Many operations involve the injection of fluids into the formation around a
well. In many cases, the fluids contain colloidal particles, either initially
present or introduced during the operation through dirt or naturally occurring
particles. Therefore, all injection schemes potentially suffer from injectivity
decline. This injectivity decline is caused by clogging of the formation by
particles, forming an external filter cake on the surface of the formation and
blocking the pores inside the formation.
This paper reports on the effects of gas on the injectivity of particles in
sandstone. Experiments were performed in which water containing micron-sized
particles (hematite) was injected into sandstone cores with or without small
gas bubbles (nitrogen) present in the water. The position and amount of
particle deposition could be determined both visually and by chemical analysis.
It was found that the presence of gas reduces the external filter cake formed
on the inlet surface of the core. Also, with gas, the particles penetrate
deeper inside the core and more particles pass through the core and are
detected in the effluent stream.
The same effects are enhanced when the mixture of gas bubbles and water is
replaced by foam. This suggests that the presence of gas/water interfaces has a
major influence on the retention of particles in the sandstone. Possible
mechanisms are discussed.
The pressure drop across the core when gas or foam is present is initially
higher than in an identical test without gas because of relative permeability
effects or foam-flow resistance. However, because fewer particles are retained,
ultimately the pressure drop is significantly less when gas is present. This
effect may be significant in injection operations involving foam and offers
ways to mitigate injectivity loss.
© 2010. Society of Petroleum Engineers
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- Original manuscript received:
1 April 2009
- Meeting paper published:
28 May 2009
- Revised manuscript received:
15 April 2010
- Manuscript approved:
25 May 2010
- Published online:
11 November 2010
- Version of record:
15 March 2011