Innovative PDC Bit Design to Improve Drilling Performance in Highly Abrasive Sandstone Reservoirs

Abstract

Abstract Drilling heterogeneous and abrasive sandstone reservoirs horizontally with conventional PDC bits pose significant challenges due to early worn out cutters requiring multiple bit trips. This negatively impacts rate of penetration (ROP) resulting in excessive time to drill and complete horizontal sections. This paper describes how the use of rolling cutter PDC bit technology, can overcome this challenge by improving ROP to drill the entire section in optimal time. A detailed analysis of historic drilling parameters and bit dull gradings in the field showed that abrasive wear and chipping on bit shoulders was the most common dull characteristic causing reduced ROP performance and requiring a BHA trip for the bit change-out. To address the challenge, finite element analysis (FEA) was performed to identify the locations of high cutter wear. Subsequently, a new bit design with fully rotating cutters strategically placed at high bit wear locations was developed. The new design ensures that the wear on diamond cutter faces is minimized, and prolongs bit life durability. In order to test the efficiency of the bit, it was run on a motorized rotary steerable (MRSS) assembly to drill one of the horizontal sections with abrasive sandstone. The bit drilled the entire horizontal length of around 4000 ft in a single run. Previous bit designs drilled through similar reservoirs with multiple conventional PDC bits, or in the best-case scenario, with low ROP in a single bit run. The new bit design achieved unprecedented results by delivering ROP performance with an increase of 100% compared to the average bit run. This improved performance eliminated the risk of extended open hole exposure which often leads to wellbore instability induced by reactive shales, further warranting a dedicated reaming trip. Historic analysis also determined that conventional PDC bits fitted with premium cutters uses only a small portion of the diamond table to contact the formation. Once the diamond table on the cutters face gets worn or chipped, the drilling efficiency is compromised. These worn flat cutters generate a high degree of frictional heat while drilling through the abrasive sandstone, which breaks down the diamond bond. The new bit design with fully rotating cutter technology does not face the same challenge. The paper will also discuss how precise positioning of the diamond cutting elements relative to contact with the formation is a prime concept to achieve efficient element rotation in order to keep the elements sharp for long intervals. As a result, roller diamond element bit durability is sustained and drilling run length is increased in comparison to conventional fixed cutter bits.