This paper reviews the rationale and first results of the gas injection pilot that was performed in 2014-2015 on a conventional offshore mature field. This field is a low permeability heterogeneous reservoir under water-flood with undersaturated viscous oil (21°API). The objective of the pilot was to check in a low-cost environment if injecting rich hydrocarbon gas in this oil would be beneficial for oil production.

Preparatory work included PVT experiments and SCAL data. The SCAL data allowed to estimate the gas/oil relative permeabilities for gas injection. The PVT work allowed to quantify the gas-oil interactions, especially swelling and deviscosification of the viscous oil. In the field, the pilot was planned and safely implemented in a low-cost environment, using the Huff and Puff approach: an existing producer was used as a gas injector using the gas-lift facilities, and after a 2 week soaking period, it was put back on production, and production data were closely monitored for each cycle.

Pressure and Temperature conditions imply that the injected HC gas is not miscible, but since the oil is strongly undersaturated, it was found that the beneficial effect of the gas injection was quite strong on oil properties (Bo and viscosity). Moreover, the richness of the gas allowed a condensing gas drive that is more efficient in terms of deviscosification than what could be achieved with a lean gas.

In terms of implementation in the field, a phased approach was adopted. The pilot was started in 2015 using the Huff and Puff technique, with Cycle 1 & 2 showing good results: a beneficial effect has clearly been seen on the liquid and oil rates at the producer when injected gas rate was sufficient, and could be history matched sucessfully.

A way forward is also proposed, as a further cycle 3 is currently planned early 2018, in order to derisk the mechanism for larger injected gas volumes, with a possible phase 2 to be planned later on.

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