Performance Analysis of a Downhole Regulator on Rate-Of-Penetration and Drilling Efficiency: An Autonomous Load Management at Bit

Over the last years, the use of autonomous solutions for balancing the loading on the drill-bit has increased annually. By 2021, downhole tools for this purpose have been used for more than 1, 500 wells and these become possibly the fastest growing trend in drilling. Polycrystaline Diamond Compact (PDC) drill-bits represent a great potential for drilling economics when steady cutting is attainable. Deep drilling, however, typically involves long drillstring causing an array of dynamic instabilities preventing steady cutting conditions at the bit. Such behavior affects drilling performance in terms of the rate-of-penetration (ROP) and system damage and failure. This leaves a big potential for improvement of drilling performance. The first experiments with an autonomous downhole regulator constructed were completed at Ulrigg in Stavanger almost twenty years ago to tap into this potential. Several versions of similar tools have since developed using a variety of mechanical and hydraulic functions to modify and shift the forces acting on the drill-bit in order to improve drilling performance. The Norwegian operator Equinor has participated from the very start of this new automation trend. By 2020 they had deployed downhole regulators to a total of 93 well sections on the Norwegian Continental Shelf alone. In this paper, Equinor shares statistic plots from comparing these first 93 sections to well section with conventional BHA's. The data show how the continuous improvement of the regulator eventually led to gradual improvement of both ROP and footage - in addition to its initial task of reducing vibrations. By utilizing a variety of dynamic models, predictions and sensitivity analysis, it has been revealed that the downhole regulator could change the dynamic response of the bit such that the friction losses at the bit are reduced and the rock cutting efficiency is improved. In this paper, it is shown that such benefits can also be expected in real-life scenarios in which two key aspects play a role: 1) a PDC bit penetrating heterogeneous layers of rock formations, and 2) involving two frictional losses due to borehole - drillstring contact in deviated wells. This paper brings a unique insight to the fundamentals, advanced mathematical models, and statistical results from a new line of drilling technology. The autonomous regulators bring a combination of reduction in risk and time to drill that makes a significant impact on cost.