Restudy of Main Factors of Effects on ASP Flood and Expansion of Capillary Theory in Heterogeneous Reservoirs

Abstract

Abstract The demonstration projects of ASP flooding have been implemented in Daqing oil field. With the enlarging of the scope of testing areas, the effects of the scale production resulted from high concentration of alkali (1.2%wt) have been gradually exposed. It resulted in many questions, such as the increase of the resistance of formation's percolation, the decrease of production and the blocking of pumps. All these have become the severe obstructer of the application of ASP flooding. As to the formation conditions in Daqing oil field, the effects of alkali concentrations on the curling degree of polymer molecules in ASP solution have been studied by using Nanoscope IIIa type AFM in Digital Instruments Company in America. The results show that the chains of polymer molecules spread in liquid phase without alkali, but the chains curl for adding alkali. In the condition of high concentration alkali, the curled chains of polymer molecules are very tight. The polymer molecules do not spread fully, and exist in the state of assembling of many molecules on their sides. Correspondingly, the rheological characteristic of ASP solutions has been studied by using HAAKA apparatus for analyzing rheology. Moreover, the physical simulations of ASP flooding on three-dimensional heterogeneous models and filling sand tubes have been performed. The results show that the ASP solution with a low alkali's concentration and a higher viscoelasticity can get a very high oil recovery by enlarging sweep efficiency and unit displacement efficiency. To heterogeneous reservoir, the viscoelasticity of ASP solution plays a more important role than the ultra low interfacial tension. Else, since the effective distance of action of the surfactant over 60% of ASP cost is very limited in formations, the ultra low interfacial tension is difficult to bring a benefit which it should does. Through a lot of calculations, the revised correlation of capillary number has also been presented in this paper. Finally, through analyzing of the effect of the demonstration project in west of Xing-2 area, the significance of the viscoelasticity has been verified again from the field tests. The feasibility of ASP flooding with low alkali has been determined further, and a new method has been studied for solving alkali scale in ASP flooding in this paper.