Enhancement and parametric analysis of a model of drilling assembly equipped with a rotary steerable system

Abstract

Demand in products derived from crude oil and the decrease of the gas and petroleum reserves have been boosting the petroleum industry to always beat back the limit between reserves and resources, explaining why the interest for directional drilling has been growing up during the last several decades. Nowadays, rotary steerable systems are so efficient that they are becoming the benchmark for the industry. More than one million feet of well-bore are drilled every year using this technology. The drilling industry handles dimensions and times that cover several order of magnitude. The time scale ranges from seconds for the bit revolution to days for the drilling of a well, while the length scale ranges from hundredth of millimetres for the penetration parameters of a bit in a rock formation to kilometres for the length of a drillstring. This makes the drilling industry such an unfamiliar field which confronts engineers to unconventional challenges. This complexity may explain why, despite the substantial resources of the oil industry, directional drilling processes are still misapprehended. Indeed, the industry continues to rely on trial and error to control the direction of an oil well. Nevertheless, relatively recent theories try to comprehend the directional behaviour of a drilling assembly in order to predict, with relative success, the geometry of the borehole drilled. Mathematical models of the near-bit region of the drillstring already exist. However the literature covers especially drilling assembly equipped with a pushthe-bit system. The main purpose of the second part of this work is to develop a mathematical model of a drilling assembly equipped with a point-the-bit system. This one is an enhancement of the Mathematical Model of the Near-Bit Region of an Advancing Drilling System developed by Detournay (2007). The model is composed of three interacting components: (i) the equations governing the geometrical evolution of the borehole, (ii) the laws that link the kinematical bit-rock penetration variables to the forces on the bit, and (iii) the relationships between the forces on the bit and the loads on the drillstring. The third part of this work presents the results of a parametric analysis of this mathematical model. Theparametricanalysis, ledintheframeworkofplanarboreholetrajectoriesandstationary solutions, focus on the the borehole curvature and distinguishes the two configurations of the BHA: with and without rotary steerable system. Finally, a brief case study of a commercialised point-the-bit system is presented in the fourth part. The goal of this last section is to validate the mathematical model developed and highlight the limitations of this one. Some commonly accepted thoughts are also approached.