Recent successes with the RamRig design in the North Sea are proving the concept's viability. Working through the initial learning curve, and some situations beyond their control, Maritime Hydraulics continues to fine tune an already operational design. The concept was first launched in 1987, with further development boosted by the EfEx (Efficient Exploration) program for Saga Petroleum in 1994. Third party function feasibility verification was issued in September 1995.
Maritime Hydraulic's RamRig concept consists of its proprietary Ram-Guide, rams, traveling yoke, and hoisting wires. The Ram-Guide replaces the mast of conventional rigs, and the Rams are two hydraulic cylinders, used for hoisting and drillstring compensation.
Compensation is applicable in active and passive modes. The maximum compensating stroke is equal to the length of the cylinders, up to 120 ft, and not limited to the 25 ft with conventional hoisting systems. In passive compensation, the limit is a 50-ft stroke. The accuracy and dynamic capability of the compensation system is especially impressive. Total hoisting capacity of the design ranges from 150 tonnes to 750 tonnes.
System advantages
The advantages of the RamRig design, according to the designers, are:
- 20-30% reduction in weight compared to conventional rig
- Lowered center of gravity (COG)
- Increased vertical deckload (VDL) capacity
- Reduced rig footprint compared to conventional rig
- Improved employee safety
- Reduced noise (acoustic noise was actually introduced in the drillers cabin on Oseberg East platform rig to remind the driller when hoisting is ongoing)
- Reduced manning when drilling crews become familiar with the operations
- Integrated active/passive drillstring compensation.
"The basic challenges with the design and delivery of the RamRig have been workload and parallel activities," explains Torstein Bringa, Vice President, Maritime Hydraulics AS. "To improve the situation and test the design before it was actually built, we built a complete RamRig simulator. System multi-functionality was simulated with hands-on training in a purpose-built driller's cabin, and use of advanced computer graphics. Also, we used personnel with operational drilling experience in the different projects. Both of these steps were considered crucial, in order to overcome the challenges we had experienced.
"Topics for future RamRig development as we see it today are improved tripping speed and improved drillfloor arrangement," Bringa continued. The Oseberg East RamRig was the first rig to receive adjustments to achieve these improvements. As part of Oseberg East's preventive maintenance program, production was shut down on the platform for approximately two weeks in June.
Maritime Hydraulics and Norsk Hydro used this opportunity to do some modifications to the RamRig systems. The changes related to increasing tripping speed, late adjustments to the hydraulic system, the pipehandling system, and the control system software.
Due to limited time and rig availability the following were not implemented during this shutdown, but are scheduled for implementation later:
- Reprogramming of the iron roughneck to optimize performance
- Preparations for implementation of a "monkey tail" to reduce the roughnecks traveling distance during tripping operations
- Optimize anti-collision restrictions.
Drilling optimizer
The recent successes have allowed the Maritime Drilling Optimizer (MDO) to be further tested and evaluated for the RamRig. The MDO was originally designed for conventional rigs with a typical derrick and drawworks system, aiming to maximize rate of penetration (ROP) utilizing a number of high-resolution sensors and flexible software algorithms for hardware monitoring and control.
Many Maritime applications can be realized with this system. The applications are known as Drumdrive, Autodrill, AutoROP, Turbodrill, Soft Torque, MaxROP, Drill Off Testing, Stall Detector, and Autocirculate. The most applicable function to a driller is Drumdrive, allowing millimeter control of the block position and eliminating the conventional drawworks limitation of clutching-in at high hook loads. Autodrill allows effective measurement of hookload, thus eliminating the "brake-on, brake-off" scenario of conventional rigs. AutoROP allows drilling at constant speed instead of constant weight. Turbodrill monitors standpipe pressure and can improve steerable motor efficiency by maintaining constant pumping pressure, and thus consistent motor torque. Soft Torque reduces torsional vibrations by changing top drive speed with changing torque. Autocirculate allows a preset range of automatic vertical movement of the block, giving the driller freedom to monitor other operations more efficiently. The system is particularly suitable for the RamRig concept.
Learning curve
"The RamRig concept has exhibited satisfactory performance so far," stated Bideford Dolphin's Rig Manager, Terje Tjelta. "Drilling continuity and uptime has been better than expected.
"Downtime has been limited and related to minor stops and adjustments. The concept gives better control and accuracy over the drilling operations. Examples are tripping in and out, where automated and improved control systems give better control and reduced probability of tighthole and stuck pipe problems. The Soft Torque and Autodrill functions (not yet fully implemented) give better control over the bit, resulting in improved ROP, faster deviation control in wells, and a smoother (more direct) wellbore/wellpath.
"Traditional drill crew tasks during drilling operations are reduced. During this startup phase, the crew has been used for extra supervision/maintenance. There is a potential for permanently decreasing manpower after the start-up phase. Remote operated and controlled pipe handling is functioning very well, and is superior to other remotely operated pipe handling systems."
The RamRig is a compact drilling rig design that is also a fully automated rig with hands-free pipe handling and limited need for personnel to actually perform work on the drillfloor. In some regions around the world, working environment is an important issue for worker safety. Observations by the Norwegian Petroleum Directorate (NPD) about the smaller work area for hardware/human interface have been noted, and future design improvements are already addressing these observations.
The biggest challenge
The first two wells, using the RamRig design, on Norsk Hydro's Oseberg East platform revealed three key areas of improvement. The tripping/drill floor arrangement has already been discussed, fine-tuning of existing equipment, and the third is educating drilling personnel on the new concept. After addressing the mechanical issues and more focused attention to training personnel, the second well showed considerable improvement over the first well - even with increased downtime due to weather.
Increasing understanding of this new drilling concept is the biggest challenge surrounding this technology. Teaching personnel how to take advantage of the improved control systems, data aquisition functions, automatic monitoring and drilling functions, and to use these tools to constantly analyze and improve drilling efficiency and control, is critical to optimizing the design's performance potential.
Normally, a typical drilling crew requires 12-18 months to work efficiently with a new rig. Tjelta estimates that the RamRig's full potential can be realized within 6-12 months since the Bideford Dolphin is already well underway with the learning and familiarization process.
The main improvement area at present is to simplify the current alarm system. Currently, the driller is presented with numerous alarms and drilling feedback data. Some of these are considered to be of low importance and not critical to real-time monitoring and operations. The solution is a change from "alarm signaling" to "information messaging." This is available in real-time as extra information, displayed conveniently for the driller's review.
Future operations
Systematic experience transfer is a key element in finalizing the remaining four RamRig projects. Experience and operational feedback from completed wells are currently being applied to current projects. The main question in the industry to date has been: "Will the concept work?"
With two rigs now in operation, and four more, both for platform and semisubmersible drilling units, due for operational startup within the next two quarters, the question now is, "When will the second generation RamRig begin development?"
Author's Note: The oil and gas industry's push into deepwater is forcing more development of subsea production, well control, and drilling systems. Designs for seafloor drilling platforms already exist (Offshore Magazine - September 1999). Conventional rig systems will be difficult to adapt to this environment, but the RamRig concept has potential application subsea, since it operates with a closed-loop hydraulic system.
