Development of a PDC-Tricone Hybrid Technology to Solve Drilling Problems of Surface Holes in North Africa

A major oil company started a drilling campaign onshore South Tunisia, where wells require long, 16-in. diameter surface holes to be drilled through a variety of lithologies that present several drilling challenges.. The challenges in this section start with mud losses that usually require controlled rate of penetration (ROP) to manage the volume of cuttings. The second drilling challenge comes while drilling through clays, which can cause balling of the bit and stabilisers. The third and most difficult drilling challenge is presented when Pyrite and sometimes Chert nodules are encountered.. To overcome these challenges, a novel PDC-Tricone hybrid bit technology was designed and tested as a potential solution. The bit's combined cutting structure can drill with the efficiency and aggressiveness of a PDC bit and handle a hard nodular formation like a Tricone bit, without suffering any damage. The bit enabled the operator to drill the entire section in a single run and saved more than 55,000 USD on the first well. Following this run, the bit was modified to increase its aggressiveness and durability and was run in more wells, confirming the initial success.. As the operator and the service company became more confident that the hybrid bit could drill the entire section without suffering damage, the operating parameters were raised to gain higher ROP. Additional improvements were made to adapt to the more demanding conditions, and the PDC-Tricone hybrid bit matched the performance of conventional PDC bits, generating financial gains for the operator.. Based on the success of this campaign, the same bit type was proposed to other operators, drilling offshore Morocco, with the ambitious objective of drilling a long chert-bearing section in one run.. This paper describes the development of the PDC-Tricone hybrid bit design, the results of lab testing conducted during this development, design iterations, and the results of its application in North Africa. Details performance compared to conventional PDC bits and results of offshore applications will be also presented.