New Method for Calculating Relative Permeability in Low-Permeability and Tight Gas Reservoirs Using Mercury Injection Experimental Data

In our study, we initially analyzed extensive mercury injection data from cores with varied permeabilities, observing the Corey capillary pressure model’s inadequacy in fitting the data. This observation led us to the development of a suitable capillary pressure model, which aligns more accurately with the experimental data, especially at lower mercury saturations. Building on the Burdine (1953) approach and our new capillary pressure model, we developed an enhanced relative permeability model. To assess the adaptability of the proposed model to different reservoir types, the reservoirs were then classified into four types based on porosity, permeability, FZI, and capillary pressure curve morphology, each type featuring distinct capillary pressure characteristics. Utilizing a normalization method for these curves, we generated normalized capillary pressure curves for each reservoir type. Following this, we applied a nonlinear regression approach to obtain gas-water relative permeability curves for these categories. We subsequently undertook an examination of their capillary and permeability curve features and flow capacity variations. Finally, employing Burdine’s (1953) numerical integration, we computed capillary pressure and relative permeability curves, comparing these to our newly established models and the traditional Corey and Brooks-Corey models. The results show that the fitting effect of the model with the novel normalized capillary pressure curve and the fitting effect of the data at the saturation of the wetting phase fluid close to zero are significantly improved compared with the Corey model. In addition, the improved relative permeability model is more accurate in fitting typical relative permeability data obtained using numerical integration methods compared to the Books-Corey model. Finally, the average relative permeability curve diagram of different kinds of oil and gas reservoirs have significant differences with the permeability of oil and gas reservoirs deteriorates, the water saturation at the isotonic point gradually increases and the relative permeability gradually decreases.