Abstract:Complex reservoirs of similar porosity gene-rally have largely different permeability. To reveal the reason for this phenomenon, we conduct experiments such as those with casting thin sections, nuclear magnetic resonance (NMR), and computed tomography (CT) scan imaging to evaluate the connectivity of pores. Connected porosity is a main contributing parameter to permeability. For this reason, approaching from the conductive mechanism of rock pore spaces, we build a calculation model for connected porosity with conductive porosity as a bridge. Then, the functional relationship between connected porosity and total porosity is analyzed for 12 types of rocks. A universal NMR T2 model is built on the basis of the calculation model for connected porosity. With limestone re-servoirs as an example, a porosity index model is derived and developed from the perspective of the permeability difference among different types of rocks under the condition of similar porosity. The distribution range of the porosity index is thereby determined. With the universal NMR T2 model, the average absolute error in permeability prediction for limestone reservoirs is reduced from 20.41mD to 0.83mD. The proposed method holds great theore-tical and practical significance.
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