The crystalline basement of Lithuania is composed of the high-gade 
metamorphic and igneous rocks of the Early Proterozoic age in some places 
intruded by Middle Proterosoic cratonic granitoids and associating mafic rocks. 
Two major lithotectonic domains are identified in Lithuania, i.e. the East 
Lithuanian Domain and West Lithuanian Granulite Domain. The latter is 
characterized by increased heat flow, in some places attaining 80-90 mW/m2. 
The concept of HDR can be a prospective alternative (to geothermal aquifers) 
option for exploitation of the geothermal energy in west Lithuania. The 
exploration of the HDR systems is rather difficult, as the basement is overlain by 
about 2 km thick sediments of the Baltic sedimentary basin. The base of the 
basin is composed of the Cambrian petroleum play, represented by the Lower 
Cambrian shaly source rocks and Middle Cambrian siliciclastic reservoir. It 
directly overlies the crystalline basement. A few hundred exploration wells were 
drilled in west Lithuania, most of them penetrating the basement rocks. Still, 
the drill cores are not sufficient to image the structural grain of the basement. A 
number of 3D oil exploration seismic experiments were performed in west 
Lithuania seeking to better understand the architecture of the oil fields hosted 
by the Middle Cambrian reservoir. The 3D seismic data of the Girkaliai oil field 
were provided by AB “Geonafta” for investigation of the possibility of application 
of seismic data for imaging the basement structures. These data are 
supplemented by drill cores from the four oil exploitation wells drilled into the 
basement for 10-350 m deep. Furthermore, the 3D seismic area also covers the 
Vydmantai geothermal area, where two deep wells were drilled to the 
basement more than dozen years ago for utilization of the Cambrian and 
basement geothermal resources. Due to economic perturbations the wells were 
conserved. One of them was drilled to the depth of 2560 m (450 m into the 
basement). Two large-scale shear zones were identified in the basement by 
drilling and seismics. Also, a number of the smaller scale tectonic features were 
recognized in the basement that well correlate with the borehole data. The 
quality of the seismic data enables consistent identification of the structural 
features down to the depths of 6-7 km where the temperatures reach 200-
250oC. The experiment shows that this complex can be applicable in the other 
areas of west Lithuania, where 3D seismic data are available.

Campus SIAF, SP del Monte Volterrano
Localita' Il Cipresso
Volterra, Italy