Abatement of greenhouse effect, enhanced oil and gas recovery, and energized fluid fracturing technologies require thorough studies on acid gas impact on geologic formations. This contribution based on laboratory experiments coupled with hydrogeochemical models, considering the impact of CO2 and H2S and their mixtures on rocks representative for the Upper Silesian Coal Basin (USCB). In our study, by means of SEM and EDX analyses, we identified significant changes in structure and composition of rock samples influenced by acid gas in autoclave experiments. Dissolution of skeletal grains was the most distinct in carbonates and chlorite, and led to porosity increase. Experimental results were used in modeling, which allowed for geochemical reactions identification, assessment of the volume of secondary minerals, and amounts of gases sequestered in 10 000 years of simulated storage. The maximum calculated mineral-trapping capacity, for the mudstone of the USCB paralic series, reached 28.2 kg CO2/m3 for CO2 injection. The Dębowiec Formation rocks were characterized by high capacity for H2S sequestration amounting to 15.5 kg H2S/m3. Results of modeling demonstrated, that in the case of geological storage of H2S, a release of significant amounts of CO2, from dissolution of primary carbonates, should be expected.