Optimized Foam Drilling Improves Drilling Performance in Iranian Carbonate Fields

Abstract

Abstract The advantages of foam drilling over conventional mud drilling have long been recognized and include faster penetration rates, longer bit life, prevention of lost circulation and less formation damage to the producing reservoir resulting in overall drilling cost reduction and higher production rates. Careful practical design and control of gas and liquid volumes, injection pressure and annular backpressure must be applied in foam drilling to achieve the optimum results. Optimization of foam drilling is done by drilling with the lowest acceptable bottom hole pressure and making sure that the wellbore is kept clean. This is done by applying an integrated flow model that accounts for both the compressibility of the foam, the hydrostatic column and the frictional pressure losses in conjunction with minimum hole cleaning requirements. The model is integrated with the hole cleaning requirements to obtain the balanced and lowest bottom hole pressure for the operation. The equations, procedure and sample application of this method are presented herein. Using this UBD approach on Iranian oil fields indicates large cost savings. The drilling operations in the Shanoul and Parsi fields shows as much as 60-70 percent reduction in bottom drilling time using foam drilling compared to conventional mud drilling. Using the optimum volumetric model for foam drilling and a series of simplified hole cleaning charts presented herein, the foam drilling program for the Shanoul field enabled determination of optimum drilling and hole cleaning parameters in this field. This paper presents results from programming of near balanced conditions using a new foam drilling program designed for the Shanoul field. The target formations were hard, fractured and depleted limestone formations with low pressure. The paper also compares the results to similar wells drilled with aerated fluids and conventional muds, which indicates the foam drilling as being superior in terms of rate of penetration longer bit life and less wellbore instability. A drilling cost study comparing conventional, aerated and foam drilling is also presented.