DEVELOPMENT AND APPLICATION OF PDC CORE BITS FOR DOWNHOLE MOTOR LOW-INVASION GORING IN THE ARAB CARBONATES

A method has been developed for low-invasion, downhole motor coring in the Arab formation, Arabian Gulf. Motors were used for the first time in the Arab formation to achieve higher bit rotational velocity and h igher coring rate for low filtrate invasion when using a water-based m ud. Earlier, a field test of motor coring with pre-existing low-invasi on core bits showed that antiwhirl core bits were superior to other co re bits at high bit-rotation rates. Two new antiwhirl, low-invasion co re bits with improved polycrystalline diamond compact (PDC) cutters we re designed and laboratory tested for coring the Arab carbonates and a nhydrites. Laboratory coring tests indicated a two-fold increase in co ring rate for the new fore bits with a motor compared to use of only t he top drive. The low-invasion water-based coring mud and core bits te sted in the laboratory have been used to cut 278 ft of core on the Al- Rayyan field in the Qatari section of the Arabian Gulf. A downhole mot or and top drive provided rotational rates at the core bit exceeding 2 00 rev/min compared to 100 rev/min with top drive alone. Motor coring has provided a two-fold coring-fate increase. Core quality was excelle nt, and core recovery was 99% with low filtrate invasion confirmed by potassium iodide tracer. Well-fog and capillary pressure-derived water saturations agree with the core.