An integrated, automated mud system has combined recent developments to produce an overall package which offers characteristics of safety, environmental acceptability, efficiency, economics, operability and ergonomics. Some of its key sub-components are:
- Automated monitoring of solids control equipment.
- Automated addition of mud chemicals.
- Continuous monitoring of key mud parameters.
- Automation of mud system valve control and tank line up.
- Central monitoring and integrated process control.
This mud system will help to define the system and will form a bench mark against which the benefits
of the new system, in terms of HSE; cost reduction and quality, can be evaluated.
Many other industries have reaped HSE and efficiency benefits by the application of integrated automation to their processes. To date this has not been the case within the offshore drilling industry where automation tends to be legislation driven and hence is implemented in a piecemeal fashion. There are many reasons given for mechanising or automating processes; the main ones being:
- Avoid Human errors
- Improved performance
- Consistency & Quality of operations
- Manning levels
It is axiomatic that HSE benefits can be obtained from mechanisation and automation, but efficiency benefits need to be proved. Tubular handling and the mud system operations are activities which utilise the most manpower and offer the greatest potential hazards to personnel and the environment. Previous studies have shown that significant economic benefits can be achieved by closely controlling the mud system.
Because the mud system is key to a range of activities on the rig there are many people in various locations who need to know the status of certain parts of the mud system at different times. This makes the mud system a natural starting point for integration studies. Traditionally the derrick man works on both the mud system and tubular handling activities. For these reasons the project was set up to demonstrate the potential benefits available from integrated automation of the mud system and to assess how this could be extended into the area of tubular handling in the future.
The project’s objective was to demonstrate on a large enough scale the HSE and efficiency benefits of integrated
automation on an offshore drilling rig. Two major points to be addressed were equipment suitability and reliability for this particular duty and the costslbenefits equation. The initial remit was to look at new build rigs where such systems can be implemented from the early design stage and incremental costs are relatively small. However, in light of the lack of new build rigs we have focussed more on retrofitting to existing rigs. This means that much of the experience gained in designing and installing the demonstration system can be directly applied to future retro
The project has four phases
- Equipment Fabrication and Installation
- Offshore Demonstration
each of which is described below.
Mud System Concepts
The original idea was to define the “Ideal” mud system, identify the unavoidable constraints which exist on a rig and combine these to define the “Optimum” mud system. This proved to be an unworkable methodology and we moved to a parallel “Top Down Bottom Up” approach. In this the key attributes of the “Ideal” were defined and used as targets for the “Optimum”. Appendix A gives a global list of attributes for future mud systems and the sub set of the Key Attributes which were used as design guides for the demonstration phase of the project.
At the same time a review of how things are done today and what is available in the market, including areas outside the oil industry, was carried out to assess how many of the target attributes were achievable within the time and cost constraints of the project. This also allowed us to identify those things which should be avoided in future designs.
The focus on “need” highlighted the fact that integration is not just about technology, but about the overall integration of the appropriate technology with the correct people to enable them to perform their required roles as efficiently as possible. This led to challenging a number of ways things are done today, which means that implementation on a new build rig would be different from that implemented as a retro fit to an existing rig.
The requirements for the mud system can be broken down into a number of key areas:
- Mud storage and transfer.
- Fabrication and maintenance (mixing)
- Solids control
- Mud properties
- Equipment performance
- Integration with other rig systems
In order to ensure that the methods being proposed were viable and did represent an improvement on existing methods the necessary functions within the mud area were broken down into a number of key tasks which were analysed in detail. These task analyses were performed for both current methods and for the proposed new methods. The analysis covers both the people needed to perform the task and the necessary communications and interfaces between them; hardware requirements are inherent in the task analysis. Examples of today’s and future methods for adding chemicals to mud are given in Figs 1 and 2. As can be seen in these figures the number of people involved is reduced and the communications are much simplified.
