bay, which required the construction of a wellsite on the Goathorn Peninsula. The investment increased the reserves base once more, this time to 500 MMbo.
Output peaked in 1997 at ~110,000 bopd and since then oil production has gradually declined. Production continues at levels of around 19,000 bopd and substantial oil reserves in the region of 43 MMbo are believed to remain.
