RIG AUTOMATION-1 AUTOMATION TO BENEFIT CURRENT, FUTURE RIGS

April 9, 1990
Will L. McNair Texas Engineering Extension Service College Station, Tex. Old rigs are being modified piecemeal with various technological improvements to increase drilling performance. On the horizon are the completely automated drilling rigs that are promising safety and efficiency to rig floor operations. In this first installment of a two-part series, the benefits of the technology to automate a complete rig and the modules needed to modify existing rigs are analyzed. The second installment
Will L. McNair
Texas Engineering Extension Service
College Station, Tex.

Old rigs are being modified piecemeal with various technological improvements to increase drilling performance.

On the horizon are the completely automated drilling rigs that are promising safety and efficiency to rig floor operations.

In this first installment of a two-part series, the benefits of the technology to automate a complete rig and the modules needed to modify existing rigs are analyzed. The second installment will detail how automation can change specific drilling operations.

DRILLING LAGS BEHIND

Drilling rigs have evolved over the past 50 years. The slow-moving mechanical systems driven by internal-combustion engines of the past, first changed to rotating electrical generator-motor systems. Now, over 50% of all rigs have electronically controlled, silicon-controlled rectifier (SCR) variable speed drives.

This electronic evolution has created tools and downhole data acquisition devices that reduce the guesswork involved in the drilling process.

While significant improvements have been made in the drilling industry, the technological changes lag considerably when compared with other segments of the petroleum industry.

For example, the production and processing segments of the industry have introduced microprocessor-controlled data acquisition and control systems for offshore production platforms, pipelines, and petrochemical processing plants.

Scada (supervisory control and data acquisition) systems use automatic computer controls to monitor and control offshore platforms from a central land-based location as shown in Fig. 1. In these areas, computer control has been applied to reduce manual labor, optimize processes and performance, and improve safety in operations.

Throughout petrochemical plants and field production sites we find variable frequency, variable speed, ac motor drives in pumping and mixing applications. Pipelines use these same variable speed drives at booster stations to pump liquids at a reliable, remotely controlled pace with reduced maintenance.

The conclusion we draw from witnessing these applications of technology is that the drilling industry is missing out on an opportunity to solve some of its current and future problems.

DRILLING INDUSTRY NEEDS

The past 5-8 years of the drilling industry downturn and depression has seen the stacking of land rigs and mobile offshore drilling units (MODU's), very low sales of new rig equipment except in occasional non-U.S. areas, low investment in new technology and rig improvements, significant layoffs of personnel, closing and merging of drilling companies, and an attrition of experienced "hands" from the industry.

The current status of the drilling industry shows a few survivors who have reorganized, refinanced, restructured, and refined operations to the point that a skeletal structure exists.

There are signs of a slight upturn in drilling, and the first requirement is to hire more "hands" to get the rigs back to work. But the problem now is that the reservoir of personnel to operate the rigs has diminished, since the industry no longer provides the security and incentives it once had.

CURRENT DRILLING TECHNOLOGY

What we now have in certain cases, even with the downturn, is a modern drilling rig that offers these technology improvements:

  • SCR-type variable-speed dc motor drives

  • Top motor drives that reduce stuck bits and lost holes

  • Measurement-while-drilling systems that provide downhole data for improved performance

  • Directional and horizontal drilling techniques that improve downhole production

  • Computer-controlled automatic weight-on-bit coring controls that reduce drill bit wear and increase core lengths

  • Automatic pipe-handling systems that lift, position, and makeup/breakout drill pipe

  • Electronic-controlled BOP systems.

Each of these technology improvements meets the needs for improved safety, fewer lost holes, reduced, drilling time, and improved drilling performance.

In most cases, however, the drilling contractor's rate will increase when he adds new technology equipment. But the producer/operator is willing to pay this premium when he gains confidence in the added benefits produced. In these cases, it represents a win-win situation for both parties.

Fig. 2 shows a typical top-drive system that allows the driller to drill complete stands of pipe (three joints) before connections are made as compared to individual joints of drill pipe used in rotary table-operated systems. This reduces lost time that can be used for productive drilling.

Another significant advantage of the top drive is the ability to rotate while the bit is lifted off bottom, thereby reducing the possibility of a stuck bit and resulting fishing job.

Another significant advancement has been made in coring with the automatic weight-on-bit control system introduced by Parker Drilling Co. The system (Fig. 3) uses an electronic load cell positioned above an in-line top-drive motor to weigh the complete drillstring. Once the bit touches bottom, the drillstring relaxes an amount equal to the weight on bit.

This feedback through a closed-loop automatic-control system allows maintaining the bit weight within 0.1% of the desired setpoint. After each core section is drilled, new data update the computer to continue the coring process (Fig. 4).

