Lopra Well No. 1, Suduroy, Faeroe Islands. Geological Well Completion Report. Including Appendix A-D

From July to November 1981, a 2178 m deep well was drilled in the southernmost part of the Faeroe Islands near the village Lopra on Suduroy as a part of a drilling project organized by the Faeroese Government. The aim of the Lopra well was to explore the unknown strata beneath the exposed part of the Faeroe basalt plateau down to a depth of about 2 km. The drill site was located stratigraphically less than 100 m above the oldest exposures of the lower basalt series in the southern updomed area of the basalt plateau.

The Lopra bore hole did not penetrate the lower basalt series, and this series is therefore more than 3 km thick. The penetrated formation consists of subaerial basalt flows with an average thickness of 20 m, which is similar to the thicknesses in the exposed part of the lower series. The flows consist of tholeiitic basalt, and most are macroscopically aphyric or microphyric. Two doleritic intrusions (probably dykes) occur in the upper part of the hole. Fine-grained interbasaltic sediments (red boles) form 2-2. 5% of the penetrated lava sequence. The sediment beds have a maximum thickness of roughly 4 m and do not suggest major breaks in the volcanic activity. Paleomagnetic studies however, on 5 basalt cores suggest at least two new paleomagnetic zones below the normal zone of the deepest exposed part of the lower series.

A number of petrophysical logs were run, and these correlate well with the stratigraphy as determined from ditch samples. The temperature in the well was also measured several times.

The secondary alteration varies with depth. The zeolites in the uppermost part of the hole are characteristic of Zeolite zone 2 of Icelandic geothermal areas while the zeolites in the deepest part of the hole are characteristic of Zeolite zone 4 in Iceland and probably have formed at temperatures between 100 and 200 degrees.

The top porous zones of the lava flows and the above lying sediments become more red with depth, possibly as a result of diagenetic alteration. However, the non-vesicular parts of the flows are usually only slightly affected by alteration, even in the deepest part of the hole, and fresh olivine is preserved in a core from the very bottom of the hole.