Foam flooding has been widely studied and implemented in recent years to alleviate reservoir heterogeneity and increase oil recovery. Previously, foam flooding was employed for conformance control and improving sweep efficiency, and little attention was paid to displacement efficiency. Thus, foam flooding usually had a poor ability to trip off oil film. Moreover, the effectiveness of many of the foam pilots lasted only a few months, and, in some cases, only a few weeks, which limited the long-term development of foam in field applications as the time to maximize effectiveness was too short. In this paper, a foam pilot selection, formulation design, and N2 foam pilot implementation are presented towards providing an effective method for transforming the development mode after water flooding in low-permeability reservoirs.

Two well groups (two injection wells and 17 production wells) were screened as candidates for the N2 foam pilot. Laboratory investigations included bulk foam screening, imbibition recovery, and natural core flooding tests. One formulation of eight tested (No. 6) showed excellent foam properties as well as a strong ability to strip oil from sand, and natural core scale work under reservoir conditions resulted in a total recovery of 66.92%, with an incremental recovery of 25.25% by N2 foam after water flooding.

The pilot was deployed using a new injection strategy of a surfactant alternating gas method in which surfactant was injected into water for 1 d at a normal injection rate followed by N2 injection for 1 d at a large injection rate. A positive response was observed after injection for approximately 1.5 months, daily oil production climbed sharply, and water cut also decreased after processing of 1% of pore volume with foam solution. Moreover, production was sustained for 18 months after foam injection, which resulted in approximately 4375 t of incremental oil. The foam pilot was successful in addressing the challenges associated with dominant channel and low displacement efficiency of water flooding in low permeability sand reservoirs.

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