CO_2-RELATED SEAL CAPACITY ENHANCEMENT IN MUDSTONES: EVIDENCE FROM THE PINE LODGE NATURAL CO_2 ACCUMULATION, OTWAY BASIN, AUSTRALIA

摘要

Understanding CO_2-related reactions in low permeability mudstones is necessary to determine seal effectiveness in CO_2 geological storage. The Pine Lodge Field contains natural CO_2 within the Belfast Mudstone, a seal for many gas accumulations throughout the Otway Basin, Australia. The Pine Lodge CO_2 accumulation occurs in fractured shale and interbedded siltstone/sandstone. This natural analogue for CO_2 storage provides evidence of seal modification by CO_2.rnPetrological examination of the Belfast Mudstone reveals substantial CO_2-seal rock interaction, with alteration of feldspar, clays, and volcanic fragments. Siderite has also precipitated within the mudstone proximal to natural fractures. The siderite δ~(13)C isotopes are consistent with a magmatically derived CO_2 source. Siderite has precipitated into all available pore space near the fracture edges and in sandier units. Infiltration of the CO_2 from the fractures into the rock and resulting precipitation of siderite is limited to relatively higher permeable zones. Seal capacity measurements combined with petrological evaluation show a correlation between seal capacity enhancement, siderite precipitation and original porosity/permeability of the rock.