No abstract

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.

Improvements in measurement while drilling (MWD) and service reliability over the past 25 years has made MWD tools the most cost-effective method for calculating wellbore survey position while drilling. However, with more complex well trajectories required to reach more challenging targets, reducing lateral uncertainty has also become a new challenge. It is accepted that no geomagnetic model can properly account for the geomagnetic spatial and temporal local complexity for calculating MWD geomagnetic reference values. It is also well known that measuring local geomagnetic reference requires frequent absolute measurements in order to perform QA/QC, and that those absolute measurements could only be done manually so far, and consequently very few magnetic observatories are in operation. Therefore, solutions have been engineered to enhance the geomagnetic reference model with In-Field Referencing (commonly termed as IFR). Then, its combination with Multi-Station Analysis (MSA) correction algorithms has become a common method for addressing and reducing most of the correctable MWD azimuth, survey position error and lateral uncertainty. Enhanced wellbore positioning could be a real game changer to achieve in-fill wells with high collision avoidance constraints, to develop projects that require high precision to hit the reservoir targets, or those located in specifically difficult areas, from a geomagnetic perspective, such as high latitudes and zones with crustal anomalies. This paper presents the results of the new temporal magnetic field method "IFR4D" that was successfully used to drill two onshore wells in Argentina. The wells targeted the Vaca Muerta shale play, and demonstrated the ability to improve the wells absolute positioning while reducing the lateral aspect of "ellipse of uncertainty" by a combination of: A unique autonomous, remote real-time observatory developed to monitor and allow corrections for the local geomagnetic vector with frequent absolute control of the local and temporal geomagnetic vector field (Dip, Declination and Field Intensity), andA dedicated MSA algorithm defined to use local and temporal In-Field Referencing (IFR2) data at the position and time for each MWD survey station. Once installed on location, the autonomous observatory measured all geomagnetic properties (Dip, Declination and Field Intensity) with no personnel onsite for more than one year, delivering a new level of geomagnetic accuracy to use as the standard reference for the life-time of the field. The data from the observatory was then used remotely while drilling to correct and optimize wellbore position and reduce the lateral aspects of the "ellipse of uncertainty" (EOU).