This paper presents a mathematical model for calculating bit pressure drop for gasified drilling fluids. The theory, which is valid for both sonic (critical) and subsonic (sub-critical) regimes, is based on the solution of the general energy equation for compressible fluid flow. Unlike the existing models in the literature, the proposed model takes the kinetic energy term, compressibility factor of the gas phase, and internal energy changes throughout the bit into consideration. In addition, the model uses a "mixture sound velocity" approach for determination of the sonic velocity boundary for the fluid. The results of the model have been compared with the results of existing models.

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