Petrophysical Characteristics and Model of Lacustrine Carbonate Reservoir in the Upper Fourth Member of Shahejie Formation in the Zhanhua Sag

Abstract

The Zhanhua Sag is a significant oil and gas exploration area in Jiyang Depression, Bohai Bay Basin. Lacustrine carbonate reservoirs of the upper fourth member of Shahejie Formation are the key exploration target in this sag. To further reveal the relationship between lithology, sedimentary microfacies and petrophysical parameters of lacustrine carbonate reservoir, in this paper, the upper fourth member of Shahejie Formation in Zhanhua Sag was taken as the target. The petro-logical characteristics, sedimentary microfsacies, petrophysical parameters and parameter sensitivity characteristics of lacustrine carbonate reservoirs are systematically characterized by comprehensive use of petrological, physical characterization and petrophysical testing data, and re-servoir petrophysical modeling is carried out. The results show that the lacustrine carbonate rocks in the upper fourth member of Shahejie Formation in the Zhanhua Sag are mainly limestone, the secondary is mixed rock, and the dolomite is less developed. It mainly develops lime-reef, lime-beach and lime-mud, including microfacies of reef core, reef front, channel among reefs, reef back, reef margin, beach core, beach margin and channel among beaches. In the case of dry and saturated samples, the velocity of P-wave, S-wave, bulk modulus, shear modulus, Young’s modulus and Poisson’s ratio of the beach core microfacies are higher than those of the beach margin mi-crofacies. The velocity of P-wave, S-wave and volume modulus of biogenic limestone is higher, the velocity of P-wave, S-wave and volume modulus of calcarenite is larger, and the Poisson’s ratio of limy dolomite, calcarenite, sandy limestone and micrite is lower. The intersection of the density, the ratio of P-wave velocity to S-wavevelocity and λ shows that fluid has no influence on the re-servoir lithology. The ratio of P-wave velocity to S-wave velocity and shear waves and λ has different sensitivity characteristics to distinguish sedimentary microfacies under different fluid conditions. The carbonate reservoir is predicted by Gassmann petrophysical model as a whole, but locally by DEM petrophysical model. The DEM petrophysical model is more accurate than the Gassmann model as a petrophysical model of heterogeneous reservoir with micro-fracture development