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    STUDIA GEOLOGIA - Issue no. 3 / 2003  
         
  Article:   LOW MAGNITUDES OF MATRIX STRESS RELATED TO AQUATHERMAL EFFECT AND MONTMORILLONITE DEHYDRATION IN THE CĂLDĂRUŞANI-TULNICI GEODYNAMIC POLYGON, ROMANIA.

Authors:  DOREL ZUGRĂVESCU, GABRIELA POLONIC, VICTOR NEGOIŢĂ. 		 
       
         
  Abstract:  On the basis of various physical measurements carried out in very deep wells, a method for determining the subsurface stress magnitudes was elaborated by the Geodynamic Institute of the Romanian Academy. Using such a methodology a stress study was undertaken within the Căldăruşani-Tulnici Geodynamic Polygon (depth interval 5-7 km) whose results were discussed on the occasion of the International Geophysical Conference (April 2000, Bucharest-Romania). The significance of the stress magnitude variations within the polygon areal was also presented on the occasion of the International Geological Correlation Program IGCP-430 Workshop (June 2000, Covasna-Romania). The conclusions of this work focus on the Oligocene deposits units from the western part of the polygon, in which the grain-to-grain stress (matrix stress) decreases drastically. As a cause of registered low stress values, an other essential information was specified in the above mentioned work, stating that "the thick pre-Sarmatian detritic sedimentary sequence (mainly shales with local evaporites) was rapidly and deeply buried to more than 8 km, giving rise, in sealing circumstances, to very large overpressures within the filling fluids of the rock pores. All these overpressured geological formations, located along the western limit of the geodynamic polygon have been studied in our institute. We found, as a rule, geopressures as much as 30-50 MPa above the normal hydrostatic pressures. The geological formations are also characterized by shale undercompaction and pore space waters less saline compared with their surroundings. ...  
         
     
         
         
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