The Zeit Bay field reservoir units consist of sandstone and carbonates, partially overlaying a tilted block of fracture basement reservoir with a complex drive mechanism. A secondary recovery scheme of gas re-injection into the original gas cap was initiated to maintain reservoir energy and minimize pressure decline. Over 70 development wells are actively depleting the reservoir.
The original oil leg was 850 ft-TVT. However currently the oil leg varies from 150 to 250. With this limited oil leg different problem arise. The most serious problem was the increase in gas production that resulted in a decrease in gas injection to gas production ratio (GI/GP). The decrease in (GI/GP) ratio results in a significant drop in production increase in wells water cut and reduction in the field sweep efficiency. In addition this decrease will hinder the gas cap expansion, this has lead to activate the aquifer water breakthrough.
The gas sweep being preferred because it's low residual oil. As the oil leg gets smaller, the production strategy is adjusted to maintain the dynamic equilibrium and increasing the (GI/GP) to enhance gas expansion which slow down water rise in the reservoir, control water cut in the wells and minimize residual oil.
The paper represents a case study of applying the gas injection to reduce the field decline from 30 to 14%, controlling water production and improve reservoir sweep efficiency.