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 unexpectedly remained on the southern side of the Colter Prospect bounding fault but encountered oil and gas shows over a 9.4 m interval at the top of the Sherwood Sandstone reservoir. A petrophysical evaluation of the LWD data has calculated a net pay of 3 m. 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. 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 the Colter Prospect is smaller than pre-drill estimates. The Colter South discovery remains an opportunity to evaluate further as it is now 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 licences held by the joint venture. The data from these well results and existing data will be incorporated to determine the best forward plan.
Corallian and its joint venture partners would like to thank the well operator Fraser Well Management, rig operator Ensco and all the many contractors who assisted with the drilling operations which have been completed safely in an environmentally sensitive area.
Read the article online at: https://www.oilfieldtechnology.com/offshore-and-subsea/08032019/colter-well-and-side-track-completion-of-drilling-operations/