Handil field: Three years of lean-gas injection into waterflooded reservoirs

The giant Handil field comprises more than 500 hydrocarbon accumulations in structurally stacked and compartmentalized fluviodeltaic sands. Most of th e accumulations consist of a large column of saturated oil underlying a gas cap, trapped in reservoirs with good rock properties, and produced by wate r injection or strong natural waterdrive. In 1995 five reservoirs representing nearly one-fifth of the field's total original oil in place (OOIP)-and which had reached their final stage of wat erflood development (58% of the total oil in place had already been produce d)-were submitted to further development with lean-gas injection to increas e the ultimate oil recovery. To date, after 3 years of gas injection, the r ecovery factor for these five reservoirs has increased by 1.2% of the oil i nitially in place, and the project is considered both a technical and an ec onomic success. The predominant drive mechanism with lean-gas injection has been confirmed by field data. The previous decline of oil production has been stopped, and the oil rate is now stabilizing. The main monitoring challenge has been th e control of gas cycling for most of the producers, particularly during per iods of higher injection rates, to compensate for low injection periods imp osed by gas availability. The very close monitoring of well and reservoir performance, the numerical simulation, and material-balance studies have helped provide a better under standing of the mechanisms involved and have led to a revised and more effi cient policy to maximize oil production. The experience gained and the analysis of this 3-year-old project gives us the confidence to pursue the extension of the lean-gas injection developmen t to other Handil field reservoirs.