ROP Optimization and Improved Wellbore Quality with New BHA and Drill Bits Modeling in Soft Shallow Formations

Abstract

The paper introduces a method that enables the drilling of a directional trajectory in shallow and unconsolidated formations of riserless phases through the adjustment of parameters, Rotary Steerable System (RSS) settings and PDC bits configurations. The technique was designed for some specific scenarios: exploratory projects in which maintaining verticality in shallow formations/hazards is mandatory, post-salt projects with significant inclination build in riserless phases, and projects that require kickoff in large diameters. There has been a substantial shift in drilling BHAs historically used in riserless drillings with KOP in shallow formations. The use of positive-displacement mud motors (PDM) combined with tricone bits was replaced by RSS and PDCs bits. To enable the change of BHA and the consequent optimization of performance, some parameters and drilling settings were adjusted, such as: an increase in TFA, flow rate reduction, HSI reduction, increase in the frequency of viscous pills, use of the Pump & Dump technic and readjustment of drilling parameters. The main optimization achieved by the adopted methodology is related to the increase in ROP and improvement in wellbore quality. The performance optimization with RSS and PDC bits was observed not only in the directional part of the trajectory, but also in the vertical section. Another relevant aspect of the method is that it enables drilling trajectories in challenging scenarios: riserless phases in large diameters, such as the "chaotic" ones in the Santos Basin post-salt; shallow or friable formations. These actions have allowed the installation of casings or completion tubings without excessive drag and/or bumps, due to the simplification of the directional design and improvement of wellbore quality. An increase of 39,3% in the average ROP in the worst case scenarios and 112,1% in the best ones were observed, as well as a reduction from 20% in caliper ratio washout to 12% (related to less formation washout due to the application of lower flow rates), an improvement in wellbore quality. In addition, the reduction in flowrare and drilling time allows the use of the Pump & Dump technique, which guarantees geomechanical stability at high inclinations, typical of ultraslender projects. The methodology has ensured risk mitigation (involuntary sidetracks, high drag during installation of completion equipment, improvement in cementation hydraulics, absence of overpull margin and reduced bottom drilling torque available), project scope optimization (reduction in the number of phases in pre-salt projects, ultraslender configuration in the post-salt Campos Basin) and increase in ROP and consequent reduction in well construction time.