Upper Zubair Horizontal wells in North Kuwait pose a unique challenge; the challenge of building angle at High DLS, to achieve horizontal profile within short section of TVD. While normal DLS in Horizontal wells had been in the range of 5–7 deg. /100ft. in the 8½" section, the planned DLS to achieve the horizontal in upper zubair required a Build of 10–11 deg. /100 ft. This exceeded the capacity of normal Rotary Steerable Systems and it was something which was never attempted before in the entire Middle East region. Kuwait Oil Company strived for technological solutions and successfully carried out the job.
The need for sharp DLS arises primarily to counter the complications from formations in the section previous to it. High angle of inclination through shaly formations compounded with total loss, leads to quick destabilization of the hole creating an unstable hole. These issues enforce a strategy of not building beyond 40° inclination at the casing point, leaving the onus of building to horizontal in a short section of TVD. Completion strategies with ICD and Swell Packers in the lateral further tightened these requirements to a very smooth curve.
With proper operational control, the curve section was drilled with a proprietary RSS along with a specialized bit, cased and cemented successfully. Later the successful deployment of a stiff ICD completion proved the portability of this success to other challenging projects. The total savings realized on account of lesser directional work is over $700,000 US.
The paper outlines the planning efforts, risk assessment and operational details in achieving success. With capabilities of reaching DLS of 15°/100 ft. through these special RSS systems, new vistas have opened up for drilling of such challenging profiles. Sharper profiles with lower Kick-Offs could have huge potential for optimization in terms of lower directional costs and cycle times.
