Successful Application of Casing-While-Drilling Technology to Drill and Case Through Troublesome Tar Layers in North Kuwait Field

Abstract

Drilling through tar-bearing formations remains a persistent challenge in Kuwait and worldwide. These intervals, particularly in directional wells, often result in stuck pipe, lost BHAs, and costly sidetracks. Traditional mitigation methods are insufficient when encountering thick tar zones. This paper documents the first successful application of Casing-While-Drilling (CWD) technology to drill and case through multiple tar layers in North Kuwait. A 20°-inclined directional well exhibiting several tar intervals was drilled conventionally using rotary steerable systems (RSS) and rotary BHAs, but two stuck-pipe events and multiple sidetracks occurred. To overcome these issues, an engineered 12¼-in. × 9⅝-in. CWD system was deployed. Torque and drag simulations confirmed operational feasibility. The CWD assembly included a custom drillable bit and BTC-type connections with MLT rings to handle high torque. The CWD operation drilled 582 ft of tar/coal formation in 61 hr — the longest and most time-efficient CWD run in Kuwait. The 9⅝-in. casing was successfully cemented, and the drillable bit was later drilled out with an 8½-in. PDC. The method reduced total well delivery time by 30 rig days and saved approximately 360,000 KD. This pioneering success demonstrates the viability of CWD as an effective solution for drilling through tar/coal formations while minimizing operational risk and cost.