Directional drilling has been used in oil and gas operations since the 1930s when onshore drillers employed the technology to reach offshore reservoirs. Over the years, technologies have been introduced to improve precision and control and at the same time have allowed multiple reservoirs to be produced through a single well, which reduces drilling costs and minimizes the environmental impact of the drilling process. In designing drilling plans, operators have considered economics when deciding whether to employ the traditional process of rotating the drillstring to control well trajectory or use more precise directional drilling techniques, but an either/or approach is not always the best one. The introduction of software that analyzes drilling conditions and determines the most appropriate drilling solution is changing the status quo, streamlining the drilling process and changing the playing field for drillers.
The widespread adoption of horizontal drilling from narrowly spaced slots on a centralized pad location has led to the introduction of complex wellbore geometry intended to maximize field development while minimizing geographical footprint. The growing need for precise execution of complicated well trajectories increased the demand for directional drilling expertise. Using a steerable bottomhole assembly (BHA) comprising a mud motor with a bent housing, an experienced directional driller can orient the bend of the motor in the direction prescribed on the well plan to steer the well on the intended trajectory in a process known as sliding. When the well trajectory is intended to remain relatively straight, the entire drillstring is rotated from surface in a process referred to as rotating.
Experience and research have shown, however, that the well trajectory is rarely straight during periods of rotation due to rotational tendencies, a combination of systematic and random influences from BHA design, drilling parameters, and geological formation characteristics that can cause a significant divergence from plan. Rotational tendencies, along with designed well plan deviations, often require sliding to ensure the well follows the planned trajectory.
All else being equal, it might seem that sliding should be applied across the board, but there are two reasons that sliding is not the default solution.