Characterization of stray gas through geologically realistic sedimentary structures using light transmission techniques

ABSTRACT: Public demand for renewable energy and cleaner alternatives to heavily refined crude oil and coal has resulted in an increase in natural gas production. Producing and decommissioned natural gas wells can leak, which can result in stray gas migration. Stray gas migration (gas flow outside of a well casing) can degrade the quality of groundwater resources. There have been few laboratory investigations into stray gas migration despite the associated risks and prevalence of natural gas extraction in Canada. Those that have been conducted have used homogeneous or simplified heterogeneous permeability configurations. More comprehensive characterization of stray gas migration and mass transport through geologically realistic structures is needed to aid in future modelling and monitoring efforts. This study aimed to quantify stray gas migration and mass transfer throughout different geologically realistic sedimentary structures compared to homogeneous controls. Geologically realistic herringbone cross beds and homogeneous controls were deposited into a transparent 2D experimental flow cell (39.6 cm x 40 cm x 1.2 cm) using a modified 3D printer and two unique homogenized combinations of sand. After deposition and saturation, methane gas was injected through a needle in a bottom port of the flow cell at 10 ml/min until gas breakthrough at the top of the cell. After gas emplacement, water was pumped through the side ports, and integrated effluent samples were collected to develop dissolved methane breakthrough curves. A modified light transmission method was used to quantify local gas saturations at a high spatiotemporal resolution throughout each experiment. Preliminary results show more gas pooling and longer dissolution times in the heterogeneous deposits compared to homogeneous, as well as gas persistence due to the partitioning of background dissolved gases after all of the methane was dissolved. Results relating sedimentary structures to trapped gas architecture and mass transfer will also be discussed.