Two major trends in offshore stimulation operations - improved electronics in measurement systems and improved fluid engineering - are improving the efficiency and functionality of vessels especially designed to provide stimulation.
Improved electronics in measurement systems such as densimeters, mass flow meters, and level sensors have made realtime measurement easier and more accurate. New fluid engineering designs have decreased the amount of product required for similar completion practices. Both of these working together to increase operational efficiency and optimize vessel utilization.
This issue of Offshore features the inaugural international survey of marine well stimulation vessels, which appears on the following pages.
World distribution of the current 24 stimulation vessels is concentrated in the Gulf of Mexico, comprising almost 60% of the total world fleet. The remainder of the fleet is deployed in South America, North Sea, Middle East, and one vessel in West Africa. Future growth potential resides in the West African, South American, and Canadian North Atlantic regions.
This year's survey revealed two other major shifts - a move to larger vessels and development of more environmentally friendly fracturing fluids. Both are necessary to keep up with the demands of deeper water operations. Open ocean environments require better station maintenance capabilities. Also, vessel dynamic positioning systems (DPS) are continually being upgraded. Newer vessels, and those in various stages of construction, are larger and/or better equipped for station maintenance and storage capacity.
"Vessels are being built larger, wider, and deeper to withstand the demands of the deepwater environment," explains Pat Saunders, Halliburton GOM Operations Manager. "Anti-roll technology is being utilized, along with innovative hull designs to allow these vessels to supply the deepwater rigs in weather conditions just short of hurricane force."
"Vessels must be efficient and cost effective," added Ricardo Aboud, International Technical Coordinator for BJ Services. "Volume capacity and adaptability to meet a variety of needs without returning to port saves the operator time and expense. A stimulation boat must have sufficient storage capacity to perform multiple jobs, without returning to shore, as well as enough backup equipment on board to satisfy each task and perform stimulation jobs on many of the fields in the area."
Fleet analysis
Analysis of survey information reveals the average vessel length is approximately 220 ft, with only 30% of the vessels substantially greater than this average. Navigational engine horsepower averages 3,000 - 3,200 hp, with cruising speeds an average of about 12 knots. Storage capacities, below and above deck, are where the vessels tend to differentiate themselves.
There are noticed differences in the storage/tankage philosophies between vendors. Acid, additive, and gas storage capabilities dominate this difference. Wide variation in above-deck storage capabilities is evident. "On-the-fly" capability is available in approximately 60% of the vessels, with focused attention on retro-fitting the remainder of the vessels for this function. Average fracture pump hydraulic horsepower is 7,900 hhp. Only two vessels have more than 12,000 hhp. The average number of pumps per vessel is about five, with two vessels having eight or greater.
The fundamental function and purpose of these vessels has not changed: providing safe, timely, and efficient well stimulation services. Pat Saunders of Halliburton feels, "that in recent years client completion designs have been influenced by the vessel and its' capacity to deliver. The majority of the current stimulation vessels are converted supply boats.
As the industry moves to a new generation of deepwater vessel, coupled with systems designed to complement and support the well stimulation needs, clients can design for the reservoir's needs, rather than within the vessels' capacity." This should be of major concern to both operators and contractors.
Pushing existing technologies to the limit, forces operators and service providers into a high-risk, "gambling" approach to completion engineering design. Larger boats with more functional capability will help reduce this risk and give clients more freedom in their respective completion engineering designs.
Improvements
Recent improvements in marine well stimulation operations revolve around "on-the-fly" mixing, measurement electronics, and polymer-less fracture fluid technologies. Joseph Ayoub, Schlumberger Well Production Services Technical Manager says that "availability of more automated, continuous mix, on-the-fly technology better optimizes additive use and mixing efficiencies. This mixing capability, and new-design fracturing fluids are helping increase vessel efficiency and utilization by decreasing the amount of additive required per job, and not having to "pre-mix" treatment fluids. New design fluids can require as low as 2 components - down from as many as 8 in the past - and achieve better stimulation results by eliminating damage caused by polymer based fluids."
