Optimized Foam Drilling Improves Drilling Performance in Iranian Carbonate Fields

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. Introduction Parsi field is located approximately 100 Km South East of Ahwaz and Shanoul field location is at south of Fars provience. Parsi field is one of the largest Iranian oil and gas fields. So far 68 wells have been completed in Asmari formation of this field. The initial reservoir pressure of Parsi Asmari was approximately 3800 psi. By December 2001, about 1.48 Billion STB had been produced, with a pressure decline of about 800 psia. Shanoul field is still producing oil and gas with a high formation pressure condition (over 3500 psi) and it seems that the average reservoir pressure has been declining during four years of production with no pressure maintanance. Stable and Stiff Foam Drilling is the best UBD technique that can be proposed for drilling these field formations for the following reasons:Stable foam possesses a solids carrying capability much higher than that of liquids.Drilling with foam gives faster ROP.Foam velocity and pressure consideration help us to control washing effects and also formation water influx.