Estimation of Porosity, Permeability and Water Saturation in Tight Sandstone Reservoirs Based on Diagenteic Facies Classification Method: Case Studies of Chang 8 Formation in Northwest Ordos Basin

摘要

Porosity, permeability and water saturation cannot be effectively estimated from conventional logs by using the classical methods in tight sandstone reservoirs due to the complicated mineral components, pore structure and strong heterogeneity that caused by the diagenesis in the Chang 8 Formation of northwest Ordos basin, In this paper, based on the difference of diagenetic facies, effective formations are classified into three types, the relationships between conventional density log and core derived porosity, core derived porosity and permeability are established in every type of formation. In the meanwhile, the laboratory resistivity experimental results are also classified based on the diagenetic facies, and the cross plots of porosity and formation factor, water saturation and resistivity index are drawn to obtain the rock resistivity parameters, separately. These results illustrate that for formations with different diagenetic facies, the matrix densities are diverse, the relationships between core derived porosity and permeability are also different, and they contain different rock resistivity parameters. By using the diagenetic facies classification method and chart proposed by Xiao (2012), the effective Chang 8 Formation is classified into three types, and the corresponding models are applied to calculate porosity, permeability and water saturation. Comparisons of estimated porosity, permeability and water saturation by using the proposed techniques and the core derived results illustrate that the proposed techniques are valueable in tight sandstone reservoir parameters evaluation.