The Effects of Operational Parameters on the Flow Characteristics in Annular Space During Under-Balanced Drilling Operations

Document Type : Full Lenght Research Article


1 Mechanical Engineering Department, Faculty of Gas and Petroleum, Yasouj University, Gachsaran, Iran

2 Department of Mechanical Engineering, Ahvaz Branch, Islamic Azad University, Ahvaz, Iran


In this research, gas-liquid-solid three-phase flow in the annulus during under-balanced drilling operations is simulated numerically. One-dimensional form of steady-state governing equations including mass and momentum conservation equations for each phase, gas equation of state, and saturation constraint equation in the Eulerian frame of reference are solved by a proposed algorithm. The computational code is validated by using experimental data from a real well, gas-liquid two-fluid numerical simulation, and also some mechanistic models of WellFlo software. Moreover, the results are compared with the experimental data from a laboratory study. The numerical code succeeds in predicting bottom hole pressure and obtaining the characteristic flow behavior during under-balanced drilling. Due to the importance of controlling flow characteristics during the drilling operations, the effects of change in the injected liquid flow rate, gas injection flow rate, choke pressure on the gas, liquid, and solid volume fractions, as well as gas, liquid, and solid velocity distributions along with the annulus, are investigated. According to the obtained results, the effects of liquid injection flow rate and injected gas flow rate on the flow characteristics are decreased along the annulus in the flow direction, but the effects of choke pressure on the flow characteristics are increased along the annulus in the flow direction. Consequently, to change the flow characteristics in the wellhead area, it is better to change the choke pressure and to affect the flow characteristics in the bottom-hole area, it is preferred to change the gas and liquid injection flow rate. In other words, depending on the required situation of flow characteristic changes, the appropriate operational parameter can be used.


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