Analysis of 6‑year fluid electric conductivity logs to evaluate the hydraulic structure of the deep drill hole at Outokumpu, Finland
2016 (English)In: International journal of earth sciences, ISSN 1437-3254, E-ISSN 1437-3262, Vol. 105, no 5, 1549-1562 p.Article in journal (Refereed) Published
Over the last two decades, the flowing fluid electric conductivity (FFEC) logging method has been applied in boreholes in the well-testing mode to evaluate the transmissivity, hydraulic head, and formation water electrical conductivity as a function of depth with a resolution of about 10–20 cm. FFEC profiles along the borehole are obtained under both shut-in and pumping conditions in a logging procedure that lasts only 3 or 4 days. A method for analyzing these FFEC logs has been developed and successfully employed to obtain formation parameters in a number of field studies. The present paper concerns the analysis of a unique set of FFEC logs that were taken from a deep borehole reaching down to 2.5 km at Outokumpu, Finland, over a 6-year time period. The borehole intersects paleoproterozoic metasedimentary, granitoid, and ophiolite- derived rocks. After the well was drilled, completed, and cleaned up, FFEC logs were obtained after 7, 433, 597, 948, and 2036 days. In analyzing these five profiles, we discovered the need to account for salinity diffusion from water in the formation to the borehole. Analysis results include the identification of 15 hydraulically conducting zones along the borehole, the calculation of flow rates associated with these 15 zones, as well as the estimation of the variation of formation water electrical conductivity as a function of depth. The calculated flow rates were used to obtain the tentative hydraulic conductivity values at these 15 depth levels.
Place, publisher, year, edition, pages
2016. Vol. 105, no 5, 1549-1562 p.
Flowing fluid electric conductivity logging, Long-term monitoring, Deep formation water electrical, Salinity diffusion, Outokumpu deep drill
IdentifiersURN: urn:nbn:se:uu:diva-293667DOI: 10.1007/s00531-015-1268-xISI: 000379025900015OAI: oai:DiVA.org:uu-293667DiVA: diva2:928132