Most of the high permeability reservoirs in Daqing Oilfield have been conducted by water flooding and polymer flooding. The average recovery percentage of OOIP has reached to 52.6% 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 remaining 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 of foam and 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 foam formulation, ASP formulation and hybrid of foam/ASP flooding for Daqing reservoirs have been performed after polymer flooding. Several key parameters of the hybrid systems of foam/ASP flooding that influences on oil recovery efficiency were investigated and optimized. Further EOR effect of the hybrid flooding on core flood was evaluated.
The main factors that influences on oil recovery efficiency by a hybrid of foam/ASP flooding were described as below. Firstly, the properties of foam formulation and slug sizes were the key factors to ensure high performance of recovery. The foam formulation was optimized with good performances of foamability and stability. Secondly, the properties of ASP formulations and slug sizes also play important roles in EOR efficiency. The ASP formulations were optimized with ultralow interfacial tension. Concentration of chemicals and slug sizes were the main factors for oil displacement efficiency. Thirdly, a hybrid of foam and ASP flooding was optimized at the reservoirs condition. EOR effect of the hybrid flooding was studied upon three-layer positive rhythm sandpack cores flooding tests. The results indicated that hybrid flooding contributed 17%-20% of OOIP recovery as the recovery background was already 53% after polymer flooding.
The foam flooding could block preferential flow path of high permeability layer in heterogeneous reservoirs. On the other hand, ASP flooding also had higher oil displacement efficiency for the relatively low permeability layer. The hybrid of foam/ASP flooding might become a promise alternative further EOR method for Daqing reservoirs after polymer flooding.