An oil discovery has been confirmed in the Horse Hill exploration well, two miles from Gatwick Airport.
Analysis of oil shows encountered earlier this month reveals an oil accumulation in the Upper Jurassic Portland Sandstone reservoir, at a depth of 1,791 feet.
The Lower Portland, Corallian and Great Oolite exploration targets were unsuccessful.
The new oil discovery is estimated to contain 3.1mln barrels of gross in-place hydrocarbons, with some 16mln barrels of prospective resources in a separate untested Portland interval providing upside.
Prior to drilling, even a modest find was believed to have a good chance of being commercial, given relatively low well costs and the onshore location.
Nevertheless, the size of the discovery does not live up to the high hopes in the retail investment community. Some pre-drill estimates for the well were phrased in hundreds of million barrels.
Just how much of the discovered 3.1mln barrels can be recovered will be determined by ongoing analysis.
Drilling, meanwhile, is set to continue as the well will be deepened over the next two weeks to assess a gas target.
“The presence of a larger, unappraised, Portland feature creates considerable further upside,” he said in a stock market statement.
“We are now looking forward to drilling the Triassic, which is a new and untested exploration target in the area and which, if successful, may contain appreciable volumes of gas."
The detailed Horse Hill results reveal that the Lower Portland reservoir was water wet, as it was in Esso’s 1964 Collendean Farm well.
Two other exploration targets, the Corallian and Great Oolite, were not seen to contain moveable hydrocarbons.
It was also concluded that further evaluation of several thick Kimmeridgian-age limestones may show additional oil potential within the well. Hydrocarbon shows and elevated mud gas readings were observed here during drilling.
For the discovery in the Upper Portland reservoir it is estimated that there is between 1.5mln and 4.8mln barrels of discovered oil (estimated on P90 to P10 basis), with the medium (P50) or ‘most likely’ figure estimated at 3.1mln barrels.
The estimated undiscovered oil volumes range from 7.8mln to 29.7mln barrels (P90 to P10), with the medium (P50) or ‘most likely’ figure estimated as 16.8mln barrels.
The exploration licence is 65% owned by a special purpose vehicle called Horse Hill Developments Ltd (HHDL), which is operator, while Magellan Petroleum Corporation has a 35% interest.