A new joint venture operator, established to take over an existing strategic producing field with ongoing drilling operations, took the opportunity to design a new collision avoidance standard, based on the latest WPTS (Wellbore Positioning Technical Section) probability method collision avoidance rules. This has been combined with an innovative execution approach to safely and successfully unlock slots on congested platforms and drill some of the most difficult well trajectories in this complex field from the very first well.

Al Shaheen field, offshore Qatar, is one of the most challenging fields worldwide in terms of collision avoidance. When drilling extended-reach wells from the last-remaining and most challenging slots, with top-hole separation as low as three feet centre-to-centre at the conductor pipe shoe, close collaboration with all parties is required to manage collision risk, minimise production loss, and ensure all well objectives are achieved. The execution strategy includes simple jetting and rotating BHA designs for 3D-profile trajectories, remote real-time monitoring including 24/7 survey QA/QC and validation, and mitigation through a decision-making matrix customised for the specific drilling challenges.

The platform configuration and challenges in the drilling environment are discussed, together with the theory of the selected collision avoidance rule and the resulting risk matrix. A brief review of why jetting is selected as the only allowable drilling technique in major risk situations plus the story of the evolution of Al Shaheen jetting BHAs follows. Finally, three case studies of top-hole operations describe the practical application of the techniques discussed. The selected case studies describe the jetting operation from the deepest CP (Conductor pipe), the deepest well jetted, and the first 23-in jetting operation carried out by the operator.

The combination of risk analysis through genuine probabilistic considerations, jetting operations, and appropriate oversight has been used successfully for more than two years and has allowed over twenty of the remaining, most challenging, slots to be saved, ensuring the assets are optimised in the ongoing economically-constrained environment.

The WPTS have now published their proposed industry-standard probability-based collision-avoidance rule. These case-history examples of a similar rule from extreme close-approach drilling will assist other operators considering uptake of the new guidelines, as will the risk matrix developed by the operator. In addition, the jetting technique used as a major mitigation factor is seldom used today in the industry and the lessons learned in jetting BHA design have already benefited another operator in the region.

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