--> Using Ultrasensitive Surface Detection to Evaluate Potential and Actual CO2 Sequestration Sites

AAPG ACE 2018

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Using Ultrasensitive Surface Detection to Evaluate Potential and Actual CO2 Sequestration Sites

Abstract

A primary mode of Carbon Capture and Sequestration (CCS) is geologic sequestration in which carbon dioxide (CO2) is injected into underground geologic sinks. Critical to the success of geologic sequestration is the need to ensure that underground storage sinks have adequate seal and do not leak to pose a potential threat to human health and the environment.

However, the ability to determine if these subsurface structures have adequate seal prior to CO2 injection and that those seals remain leak-proof is difficult since there are not many CO2 monitoring technologies available to provide adequate sensitivity and coverage for underground sequestration. However, ultrasensitive passive geochemical sorbers at the surface can provide the ability to monitor coinjected chemical tracers at nanogram mass levels (10-9 grams), thereby assessing the effectiveness of containment.

This case study took place in the Yibal field located within the Fahud Salt Basin in northwestern Oman. The purpose of the survey was to ground-truth the ability of high sensitivity surface geochemical imaging to map elevated hydrocarbon compound response along faults, as a proxy for CO2 tracers, and thus to identify segments of potential fault leakage from the Natih A reservoir.

Ultrasensitive samples were deployed at the surface over structural closures at depth (i.e. depleted petroleum reservoirs) to monitor indications of natural leakage pathways. After deployment, collection, and analysis, hydrocarbon signatures were detected and differentiated along fault trends. Enhanced light hydrocarbon signatures were mapped along coherent segments of fault projections inferring reservoir leakage along specific fault traces. The surface geochemical survey was able to detect subsurface leakage at parts per billion (ppb) levels.

In other projects involving this survey technique, fluorinated hydrocarbon tracers have been mixed with CO2 and injected into structural closures, with geochemical data used to establish baseline leakage profiles for long term monitoring efforts. This work took place on three continents, as recently as 2015, and has shown that ultrasensitive passive geochemical sorbers can be used in CCS monitoring programs.