Wellbore fluid sonic conditions during blowouts

The understanding of high-velocity two-phase flow is critical for predicting worst-case discharge scenarios. During a blowout, the fluid discharge rate can be very high, and its velocity may reach the sonic speed at the surface. Therefore, it is crucial to understand the fluid dynamics and flow characteristics of multiphase flow in the high-velocity range. In this investigation, two-phase (air-water) flow experiments were conducted to study the flow evolution in extreme high-velocities occurring during worst-case discharge. The experiments were performed in a vertical pipe section with a diameter of 83 mm and a length of 5.5 m. A fully transparent viewport was installed on the test section to monitor the flow pattern. The superficial gas velocities were ranging approximately from 8 to 160 m/s. During the test, the pressure gradient was monitored while increasing the gas rate at a constant liquid rate. Under subsonic conditions, the pressure gradient increase with superficial gas velocity indicating the establishment of friction dominated flow regime. However, the pressure-gradient trend changed when shock waves formed in the test section. With increasing the superficial gas velocity at a given liquid rate, the pressure gradient attained its maximum when flow transition occurred and shock waves formed in the test section, which were observed through the viewport. Under sonic conditions, increasing the superficial gas velocity a constant liquid flow rate reduced the pressure-gradient. After examining various two-phase flow sonic velocity models and measurements, a new correlation has been developed to predict sonic conditions during worst-case discharge. Experimental results are compared with predictions of existing wave propagation models and demonstrated reasonable agreement. Subsequently, a computational tool has been developed to estimate fluid flow rates for worst-case discharge scenarios involving sonic flow conditions. The new correlation has been implemented in the computational tool to forecast the establishment of sonic flow conditions in the wellbore. The computational tool shows a reasonable agreement with commercial packages for basic worst-case discharge circumstances. A sensitivity analysis performed using the computational model suggests that the discharge rate varies with the in-situ parameters such as skin factor, pay-zone height, and reservoir permeability.