Developing reserves in the North Russia, Usinsk requires the operator to drill extremely abrasive sandstone formation at bottom of 8.625-in. reservoir section. Drilling with PDC bits has been challenging due to severe cutter wear. Heavy-set standard PDC cutter bit would last on average from 45 to 100 meters depending on field. With the goal of increasing production and reducing costs, reservoir section can be from 170 up to 350 meters long.
With standard PDC bits, it would take from three to four bits to finish the interval. The operator required new type of PDC bit that could efficiently drill abrasive sandstone at high ROP and cutting structure that would remain sharp over longer interval.
To develop a durable bit solution, engineers used an FEA-based modeling system to implement an innovative bit by positioning new shearing elements (rolling cutters) to address cutter wear. Several designs were implemented that hold the cutter securely in place and allow full cutter rotation. Rolling cutter PDC shearing element utilizes the entire 360 degree of diamond edge to shear the formation while reducing frictional heat and, by strategic positioning of these rolling cutters in the high wear areas of the bit, provides longer footage and higher ROP.
New design 8-bladed PDC bit with rolling cutters was tested and compared against direct offsets in two different fields in Usinsk, Russia. In first field, rolling cutter bit drilled entire reservoir section 335 meters with 4.6 m/hr ROP improving 140% meterage and 44% ROP. In second field, two rolling cutter bits drilled reservoir section and replaced four standard PDC bits saving three days.
New concept of PDC bit utilizing rolling cutter expands the limit of PDC bit durability drilling extremely abrasive sandstone formations. New type of bit can efficiently drill in those challenging geological conditions improving the drilling time and cost.