The hydraulic communication among 16 offshore fields located in North Africa has been investigated by means of a 3D regional dynamic model, the first ever developed for this region by Eni.
Since 1976, the area has been drilled with more than 150 wells and field pressures were found to be supported by a unique aquifer. Among these fields, two giant structures have already been put in production, the Alpha structure in 1988 and the Beta structure in 2005, whilst other minor accumulations have not yet been exploited.
Starting from a detailed field data analysis, a common pressure trend in the aquifer zone was recognized, while for each mineralized structure different hydrocarbon contacts were identified. Moreover, appraisal wells drilled in the undeveloped fields, after the production start-up of the first producing reservoir, clearly showed that depletion was occurring also in the virgin structures, thus confirming the presence of hydraulic communication.
A 90×90 km2 model is therefore developed in order to describe the overall fluids behaviour inside the region by taking into account 16 different mineralized culminations and the water bearing areas among them. Despite the complexity of the work, the model is developed and tested to be robust and to provide key information useful for determining the best possible exploitation strategies.
Exploitation of oil & gas resources is strictly related to pressure regime in a reservoir. In particular, considering reservoirs with the same petrophysical characteristics, more the reservoir is depleted, more challenging is the exploitation of hydrocarbons. The application of IOR techniques or the presence of natural aquifers support, if any, may reduce the pressure drop. The size of these pressure-supporting aquifers and their strength can vary considerably worldwide and unique regional aquifers can simultaneously affect multiple reservoirs.
Very few examples in literature are present [1, 2, 3] regarding the analyses of the impact of regional aquifer support on producing reservoirs and nearby accumulations.
A regional 3D dynamic model was built by Eni to simulate the behaviour of undeveloped fields communicating with producing pools by a unique aquifer; this model allows to optimise the development plan and to mitigate the associated risk.