Computer simulation predicts unfavorable mud rate and optimum air injection rate for aerated mud drilling

In certain areas, the use of aerated mud as a circulating medium for drilling oil and gas wells is becoming an attractive practice. This is because aerated drilling has many advantages over conventional mud drilling, such as a higher penetration rate, less formation damage, minimized lost circulation, acid lower drilling cost. The importance of maintaining adequate air and mud flow rates is generally recognized in aerated drilling operations. However, it remains unclear to drilling operators as to what constitutes an ''adequate flow rate.'' On the basis of computer simulation, this paper discusses carrying capacity of an aerated mud and the optimum air-injection rate that ensures a maximum penetration rate. It is found in this study that the carrying capacity of an aerated mud is very different from that of both the conventional mud and pure air. There is an unfavorable range of mud flow rate that provides lower carrying capacity of the aerated fluid for a given air injection rate. As a unique characteristic of multiphase flow, there exists an air injection rate that gives the lowest flowing annulus pressure for a given well geometry and a mud rate. By considering both the carrying capacity and flowing annulus pressure, an optimum combination of mud and air rates can be determined. This optimum combination of flow rates should ensure a maximum penetration rate for a given well geometry. This paper provides drilling operators with a means of optimizing aerated mud drilling.