Study on Vertical Differential Velocity and Transverse Scope of Nitrogen Injection in Carbonate Reservoirs with Fractures and Vugs in the Tahe Oilfield

The fractured and vuggy carbonate reservoirs of the Tahe Oilfield suffer a deteriorating water flooding development due to the large development scale and pattern uncertainty of fractures and vugs, coupled with a high degree of heterogeneity. In order to provide references for gas injection development, the vertical differentiation velocity after nitrogen injection in those reservoirs and its effect were analyzed. Based on the mechanical relationship, the vertical differentiation velocity analytical equation of nitrogen was established under the conditions of fractures and vugs. A physical test model was constructed from 3D printing technology, and the verification of numerical simulation was based on the physical simulation test. The influences of nitrogen injection rate, crude oil viscosity, oil-water interface, and gas-water ratio on the lateral distribution of nitrogen in reservoirs with fractures and vugs were studied in combination with numerical simulation. The study results suggested that lateral sweepage area of gas will increase with the increase of injection rate, along with a decrease of crude oil viscosity and the elevation of oil-water interface. However, the effect of gas-water ratio on the lateral sweepage area of gas is irregular.