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United Oil & Gas plc: completion of Colter appraisal campaign

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Oilfield Technology,


  • 98/11a-6 well delivers a new discovery at Colter South.
  • Sidetrack to the north to delineate the original Colter appraisal target encountered the Sherwood Sandstone reservoir deeper than expected, indicating the Colter accumulation is smaller than pre-drill estimates.
  • Oil and gas shows encountered in the sidetrack in shallower Jurassic intervals mirror the producing Kimmeridge oil field, and provide encouragement for the prospectivity of the adjoining JV-held onshore licences.
  • Further work will now commence to fully evaluate all the data from the well and assess forward work programmes and options for commercialisation.

United Oil & Gas Plc, the AIM listed oil and gas exploration and development company, provides an operational update on the P1918 licence in the Wessex Basin and specifically the Colter appraisal campaign which has included the Colter North and the new Colter South prospects. United holds a 10% stake in the licence, which is operated by Corallian Energy.

As previously reported on 25 February 2019, the Colter well (98/11a-6) was drilled as a vertical well with the Ensco-72 jack-up rig and reached a total depth of 1870 m MD in the Sherwood Sandstone. The well was drilled to appraise the 98/11-3 well, drilled in 1986 by British Gas, within the Colter Prospect. The 98/11a-6 well remained on the southern side of the Colter Prospect bounding fault but encountered oil and gas shows over a 9.4m interval at the top of the Sherwood Sandstone reservoir. A petrophysical evaluation of the LWD data has calculated a net pay of 3m. Similar indications of oil and gas were encountered in the 98/11-1 well, drilled in 1983 by British Gas, within the Colter South fault terrace. Provisional analysis of the new data indicates that the two wells may a share a common oil-water-contact having both intersected the down-dip margin of the Colter South prospect. Corallian's most recent assessment of the Colter South Prospect prior to drilling the 98/11a-6 well had estimated a mean recoverable volume of 15 million bbls. This would exceed the threshold for commerciality. Further work will be required to refine this assessment with the new well data.

A decision was made by the Joint Venture to drill a side-track (98/11a-6Z) to the north to evaluate the Colter Prospect. The well has now been drilled to a Total Depth of 1910 m MD and encountered the Sherwood Sandstone below the oil-water-contact of the 98/11-3 well. Initial evaluation of the data from both wells indicates that while there are hydrocarbons present the Colter Prospect is smaller than pre-drill estimates.

However, the Colter South discovery remains an opportunity to evaluate further as it is now aerially more extensive than indicated by the pre-drill mapping. In addition, the sidetrack encountered oil and gas shows in the Jurassic Cornbrash-Lower Oxfordian interval, the producing reservoirs in the Kimmeridge oilfield. This provides an interesting potential target on trend to the west within the adjoining onshore licences held by the Joint Venture.

United Oil & Gas PLC CEO, Brian Larkin, said: "The Colter Appraisal campaign has delivered a new discovery and significantly increased our understanding of the Colter prospect. While we are obviously delighted by the discovery of Colter South, which with an estimated mean recoverable volume of 15 million bbls is an exciting discovery and appears to have exceeded our pre-drill requirements for commerciality, Colter North has not delivered in the way that we would have hoped. However, even this latest result has delivered some interesting additional data which points to further targets and prospectivity within the licence area.

"We will continue to work with the partners to evaluate the best way of commercialising the licence and the considerable data we have acquired during this campaign will help the partners decide on their next steps.

"A key part of the United Oil & Gas strategy is that of maintaining a diverse portfolio where we drive near-term activity for our shareholders with the goal of unlocking previously untapped value within our suite of assets. Whilst the evaluation of Colter and the new discovery at Colter South progresses, United will continue to have a busy calendar ahead: we will be looking to push our more mature licences such as Selva and Waddock Cross through development into production; we will be working on progressing joint-venture discussions for our North Sea licences, as well as making forward plans for our high-impact Jamaican prospects – all of which offer considerable potential upside for shareholders. In tandem with this, we will continue to identify and complete value-adding portfolio additions at minimum dilution to shareholders."

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