7Wire-line log-based stratigraphy of flood basalts from the Lopra-1/1A well, Faroe Islands

• Main Author: Lars O. Boldreel
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Faroe Islands; Lopra; Sion
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.598.1962; http://www.geus.dk/publications/bull/nr9/nr9_p7-22.pdf

The present study shows that it is possible to use conventional borehole logs to perform a detailed lithological/stratigraphical division of a column of subaerially extruded basalt. A stratigraphical divi-sion of the subaerial flood basalts penetrated by the Lopra-1/1A well has been carried out using new wire-line logging data measured in 1996 in the interval 200–2489 m depth. Resistivity data acquired in the interval 200–2178 m depth during 1981 after the initial drilling of the Lopra-1 well have also been incorporated. Eighty-six individual flow units, 18 compound flows and two dolerite dykes have been identified by combining the NPHI porosity, RHOB density, P-, S- and Stonely-sonic transit time, calliper and resistivity logs. Fifty-two sedimentary/tuffaceous layers have also been identified using the CGR and SGR gamma ray and potassium logs in combination with the aforementioned logs. Within the flow units, sonic velocity, density and resistivity are highest in the core where porosity is lowest. This relation is reversed in the uppermost and basal zones of the flow units. The sonic velocity in the core seems to be independent of the thickness of the flow unit. Porous zones seem abundant in some cores and the total section of cores containing porous zones constitutes more than 70 % of the thickness of its flow unit, but where porous zones are absent the core makes up only roughly 50 % of the thickness of the flow. It is suggested that the flow units with porous cores repre-