Prior to any analysis of its chemical composition, porewater has to be extracted from the rock matrix, which is not trivial in the case of low-permeability rocks such as claystones or crystalline rocks. In order to compare different extraction techniques such as aqueous extraction or squeezing, and to understand what chemical and physical processes occur during extraction, various extraction methods are applied to samples with known porewater composition. Such samples need to be prepared in the laboratory.
