Micro doglegs are a natural effect of any vertical or directional well that can explain a wide variety of down hole problems, from additional torque and drag to an inability to run completions. These doglegs are inherent to the rock drilling process and can generate borehole spiraling in vertical sections or slide-rotary pattern when using steerable mud motor in horizontal sections. Standard surveying every 95ft or so cannot detect these micro doglegs and only gives a partial look at the actual well path. This paper presents the results of a case study showing how accurate downhole measurements combined with advanced drill string modeling can detect borehole tortuosity and better quantify the down hole drilling efficiency. A trajectory prediction model able to calculate the inclination and azimuth each foot or so has been developed to estimate micro doglegs using standard surveys, bottom hole assembly (BHA) data and steering parameters. In the demonstrated case, a slick motor assembly was used to drill a horizontal well in a single run. The predicted trajectory was then compared to actual continuous inclination data gathered by the measurement while drilling tool during drilling and showed a good match between the predicted trajectory and the actual drilled trajectory. Transitions between sliding and rotating modes are highlighted by micro doglegs and downhole forces, such as bending moment close to the bit, are well reproduced by the model. This new methodology combining downhole data measurements with drill string modeling analysis highlights the potential for drilling optimization and wellbore placement. Having a better definition of the well path is very critical for torque and drag analysis and wellbore placement. This paper presents for the first time a comparison between continuous survey measurements and computer modeling to highlight the importance of micro-doglegs in evaluating drilling performance.

As the industry continues to drill increasingly complex wells, the demand put on drilling equipment has increased and will continue to increase. Preventive maintenance often falls to the wayside in favor of keeping the same equipment operational for longer until a failure occurs, which can be very costly and potentially catastrophic to the equipment provider. Fatigue tracking makes it possible to predict failures ahead of time and prevent such incidents. However, the most commonly used fatigue tracking methods are based only on rotating hours and do not take the bending stress into account. Electronic drilling recorders (EDR) coupled with bottom hole assembly (BHA) models allow for better estimation of the fatigue performance by calculating the actual bending stress along each piece of equipment, such as the mud motor or measurement while drilling (MWD) tool, leading to a more reliable fatigue tracking method. A case study of fatigue on a common motor and MWD over the drilling life of a well provides valuable information on how to monitor and react to different fatigue scenarios. By using an advanced stiff string model to calculate stress distribution along the motor or MWD coupled with standard fatigue prediction models, valuable information can be learned about the motor and MWD conditions. One case that will be examined involves a typical well trajectory such as those drilled in the US land market today which involve a high dogleg curve to reach a target formation, with dog leg severity (DLS) locally reaching 18 (deg/100') generating high bending stress and thus fatigue. The consequence on fatigue life can be dramatic through the BHA for even just one exceptionally high dogleg. By using the continuous surveys taken by an MWD tool, to account for the actual tortuosity of the well, the potential fatigue becomes even more significant. Another decision that is commonly made without much regard for fatigue consequences is that of stabilizer placement along the BHA which can dramatically shift the distribution of bending moment and thus extend the life of a mud motor. Simulations will show how wellbore tortuosity can affect dramatically the fatigue life of mud motor and MWDs. By illustrating several common examples of fatigue influencers, engineers will be better equipped to determine the impact of different decisions on the potential motor and BHA fatigue. Better understanding of the nature of fatigue and the consequences of larger bend motors, higher doglegs, and better surveying practices, for example, can lead to better decision making and the reduction of fatigue failures.

Aluminum drill pipe has already been proven as a viable alternative to steel drill pipe when drilling long horizontal wells thanks to its lighter weight that does not compromise resistance to yield and buckling. At the same time, the development of unconventional wells has seen the deployment of numerous technologies to further improve the performance and increase the lateral section to reduce costs. An operator has recently and successfully tested a new aluminum drill pipe with an axial oscillation tool to push further the limits of the drilling system. This paper presents the key findings of the case study using a mixed aluminum-steel string combined with an axial oscillation tool. First, the innovative drill pipe design is presented, followed by lessons learned during rig operations regarding pipe handling practices, rig compatibility and pipe inspection. Then, results of the drilling simulations performed during the well planning phase are presented. This modeling led to an optimum drill string design associating the steerable mud motor assembly, aluminum drill pipe, axial oscillation tool and steel drill pipe. The number and placement of aluminum drill pipe along the string was key to reducing friction and improving weight transfer between the bit and the axial oscillation tool. Through extensive modeling and field data interpretation, this paper presents the comparison of the overall drilling performance between steel only and aluminum-steel drill pipe strings, and provides metrics in terms of weight transfer and rate of penetration improvement. This innovative and promising drill string design opens the doors to set new limits in terms of horizontal departure.