PDC Cutter and Bit Development for Challenging Conglomerate Drilling in the Luno Field - Offshore Norway

The Luno discovery in the Norwegian sector of the Southern North Sea, with an estimated 180 million recoverable barrels of oil (Greater Luno area including Tellus) in a conglomerate and sandstone reservoir, has proven to create unique drilling challenges. The reservoir, planned with horizontal or 60° slanted producers and inclined water injectors, consists of both sandstones and conglomerates with granite clasts of varying sizes. During the exploratory phase the conglomerate was mainly cored with diamond impregnated bits. The recorded rate of penetration (ROP) through the conglomerate spanned from 0.5- to 3.5-m/hr; for most of the time it stayed at between 1- and 2-m/hr. Reduced well cost was one of the early identified major potential field development savings if the conglomerate can be drilled with polycrystalline diamond compact (PDC) bits capable of an ROP of 10- to 15-m/hr, and which would last for 500- to 1000-meters reservoir sections. To investigate the feasibility of using PDC bits, after reaching the target in appraisal well 16/1-13, the well was deepened utilizing two different types of PDC test bits. After the PDC field tests were conducted with the first bit ringed out after 70 meters and the second bit partially worn out after 34 meters of rough drilling, it was decided to initiate a PDC development project to develop a PDC bit with cutters that could withstand the challenging drilling of the conglomerate for the upcoming field development/production phase. A conglomerate pie test block was manufactured and used in a vertical turret lathe to conduct single cutter PDC testing. Utilizing the improved wear and impact resistance of the new enhanced cutters developed based on results from the testing, an experimental bit with different cutter types was used in another well with hard basement rock. From the cutter and bit performance observed during the field test, further laboratory- and field testing was conducted with these cutters showing preliminary performance results of 3- to 4-times initial durability potential for a constant ROP