Saudi Aramco is developing gas fields in various areas utilizing vertical and horizontal wells with rotary as well as motor BHAs. This application requires Saudi Aramco to drill laterals through an extremely tight sandstone formation with inclination varying anywhere from 72° to 90°. The highly abrasive formation is causing inconsistent PDC bit performance while drilling the 5 7/8-in. horizontal section resulting in exceeding the authorization for expenditure (AFE) of the wells. Saudi Aramco, in collaboration with the bit company, analyzed the field data, which showed extensive cutter damage, with abrasive wear being the most common dull characteristic. The cutter wear was causing short runs and frequent trips to change out the bit. A step change in bit design was required to extend bit life and increase rate of penetration (ROP) in areas where poor drilling performance is expected.

The fixed PDC design creates an inherent limitation because only a small portion of the cutter contacts the formation, and drilling efficiency declines as the cutter wears. The resulting wear flat generates a high degree of frictional heat, which can break the diamond-to-diamond bonds in the cutter diamond table and lead to accelerated cutter degradation. An R&D initiative was launched to investigate different methods to enable a PDC shearing element to fully rotate while drilling to increase overall cutting efficiency and bit life. Several different retention methods were investigated, and a specialized fixed housing that is brazed into the bit blade was developed. The rolling cutter assembly has essentially the same outside diameter (OD) as a standard PDC cutter, which helps maintain design flexibility and cutter placement options.

The newly designed 5 7/8-in. PDC was manufactured with strategically positioned rolling cutters and was run in a gas well. The objective was to achieve an average ROP of 4.7 ft/hr and drill a minimum of 240 ft of lateral hole section to achieve proposed 5% reduction in cost-per-foot. The bit achieved a record ROP of 14.85 ft/hr while drilling 527 ft of the abrasive sandstone formation.

After achieving positive results from tests in lateral sections, the new bit design was also tested in a two vertical sections through the same tight sandstone formation on rotary assemblies. In these applications, the new bit design performed better than those in offset wells, with one of the two drilling from shoe to shoe for the first time in that field.

This paper will discuss the application and evolution of rolling cutter bits, along with the results achieved by bits fitted with these cutters in Saudi Arabia.

You can access this article if you purchase or spend a download.