Abstract

Origin Energy Pty Ltd ("Origin") completed its first extended reach drilling (ERD) project in southeast Australia to access offshore targets from an onshore location. The project targeted the Halladale gas field which is located 5.5 km offshore and 1.8 km below the seabed. For this operator, the challenge was to access offshore reserves using onshore drilling and production infrastructure to minimize project development costs and avoid working in sensitive marine environments.

To mitigate depth uncertainty at the target location, an S-shaped trajectory was selected for the Halladale-2 production well. This started with a shallow kick-off followed by a sub-horizontal section that travelled laterally offshore and ended with a drop-off section to intersect the reservoir target. Advanced drag management techniques were required to drill the 12 ¼-in. and 8 ½-in. hole intervals, install the 9 ⅝-in. production casing, 7-in. production liner, and 5 ½-in. intelligent upper completion. The 9 ⅝-in. casing was installed using the buoyancy-assisted method (floatation), such that it could be "pushed" and "reamed" in the hole beyond the point of negative weight. Due to the geological environment and potential for mud losses, special attention was required in order to have the system designed for reduced hydrodynamic loads and still maintain appropriate mud weight for wellbore stability.

The 9 ⅝-in. casing was run completely empty and required rotation in order to reach total depth. During the operation of landing-out the casing on the well head, the use of rotation to overcome axial drag was not an option; therefore, adequate contingency planning was required. A casing selective floatation collar was installed to provide additional weight should it be required by filling the top portion of the string with drilling fluid as total depth was approached. This allowed the lower portion of the casing in the high angle interval of the wellbore to remain empty, and thus neutrally buoyant. This contingency was in addition to the risk assessed push-down weight that the top drive could provide. A process was adopted to ensure that every member of the team understood the program and was committed to the successful delivery of the wells. These measures resulted in significant cost savings for the project.

Technical challenges were overcome with design solutions and operational practices developed with the aid of modeling and simulations performed during the planning phase. The preparation of comprehensive multi-well program, the use of real-time data to validate the engineering models and a systematic approach to well planning contributed to the success of the project. When the rig limitation is accounted for, the Halladale-2 ERD well was a world-class challenge that was successfully overcome.

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