Casing while drilling - An alternative approach in drilling operations for Arabian formations

Casing While Drilling (CWD) has become increasingly attractive as an alternative drilling technology, which provides a means of reducing operational costs substantially as well as avoiding various drilling related problems. The CWD involves drilling and casing a well simultaneously and hence, overall cost of drilling may be reduced significantly by lessening drilling time and various unexpected drilling problems encountered during the conventional drilling process. This technology is readily applicable, specifically in depleted reservoirs as an alternative to under-balanced drilling, which requires special equipment. This article presents the applicability of the concept of CWD in the context of drilling wells in Arabian formation. Complexities associated with drilling these formations, such as unscheduled hole problems, lost circulation, differential sticking and casing jamming due to tight-hole whilst running casing after withdrawal of conventional drill-string etc. are identified. It has been revealed that the CWD technology can be useful to overcome most of these complexities. In order to evaluate the adequate size and capacity of a rig for CWD operation, prediction of torque and drag is vital. Accurate prediction of such torque and drag on drilling deviated wells using CWD techniques is a complex task. In this article, however, a simplified method for predicting torque and drag, especially in drilling deviated wells using a casing string, is proposed. Valuable guidelines are provided based on a field sample case study using the proposed method.