Summary
Technological advancement in horizontal drilling and openhole completing
techniques for soft-rock formations finally has bridged the gap between the
drilling and completion disciplines. The success achieved with openhole
gravel packing has created a mainstay completion technique that has been used
in deepwater developments in Brazil and West Africa to deliver reliable,
high-rate well completions. The technology also has been an enabler for
heavy-oil developments [American Petroleum Inst. (API) gravity < 20°, y
> 0.934] in Brazil and the North Sea that otherwise would have been
uneconomical.
This article discusses where the industry started, how technology has
evolved, and the lessons learned that are being applied to increase the
application envelope and reliability of this completion method. The review
covers advances in openhole-drilling techniques that eliminate hole tortuosity,
gravel-pack fluids that can reduce rig time and enhance well productivity, and
improvements in downhole tools that have, or potentially will, reduce risk
while reducing completion cycle time. This review also will briefly examine a
possible replacement technology.
Introduction
Completion reliability and the potential to achieve significantly higher
sustainable production rates are two major drivers that have led to openhole
horizontal gravel packing (OHHGP) acceptance as a mainstay deepwater-completion
method. Interval lengths in excess of 2,500 ft are now fairly common. In
January 2003, the latest world-record horizontal gravel pack was completed with
a length of 8,305 ft (2531 m) in the Captain field in the North Sea (Wehunt et
al. 2003).
During the early 1990s, the development of enhanced drilling and fluids
technology led to advances in extended-reach and horizontal drilling (Restarich
1992, 1993; Jones et al. 1997). Screen-only completions became a favored
completion mode for completing in long, openhole soft-rock formations, with
wells providing the capability to deliver high production rates (Ghiselin 1996;
Harrison et al. 1990; Marestad et al. 1996). This technique is still being
used successfully in West Africa, the North Sea, and lower-pressured gas sands
in the Gulf of Mexico shelf. But partly because of the huge variance in
formation types and lack of shale isolation, this completion method experienced
high failure rates as dirtier, more laminated reservoir sands were completed
(Ali and Dearing 1996). The move from the shelf to deep water was another
primary driver in efforts to increase reliability while maintaining the high
flow-rate capability required for project sanction. Also, the capability
to expose increased reservoir rock in low-productivity reservoirs has led to
higher productivity than what has been possible with a conventional vertical or
moderately deviated wellbore. In the mid to late 1990s, the horizontal openhole
gravel-packing technique was refined with the basic downhole-tool systems being
used today (Foster et al. 1999; Duhon et al. 1988; Chambers et al.
2000).
The ongoing improvements in drilling equipment, drilling and drill-in
fluids, filter cake, downhole tools, and screens continue to further expand the
application envelope for openhole horizontal gravel packing. However, as
with any other evolving technology, there are still limitations that must be
addressed. One of these has been that the reservoir completed must have a
sufficient pressure difference between pore pressure and fracture gradient to
allow gravel-pack placement. Devices to lower equivalent circulating
density to allow the successful packing of longer intervals with tighter
pressure spreads are now available. Invert gravel-pack fluids that eliminate
the need to switch from an oil-based mud (OBM) or synthetic oil-based mud
(SOBM) system to a brine-based, solids-free, gravel-pack fluid are now being
marketed. Further improvement in brine-based, gravel-pack fluids has led
to the development of an in-situ acid-generating fluid that has been designed
to eliminate the need for a post-acid treatment in injection wells and
producers.
Drilling equipment also has been advancing. Bottomhole assemblies
(BHAs) that drill straighter holes and eliminate the spiraled tortuosity
normally associated with conventional drilling assemblies are now
available. These aid in placing the screen assembly on depth and in
achieving successful sand placement by enhancing hole cleaning and reducing
torque and drag.
© 2006. Society of Petroleum Engineers
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History
- Original manuscript received:
30 January 2004
- Revised manuscript received:
18 October 2005
- Manuscript approved:
10 November 2005
- Version of record:
20 March 2006
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