Slimhole Drilling Techniques For Deep Groundwater Exploration- A Review

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Journal Article: Slimhole Drilling Techniques For Deep Groundwater Exploration- A Review

The aim of this study is to present the slimhole drilling technology and to evaluate its feasibility for the exploration of geothermal resources. There is no univocal definition of the term slimhole, but it concerns any borehole whose diameter of the production zone is notably smaller than the one in a conventional production well. This study is based on a bibliographical review, during which six data bases were interrogated. The following slimhole techniques can be used: continuous coring, rotary, mud motors with coiled tubing, downhole hammer and reverse circulation (hammer and rotary bit). In the fields of ore and oil exploration, all the slimhole methods have been used so far. For geothermal prospection, Japan and the USA are the countries where the slimhole technique has been mostly practiced. All geological environments and rock types have been drilled by slimholes, while there is no depth limit for geothermal slimholes: coreholes can indeed reach 3000 to 4000 m, or even 6000 m in extreme cases. The first and main interest of the slimhole drilling is economic: all the comparisons carried out between the conventional borehole and the slimhole favour the latter one. Usually, the lower cost of a slimhole results from a global reduction on all the drilling activities. Moreover, the environmental impact of a slimhole is also strongly reduced. Each of the slimhole techniques is characterized by a series of advantages and drawbacks, but the major problems have been progressively solved, in particular the average penetration rate, which can presently reach the one obtained by large diameter conventional rotary boreholes. The main question to be answered is how the exploration slimhole may be changed into a production well, in case an aquifer has been discovered. Experiments have shown that for a discharge of 60 m(3)/h, a diameter in the production zone between 89 and 127 mm (3 1/2" and 5") is adequate. A cost analysis indicates that the slimhole technique allows savings of 25 to 50%, sometimes more, according to the drilling site and method, the number and depth of the wells.

F. D. Vuataz

Published Journal 
Eclogae Geologicae Helvetiae, 1997

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F. D. Vuataz. 1997. Slimhole Drilling Techniques For Deep Groundwater Exploration- A Review. Eclogae Geologicae Helvetiae. (!) .