Experimental and numerical evaluation of the feasibility of nitrogen injection into a mature layered light-oil reservoir

This paper investiges the feasibility of nitrogen injection into a layered sand-stone reservoir containing very light oil (45°API, 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), the recovery factor of the primary production was very low despite high original oil in place. An enhanced oil recovery application was targeted to increase the recovery factor. Another zone of high permeability (100-300 mD, Sand Drain, SD) was watered out by strong aquifer influx. The response of the two formations (UHS and SD) to nitrogen injection, as a secondary and tertiary recovery method, respectively, was tested in the 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 the already water-flooded high permeability SD zone. The recovery was found to be 5 to 10% after 70-75% waterflood recovery. Next, the nitrogen injection performance was studied using a full-scale field simulator. After obtaining a history match, the option of using an abandoned down-dip well as an injector and the up-dip 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.