Evaluating Top Seals within a Sequence-Stratigraphic Framework: Impact on Geological Carbon Sequestration

Geological Carbon Sequestration (GCS) needs to increase in scale by a hundred to thousand-fold to achieve the climate targets set out by the 2015 Paris Agreement. As such, assessment of storage potential and containment risk is required across many types of subsurface opportunities (including depleted fields and saline aquifers). In particular, the assessment of containment risk can be a daunting task, as it requires rock property calibration of heterogeneous intervals that are usually poorly sampled. The sequence-stratigraphic method is applied here using two case studies to illustrate how it can be utilized to articulate containment potential and risk for storage of immiscible supercritical Carbon dioxide at basin-to-prospect scales. In the onshore case studies presented here, facies dominated by (detrital) clay-mineral aggregates provide the most consistent excellent seals capable of retaining in excess of 200 m Carbon dioxide plume heights. Perhaps contrary to held paradigms, more distal basinal facies tend to be more inconsistent seals, due to a dominance of biogenic depositional components and complex diagenetic alterations. In the case studies, thick successions of argillaceous mudstones are typically associated with transgressive to early-highstand retreating to aggrading muddy clinoform deposits. These cli-noform deposits can be shore (delta) attached or represent more distal offshore contourite mudbelts. In addition to the broad sequence-stratigraphic setting of appropriate lithofacies, the combination of basin type and sedi-ment delivery will govern the geometry and lateral extend of favourable top seal deposits. Continental-crust foreland basins may develop favourable accumulations across thousands of square kilometres, whereas failed basins tend to exhibit much narrower facies belts. Finally, while perhaps logistically challenged, continental slope to basin-floor post-rift sediments of passive margins connected to large river input systems provide broad and thick favourable mud facies belts over distributive reservoir deposits.

Automated summary

This study applies the sequence-stratigraphic method to assess the containment potential and risk of geological carbon sequestration. The findings suggest that clay-mineral aggregates provide the most consistent excellent seals, while more distal rock facies have lower containment capacity. The geometry and extent of favorable top seals are influenced by the basin type and sediment delivery.