A recurring theme in all of the task analyses performed was communication between different rig personnel; this
highlighted the need for a good communication network and data integration.
To check the validity of the description of today’s methods and to ensure that the project was correctly focussed on areas where potential benefits exist a worldwide survey of operating methods was carried out. At the time of writing data covering 1000 shifts of drilling operations had been collected and analysed. This data includes 150 shifts of
exclusively OBM usage and covers all operational aspects. The data from different rigs is remarkably consistent and its validity has been checked by conducting “snapshot” time and motion studies of mud area activities on three rigs. Figs 3 to 8 give a synopsis of the data.
Fig 3 shows the number of times a particular category of personnel is required to make at least one visit to the mud area as a percentage of the number of shifts in the data set. Fig 4 shows the same data for OBM operations.
Fig 5 shows the average manhours per shift spent in the mud area by the different categories of personnel. Fig 6 shows the same data for OBM operations.
Fig 7 shows the total manhours (excluding the mud engineer) spent in the mud area broken down into main activity
groups. Fig 8 shows the same data for OBM operations.
The major results from the survey for the project can be summarised as:
- Monitoring mud area equipment and mud properties account for about 50% of mud area activity.
- Mixing accounts for less than 15%, which is much lower than expected.
- Cleaning and maintenance activity is significantly higher than anticipated.
- OBM requires much less effort than WBM.
- The project is well focussed on areas which have potential for both HSE and efficiency benefits.
Mud System Design
Mud system design aspects of the project fell into two distinct areas; one a generic design for new build rigs taking into account the tasks, personnel and equipment envisaged for the future, the other the specific design for the demonstration installation on the semisubmersible drilling rig.
In both cases the design work was undertaken with a view to the long term. For new build rigs the objective would be to have only one system sensing any parameter and for all other systems to acquire this information from a rig network. Similarly users of information would be able to extract any available data from this network and use
it within their own system. Thus, for example, a directional driller could have all of the normal drilling monitoring parameters available immediately and the toolpusher would be able to view directional drilling data on his normal terminal without needing any extra hardware.
The generic design focussed on defining requirements for tank volumes, mixing rates and quantities, solids control equipment and avoiding cleaning problems. These specifications were augmented by considering methods of monitoring equipment performance and status remotely so as to avoid the need for personnel to be confined to an unpleasant area for long periods of time.
Mud tank sizing is dominated by the need to store mud recovered from the hole when displacing from one fluid to another. It is possible to reduce active surface volume by close monitoring of mud properties and being able to adjust those properties quickly with the mixing system. Major benefits in reducing tank cleaning can be obtained by the use of cylindrical, dished bottom tanks with no internal obstructions.
Mud mixing will continue to be a batch operation for the majority of cases. However there are potential benefits for on-line mixing of kill mud. It eliminates the need for a dedicated kill tank and avoids mixing weighted kill mud unless it is needed. Land based trials using a continuous, on-line cement mixer proved that it is possible to mix and pump kill mud at the required pumping rate while maintaining accurate density control. This has the added advantage of providing kill mud· at the required weight immediately rather than having to weight up or cut back pre-mixed kill mud to the exact requirements. Reliability of such a system is clearly essential.
Correct use of solids control equipment is essential to optimising mud usage. Earlier work on solids control equipment effectiveness was reviewed and compared with recent experience. The original conclusions remain valid with the major workload being taken by linear motion shale shakers supplemented by centrifuges. Thus the remote monitoring of the status and performance of these devices is a key requirement to allow this part of the mud area to be unmanned during normal operations.
With the equipment and monitoring needs specified the necessary information and control functions need to be made available to the appropriate personnel. In order to enable free choice of the basic equipment the control and monitoring systems need to be OPEN and comply with international standards which are accepted both in the drilling industry and by the potential equipment suppliers. Reviewing the needs in this area shows two different forms of communication are required. Management decisions require a wide range of information from many different sources to be displayed in a comprehensible format which can be changed by the user. For this type of data time delays of order five seconds are perfectly acceptable and a significant improvement on today’s manual communications. For front end control purposes communications are required over a much reduced set of parameters, but time response must be in fractions of a second. At some point in the overall system there is the requirement for a link between the two types of data.
