Processing and interpretation of geophysical well logs from well KJ-32, Krafla geothermal field, NE-Iceland

Abstract

The purpose of this study was to improve the understanding of the litho-stratigraphy of the geothermal reservoir rocks in the Leirbotnar field of the Krafla geothermal area. The geological structure of the reservoir has important bearing on the reservoir properties and the location of feed zones. Drilling in the Krafla geothermal area is proceeding northwards to the northern Leirbotnar field. KJ-32 was the first well to be drilled into this part of the reservoir. The well was drilled directionally using a mud motor and high drilling rates. This resulted in low depth resolution of the cuttings record, and cuttings are entirely lacking from sections drilled with total loss of circulation. A study was made of the natural gamma ray, neutron-neutron and resistivity logs in the production part of well KJ-32. Through detailed comparison and correlation between the logs and the cuttings record it was possible to make significant improvements to the litho-stratigraphy of the reservoir. The litho-stratigraphic boundary depths determined from the cuttings were found to be shifted upwards by 3.5-6 m ...