- On-the-fly mixing allows these two components to be mixed while being pumped downhole to the treatment zones. The end result is more available tank storage volume for extra additive/chemical. From this, service providers are recognizing that multiple jobs and bigger, single jobs are now possible. From an operator's point of view, completion/stimulation program design is not dependent on vessel operational limitations, as in the past.
- Ricardo Aboud of BJ Services lists twelve benefits of "on-the-fly" mixing capability:
- Fewer people required, even for complex jobs
- Greater range of rate delivery with regard to very low and high rates
- Improved accuracy and quality for any delivered product
- More storage capacity of the vessel because batch tanks are not required
- Cost savings for the customer because they only pay for what was used
- More environmentally friendly because of the no waste issue
- No waiting time required for "batching up"
- A greater variety of systems and more complex systems can be offered
- The problems encountered with high volume multiple stage treatments are eliminated
- The footprint required for all the above advantages is surprisingly small
- Near to or complete automation is possible
- Documentation of jobs is more complete, credible, and verifiable.
New vessels
Recent construction trends lean toward new design boats over retro-fitting existing vessels. Environmental concerns are causing one contractor to re-implement an older design philosophy - completely enclosed pumping systems. BJ services says that due to logistics issues and the recent cost environment, stimulation boats have been constantly upgraded to have more storage capacity, so that each vessel can perform a higher number of jobs without having to spend time otherwise required to reload at dock. For this matter, the contribution of research with fracture fluids resulted in the formulation of concentrated versions of conventional fracture fluids, creating an extra storage capacity in stimulation vessels.
Halliburton has a different philosophy, suggesting that retrofitting is a temporary band-aid. For the most part, the existing supply boat fleet is restricted to working in 6-8 ft seas. Due to the huge investment, and daily expense, of a deepwater project, newer vessels are required that can work in more demanding conditions. More product must be delivered to the wellsite with fewer trips.
DP utilization and improvements revolve around a current industry minimum function - compliance with the operator's deepwater and/or individual rig requirement(s). Most vessels are currently upgraded for the latest DP systems. The best alternative currently available for deepwater applications would be DP01, which allows for movement of both the rig/platform and the marine vessel. Quick advances in technology will result in additions to the current DP system types.
The general trend seems to be toward completely DPS stationed boats, minimizing tie-off to rig/platform as in the past. This decrease in fixed-point connections would allow more harsh weather, station-keeping maneuverability. Lee Kilpatrick, OSCA Service Line Manager, said that SOLAS Certification is an ever-increasing necessity of all stimulation vessels.
Process control
Safety improvements to be realized in the near future revolve on "process control." Dowell stated that the trend toward more automated "process systems" control has reduced the human-to-equipment interface. This helps to decrease personnel hazard exposure. Again, advances in electronic components have yielded the ability to shift focus from the individual tasks involved to the entire "process."
More development and management of this "process" will further minimize the human interface currently required for marine stimulation service operations, and ultimately reduce personnel hazard exposure risks. All vessels have one-button auto shutdown capabilities, hose reel quick disconnect, and QA/QC labs. Some differentiation between the vessels exists with the quick disconnect capability during a power loss.
Other attention to personnel safety risk was cited by OSCA's Service Line Manager, Lee Kilpatrick. "Dedicated surface landing areas for chemical and bulk on-loading operations are a necessity. More open ocean operations bring with it an increased exposure to harsh weather environments, bigger boats will help address this highly critical safety issue."
Acknowledgement
The following contributed to the compilation of Offshore's 1999 Global Marine Stimulation Vessel Survey: Scott Strittmatter, BJ Services; Walt Glover, Halliburton Energy Services, Jim Tycer, OSCA; and Leo Burdylo, Schlumberger.
