Rostagno, Ian (The University of Texas at Austin) | Yi, Michael (The University of Texas at Austin) | Ashok, Pradeepkumar (The University of Texas at Austin) | van Oort, Eric (The University of Texas at Austin) | Potash, Ben (Pioneer Natural Resources) | Mullin, Chris (Pioneer Natural Resources)
Pipe rocking is a process used during slide drilling to reduce friction between the drillstring and the wellbore. Pipe rocking is widely practiced in unconventional drilling operations, either conducted manually or through an automated system. Often times, the rocking regime adopted in the field is based only on experience and may not be at optimum, leading to higher friction with poor force transfer to the bit and reduced rate of penetration. In addition, non-optimum pipe rocking can lead to accidental connection back-offs and poor toolface control.
This paper introduces the first rocking simulator based on real time and contextual data to provide the driller with a robust recommendation of the optimum rocking regime, i.e. guidance on the optimum number of forward and reverse wraps in the drillstring and the time period in which to generate these wraps.
A model was developed to optimize the pipe rocking regime, determined by the specifics of rotating the drillstring at a certain RPM for a certain number of turns in forward and backwards directions. The objective was to keep the directional toolface constant while optimally reducing sliding friction between the drillstring and the wellbore. A torque and drag model was used to obtain the frictional forces between the drillstring and the wellbore. Drillstring dynamics was then simulated using a torsional damped wave equation applying finite difference approximations. Finally, the angular deformation as a function of time and measured depth for each drillstring element was calculated.
Static friction is an important performance limiter when slide drilling with a downhole motor. Pipe rocking can be used as a low-cost technique to break the static friction in a section of the well and thereby reduce its negative effect. Pipe rocking simulation was used to find the rocking regime that maximizes the section of the string under conditions of dynamic friction, without losing toolface control. The torsional damped wave equation was used as a drillstring dynamics model because it successfully accounts for the surface rotational energy that is dissipated as elastic energy stored in the drill pipe and friction against the wellbore. Simulations resulted in recommendations to the directional driller on the optimum pipe rocking regime to adopt. The methodology was applied on a historical data set consisting of more than 100 US land wells. It was observed that improper pipe rocking could lead to back-off events, poor toolface control and reduced force transfer to the bit. By minimizing friction, longer horizontal sections and reductions in tortuosity can be achieved. An advisory software program was developed to guide directional drillers on favorable pipe rocking regimes based on contextual and real time data.