Deployment of the Longest 9.625-in X 12.25-in Non-Directional Casing While Drilling (CWD) Worldwide Through Unstable Formations in a Production Hole Section in Adnoc Onshore. A Case Study in Drilling Efficiency and Well Integrity
Authors: Bethancourt R. , Kodiah B. , Aljabery R. K. , Al Reyami M. , Alwahedi K. , Alsaweafi K. , Faghaly T. , Ameh U. , Kosset T. , Jouzy N. , Syafitri D. , Roberie J. , Balen A. V. , Halma J. 
Published: November 2024

Abstract
Conventional drilling methods encountered serious operational challenges while drilling 12.25 in. production hole sections, such as wellbore instability and drilling fluid losses across aquifers. These challenges affected both the drilling productivity and the well integrity. The adoption of Casing While Drilling (CWD) was a significant paradigm shift in resolving these issues by maintaining well integrity and improving well delivery performance. This paper will illustrate how the CWD technology enabled drilling the longest 12.25 in. by 9.625 in. section in one run through unstable aquifer formations, saving 1.2 days of rig time and attaining achieving cementing quality
The Non-Directional CWD Technology was deployed in a vertical production borehole section. The CWD used a casing string with a drillable body PDC bit and solid body centralizers for cementing. The approach emphasized careful engineering planning and preparation stages, customized to the requirements to overcome the main challenges for the CWD deployment in pilot stage for final evaluation: Drilling the section in one run and ensuring well integrity across aquifer zones during the cementing job.Drilling dynamics, hydraulics, bit design, offset well and casing centralization analysis were the keys to assess the feasibility of the CWD application through interbedded and unstable formations.Drilling with casing through highly interbedded zones with different hardnesses and mechanical properties
The CWD operation was finished in a single run with Zero QHSE incidents and minimum exposure of personal to manual handling of heavy tubulars enhancing rig crew safety. The successful CWD implementation resulted in a time-saving of 1.27 rig days, in a production interval drilled in a single run (5,175 feet) through interbedded formations at a competitive Rate Of Penetration (ROP) of 47 feet per hour, enabling this to become the longest Non-Directional CWD worldwide.The ROP was lower than the conventional drilling ROP in this application. However, the savings were mainly attributed to the elimination of casing-running flat time and Non-Productive Time (NPT) associated with clearing tight spots, wiper trips and water collection due to losses.The verticality was maintained at an average inclination of 0.3 degrees and a maximum displacement of 42 feet.The encountered losses were effectively reduced from 350 barrels per hour to 200 barrels per hour, demonstrating the plastering and wellbore strengthening effect of CWD which resulted in the subsequently good cement bond log across the aquifer formations.Exceptional cement bonding was maintained around the 9.625 -in casing indicative of good hole quality despite the significant dynamic drilling fluid losses.