Abstract

Most of the high permeability reservoirs in Daqing Oilfield have been conducted by water flooding and polymer flooding. 507 million tons geological reserves have entered post-polymer flooding stage. The average recoverable oil recovery has reached to 53.2% after polymer flooding. Currently, the further development of such reservoir has become a big challenge due to both of serious heterogeneity of reservoir and highly dispersed residual oil. The reservoir development has entered into quaternary recovery stage. Most of conventional enhanced oil recovery (EOR) techniques could not achieve the desired effects. A hybrid flooding combine movable gel (MG) with alkali-surfactant-polymer (ASP) flooding, as a candidate further EOR technique integrating both properties of mobility control and oil displacement has been proposed for Daqing reservoir after polymer flooding.

In this study, systematic laboratory experiments on MG formulation, ASP formulation and hybrid of MG/ASP flooding for Daqing reservoirs after polymer flooding have been performed. Several important parameters of the hybrid systems of MG/ASP flooding were investigated and optimized based on formulation selection and core flooding experiments. Further EOR effect of the hybrid flooding on core flooding was evaluated.

The main factors that influences on oil recovery by a hybrid of MG/ASP flooding were described as follows. Firstly, the properties of MG and slug sizes were the key factors to improve the mobility ratio. The MG formulas were optimized with good performance of gel property and indepth profile control property of displacement fluid. Secondly, the properties of ASP formulations and slug sizes play the important roles in oil displacement efficiency. The ASP formulations were developed with ultralow interfacial tension between crude oil and ASP solution. Concentration of chemicals and slug sizes were optimized for high EOR efficiency. Thirdly, a hybrid of MG/ASP flooding was optimized at the reservoirs condition. EOR effect of the hybrid flooding was studied upon three-layer positive rhythm sandpack core flooding experiments. Results indicated that hybrid flooding could contribute to incremental oil recovery of 14.7%-18% (OOIP) even if the recovery after polymer flooding was nearly 53%.

The MG could block preferential flow path of high permeability layer in heterogeneous reservoirs, and avoid the fluid channeling during oil displacement process. On the other hand, ASP flooding also had higher oil displacement efficiency for the relatively low permeability layer. The hybrid of MG/ASP flooding might become a promise alternative further EOR method for Daqing reservoirs after polymer flooding.

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