The recommended communications system for management data is WITS over Ethernet. WITS is well accepted in the oil industry and many service companies can transmit and receive data in this manner. This means that specialist data can be added to the system during specific activities very easily.
For the offshore demonstration we· wished to install new equipment for monitoring and controlling the mud system
and integrate this with other rig activities. For this reason we selected a rig equipped with a computerised, drilling monitoring system. This allows us to share drilling data with the mud system operators and to provide mud related information to the driller. Any monitoring system capable of providing comprehensive drilling data in real time WITS format could be used.
The demonstration system for Sedco 712 was designed to be a large enough subset of an integrated, automated mud system to demonstrate the HSE and efficiency benefits. Existing tanks and solids control equipment were not changed and monitoring devices were used only on selected items. The system installed comprised:
- Batch, automated mixing system.
- Automated valve actuation and fluid transfers.
- Continuous monitoring of mud properties.
- Mud solids measurements.
- Central monitoring and control system.
- Links to existing drilling monitoring system.
The key personnel on the rig for the use of the integrated system are:
- Toolpusher / Company man
- Fluids Operator (Derrickman)·
- Mud Engineer
For the demonstration to be successful it was essential that each of these key personnel saw some direct benefit.
For the toolpusher I company man this is provided by giving him a wider window on the rig’s status and to allow him to view information from multiple sources in the combinations he selects.
The driller is provided with schematic views of the mud systems of relevance to his function together with key data. This allows him to check that solids control equipment is correctly lined up and running before starting the mud pumps and to know the quantity and properties of the different muds available to him.
In order to demonstrate the efficiency benefits for the driller the systems have been set up to allow him to line up a slug from the brake. He can check that he has sufficient mud of the correct weight and by a single button push select it. A series of command messages are exchanged and the automated valve system operates the necessary valves in the correct sequence, provided it is safe to do so. The driller retains direct control of the mud pumps throughout this operation. He can monitor progress of the slug pumping operation and ensure that the correct quantity has been pumped before using the system to revert to active mud to displace the slug.
The derrickman is able to line up the mud system and add chemicals remotely by using the automated valve and mixing systems. However the integration of the systems gives him the additional benefits of being able to see the status of the drillfloor operations in real time. Data from the drilling monitoring system is displayed on his mixing
system terminal so that such parameters as pump flow rate and ROP, essential knowledge for optimum operation of the solids control equipment, are available continuously. Data such as “kelly down” depth are also available to allow him to plan his activities.
The mud engineer is similarly able to see current drillfloor and mud area status in real time. He is able to use this information in conjunction with the continuous monitoring of mud properties to optimise mud treatment and minimise the amount of mud mixed. In addition he has the ability to pass commands directly to the automated mud mixing system via the integrated network. Thus if he identifies the need to add viscosifier over a circulation he can pass the appropriate data, total quantity to add and addition rate, to the mix system which will perform the task and send feedback data throughout the mix operation.
In all of the above cases the Programmable Logic Controller based process control systems maintain the safety integrity of the mud system by monitoring remote commands for validity. For example, the slug line up command from the driller will not be implemented until the main mud pumps are stopped, thus preventing potential damage due to starving the pump suction.
The correct operation of all of the above elements was successfully proved during land based commissioning, using simulated data, prior to dispatching any equipment to the rig.
EQUIPMENT FABRICATION & INSTALLATION
The basic equipment layout and communications structure is shown in Fig 9. As shown the automated mixing and valve control system uses proprietary communications standards for internal communications and WITS is used for all inter systems communications including control functions. This was achieved by defming non-standard records for control and valve monitoring purposes. It provides an elegant solution to our needs for demonstration purposes, but should not be considered as a model for the future.
