Summary
Sand production is a major issue facing many operators in the mature
southern North Sea (SNS) gas fields. Historically, sand-control completion
decisions have often been based on the assumption that sand control will occur
and have been constrained by the restrictions imposed upon sand entering the
gas transport pipeline. The inherent conservatism of this approach leads to
significant increases in completion costs and misses potential productivity
gains.
A holistic sand management strategy has been developed for the southern
North Sea to challenge the conservative paradigm. This is based on a complete
understanding of SNS reservoir rock properties and sand control completion
performance in gas wells and has been tuned by learnings from SNS and analogous
fields. It combines sand failure prediction, methodical and structured
selection of sand control approach (including consideration of production
performance, longevity, and risks), and novel solids lifting and erosion
assessment models to achieve better quantification of the risk and consequences
of sand production for wells and facilities. Key selection criteria areused
instead of arbitrary decisions based on limited and often unaudited data. The
role of an asset focal point with clear ownership of all relevant sand
production data and issues is fundamental to the success of this integrated
strategy.
Tools are available to predict when, where, and even how much sand will be
produced, how much sand will be lifted to surface, and how much erosion it will
cause. Methodologies are also available to evaluate and rank the available
sand-control techniques in a consistent and systematic manner.
This systematic and integrated approach to sand management has enhanced well
productivity and reduced completion costs without compromising sand management
or exceeding sand production constraints. Challenging sand management
convention in the demanding environment of the SNS compels operators to use
these methodologies to much greater effect.
Introduction
The SNS gas basin in the U.K. Continental Shelf (UKCS) is a relatively
mature basin, with many fields being on production for over 30 years. The
principal reservoirs in the SNS are the Rotliegendes Leman sands of Permian
age, though gas accumulations are also found in deeper Carboniferous
sandstones. The Leman sandstone is an entirely continental sequence of
interbedded aeolian, fluviatile, and sabkha deposits. Rock quality tends to be
facies-dependent, with facies dominated by aeolian dune and sheet sands which
have the best reservoir quality.
The recent increase in gas prices, coupled with the realization that the
U.K. will soon become a net importer of gas, has encouraged smaller,
independent operators to move into the SNS, taking advantage of the U.K.
government’s Promote licenses, substantial existing infrastructure, lower risks
and cost of entry, and a different mindset regarding exploration and
production. These smaller independents, as well as existing operators, are
planning to drill new wells to exploit infill opportunities and to appraise
satellite accumulations. This involves many challenges associated with drilling
wells in mature, depleted gas reservoirs. Depletion increases the risk of mud
losses, formation damage, and sand production. As many new wells are completed
subsea, the impact of sand production will be more severe than in wells where
intervention and workover opportunities are less limited.
Sand production is a major issue facing many operators. Examples include the
Jupiter fields (Burton and Boggan 1998), where sections of the Ganymede and
Calisto reservoirs have unconfined compressive strength (UCS) values less than
200 psi; many ConocoPhillips wells (Burton et al. 1998), where sand production
is related to the presence of weaker, mainly aeolian dune facies; and Shell’s
Brigantine fields (Weekse et al. 2002). Selfridge et al. (2003) report a
significant increase in unplanned hydrocarbon releases in the mid-1990s, which
was ascribed to an increase in solids production leading to accelerated
erosion.
© 2007. Society of Petroleum Engineers
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History
- Original manuscript received:
24 October 2005
- Revised manuscript received:
26 June 2006
- Manuscript approved:
9 July 2006
- Version of record:
20 May 2007
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