Automatic pipe-handling equipment has been introduced on a limited basis on small land rigs and on European offshore rigs. On a long-term basis, this represents a major improvement in improving safety for personnel and reducing damage to pipe threads caused by improper positioning.

Downhole drilling techniques are allowing drillers to direct accurately their bits at a slant or completely horizontal to penetrate multiple pay zones with the same drilling operations. Significant production improvements are being made using these techniques which use sophisticated electronic packages downhole and at the surface.

Power management controls for the diesel-generator packages have been available for many years but few drilling contractors have taken advantage of them. Complete application of this technology would allow rotation of individual units to reduce maintenance, automatic start-up and removal when power demands require this action, and proper loading to optimize use of diesel fuel.

DEFINING AUTOMATION

The evidence we see in the technology being developed and added to new rigs is a trend toward automatic rig operation. While only individual pieces are currently being employed to perform certain functions, these can form the basis for future drilling automation.

Automation has been employed in many industries for the following reasons:

  • Replace manual, repetitive, tasks with machines

  • Remove personnel from hazardous areas

  • Improve processes by more precise control

  • Produce better quality at higher performance levels

  • Optimize the time to perform certain functions

  • Perform multiple functions simultaneously.

If we analyze each of these reasons, we find many applications in the drilling process. For example:

  • Setting up a drilling rig at spud-in could be accomplished with automatic machinery as compared to the exposure of personnel to injury.

  • Handling and processing the drill pipe could be accomplished with automatic pipe-handling equipment with minimal manual effort required.

  • Automatic drilling controls to maintain bit weight, penetration rate, or other variables could be used to improve the drilling process.

  • The mud system could employ mud mixing and weight control, flow control, and pressure detection.

  • Variable-speed drives could be controlled from a central console to optimize drill-bit speeds based on downhole conditions.

  • Diesel-generator sets could be automatically started, paralleled, load shared, and removed based on operating conditions of drilling or tripping.

  • Detection of down hole gas "kicks" signifying potential blowouts could be automatically controlled with increased mud weight or shut in of the BOP system as required.

AUTOMATED EQUIPMENT

The obvious question when discussing automation of drilling rigs is "what type of equipment must be added to existing rig designs to automate the process?"

While this question cannot be answered in simplistic terms, a general grouping of component functions can be identified. These functions include the power system, actuator, sensors, control signal processing, and control cabling.

POWER SYSTEM

In the early days of drilling, mechanical power from diesel engines was used through chain and gear transmissions to perform the functions of rotary drilling, mud pump control, and drawworks hoisting. From that point, hydraulic and pneumatic power techniques were implemented primarily because of the hazardous environment of gas present at the rig.

As the rig has evolved to its current design, more and more electrical power equipment has been added, with explosion-proof types being used in hazardous areas.

While some hydraulic and pneumatic equipment will still find suitable application on the rig, the primary need will be for electrical power on the rig.

ACTUATION

The component used to move, position, accelerate, torque, and change equipment such as pipe and mud-handling systems is the actuator. This actuating equipment can be powered by either electric, hydraulic, or pneumatic means to produce the desired mechanical output of torque, pressure, force, speed, and flow.

Because a significant amount of automation is based on electronic controls and sensors with electrical outputs, the obvious and simplest method of interfacing is electrically powered actuators such as electric motors and linear actuators.

SENSORS

Devices used to sense equipment position, speed, torque, pressure, flow, depth, tension, strokes, temperature, acceleration, and other physical parameters are referred to as sensors.

The most reliable and accurate types currently used in industry are in the form of semiconductor elements that produce an electrical output. It is this type of sensor that interfaces well with electronic signal-conditioning devices and in closed-loop control systems.

CONTROL SIGNAL PROCESSING

With the introduction of the personal computer and other digital devices, the device that has had the most significant impact is the microprocessor.

It has the capability of accepting multiple inputs and producing an output in response to a predetermined program description.

The microprocessor represents the ideal device for designing an automated rig in a closed-loop control system.

CONTROL CABLE

One of the critical elements involved in a control system is the electrical cable used to transmit low-power control signals from the sensor to the controller and to the actuating device.

Small copper cables can be used in some cases but due to the significance of the signals being transmitted, shielded pair cables are preferred.

Both analog and digital signals can be transmitted over these cables.

With the proven application of fiber-optic cables, these represent the preferred method of transmitting digital signals in an environment containing "noisy" electrical power such as exists on drilling rigs.

AUTOMATING EXISTING RIGS

While most of us have envisioned an automatic rig from the standpoint of a specially designed machine that is out of reach of most contractors, limited automation can be implemented into existing rigs. By using a modular approach where each major drilling function is packaged separately into an automated package, varying degrees of automation can be implemented to meet particular needs.

Typical segments of the rig that can be modularized include:

  • Pipe-handling system to move pipe from ground level to rig floor prior to makeup connections.

