Abstract

GDF SUEZ and Sonatrach will develop in partnership the main fields of the prolific Sbaa basin, SW Algeria. In this basin, the main gas levels comprise the Cambrian and Upper-Ordovician reservoirs, sealed and sourced by the Silurian "Hot Shales" Formation. Average CO2 content of raw gas is in excess with regard to sales gas specifications. As a result, CO2 removal is required as part of gas treatment and it is intended to install an amine unit in the future Central Processing Plant for such purpose. Regeneration of the amine results in the release of significant quantities of CO2, which amounts to ca 1200 t/day. Looking for a solution to re-inject underground this CO2 was decided, within the project exploitation perimeter. Such an initiative has materialized with the achievement of a screening and feasibility study during the development conceptual phase, which identified the two best structures for underground CO2 sequestration. In both cases, CO2 should be re-injected in the aquifer, in the water leg, away from gas production area. A pilot well will be drilled to address the geological and reservoir uncertainties, so as to validate the concept.

For now, preparatory sensitivity studies, using Cougar® software (developed and marketed by IFP) were performed to identify key parameters controlling the CO2 re-injection performance. These probabilistic results show that, if effective permeability and reservoir heterogeneity are from far the main drivers, the mobility of fluid in place, such as gas or formation water, strongly controls the performance, ranging from 55 to 98 % of CO2 to be injected. Based on experimental design type of approach, this study enable to rank the main uncertain parameters (such as type of wells, number of injectors and maximum operating pressure) and to quantify their respective contribution to the underground CO2 storage performance.

This type of study helps to determine the priority in the data acquisition program of the future pilot well and to set-up the basis of design of the CO2 sequestration facility.

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