Jetting is a widely applied technique for conductor installation, which allows great time savings in comparison to conventional drilling and cementing of the conductor.
According to Kan et al. (2018), the key parameters for a successful jetting operation are: pump rate, ratio of bit-to-conductor dimensions and bit stick-out, that is, the length of bit bottom out of conductor shoe, during jetting. The influence of these key parameters was studied, with regards to excavation rate.
The present work used a finite volume method to model the impingement of maritime soil by a jetting assembly, comprised of a rotating drillbit and conductor. The soil was modeled as a highly viscous fluid, described by a modified Herschell-Bulkley viscosity model.
Velocity and pressure fields were obtained for the fluid surrounding the jetting assembly. The integration of static pressure acting over certain walls allowed for the calculation of fluid forces acting on the tools. Excavation rate was measured and compared to field-obtained data, for calibration purposes. The comparison of excavation rates obtained for different configurations showed that some stick-outs were more efficient than others.
By measuring the hydraulic energy of each fluid phase, it was possible to understand the physics underneath the jetting operation, which is associated to fragilizing the soil. This fragilization will eventually lead to lower drag forces, if conductor reciprocation becomes necessary.