Fit for Purpose Underbalanced Coil Tubing Surface Equipment Permits Safe Drilling of High H2S Horizontal Gas Wells in Saudi Arabia with Higher Productivity Results

Abstract

This paper describes the underbalanced drilling (UBD) surface package used in the Saudi Aramco underbalanced coiled tubing drilling (UBCTD) project. A brief description on each item of this equipment is presented, as well as a description of the overall process flow. Moreover, the evolution and modification of the package throughout the period of the project and the optimization of the equipment to meet new challenges and to overcome some drilling hazards, such as erosion and high H2S levels, is discussed. The objective of the project is to drill reentry horizontal lateral sections in a hole size of 3⅝" with coil tubing (CT) using the UBD technique specifically the "Flow drilling" technique to increase the hydrocarbon’s productivity without damaging the formation, increasing the rate of penetration (ROP) and eliminating risk of losses or wellbore instability. The UBD surface equipment used for the UBCTD project was designed to handle maximum allowable rates to drill the well within safe limits. The equipment were selected and designed on the basis of historical data gathered from offset wells in the same specific field. The main focus in this paper will be on the lessons learned throughout the period of the project regarding the UBD surface equipment, which was specially built for this project.