Drilling boreholes in sulphureous groundwater areas: elements of some case studies in Portugal

Abstract

In Portugal there is a special market niche, which is the medical spa sector. These are supplied by special groundwater, being the sulphureous type water, the most frequent water in this activity. These waters essentially have a long geohydraulic circuit, associated to granite massifs, in confined to semi-confined aquifer systems of the fissural type, and natural discharge sites are often associated with structurally very complex areas, with faults sometimes of great thickness, that lead to sudden variations, from very fresh rock to clay. However, this situation is very favourable to unexpected collapses of the borehole under construction, with terrible problems to overcome, sometimes leading to involuntary deviations in the spatial position of the drilling in progress. On the other hand, because one of the current solutions is the use of cementations, associated with re-drilling, there is also the problem, of the difficulties of cement grouts in a common situation, not gaining strength, due to the chemical composition of sulphureous groundwater. It should be noted that these aquifer systems have the potential to provide natural hot water, when the boreholes reach great depths and can leverage geothermal uses, at the same time as uses in medical spas. Therefore, it is necessary to know these aquifer systems well, to lead to more efficient projects in the future. Therefore, in that sense, after presenting the typical chemical composition of the sulphureous groundwaters understudy, the experiences acquired in the drilling of some boreholes in Portugal, namely in the Carvalhal Medical Spa, Longroiva Medical Spa, Águas do Graben, Unhais da Serra Medical Spa, and the new mineral water of Granjal (Santa Comba Dão), are briefly presented. The comparison of the objectives defined at the beginning with the results obtained is generically presented, namely the depth of drilling, giving emphasis to the problems of collapse of the walls of the boreholes, cementing, additives, among others. At last, some final notes are presented in the sense that the drillings in this type of hydrogeological systems, in the future come to be increasingly efficient and reach greater depth, not only to acquire water with quality freer of interferences with fluids of superficial aquifers, but also, in the sense of reaching temperatures that make the use of geothermal energy viable.