Corallian finds Colter prospect to be smaller and Colter South larger than expected

  • Exploration & Production

UK-based Corallian Energy has completed its Colter appraisal campaign off the UK, which has included the Colter North and the new Colter South prospects, discovering that the Colter prospect is smaller but the Colter South prospect is larger than expected.

Ensco-72 jack-up rig; Author: SP Mac

Corallian is the operator of offshore license P1918, which contains the Colter oil discovery located two kilometers south of Wytch Farm – Europe’s largest onshore oil field.

As previously reported on February 25, 2019, the Colter appraisal well (98/11a-6) was drilled as a vertical well with the Ensco-72 jack-up rig and reached a Total Depth of 1870m 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 unexpectedly 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 mmbbls. HOwever, Corallian said on Friday that further work will be required to refine this assessment with the new well data.


Colter side-track


Following the appraisal well in February, 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 1910m 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 the Colter Prospect is smaller than pre-drill estimates. The Colter South discovery remains an opportunity to evaluate further as it is now really more extensive than indicated by the pre-drilling mapping. In addition, the side-track encountered oil and gas shows in the Jurassic Cornbrash-Lower Oxfordian interval, the producing reservoirs in the Kimmeridge oilfield, and this provides an interesting potential target on trend to the west within the onshore licenses held by the joint venture.

The data from these well results and existing data will be incorporated to determine the best forward plan, Corallian concluded.

Corallian’s partners in the license are Baron Oil and United Oil & Gas.

Following the completion of the appraisal drilling campaign, Malcolm Butler, Chairman and CEO of Baron, commented: “While the drilling campaign indicates that the Colter Prospect is smaller than expected, it has demonstrated that the Colter South Prospect is larger than initially thought and has also given encouragement for our adjacent onshore prospects by encountering good shows in the Middle Jurassic. We will now integrate the results of drilling into the seismic data and evaluate the way forward to commercialization of the Colter Prospect and the enlarged Colter South Prospect.”

United Oil & Gas 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 mmbbls 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 license area.

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

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