Enhancing oil recovery by nitrogen injection in well group of Tahe Oilfield

Over years of development, the carbonate fracture-cavity reservoirs in the Tahe Oilfield suffered bottom water coning,making the waterflooding effect become gradually poor, and the remaining oil is mainly enriched in the form of attic oil. For the purpose of improving the reservoir development effect, a pilot test of nitrogen injection in well group was conducted in the multiwell fracturecavity unit A of the Tahe Oilfield in 2014. The response of offset wells gradually appeared. As to August 2015, 3×104 t incremental oil had been obtained, showing that the nitrogen injection in well group can effectively displace the interwell attic oil. The pilot test results show that the well group of injection in high permeability layer and production from low permeability layer is characterized by high gas injection rate, slow response and large swept volume, whereas the well group of injection in low permeability layer and production from high permeability layer is characterized by fast response but easy gas breakthrough. The oil recovery technology of nitrogen injection in well group is an effective technique for enhancing the oil recovery.