Automated Geometric Path Correction in Directional Drilling

Abstract

AbstractFor a drilling engineer, designing and following an optimum well path is of foremost importance to ensure efficient wellbore placement. But the departure from a planned path is quite common. The objective of this research was to define algorithms to detect a well going off from a planned path and to find the most efficient corrective path to enable downhole directional automation. The closed-loop algorithms were examined using a hardware simulator and a software simulator.The path correction algorithms combine survey calculation methods like Minimum Curvature, Balanced Tangential and Natural Curve methods with complex curves like a cubic spline, Bezier, Catenary, and clothoid to describe the corrective path. Here, the corrective path is divided into two sections. The curve properties like curve length, curvature and torsion are determined based on the location of the nodal point between these sections which in turn defines the Well Profile Energy or WPE of the curve. In this work, the WPE was chosen as the efficiency parameter because it considers both bending and twisting of a curve while providing a quantitative value which signifies efficiency of a curve. Combining a curve with a survey calculation method yields a unique well path corresponding to the minimum WPE for that combination and the most efficient corrective path will be chosen by comparing WPE for all twelve possible combinations of curves and survey methods.To test the applicability of the path correction algorithms in a continuous downhole system, a MATLAB-based software simulator was designed. The dynamic deviation of the well due to factors like bit walk, formation heterogeneity, local stress regimes, bit walk and error in the directional drilling tools was applied using an arbitrary ‘Deviation Factor’. With its inclusion, we could simulate dynamic downhole drilling conditions in the simulator. Several parameters like maximum allowable curvature, torsion, maximum allowable inclination, allowable length of the corrective path were used to ensure a realistic, drillable path. Real-time application of the closed-loop algorithms was successfully examined by designing a hardware prototype controlled by a microcontroller. The directional changes were applied using two linear actuators and the resulting directional survey was recorded using a three-axis accelerometer.This study provides three-dimensional algorithms for detecting when a well goes off path and finds the most efficient corrective path. The corrective path replaces the planned path and is continuously tracked for accuracy, making this a continuously closed loop system that, if combined with a MWD system, can enable an automated downhole directional drilling system.