The New Well to Obtain Hot Water and the Drilling Problems in Very Fractured Granitic Massif in Unhais da Serra Spa - Portugal

Abstract

A study is presented in this paper with the objective to drill a geothermal well with a depth of 1000 m to be applied in urban spaces, bathing waters, and at Unhais da Serra Medical Spa in Portugal. Drilling took three years to complete and was not completely successful in terms of the initial goals due to some very peculiar geologic and structural characteristics of the drilling site. The many occurrences of alternate semi-vertical fractures with resistant granite reaching great depths were especially abnormal.
Several aspects of the construction of this drilling, the techniques applied to this perforation, lithological classification, drilling speed, material recovery, rock quality (RQD), and the explanation of the events that led up to the decision of drilling are presented in this article. Negative geological characteristics led to frequent collapsing of the perforation walls, necessitating frequent injections with cement to stabilize them. The techniques of deviation are also discussed. Finally, the production capacity of the new well producing mineral water at 38ºC and considerations about the energetic potential of this resource are presented.