Drilling Automation: An Automatic Trajectory-Control System

Abstract

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 143899, ’Drilling Automation: An Automatic Trajectory- Control System,’ by Dimitrios Pirovolou, SPE, Clinton D. Chapman, SPE, Minh Chau, Hector Arismendi, Mbaga Ahorukomeye, and Juan Penaranda, Schlumberger, prepared for the 2011 SPE Digital Energy Conference and Exhibition, The Woodlands, Texas, 19-21 April. The paper has not been peer reviewed. Rotary steerable systems (RSSs) enable faster drilling, smoother wellbores, and extended-reach drilling. Still, a drilling assembly built around an RSS tool is sensitive to factors such as bit type, operating parameters, type of drilling fluid, lithology, and borehole diameter. Therefore, it is not always optimal for a human operator [typically a directional driller (DD)] to select and issue the correct commands to the drilling tool at the correct time. This situation becomes even more challenging when those decisions must be made in a matter of minutes. Introduction Typically, the DD monitors the path of a wellbore by use of stationary surveys, which include measured depth, inclination, and azimuth at the downhole survey station and the three computed Cartesian coordinates: true vertical depth (TVD), north/south (N/S), and east/west (E/W). Also, the DD sometimes uses continuous surveys (i.e., while-drilling vs. static surveys) to monitor the steering behavior of the drilling tools qualitatively. All this information is used to estimate the actual trajectory being drilled. An RSS generally works by pointing or pushing the bit in a particular direction with a specified amount of force. The direction and force are set by issuing steering commands from the surface to the RSS tool. By downlinking steering commands while the well is being drilled, well paths can be created that follow a specific predefined plan. However, the steerability of the system can be affected by operating parameters such as weight on bit, rotary speed, and hardness of the formation being drilled. In remote operations, when a DD may be monitoring or executing more than one job, the expertise generally must increase as the time constraints tighten. This requirement further necessitated tools that could assist the DD to maintain the desired plan. Steering Application Use of directional information enables correlating a drilled path to the RSS commands that were issued to drill the wellbore. Measurements can be from either a static or a continuous (while-drilling) survey. The problem has two main components and is diagrammed in Fig. 1. Understanding the steering behavior of the drilling tool on the basis of steering commands (input) and actual steering responses (output)—Blocks 1 and 2 of Fig. 1. Suggesting the optimal steering command to send to the RSS tool that will produce the desired steering response—Blocks 3 through 5 of Fig. 1.