Modelling and Early Monitoring of Miscible Gas Injection in the Tight El Gassi Field, Algeria

Abstract

Abstract The El Gassi field is a Cambrian age sandstone oil field, located in central Algeria. The field lies approximately 100km south of the giant Hassi Messaoud field and shares many characteristics with its larger cousin. Production from El Gassi began in 1959 and has continued in depletion mode up to 2004. In 2000 a joint venture between Amerada Hess and Sonatrach, SonaHess, took over operatorship of the field. Because of the low permeability and adverse mineralogy for water injection, secondary miscible hydrocarbon gas injection was planned in El Gassi. Early gas injection (EGI) began in 2004 and an extensive data collection program has been conducted. Between 2001 and 2004, an extensive integrated reservoir study was undertaken, with a view to predicting the likely increase in reserves from miscible gas injection. The study integrated Geophysics, Geology, Petrophysics, Production and Reservoir Engineering and lead to the development of a detailed Full Field simulation model. This paper presents the main findings from the integrated study, with emphasis on the development and predictions arising from the resulting reservoir simulation model. Results from the ongoing monitoring of EGI indicates a positive response to gas injection. Field data are also presented and compared to the simulation results.