Mobilisation of organic compounds from reservoir rocks through the injection of CO2 —Comparison of baseline characterization and laboratory experiments

Abstract

In the framework of CO2 storage activities, the aim of our investigations is mainly to evaluate the effects of supercritical CO2 (sc CO2) on the quantitative and qualitative extraction of organic compounds from reservoir rocks. Within the scope of the CO2 storage project CO2SINK the major task was to identify key mechanisms occurring in the reservoir as a result of the injection of CO2 into a saline aquifer. Here, it is of special interest what types and amounts of organic matter will be extracted and mobilized from the reservoir rocks in conjunction with the injection of sc CO2. Thus, our investigations may help to evaluate the efficiency and reliability of the long-term storage of CO2 in such a geological system. Here, we present compound-specific results from laboratory sc CO2-extraction experiments on reservoir rock samples from the CO2 storage site in Ketzin, Germany. Low molecular weight organic acids (LMWOA) as well as polar lipid fatty acids (PLFA) extracted by sc CO2 were analysed using ion chromatography and gas chromatography-mass spectrometry, respectively. Through the exposure to sc CO2 mainly formate and acetate, but also other LMWOA were released from the rock samples in varying amounts. PLFA profiles of sc CO2 extracts were dominated by saturated and unsaturated fatty acids with 16 and 18 carbon atoms of bacterial origin. The results of sc CO2 extraction are compared with the characterization of the organic inventory of pristine rock samples and fluid samples from observation wells of the Ketzin site to obtain information on quantitative and qualitative significance of the solvent potential of sc CO2.