Multiple relief well planning for an HPHT blowout in Southern Mexico

Following a catastrophic blowout incident onshore Southern Mexico on the Terra-123 well during due to an uncontrolled leak on the side valve of the wellhead, along with the loss of a barrier in the well, surface capping control operations and planning activities for three relief wells (RW) were initiated to intercept the target well (TW). This paper describes the planning and design process for the three RWs. The main objectives were set to intercept the target well and then killing it safely and efficiently. The tasks performed for the relief operations included complete project management, well engineering, well bore positioning, communication protocols, hazard analysis and risk control (HARC), casing design, and hydraulic killing simulations. Wellbore positioning was one of the main challenges due to the gross errors in survey data and local procedures, for this advanced geomagnetic referencing techniques were employed to identify the TW's position and design the RW's survey program. Active ranging techniques for well interception and detection were discarded due to salt interference; therefore, passive ranging and acoustic ranging (BARS: Borehole Acoustic Reflection Survey) techniques were selected as the best alternatives. Additional measurements while drilling (MWD) surface tests were performed to ensure the detection of the target casing. As part of the hydraulic communication design, tubing-conveyed perforating (TCP) was planned as the communication method. All the RW trajectories were designed to accomplish the kill operation as standalone wells, meaning that the other two RWs are not needed if one is successful. A new casing design criterion to ensure low-risk scenarios during the interception and hydraulic communications was considered. Directional requirements based in the survey accuracy to determine the 3D relative positioning of the target well and RW were defined.