A WAG injection project is foreseen in a North-African field, which was first brought on stream in 2004 with production coming from two separate hydrocarbon columns within the Upper and Middle TAG-I Triassic sandstone reservoirs. The crude oil is light (44°API) and develops multi-contact miscibility with its own solution gas. The current development strategy centers on gas injection as well as water injection for pressure maintenance. Recently, the maximum gas separation capacity was reached, and because the operator respects a zero-flaring policy, a key element of the development strategy involves active gas management which may influence a number of smaller satellite fields that also tie in to the same production facilities.
This paper describes efforts to further increase oil recovery in the considered field by means of miscible hydrocarbon gas injection implemented as a tapered WAG. We describe our monitoring plan which involves, among other things, systematic use of diagnostic plots to constrain and assist history matching of the field performance. Some gas breakthrough data indicate arrival of a methane bank ahead of the main gas front, which suggests that the multi-contact miscibility may not be entirely preserved due to dispersion effects. The pattern performance analysis is inspired by earlier gas injection projects and its main purpose is to enable the operator to benchmark patterns and make efficient use of the available injectant. Current gas utilization ratio is around 25–30 Mscf/stb for continuous gas flooding. It is estimated that full-field implementation of a tapered, miscible hydrocarbon WAG will lower the gas utilization ratio further and push the recovery factor towards 60%.