3D architecture of the Aquistore reservoir: Implications for CO2 flow and storage capacity

Abstract

Quantitative assessment of the Aquistore CO2 storage reservoir has been conducted using a 30 km2 3D seismic volume and a suite of well logs. 3D porosity was calculated using acoustic impedance from model-based seismic inversion and a log-based porosity-impedance relation. The reservoir has a mean thickness of 219 m ±ơ = 3% comprising 51% of pay. Strata dip at ∼1.75% SSE and include a prominent SSE-NNW structural fabric dominated by a ridge that corresponds to a Precambrian basement fault and overlying flexure. Porosity maps for Black Island and Deadwood reservoir zones show mean interval porosities of 0.071 ± ơ = 18% and 0.075 ± ơ = 9%, respectively with a weak degree of directionality that is sub-parallel to the strong NNW-SSE structural trends. Lateral spread of injected CO2 will be strongly affected by the NNW-trending structural relief and bulk porosity/permeability trends. Local topographic channels may control CO2 flow particularly when injection rates are low and local closed topographic structures may constitute traps for CO2. CO2 static capacity estimates from well-based mean values are less than comparable seismic-based estimates by <15% due to porosity differences and <5% due to thickness differences. Variations in the Deadwood thickness of up to 25 m from the mean value would have resulted in capacity estimate differences of up to 25% if an alternate well location had been chosen.