| Abstract |
Geothermal energy will play an increasingly important role in carbon dioxide emission-free energy production in the new millennium. High fluid production rates are essential for circulating geothermal systems to be economically viable. However the financial viability of the geothermal systems often suffers from a permeability decrease of clastic reservoirs, particularly in the vicinity of an injection well. Moreover, a number of projects that dealt with development of low enthalpy aquifers in Europe were abandoned because of the drastic drop of the aquifersà permeability during their exploitation. The decline of well injectivity is commonly caused by transport of clay particles, which are always present in sedimentary rocks. In spite of extensive research, internal clay and colloidal particle transport is still one of the issues that is poorly understood. Therefore development of reliable methods preventing clay plugging can significantly improve geothermal economics. In the paper we highlight the effect of the main physicochemical factors, such as salinity, type of exchangeable cations, pH and temperature, on the stability of clay particles in sandstone and their influence on the rock permeability. Through percolation experiments with Bentheim sandstone, combined with scanning electron microscope image analysis, we have found a strong correlation between the effect of the physico-chemical factors on the permeability and the parameters of the rock microstructure. The applied integrated approach that incorporates physical modeling, DLVO theory, and rock microstructure analysis, is a reliable tool for interpretation of the laboratory as well as field experiments. The formulated physico-chemical rules of clay particle stability and transport will help reservoir engineers to develop the best strategy for clastic reservoir exploitation and minimize the formation damage caused by clay migration. |