SPE Production & Operations
Volume 25,
Number 4,
November 2010,
pp. 431-437
Summary
Invasion of aqueous drilling, completion, or fracturing fluids can reduce
the relative permeability to gas and thereby causes a water block. In the case
of low-permeability formations, the capillary pressure tends to be high because
of the small pore size. Cleanup of water blocks requires high drawdown unless
water vaporization by the flowing gas is improved by using specific additives
such as alcohols.
The purpose of this work is to investigate fracture-face damage by measuring
relevant petrophysical parameters: absolute-permeability damage and gas return
permeabilities. Measurements are performed in representative conditions of a
fracturing operation in a tight gas formation: cores with an absolute
permeability of 10 μd set at Swi and experimental pressure of
200 bars for the fracturing-fluid invasion. Water and gas saturations during
the fracturing-fluid invasion and during gas backflow are monitored by X-ray
equipment. Adding alcohol in the fracturing fluid has a striking effect on
resolving water blocks. Cake formation on the simulated fracture face is also
discussed.
Numerical simulations are performed to assess relative permeabilities from
the experimental results. It is shown that hysteresis of gas and water relative
permeabilities has a strong impact on the rate of water removal. Sufficiently
high pressure drawdown is crucial to overcome capillary forces and initiate the
alcohol-assisted vaporization process. Water removal by water vaporization is
assessed and compared to the experimental results.
© 2010. Society of Petroleum Engineers
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History
- Original manuscript received:
7 March 2009
- Meeting paper published:
28 May 2009
- Revised manuscript received:
28 August 2009
- Manuscript approved:
15 January 2010
- Published online:
13 May 2010
- Version of record:
17 November 2010
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