Drilling Control System Automation to Control Axial Velocity Optimises Tripping and Drilling Performance
Authors: Bacon Robert , MacKinnon Stewart , Abrahamsen Egil 
Published: June 2022

The purpose of this paper is to document an ongoing project to optimize the drill-string tripping and casing running speeds, with the view to tripping as efficiently and quickly as the rig limitations allow, but doing so in a safe manner that prevents nonproductive time, both visible and invisible, and retains at all times the wells integrity and allows safe operations.

There are many factors that contribute to nonproductive time, these include but are by no means limited to Lost circulation, formation influx, pack-offs and other stuck pipe events which cause delays, problems, lost time, and generally increase risk, and cost of the well, during drilling operations. Such situations can, sometimes, escalate into serious problems that may result in expensive and undesirable technical sidetracks. Couple this with ever more complex wells, (whether they be long horizontal sections, multi-laterals, etc.), drilled in ever smaller and more challenging reservoirs, such as those which are depleted, or at high pressure and or high temperature.

Modelling software offers forward-looking simulations that can be used to predict drilling problems and assess the likely effects of remedial options. During real-time monitoring, advanced monitoring and trend analysis software can use downhole conditions and mud properties to forecast hole cleaning, equivalent circulating density (Estimated Circulating Density (ECD)), and temperature changes for the next depth/time interval, based on three tightly coupled real-time dynamic models - hydraulic, mechanical and thermodynamic - that simulate wellbore condition and characterize improvement or deterioration during drilling. These models continuously assess drilling performance, borehole conditions, and associated risks based on real-time symptom detection.

The solution and concept presented in this paper showcases a modelling approach which allows all of these situations to be accurately modelled in a transient setting, and then also compared and back modelled using all the available real time high frequency data. This coupled with an automated drilling control system has resulted in safe, record-breaking drilling achievements in the North Sea. The models allow updated safeguards to be applied to the drilling control system to maintain a downhole pressure within the acceptable limits of the open hole formations. It also automatically stops the movement of the drill string in case of abnormal hook loads or surface torques. Since automatic actions can be triggered in case of an unexpected situation, some standard procedures have been fully automated, including friction tests and back-reaming. In prior papers and technologies, the peak surge seen when pipe is first moved and gels are ‘broken’ has been used as the limit for safe tripping, however that precluded further optimization that exists once gels are broken and pipe and fluid is in motion. This optimization process will be discussed in detail in this paper.

This ‘dual speed’ optimization approach can be achieved by a more advanced use of mud gel-break and rheology data and a new auto sequence for stepwise axial velocity control.

This paper details a project which is a step in targeting an autonomous and optimized drilling process.