A Study of Directional Drilling Using Rotary Steerable System in Soft Shallow Formation Benin Sand – Rio Del Rey Area, Offshore Cameroon

Abstract

Rotary steerable tool has been proved reliable tool that can be used in different types of formation. But in the Rio Del Rey area in the "Benin sand" in Offshore Cameroon, directional drilling issue have been faced while drilling with rotary steerable tool. This paper present a case of study on the importance of the Bottom Hole Assembly choice versus the lithology, BHA Configuration, bit selection and trajectory requirements. Also based on lessons learned, propose some recommendations. Rotary steerable is deemed to be a reliable tool that can be used on most of type of formation but this is not always the case as shown in our case of study while drilling through the Benin sand formation which is a shallow formation in Rio Del Rey field in the Niger Delta, offshore Cameroon using the rotary steerable system. RSS BHA has been observed to perform below expectations while drilling this formation. A holistic review of the operational performance of the five Bottom Hole Assembly that was run in the hole to drill ~1000m of soft sandy formation will be summarized. We will analyze each BHA that was ran in hole and the performance achieved. Also BHA configuration and trajectory will be evaluated and reviewed. Finally, some recommendation are made. In addition, the choice of bit selected and performance will be evaluated. After detailed analysis of each BHA, RSS BHA with PDC bit was seen not to be a good choice of BHA to drill through the Benin sand formation based on the well directional objectives and BUR requirements. Motor BHA with tricone bit using the principle of jetting was used along with catenary design trajectory. This BHA and bit selection choice with catenary design trajectory helped to achieve the directional objective 100%, even exceeded the required DLS at some point. Also, adjusting drilling parameters contributed to the success seen so far. However, some irregularity was observed in the dogleg severity which may need an additional run with the rotary steerable system to smoothen the trajectory or perform a control trip in this soft formation with the potential risk of accidental sidetrack. In conclusion, a Motor bottom hole assembly with tricone bit using the principle of jetting should be used if a risk of collision is highlighted and a need to build up quickly in order to move away faster from nearest wells. A motor assembly is more recommended in soft shallow formation (0m −700m TVD) than the rotary steerable system. A better BUR behavior was observed with a motor assembly. This paper will serve as a guide / recommendation for any drilling that requireds an aggressive shallow kick off due to collision concern in soft shallow surface formation where performance of the bottom hole assembly and bit selection is critical.