An in-situ biosampling device for separating reservoir-associated from wellbore-specific microbial signals in underground gas reservoirs

Conventional microbiological sampling of underground gas reservoirs commonly relies on sump water, which may integrate wellbore-specific signals. As part of Carbon Cycle Economy Demonstration project, we developed a low-cost in-situ biosampling device for separating wellbore-specific from reservoir-associated microbial community signals under reservoir-relevant conditions. The device containing representative rock fragments was deployed for 138 days in the reservoir well above sump and was episodically seeded with fresh reservoir fluids. While sump water sample was enriched with Methanosarcina , a legacy signal of earlier methanol ingress, biosampling device fractions were practically free of it. Notably, the hydrated rock fraction hosted a microbial community almost identical to the pre-disturbance baseline observed four years earlier, whereas non-saturated rock and chamber water reflect more transient, planktonic assemblages. We conclude that rock-associated sampling provides a complementary observational window by decoupling wellbore-specific legacy effects from reservoir-associated microbial structure, advancing subsurface microbial monitoring for underground energy storage technologies. • A low-cost in situ biosampling device enables rock-associated microbiome sampling in underground gas reservoirs. • Rock-associated communities differed systematically from sump water after methanol ingress. • Microbial signal of hydrated rock fraction of the device was almost identical to pre-disturbance baseline signal. • The device decoupled reservoir-associated microbial signals from well-specific Methanosarcina enrichment. • Device advances subsurface microbial sampling by interrogating rock-associated communities in underground gas reservoirs.