MWD /LWD Challenges and Solutions for Drilling the Longest Al Hosn Gas Well in an Aggressive Subsurface Environment

Abstract This paper will detail the coordination between multiple teams and across technical discipline groups to successfully drill a +28000 feet (ft.) measured depth (MD) horizontal appraisal well in a high temperature, high hydrogen sulfide and carbon dioxide (H2S/CO2) environment and acquire high quality measurement and logging while drilling (MWD/LWD) data. Strategic tripping practices were used to reduce the risk of temperature related MWD/LWD tool failures. Extensive fluid engineering work was conducted, to design a fit-for-purpose mud system to meet Al Hosn Gas's handling requirements. Effective surface gas removal techniques were used to preserve high quality drilling mud and insure communication with the MWD/LWD tools. Hole cleaning efficiency was determined and maintained by monitoring drilling trends against calibrated models. In addition, the bottom hole assembly (BHA) drive system was designed to maximize power at the bit. Specific drilling parameters allowed for a high rate of penetration (ROP) that effectively reduced exposure time of the down-hole tools to very high temperatures minimizing tool failures. Carefully planned fluid engineering provided constant stable mud properties, which allowed the removal of H2S/CO2, and insured adequate borehole cleaning and lubricity to alleviate torque and drag. This resulted in high quality borehole images. Lubricants to reduce torque to manageable levels were selected after exhaustive in-house testing. Similar fluid engineering practices were used to select H2S scavenger. An extension of the horizontal section beyond the directional plan was accomplished within operational limits set by Al Hosn Gas after all drilling risks were fully assessed. Acquisition of required high quality LWD data was successfully accomplished. LWD borehole images were available only in memory mode, however, azimuthal resistivity curves helped in making geosteering decisions in the absence of the real-time borehole image data. Despite the well being drilled in the pay zone for its entirety, a measurement after drilling (MAD) open-hole log was employed to acquire missing density data that was required after a tool failure. A full petrophysical analysis was completed using the recorded memory data. It was included in the reservoir geo-cellular model and helped to define reservoir properties with a high degree of confidence. Close collaboration and trust between all partners to continually challenge and redefine perceived technical and operational boundaries led to the successful drilling of Al Hosn Gas's longest well. All teams and personnel were aware of the challenges and developed solutions to acquire excellent MWD/LWD data in one of Al Hosn Gas's most ambitious wells, to date.