A history of events in the exploration for the Wytch Farm oilfield, southern England

In a paper that addressed the issue of failing to identify the presence of hydrocarbons in several giant accumulations in the UK, Dean (1996) coined the term ‘undiscovery wells’. Undiscovery may arise for a variety of reasons but, if Dean’s (1996) examples are typical, often as a consequence of simple mistakes. The background for undiscovery is varied, but it often reflects operators’ unwillingness to invest resources in a project that did not immediately and unequivocally identify the accumulation for which they were exploring. Wytch Farm was an undiscovery because the significance of an oil discovery made in 1964 was both misinterpreted and, for reasons of exploration strategy, not tested in case poor test results down-graded the perceived exploration potential of the area. The Wytch Farm oilfield (Fig. 1) is the largest onshore oilfield in the UK with 365#106 BBL reserves (Hogg et al. 1996). Oil is located in three reservoirs – fractured limestone in the Middle Jurassic Inferior Oolite, very fine- to fine-grained sandstone in the Lower to Middle Jurassic Bridport Sand, and sandstone of the Triassic Sherwood Sandstone Group (Fig. 2). The reservoirs improve in quality and reserves with increasing age and stratigraphic depth. Despite its size and recent successful production history with pioneering innovative low-angle drilling technology (Payne et al. 1994; McClure et al. 1995; Hogg et al. 1996), the field has an exploration history that spans almost fifteen years (Table 1). The extended exploration history provides an insight into factors that influence exploration decisions and, as such, a useful analogue to exploration decision-making in general. Dean’s (1996) analysis of the Wytch Farm ‘undiscovery’ is, unfortunately, slightly inaccurate. If the history of an ‘undiscovery’ is to be of value in stimulating more thorough post mortem analysis of wells, possibly proving new reserves, and taking steps toward better management of uncertainty in exploration, the record of events and the decisions behind them need accurate documentation. Here, we attempt to provide a more complete record of the exploration history of the Wytch Farm field to enhance the value of Dean’s earlier analysis.