Summary
It is commonly acknowledged in the petroleum industry that water cut
increases sand-production risk, and a number of possible mechanisms have been
proposed. This paper presents the results of a series of laboratory
perforation-collapse tests aimed at demonstrating and quantifying the water-cut
effect on perforation failure and sand production.
The laboratory perforation-collapse tests were conducted on weak sandstones
obtained from downhole and outcrop. The tests were performed under simulated
in-situ effective stresses and drawdown conditions. Water was introduced into
the flowing stream of either oil or gas at various stages of the tests to
simulate water cut. The failure and sand-production processes were observed and
recorded using a borescope in real time.
The results showed that the effect of water cut on perforation strength and
sand production depends on the mineralogical composition of the sandstone and
the degree of residual water saturation. The effect is most significant for
sandstones with high clay content and low residual water saturation and is less
significant for clean sandtones or those with high residual water saturation.
The experimental results are discussed on the basis of the chemical interaction
between water and rocks—capillary stress and relative permeability. It is
concluded that water-saturation-induced rock-strength reduction is the most
significant factor governing perforation failure and sand production. Although
perforation failure is a prerequisite for sand production, the failure does not
always lead to sand production.
Introduction
Sand production in the petroleum industry is a phenomenon of solid particles
being produced together with reservoir fluids. Conceptually, this process may
be divided into three stages: failure of the rocks surrounding an open hole or
perforation, detachment of sand grains from the failed materials, and
transportation of the sand grains into the wellbore and to the surface. It
costs oil companies tens of billions of U.S. dollars annually (Acock et al.
2004).
Increase in water production in the late life of oil and gas fields is
inevitable, be it a result of water injection or water coning. On average, oil
companies today produce 3 bbl of water for each 1 bbl of oil (Bailey et al.
2000). The effect of water cut on sand production has been a major concern in
the petroleum industry. It has been observed on many occasions in the field
that initiation of sand production coincides with water breakthough (Veeken et
al. 1991; Bruno et al. 1996). But on other occasions, it has been observed that
both events do not relate to each other, and sand production may initiate
before or after water breakthough (Sanfilippo et al. 1995; Skjaerstein et al.
1997). Despite these inconsistent field observations, it is generally accepted
that sand-production risk increases as a result of water production.
© 2006. Society of Petroleum Engineers
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History
- Original manuscript received:
3 January 2005
- Revised manuscript received:
7 September 2005
- Manuscript approved:
1 October 2005
- Version of record:
20 August 2006
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