A method for permeability evaluation based on relative permeability experiments and pressure mobility

Reservoir permeability is a key parameter for oilfield development plans, but offshore coring is expensive, and some oilfields have difficulty accurately evaluating permeability due to the lack of core data. This article proposes a method for evaluating formation permeability based on core experiments, nuclear magnetic resonance logging, and pressure measurement data. The process is as follows: ① the study found that the relative permeability of the oil phase mainly depends on the saturation of the bound water in the formation. Through analyzing the experimental data of 39 core permeability experiments in the study area, it was found that the saturation of bound water in the core is well correlated with the relative permeability of the oil phase. Therefore, an oil phase relative permeability evaluation model based on the saturation of bound water was established. ② By simulating the measurement conditions of nuclear magnetic resonance logging, 27 core nuclear magnetic resonance experimental data were obtained. According to the shape of the core’s nuclear magnetic resonance T₂ spectrum, the core is divided into three categories, and the nuclear magnetic resonance T₂ cut-off values for each rock type are determined separately. Combined with nuclear magnetic resonance logging data, the bound water saturation of the formation can be calculated. Statistics show that the bound water saturation calculated using this method has a small error compared to the bound water saturation of the rock core, and the calculation accuracy of bound water saturation is high, thus enabling the calculation of the relative permeability of the oil phase in the formation. ③ Based on the measurement principle of pressure measuring fluidity, combined with experimental data on phase permeability and viscosity of formation fluids, the pressure measuring fluidity is converted into the oil phase permeability of the formation. Combined with the relative permeability curve of the oil phase, it is converted into the absolute permeability of the formation, and a formation absolute permeability evaluation model based on the Coates formulas is established. The practical application results show that: ① the error between the calculated absolute permeability of the formation and the permeability of the core is small. ② The permeability calculated based on the new method was used to predict the production capacity of 14 wells, and the predicted results were highly consistent with the actual production after drilling. Both indicate that this method has high accuracy in calculating permeability and has important reference significance for permeability evaluation in similar oil fields.