Identifying the risk of high-permeability zones in early field life: gas souring management in a Cretaceous carbonate barrier island reservoir, Miskar Field, offshore Tunisia

Robust upfront reservoir characterization is vitally important when problems arise later in the management of a field. In this case, thin high-permeability zones were mapped, even though no water injection was planned. This proved critical when, 10 years later, gas souring problems could be rapidly addressed. The Late Cretaceous R1 Inférieur reservoir comprises an upward-shallowing succession ( c. 60 m thick) of offshore to shoreface and foreshore carbonates, which passes conformably up-section into an anhydrite-bearing lagoonal–peritidal succession ( c. 13 m thick), the R1 Supérieur. H 2 S well monitoring confirmed the migration of H 2 S from the terrace sour gas area to the core sweet gas area of the field. High H 2 S concentrations are a safety hazard, and there are limitations on the concentration of H 2 S that the Miskar pipeline can handle. Understanding the distribution of high-permeability layers in the R1 reservoir is critical to identify preferential pathways for gas migration and resulting gas souring. Gas souring is controlled by a high-permeability layer formed by bioclastic rudstones deposited at the shoreface–foreshore interface. Identifying this thin interval in uncored wells and predicting its lateral continuity are essential to minimize the impact of gas souring on field development.