Analysis the factors of influencing the height of mud cap in controlled mud cap drilling

It is mainly relied on controlling the height of mud cap by adjusting mud pump to control bottom hole pressure in controlled mud cap drilling. The annular multiphase flow computational model was established based on multiphase flow theory and mud cap controlled drilling fundamental principle and then the model was computed by using finite difference approach. Through examples of simulation calculation, the effect of gas invasion time, discharge capacity, drilling fluid density, initial differential bottom hole pressure, gas phase permeability, well depth and drilling fluid viscosity on the height of mud cap were discussed. The result shows that the longer gas invasion time, the smaller discharge capacity, the smaller drilling fluid density, the greater initial differential pressure, the bigger gas phase permeability and the smaller drilling fluid viscosity, the height of mud cap which was needed to be adjusted is bigger. The peak value of the height of mud cap turns up much later with the deeper well when other conditions were unchangeable. The result provides the basis for adjusting the height of mud cap reasonably in controlled mud cap drilling.