Automation-Adoption Approach Maps Human/System Interaction
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This paper describes the progress of directional-drilling-automation systems along the cognitive functions and levels of automation as defined by the Levels of Automation Taxonomy (LOAT) hierarchy introduced by the Drilling Systems Automation Roadmap Industry Initiative. LOAT is based on incremental automation of the four cognitive functions of interaction. Levels of human/system interaction are described on a nine-point scale ranging from fully manual, to levels of system support for the human, to levels of automation overseen by the human, to full automation.
The LOAT Hierarchy
LOAT is a powerful tool for mapping the transition from a purely manual process, to the degree of automation that any system can achieve in the early transition phase, through a timeline to full automation. The transition levels from manual to autonomous were likened to the four cognitive functions that occur in both human interaction with machinery and automated interaction with machinery. These four functions, based on a staged model of human information processing, were translated into equivalent sequential functions applicable to both human processing and automated processing. These functions are
- Information acquisition
- Information analysis
- Decision and action selection
- Action implementation
Automation is often perceived as automation of the action-sequence execution, the implementation of the decision for action by a robot or robotic mechanism. In reality, it is easier and more reliable to apply degrees of automation to the information-acquisition and information-analysis cognitive functions of the control process before decision-making and certainly before action-sequence execution.
In a first phase of automation implementation, the automated system acquires the data and undertakes an analysis of its information. The output from this process in many automated systems is typically in the form of alarms designed to attract the attention of the human overseers. However, challenges are inherent in this process: Does the human receiving the alarm believe the alarm is real and relevant, and, if so, does the human react to the alarm effectively by making a good decision and then implementing the appropriate action as a consequence of that decision? Drilling case studies often describe human indecision and failure to act in a timely manner as a cause of catastrophic events.
The human/machine interface is the point at which the system displays to the human the situation and the human reacts and provides input through control devices. In a purely manual mode, systems simply display data that the human analyzes and uses to decide on and implement action. In staged automated modes, the system is designed to advance the automated collection and processing of data. Initially, the data are presented to the human operator to prompt a decision and implementation of an action. In the next stage, the system provides advice on which action should be taken.
The transition to the optimal level of automation in directional drilling requires that a decision be made about how to achieve the right balance between business needs, technical reliability, and human competence. Automating directional drilling is a solution, but it requires detailed planning. Consideration must be given to the way in which the human can enable the automated system, which of the four cognitive functions are being automated, the level to which the automation will be applied to each function, and the resilience and robustness of the automated solution.
Information Acquisition. The automation system uses real-time data primarily to analyze the performance of the drilling system against the instructions given and to determine borehole displacement as the well is drilled. Borehole-displacement calculations combine downhole surveys with real-time drilling data and require a knowledge of the rig operational state. Rig-drilling-data collection usually takes place in the 1–5-second range, adequate to make positional calculations several times per foot drilled.
When slide drilling, downhole measurement-while-drilling (MWD) tool-face data are used to show the driller the effects of control actions and to analyze both bottomhole assembly (BHA) performance and dynamic borehole displacement. As hole depth increases, the number of twists in the drillpipe increases, as does total wellbore friction. These effects combine to increase the difficulty for the driller to establish and maintain the desired tool face. Tool-face-data update frequency and reliability varies between MWD providers. The use of topdrive oscillators can make it difficult for an automated system to determine which drilling mode is being used. Adding a real-time signal indicating the state of the topdrive oscillator to the data-acquisition system solves this problem.
The definitive wellbore position combines the wellbore tie-in point with the list of approved surveys. Tie-in information should be made available at the start of each well section, requiring timely updates of post-drilling surveys. If this is supplied only after drilling has resumed, the directional driller or system must recalculate the current well position.
Information Analysis. Increasing rates of penetration (ROPs) achieved by modern drilling equipment and techniques are shrinking the time available for the directional driller to make and implement decisions. The necessary analyses of information are typically mathematical in nature and can be automated in a relatively straightforward fashion so that the data are available in suitable forms. Automation systems have the capability of both analyzing more data and processing that data more quickly, thereby reducing the time spent off-bottom waiting for decisions to be made.
The information required for the next step, decision and action selection, is related primarily to actual well position relative to that desired and the expected performance of the drilling system. Most systems allow the human to review the results and alter the information to be used by the decision-making system when the human identifies errors in analyses (usually caused by poor data quality) or applies additional information not available to the system, such as advanced knowledge of an impending drilling-parameter change that would affect BHA performance. Some systems are capable of passing the results of these analyses on to the decision and action selection function without human intervention. This would qualify as a step toward full automation of this function.
Decision and Action Selection. This function has three main components: deciding on the practical well path from the current state to the desired position, knowing when a directional decision has to be made, and knowing whether to slide or rotate.
It is common during the course of drilling for the well to deviate from the proposed path. The tolerance for this departure will vary from well to well, and even from depth to depth in each well. Automation provides value in this context by eliminating manual calculation errors and enabling more-continuous calculations than possible with manual capability. Additional value can also be provided by making decisions on the basis of the tolerance and anticollision rules and protocols provided by the owner of the well and then consistently implementing them through the automation system.
Traditionally, determination of a decision point is driven purely by a survey point, but decision points can be established from observations of drilling data. Drilling data might also allow observation that the rig system is not achieving the desired build in the slide length being implemented because of low tool-face efficiency; thus, revised steering instructions might be required.
At each decision point, the directional driller must first decide if adequate information is available to make a good decision. If not, a new survey may be required. That survey can supplement knowledge of well position or BHA and rig-system performance. Then, a decision whether to slide or rotate must be made. The final output of the decision process is a set of approved setpoints provided to the driller.
Action Implementation. This function encompasses the communication of the steering decision to the rig-control system. Traditionally, this has been done by verbal communication from the directional driller to the rig driller, who then controls the drawworks and brake, topdrive or rotary table, and pumps. Many modern rigs are now controlled by electronic rig-control systems with push-button or joystick input of control set points.
To proceed with rotary drilling, the instructions would normally consist of a target surface weight on bit (WOB), string rotary speed, and flow rate, but might include other instructions such as target ROP or differential pressure across the downhole motor.
For normal slide drilling, the instructions would normally include WOB or differential pressure and a downhole tool face to be achieved and maintained. During kickoff, whether from vertical or during an openhole sidetrack, the instruction might include a target ROP. Setting and maintaining the desired downhole tool face requires the drillpipe surface angular position to be manipulated to allow for twist and is one of the operations where experienced drillers currently excel. As drilling proceeds, the length of pipe in the hole increases and the surface angular position of the drillpipe must be adjusted. Similarly, as the downhole WOB or differential pressure changes, the quill position should be adjusted to allow for the change in reactive torque from the downhole motor.
A next step up the automation hierarchy is for the directional-drilling-automation software to pass the directional-driller-approved setpoints to the driller or to the rig-control system directly.
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