Quantifying Chemomechanical Reservoir Sensitivity to CO2 Injection Using Paragenesis, Flow-Through Experiments, and Strength Testing at In Situ Conditions, Farnsworth Unit, Texas

Abstract:

The impact of spatially-distributed chemomechanical weakening within CO₂-storage reservoirs composed of different flow units is poorly understood due to complex flow patterns, diagenetic variation among units, and dissolution and mechanical changes in susceptible units. To quantify controls on chemomechanical sensitivity, we use paragenesis and burial history combined with high pore volume flow-through experiments on chlorite- (Chl1-3) and kaolinite-cemented (Kao1-3) lithofacies of Morrow B sandstone, an active WAG and CO₂-EOR field in Farnsworth Unit, Texas. We flowed CO₂-rich and pure reservoir water through experimental cores at in situ conditions of 71°C, 290 bar pore fluid pressure, and 345 bar confining pressure. We will also present indirect tensile strength variations along tested and undamaged plugs.

Petrography reveals chlorite and kaolinite cements have rimming and pore-filling textures, and all cores contained additional disseminated ankerite cement. One kaolinite core is cemented mostly by poikilotopic calcite and disseminated siderite. Paragenesis confirms carbonate cements predate compaction, while chlorite and kaolinite cements postdate compaction, controlling their ability to support framework grains. Post-test petrography is used to understand the spatial and mineralogical patterns of dissolution.

Compared to control tests and initial fluid chemistry, downstream samples had elevated calcium, magnesium, and iron concentrations, indicating dissolution of ankerite. During dissolution, porosity increased between 0.33% to 1.26%; control samples showed changes on the order of <0.1%. However, porosity decreased 0.17% for sample Kao1. All reacted samples showed 1 to 5 mD permeability increases except Kao1 which showed no change; control samples decreased by about 1.5 mD. µXRCT data quantifies dissolution of phases and changes in the connected pore structure for six pre-post sample pairs scanned at 27 µm, with 11 µm resolution near the inlet. Post-flow ultrasonic tests show an 11% increase in P- and S- wave velocities in Chl1 and 1 to 4% change in all other reacted samples. Ultrasonic and indirect tensile strength results quantify the mechanical impact and lack-thereof of dissolution in both lithofacies. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.