PDC bits have been used extensively and successfully over a wide range of formation types. The lack of rotating parts leads to greater life expectancy and as such long bit runs are achievable with resultant time and cost savings.
A thorough review of the economics of running a PDC bit needs to be performed prior to selection due to its increased cost.
The following guidelines list the typical applications of PDC bits:
- PDC bits are typically useful for drilling long, soft to medium shale sequences which have a low abrasivity. In such formations they typically exhibit high ROP and extended life enabling entire sections to be drilled on one run.
- PDC bits are not usually appropriate for highly abrasive well cemented sand sequences. When drilling tight siliceous formations the incidence of PDC chipping and breaking is dramatically increased resulting in less than expected ROP and bit life.
- When drilling heterogeneous formations containing alternating shales and or shale limestone sequences the use of hybrid PDC bits is encouraged. This bit incorporates the use of back-up diamond studs behind the PDC cutter.
When drilling harder abrasive strings, the diamond stud absorbs the increased weight required to drill the stringer and prevents premature damage and wear to the PDC cutter.
- The use of bladed hybrid PDC bits is recommended for drilling hard formations. The deep watercourse on these bits enable optimum fluid flow across the cutter to efficiently reduce the friction temperatures induced. This efficient cooling will help minimize fracture of the PDC cutters.
- When drilling mobile, plastic formations such as salt sections the use of eccentric PDC bits should be considered. These bits have proved successful in preventing incidence of stuck pipe in many areas where salt flow problems are experienced.
- When planning the use of mud motors or turbines, the use of long tapered profile bits should be considered. In addition, radial jetting bits reduce the potential for friction induced high cutter temperatures when run on a motor or turbine which reduces temperature degradation of the cutter.