Chemicals loss and the effect on formation damage in reservoirs with ASP flooding enhanced oil recovery

Abstract

Alkali/surfactant/polymer (ASP) flooding technology has become an important approach for enhancing the oil recovery and improving the recoverable reserves. However, the issues of cost management for ASP chemicals loss in reservoirs and subsequent formation damage remain technical bottlenecks for promoting ASP flooding. A set of laboratory experiments was recently performed to investigate the chemical loss in sandstone formation during strong alkali (NaOH) ASP flooding. The loss law of alkali and surfactant in intermedium permeability type Ⅱ reservoirs is established, and the relationship between formation damage and chemicals loss is discussed. Then, the oil recovery improvement in heterogeneous reservoirs with ASP flooding is considered, and the role of ASP chemicals loss in formation during the EOR process is characterized. The losses of alkali and surfactant in type Ⅱ reservoirs are noticeable, and the loss behavior of surfactant is worse, exceeding a 90% loss rate, the formation damage is proportionately affected. The loss behavior intensifies with enhanced heterogeneity of the reservoir, and the loss in a heterogeneous reservoir with a mudstone interlayer is significantly greater due to the greater contribution of absorption and trapping in low-permeability layers. The corefloods show that the chemicals loss and formation damage in the same slug mode are much higher than those in a succession mode with the same injection volume, but an extra 4% of recovery efficiency can further be achieved by maximizing the synergistic effects of alkali, surfactant and polymer. This study is significant in that it further improves the displacement efficiency and reduces the chemicals cost in heterogeneous reservoirs with ASP flooding.