Prior to installation on the rig as much land based testing as practicable was carried out. Fluids monitoring devices such as X-ray fluorescence for monitoring the ratio of high and low gravity solids and a modular sensor package for continuous, on-line monitoring of mud properties including mud weight and rheological properties were subjected to extensive factory and field tests to prove their reliability and accuracy before the offshore demonstration.
Factory trials were performed on a continuous particle size monitor (PD 50) and an ultrasonic level sensor for monitoring liquid level over shale shaker screens to determine the viability of using them offshore. Both devices were included in the offshore demonstration installation.
The most extensive onshore testing was conducted on the integrated computer information systems to ensure that correct data was transferred between systems, command messages could be properly managed and that each system was able to make use of the new data available to it. Rig personnel were involved in helping to design data displays that were in a fonnat that suited their operational needs.
A major design criterion for these systems was that they should be capable of working in stand alone mode in the event of failure of any other device on the network or failure of the network itself. Numerous faults were introduced to ensure the robustness of the overall system.
Onboard installation of the equipment was started during a short shipyard visit by the rig. Completion of the installation and commissioning had to be done during the move to location and drilling of part of the first well. This was achieved with no impairment to the rig’s performance.
The demonstration is taking place on which is drilling three wells for Shell in the South Brent field. Operational necessities mean that certain phases of these wells have to be drilled using OBM or pseudo-OBM. This reduces the need for onboard mixing and means that demonstration of the efficiency of the automated mixing may need to be perfonned partially on shore.
The purpose ofthe demonstration was defined as:
|Cost Effectiveness||manning levels.
The initial phase of the demonstration is to train the rig personnel in the use of the new equipment and for them to gain familiarity and confidence in it. Following this, specific tests will be performed to demonstrate the benefits.
- Compare manual and automated mixing of identical pits of mud. Monitor manpower usage, spillage and quantity of chemical to reach the desired mud properties.
- Derrickman to monitor shale shaker perfonnance and adjust from remote station. Project personnel will monitor the shale shaker locally to ensure no problems.
- Driller to adjust pump flow rate after breaking circulation in accordance with monitored shale shaker level to avoid mud spillage.
- Driller to command slug line up automatically
- Mud Engineer to use on-line properties monitoring for mud treatment decisions
- Use solids monitors to detect failures in solids control equipment
These specific tests will be augmented by an analysis of the reliability and availability of the various systems and by interviewing rig personnel to obtain a qualitative assessment of the usability and effectiveness of the systems.
To date not all of the systems have been finally commissioned so results reflect only parts of the total system. Nonetheless these results are encouraging and the rig crews have been pushing for full implementation.
On-line monitoring of mud properties has shown very good correlation with manual measurements. A typical log is shown as Fig 10 illustrating how mud can be weighted up without the need for constant sample taking and mud balance tests.
The automated valve operation system has been used in remote manual mode allowing rig crews to become familiar and gain confidence.
The automated mixing system has been operated under local control and demonstrated the benefits in less spillage, manual handling and supervision.
Limited data displays have been available to the different personnel allowing them to give feedback on their usefulness and possible future extensions. This has included linking the rig’s drilling monitoring system onto the new network and transferring data across it.
Comments to date include the suggestion of a single button for the driller to allow him to switch to kill mud “on the fly” when drilling top hole in areas with shallow gas and the transfer of mud system data to the Marine Supervisor’s system to aid in ballast control operations.
- The design criteria for mud systems which can reap maximum benefit from Integrated Automation have been defmed.
- A highly automated system, including networked communications between different key rig personnel has been installed and commissioned.
- The mud system has been accepted by the rig crews and has proved to be easy to learn and to operate.
- Data from current modes of operation indicate that the anticipated benefits should be achievable.
Fig 1- 10