Successful under balanced coiled tubing drilling in horizontal slim hole sidetrack of existing vertical gas wells : three case histories : Ghawar Field, Saudi Arabia

In order to maximize productivity, one of the key strategies in Saudi Aramco's optimum gas development project includes drilling single and dual-lateral horizontal wells to achieve maximum reservoir contact. This strategy has been successful over the past few years. However, some wells have experienced obstacles during the drilling phase that have reduced effective reservoir contact and well productivity. These challenges can be attributed to formation damage, the complex nature of the Khuff-C carbonate reservoir, structural complications and drilling limitations. In order to overcome the reservoir damage challenge and increase the drilling flexibility, Saudi Aramco introduced under balance coiled tubing drilling (UBCTD) technology. This new drilling technique can work over existing low gas producers and has provided several advantages over conventional drilling, such as eliminating formation damage; allowing the drilling of more laterals; and providing real-time rate assessment. The wells drilled with UBCTD technology have demonstrated excellent productivity improvement. This paper described the successful horizontal sidetrack of three existing vertical Khuff-C carbonate reservoir using UBCTD.