PRODUCTION SYSTEMS: Extending rigless, unmanned minimal production designs into deeper water
Part of the lower-cost equation
Minimal facility concepts that are successful in shallow water offer insight into designs that might work for deepwater fields, according to Patrick O'Connor, a member of the Facilities Development team for BP's Upstream Technology Group. While some rigs and platforms are defined in terms of water depth, O'Connor said the key definition of a minimal platform, be it fixed-bottom or floating, in 300 ft or 3,000 ft water depth, is that is does not have a drilling rig. "Once you have a rig, it is no longer minimum," O'Connor said.
The majority of these are fixed-bottom platforms in water depths less than 400 ft, where a jackup rig can provide drilling support. As with most rules, the no-rig rule has exceptions, but even those minimal facilities with rigs installed can benefit from the minimization strategies adopted on minimal platforms.
The key in designing one of these facilities is to keep the systems as simple as possible. For example, minimal platforms are not typically manned. O'Connor said if a platform requires personnel to operate, then this brings with it a variety of other requirements, such as quarters, safety systems for personnel, and greater power consumption. "Our philosophy is keep people off the platforms," he said.
Once it is agreed that a facility will not be continuously manned, O'Connor said the next step is to address how often the platform must be visited. This will come down, in many cases, to the process complexity and the means of power. In the latter case, power requirements, means of power, and associated fuel storage, can add weight to the topside and generate more visits for refueling.
O'Connor said BP is looking long-term at power minimization, which allows power generation from renewable sources such as wind, wave, or solar. Other new technologies are emerging such as fuel cell technology and micro-turbines. However, such systems tend to be limited to small scale power generation. Where projects simply require more power than such systems can provide, alternative sources of power, such as the use of umbilicals, may be required.
He said that if mature areas such as the Gulf of Mexico or North Sea could be hardwired with an offshore electric grid, then a new platform would simply be plugged into the grid in the same way a house or office building is onshore. The power would be generated either onshore or by a central hub facility and distributed throughout the local infrastructure. However, while such an approach could lead to minimal facilities, O'Connor said that, based on current technology, the infrastructure investment appears cost-prohibitive.
As with most decisions, it is a constant trade-off with every installation. Process and utility equipment that is required for the proper operation of the field must be weighed, literally, against the cost of the facility and the cost of maintaining the facility to achieve an economic development. Another hurdle for O'Connor is compression.
"At the moment, the assumption is that compression automatically means people," he said. With more, smaller, lower pressure fields, the need for compression often threatens the opportunity for a truly minimal platform. O'Connor said if the obstacles to unmanned wellhead compression could be overcome, not only could it improve reservoir recovery and deliver economic developments, but it could also deliver safer facilities from a health, safety, and environmental standpoint. The fewer visits, particularly in harsh environments that have to be made to facilities, the safer they are.
This brings up the question of means of access. Means of access is an area that highlights the necessity to think out of the box when considering minimal platforms. For quite some time, O'Connor said, there have been two tried and true transportation options offshore - by boat, helicopter, or some combination of the two.
Not only are there some safety issues attached to these modes of access, but there can be other considerations. For example, O'Connor said, in some parts of the world, unmanned platforms that can be easily accessed by boat fall victim to theft and vandalism. To avoid this type of interruption requires the designers to come up with more secure means of access from sea. These methods must first be safe, but must limit access to those who have purpose-designed vessels.
Minimal platform designs were originally designed for continental shelf gas fields in the US Gulf of Mexico. In this market, with a depressed gas price, it became essential to develop fields with cost-efficient approaches. While the gas prices may have since improved, there are other drivers, such as reducing field sizes, that make minimal facilities the first choice.
Well intervention can be a very expensive proposition for a marginal field on the shelf. If a rig is called out, this cost alone could, in some cases, wreck the economics of a small project. In many ways, this reliability issue mirrors that of subsea developments albeit some independent well intervention via wireline or use of coiled tubing can be performed at lower costs on a minimal facility.
O'Connor said subsea developments have a distinct advantage over minimal facilities. Because these subsea developments are out of reach (underwater), there is no debate over whether they will be manned or visited. The systems are required to be extremely reliable because they are so remote and expensive to repair.
If this mindset is translated to surface facilities, O'Connor said, it would pave the way for cheaper, more reliable minimal facilities that had only the essential equipment topside required to support the process function. "This means installing only the equipment that is absolutely necessary, but don't clutter up the platform with utility functions, which pull people onto the platform."
In many cases, O'Connor said, production facilities include unnecessary equipment just because the space is available. This has been a real challenge, he said, in the North Sea, but in the Gulf of Mexico, there seems to be a better "balance," where minimal facilities compete effectively with subsea developments.
With the maturing of minimal facilities into more compact, space efficient designs, O'Connor said deepwater floating facilities can benefit as well. Concepts such as Atlantia's SeaStar Mini-TLP show that minimal facility designs can be incorporated into floaters to minimize topsides loads and reduce costs for deepwater developments.
While O'Connor frames the minimal platform concept as a constant battle against clutter, he does admit that the bulk of the savings in this category have been realized. There are areas beyond weight and the number of visits that could be improved for greater savings.
Installation is number one on O'Connor's list. Regardless of how cheap it is to build and run a platform, the installation cost, like intervention costs, rely on other systems/vessels and are expensive. The answer, he said, is self-installing platforms.
Much like using coiled tubing or snubbing units to perform intervention work on minimal platforms, the concept of self-installation takes the high-cost installation vessel out of the picture. In some cases, where a jackup is already required to perform drilling activities there are concepts, which allow the use of the rig itself to install the platform. "That's really the next step," he said referring to self-installation.
Beyond platform installation, O'Connor said the other big factors in the equation are the pipeline and drilling costs. To combat this cost there are a number of proposals including the idea of re-useable pipelines. "That's an area we feel hasn't come along as far as it should," he said. The other big goal is to see a dramatic cut in the facilities costs.
O'Connor said it used to be that the cost of drilling, pipelines, and facilities were more or less equally balanced in small, satellite projects. Now that the facilities costs have been dramatically reduced, it should put some welcome pressure on both pipeline and drilling costs. "It would be more of an integrated approach. That's the way I see the future going," he said.
Minimal facilities forum
A worldwide forum on minimization and unmanned operations for marginal fields, entitled "Minimal Offshore Facilities of the Future," will be held on October 9-11, 2001, at the South Shore Harbour Resort/Conference Center in League City, Texas. The forum is hosted by BP and organized by Offshore Magazine. The conference chairman is Pat O'Connor. Interested attendees, exhibitors, or sponsors should contact Samantha Holloman, at Tel: (713) 963-6251 or e-mail: firstname.lastname@example.org.