Study On The Complex Resistivity Model Of Water-Flooded Zone In Thick Oil Reservoirs During High Water Cut Stage

At present, most oil fields have entered the high water cut stage, the remaining oil exploitation in thick oil bed is our main direction for more recoverable reserves and higher recovery ratio. Complex resisivity log (CRL) is superior to conventional resistivity log and shows good potential application in watered-out formation interpretation because of the influence of formation water salinity on CRL being small. However, CRL has only been used in watered-out formation interpretation qualitatively, not been used in quantitative interpretation. In this paper, research on the ralations between the complex resistivity and saturation is based on the electric petrophysical experiment in the condition of the water flooding,polymer-flooding and alkali-surfactant-polymer flooding. Herein, an effective medium complex resistivity model for watered-out shaly sand formation has been proposed, based on experimental measurements on resistivity frequency dispersion of shaly sand samples, and symmetrical anisotropic effective medium conductance theory, and we adopt a hybrid algorithm with Newton and bisection met hods to solve the equation. By analyzing effects of some factors on the proposed model, we find that complex resistivity modules increase as frequency or clay content and clay conductivity increase. Validation with experimental measurements of watered-out shaly sand samples and log interpretation results for watered-out shaly sand reservoirs shows that the proposed model can be used in quantitative interpretation for watered-out shaly sand reservoirs, and has practical application value. Herein the research results will lay the solid foundation for further research on complex resistivity model in water flooded thick oil reservoirs during high water cut stage.