Prevention of gas migration in the area of the Carpathian Foothills in the laboratory tests

In the area of the Carpathian Foothills, gas exhalations are a frequently observed phenomenon. It is connected with the presence of many shallow gas horizons in the autochthonous Miocene. In addition, gas migration effect is intensified due to the complicated geological structure in this region. During drilling boreholes, one of the most important requirements is to ensure adequate tightness in the annular space. In connection with the above, laboratory tests were carried out in the Oil and Gas Institute - National Research Institute, whose aim was to assess the impact of applied drilling fluids on the degree of sealing the annular space on the contact hardened cement slurry - rock formation, for specific geological and technical conditions. The result of the conducted research work was a modification of the composition of washing fluids in terms of improving the efficiency of their impact on the wall of borehole and removal of mudcake formed by the drilling muds, as well as modification of cement slurry formulations by application appropriate additives to prevent gas migration. During research work have been indicated potential causes of gas migration from the annular space in the selected holes drilled in the Carpathian Foothills and preventive actions aimed at reduction gas migration and exhalation.