Computer Simulation Predicts Unfavorable Mud Rate and Optimum Air Injection Rate for Aerated Mud Drilling
- Boyun Guo (New Mexico Inst. of Mining and Technology) | Geir Hareland (New Mexico Inst. of Mining and Technology) | Jerzy Rajtar (New Mexico Inst. of Mining and Technology)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- June 1996
- Document Type
- Journal Paper
- 61 - 66
- 1996. Society of Petroleum Engineers
- 1.6 Drilling Operations, 1.11.5 Drilling Hydraulics, 4.2 Pipelines, Flowlines and Risers, 5.3.2 Multiphase Flow, 5.4 Enhanced Recovery, 4.1.4 Gas Processing, 1.7.7 Cuttings Transport, 1.12.6 Drilling Data Management and Standards, 1.10 Drilling Equipment, 1.8 Formation Damage
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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 higher penetration rate, less formation damage, minimized lost circulation and 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 "adequate flow rate". Based on 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 which provides lower carrying capacity of the aerated fluid for a given air injection rate. As a unique characteristic of multi-phase flow, there exists an air injection rate which 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 will ensure a maximum penetration rate for a given well geometry. This paper provides drilling operators with a means of optimizing aerated mud drilling.
Oil and gas drilling activity is currently limited by the affordable operation cost. Improving penetration rate of drilling has been considered as an effective means of reducing drilling cost. Among n-ny factors affecting the penetration rate, the overbalance, which is often defined as the pressure differential between the borehole pressure and formation fluid pressure, is generally recognized as the most important one. Formation pressures less than the static pressure of column of fresh water require the use of a lighter fluid, such as air, to be injected with mud in order to obtain less overbalance or underbalance both for enhancing penetration rate and for minimizing lost circulation. Therefore, aerated drilling is becoming an attractive practice in some areas. Many operators have also turned to aerated drilling as a means of maximizing the productive potential of low-permeability reservoirs. This is because the use of the aerated mud minimizes formation damage due to less liquid filtration and particle invasion into the pay zone during drilling.
Aerated drilling has been put into use only in recent years. Many problems involved in it need to be solved. Without question, the research devoted to aerated drilling hydraulics is minuscule when compared to that associated with conventional fluids. This paper is intended to answer three questions related to aerated mud drilling: (1) what is the carrying capacity of an aerated mud? (2) what annulus pressure do we expect during drilling with an aerated fluid? and (3) what are the optimum mud and air rates that assure maximum penetration rate?
|File Size||421 KB||Number of Pages||6|