  • Pipe makeup and breakout system, including position and torquing controls.

  • Power management of the diesel-generator sets.

  • Mud-system control which would include mixing mud chemical, water/oil/chemical additives, mud-weight control, mud-flow control, mud-loss detection, mud-gas detection, shale shaker and filtration system, mud temperatures, salinities, and alkalinities.

  • Rotary drilling controls of bit speed, bit weight, penetration rate, direction of rotation, torque, and drawworks lifting controls.

  • Tripping controls which would include the drawworks, drawworks braking, and pipe inventory controls.

  • Hole safety controls, including gas and pressure detection and BOP operation.

  • Use of ac variable-frequency drives with ac motors to reduce maintenance and improve safety as compared to current use of SCR-dc motor drives.

  • Systems using directional and horizontal drilling equipment. These can be added to the system as separate modules and integrated into the total system operation.

  • Data acquisition of many drilling variables can be implemented, including downhole pressure and formation information, bit weight, bit speed and penetration rates, mud flow and pressure information, hole depth, and gas detection.

One or any number of these modules could be added to existing rigs with some design and planning effort. The power modules would perform the actuating functions while the control modules would be incorporated in a central console.

With a system of this type, personnel could be removed from the rig floor during normal operations, and considerable activity could be accomplished from the central console by the drilling operator.

MODULAR SYSTEM

Fig. 5 shows a typical system for the functional blocks of an automated rig system. Individual blocks could be incorporated into existing or new rigs or the complete system could be implemented for maximum results.

This diagram also shows two paths of control. One is the power bus, and the other is the control bus where commands are given and information from sensors are received by the central microprocessor in the master console.

This concept would allow standard control signals to be implemented so that compatibility between different manufacturers is established in much the same way that personal computers use standardized bus architecture.

A standardized method of operation as described by an algorithm would form the basis for a modularized automated rig.

THE AUTO-RIG

In the early 1980s, an attempt was made to design an automatic drilling system, but significant technical and operational problems could not be overcome economically. Since that time, there have been significant advances in technology that make the auto-rig a real possibility.

One of the essential elements is the microprocessor that allows multiple inputs to be processed to a desired, programmed, output for control.

Using the microprocessor as an integral part of the system design, techniques such as multiplexing and fiber-optic transmission of signals in a noisy rig environment can be economically implemented.

Some considerations that would have to be made in the design of an auto-rig for oil field use would include:

  • Redundancy in the control signals and cabling

  • Easy implementation of replacement modules

  • Self-diagnosing of trouble to reduce the need for high-level technical assistance

  • Manual overrides as required

  • Ruggedized construction

  • Simplicity of operation.

PLANNING FOR THE FUTURE

If proper action is taken by the drilling industry, a significant change can be made in the character of its operations.

By continuing to apply new technology to reduce the activity of floor hands, we will see the employment of more technically trained personnel.

Instead of "roughnecks," we will have "rig-techs." Instead of "drillers," we will have "operators." Technicians will replace electricians. The word "hands" for personnel may become obsolete with the reduction in manual labor.

The end result of the auto-rig will be a system:

  • That allows machines to be hurt, not personnel.

  • Whose drilling performance can be optimized through data acquisition

  • That becomes compatible with ever-advancing downhole drilling technology

  • That utilizes more technically knowledgeable personnel as compared to those who learned their art through experience.

Automation and data acquisition has a number of side benefits beyond the actual field-site activities. One of these is the ability to compile drilling progress information (the "morning report") in a computer and transmit this via telephone or satellite communication on a real time basis to the home office.

In this way, the rig superintendent, who generally has several rigs under this supervision, can observe each rig's activity, problems, and performance from his desk-top computer.

He can provide immediate direction via the computer link to the field when needed and use office technical expertise to solve rig-related problems.

ACKNOWLEDGMENT

Permission has been granted by companies to use the photos, references, trade names, and concepts used in this article which may be proprietary to these companies.

BIBLIOGRAPHY

  1. Giannesini, Jean Francois, "Production technology for horizontal wells takes new direction," World Oil, May 1989.

  2. Wilson, J. E., and Bried, Frederick, "Application of Programmable Logic Controllers for Pipeline Local and Remote Control," IEEE Transactions On Industry Applications, November/December 1988.

  3. McNair, Will L., The Electric Drilling Rig Handbook, PennWell Publishing Co., Tulsa, 1980.

  4. Varco International Inc., "Top Drive Drilling System Description and Specifications," Technical Bulletin, Orange, Calif., 1988.

  5. Wagner, Bob, "Successful Hybridization of Drilling Technology For Reliable Continuous Coring Systems," Energy Technology Conference. Houston, 1988.

    Copyright 1990 Oil & Gas Journal. All Rights Reserved.