Abstract. Experiments have been conducted to investigate the effect of melt on the creep behavior of polycrystalline ice deformed in the dislocation creep regime. The transition between a mode with a stress exponent n = 3 and a mode with n < 2 is observed for both melt-free and melt-added ice samples. The large influence of the melt phase is not related to the wetting characteristics of the liquid. Owing to the large plastic anisotropy of the ice crystal, the liquid phase would attenuate the internal stress field which develops during the primary creep. The contribution to the deformation of the basal slip (the weaker slip system) would increase with the melt content.
Reasons for injectivity decline were investigated in a low-enthalpy geothermal aquifer in Klaipeda (Lithuania). It is one of the study sites within the DESTRESS project, which demonstrates different stimulation techniques in geothermal reservoirs. Due to low injectivity, production rates from the Lithuanian field are currently reduced, which lead to negative commercial implications for the site. Productivity from the same wells is measured to be 40 times higher. Injectivity decline in aquifers is often related to clogging processes in spatially correlated highly permeable structures, which control the main flow volume. We subdivided clogging processes into (1) physical, (2) chemical, and (3) biological processes and studied them by analyzing fluid and solid samples as well as operational data. The methods we used are fluid and solid analyses in situ, in the laboratory and in experimental setups, statistical interpretation, and numerical modeling. Our results show that the spatially correlating nature of permeable structures is responsible for exponentially decreasing injectivity because few highly permeable zones clog rapidly by intruded particles. In particular, field operations cause changes of the physical, chemical, and biological processes in the aquifer. Mineral precipitation and corrosion are the main chemical processes observed at our site. Microbial activity causes biofilm while fines migration is caused by changes in physical boundary conditions. Moreover, these processes can affect each other and generate further reactions, for example, microbial activity triggers corrosion in surface pipelines.
This study addresses the thermal-hydraulic-mechanical and chemical (THMC) behaviour of a research well doublet consisting of the injection well E GrSk 3/90 and the production well Gt GrSk 4/05 A(2) in the deep geothermal reservoir of Groß Schönebeck (north of Berlin, Germany). The reservoir is located between 3815 and 4247 m below sea level in the Lower Permian of the North German Basin (NGB). Both wells were hydraulically stimulated to enhance productivity. For the production well three stimulation treatments were performed in 2007: these three treatments result in a productivity increase from 2.4 m 3 /(hMPa) to
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