This paper presents the development plan using EOR techniques for a sandstone reservoir containing very light oil (45 oAPI, 0.5 cP at reservoir conditions) located in Oman. Due to low permeability (0.1 to 5 mD) of the upper part of the reservoir (Upper Haushi Sand, UHS), recovery factor was very low. However, original oil in place is quite significant in this formation and EOR application was targeted to increase the recovery factor. On the other hand, reservoir pressure is still high due to strong aquifer support. Another zone of high permeability (100-300 mD, Sand Drain, SD) has been watered out by the strong aquifer influx. Being operated by a small size oil company, the main concern was the economics – capital and operating expenditures. After a screening process the optimum solution was found to be nitrogen injection to overcome the low injectivity. The low viscosity of oil and relatively low cost of injectant also make the injection of nitrogen a favorable application.

The response of the two formations (UHS and SD) to nitrogen injection was tested in laboratory by injecting nitrogen into oil saturated core samples. The recovery obtained by immiscible displacement of oil was as high as 40 % in the tight UHS. Similarly, tests were carried out to understand the response of nitrogen injection into already waterflooded high permeability SD zone. The recovery was found to be 5 to 10 % after 75 % waterflood recovery. Next, the nitrogen injection performance was studied using a full-scale field simulator. After obtaining a history match, the option of using abandoned downdip wells as injectors and the updip wells as producers were evaluated. Relative permeability curves generated using the laboratory tests were applied and different injection scenarios were tested through a series of simulation runs. Also, the possibilities of injecting air without purifying from the oxygen were discussed from the economical, technical, additional oil recovery and safety points of view.

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