Field data presented in this paper demonstrate how anti-jamming coring technology was used to improve coring operations at Majnoon field. Majnoon field is located in the southern part of Iraq and is still early in its development phase, with many geological uncertainties. In this geological environment, core samples from the reservoir sections are essential for geologists, geophysicists, and reservoir engineers to better understand and develop a detailed reservoir model.

Previous attempts to obtain core samples in this field experienced poor efficiency, with recurring jamming and limited core recovery, resulting in additional rig time. The lithology of the cored interval consists of interbedded sand, shale, and limestone having occasional traces of pyrite, which has a tendency to damage core bit polycrystalline diamond compact (PDC) cutters.

To overcome these issues, anti-jamming technology featuring a spring loaded-spacer and double-bearing inner assembly was used to core through two compact formations of the well. This technology has already proven its value in other parts of the world; however, this was the first time it was implemented in southern Iraq, achieving its objectives and saving rig time. Seven separate runs were made to cut 151 m of core, all resulting in 100% core recovery at surface with excellent efficiency (98%).

This paper discusses the application of the new coring technology coupled with a premium cutter core head and optimized bottomhole assembly (BHA), which helped mitigate the risks associated with the previous runs and cored into an 8.5-in. section without experiencing any problems.

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