BJ Services delivered acid stimulation services using the MV Vestfonn, an offshore stimulation vessel, on three wells located in BG's Miskar Field development offshore Tunisia. The operation took place over a seven-day period, with onshore support provided by BJ Services' staff at the company's Marine Base in Great Yarmouth, England.
Previously, BJ Services carried out propped frac stimulation service operations using the MV Vestfonn for BG Tunisia in the Miskar Field in 1995. Once again, the Abiod Chalk formation of the Miskar Field posed unique challenges. The approximately 75 meter thick net section of the gas bearing reservoir formation is located at about 3,100 mSS. A 320 oF limestone consisting mainly of a hard, brittle, chalky wackestone, the Abiod Chalk was pad acid fraced at approximately 60 bpm and 6,500 psi surface treating pressure. The high rates and pressure required the Vestfonn to rig up her full complement of two four-inch Coflexip 10,000 psi hoses. The treatment itself consisted of a Spectra Frac Pad, followed by alternating stages of high and low viscosity 28% HCl acid.
"The primary benefits of using the Vestfonn are to provide the acid volumes, high rate and high pressure stimulation services required to derive maximum fracture penetration levels and fracture conductivity," said Alasdair Buchanan, Region Manager – Europe & Africa for Well Services, BJ Services. "With our experience in hydraulic fracturing technology and the special capabilities offered by the Vestfonn, we complete reservoirs in such a way that our clients, including BG Tunisia, reap the benefit of wells that operate smoothly, and produce effectively over the long-term," he added.
MV Vestfonn Celebrates 20-Year Record of Success
BJ Services' MV Vestfonn is a dynamically positioned offshore stimulation vessel that was designed to meet the technological and environmental challenges posed by the demanding conditions of the North Sea. It has delivered stimulation services on approximately 130 wells in the British, Danish, Norwegian and Dutch sectors of the North Sea over its 20-year history – which translates to more than 900 frac operations. As operators have progressed to highly-deviated, multi-zone and horizontal well configurations, BJ has upgraded her capabilities accordingly.
The early 1990s saw upgrades to the vessel's acid tank manifold system to increase delivery rates and the addition of liquid frac concentrate to allow on-the-fly mixing of gel systems. In 1997, BJ increased hydraulic horsepower (HHP) capabilities by fitting two additional 2,000 HHP units onboard the vessel (attaining 13,400 total HHP pumping capability) and enlarged the high-pressure manifold system (from 3-inch to 4-inch diameter discharge lines) to support the higher pump rates. A prior increase in proppant tank volume (from 850,000 to 1.2 million pounds) together with these changes set the stage for high-rate, high-volume propped fracture treatments into the 21st century.
Since 2001, most enhancements have involved the Vestfonn's control systems and environmental effects. BJ equipped the vessel with a fully integrated satellite communications system in 2002 for worldwide communication and remote data transfer. Together with software upgrades, this enhancement improved the crew's ability to access BJ databases for health, safety and environmental and quality assurance materials – and share real-time job monitoring with onshore customers. The vessel also received an upgrade to DP-2 status for improved safety and redundancy related to its dynamic positioning system.
The latest modifications included equipping the vessel with dedicated tanks designed to pump "reclaimed" proppant, an efficiency improvement, which represent a fitting culmination of technological advances in the vessel's 20th year of operation. Although the Vestfonn is the longest-operating vessel in the BJ stimulation fleet, her experience and state-of-the-art systems solidify her position at the helm of BJ Services' vessel-based operations.
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