1. College of Geophysics and Petroleum Resources,Yangtze University,Wuhan 430100,China 2. Key Laboratory of Exploration Technologies for Oil and Gas Resources,Ministry of Education,Yangtze University,Wuhan 430100,China 3. Institute of Deep-sea Science and Engineering,Chinese Academy of Science,Sanya 572000,China
Carbonate reservoirs have various pores and complex pore structures.However,the microstructure of rocks cannot be characterized using conventional saturation evaluation models,making it extremely difficult to perform the saturation evaluation of carbonate reservoirs.Given this,this study proposed a Thomeer saturation model combined with the nuclear magnetic resonance (NMR) logging based on the data of capillary pressure curves and NMR logging.Specifically,information about the structure of the pore system in the mercury injection data was analyzed,and then the capillary pressure curves of multiple pore types were obtained through fitting using the Thomeer function.Finally,the complex pore structure was characterized using multiple Thomeer curves.The NMR logging is the only logging method that can continuously and quantitatively characterize the pore structure of reservoirs.The Thomeer parameters Bv,Pd,and G and the modal element Porositon of the maximum pore throat diameter were calculated using the logarithmic mean of T2 transverse relaxation time for NMR (T2LM) and the NMR total porosity (MPHS),as well as the classification of pore throat R35.Accordingly,the saturation evaluation model for carbonates reservoirs with complex pore structures was constructed.This model allows for the continuous evaluation of formation pore structure that cannot be achieved using experimental methods.This model was applied to the saturation evaluation of the carbonate reservoirs with complex pore structures in oilfield X in the Middle East.By comparison with the J function model and Archie's formula,this model decreased the relative error from 0.496 and 0.442,respectively to 0.272,better characterized the variation trend,and achieved encouraging application effects regardless of the saturation of reservoirs.Therefore,this model can minimize the impacts of carbonate reservoirs with complex pore structures and improve the precision of the reservoir saturation evaluation.
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