Determining reservoir connectivity using noble gases
Item statusRestricted Access
Embargo end date30/11/2022
Scott, James Alexander
Understanding the connectivity of fluids within a hydrocarbon reservoir is critical to the viability and effective exploitation of the hydrocarbons present. Establishing reservoir connectivity using the limited datasets available during the exploration stage of a discovery is challenging. Whilst numerous tools currently exist to determine static connectivity and fluid organisation post-hydrocarbon emplacement, it is extremely difficult to determine the connectivity between fluids in different phases. Conventional connectivity studies undertaken on the Tormore field, West of Shetland Basin, UK have resolved the vertical connectivity of one oil well but have been unable to resolve any further vertical connectivity of the gas wells or the lateral connectivity of the field. The inert nature of noble gases makes them ideal tracers as they do not react with or degrade within hydrocarbon reservoirs in the same manner as organic tracers can. In addition, whilst noble gases are primarily present in the gas phase, they exhibit predictable partitioning behaviour making them ideal for assessing reservoir connectivity in both the gas and liquid phase. This research investigatesthe role of noble gases in resolving vertical and lateral reservoir connectivity and post-emplacement fluid organisation. The connectivity of hydrocarbon fluids of the Tormore field is assessed using two approaches; static and dynamic. The static approach for assessing connectivity follows the same logic as many conventional industry tools. Given time, a well-connected reservoir will reach a steady-state equilibrium with a predictable distribution of noble gases in segregated fluid column across a reservoir. Hence, a disconnected reservoir unit will have a distinctive set of isotopic abundances and ratios due to their isolation. This novel noble gas approach independently verifiesthe results of established conventional connectivity methods and further identifies a previously unknown connection between two different fluid phases separated by a poorly constrained fault. This approach also provides strong evidence for disconnection between two different reservoir compartments. The main limitation for assessing connectivity using a static approach is the lack of ability to confirm that a connection exists. To address this knowledge gap, a more dynamic approach using a numerical simulation is investigated. The aim of this numerical approach is to recreate the major controls of the distribution of noble gases across the field, from which the lateral connectivity can be resolved. The results of this modelling demonstrate that the distribution of noble gases in the Tormore field is controlled by diffusion, proving a lateral connection between the oil and gas phase. Hence, the novel noble gas connectivity models developed in this work provides a new method that compliments existing hydrocarbon exploration workflows. This new noble gas tool provides a robust means to assess reservoir connectivity to constrain the connectivity between oil and gas phases, where these methods can be applied in the appraisal phase of a hydrocarbon field.