Summary
Multifractured horizontal wells are currently the most popular method for
exploiting low-permeability tight and shale gas reservoirs. Production data
analysis is the most widely used tool for analyzing these reservoirs for the
purpose of reserves estimation, hydraulic fracture stimulation optimization,
and development planning (Ambrose et al. 2011). However, as pointed out by
Clarkson et al. (2011), a fundamental problem with the application of
conventional production data analysis to ultralow permeability reservoirs is
that current methods were derived with the assumption that flow can be
described with Darcy's law. This assumption may not be valid for tight/shale
gas reservoirs, as they contain a wide distribution of pore sizes, including in
some cases nanopores (Loucks et al. 2009). Therefore, the mean-free path of gas
molecules may be comparable to or larger than the average effective rock pore
throat radius, causing the gas molecules to slip along pore surfaces. This
results in slippage non-Darcy flow, which is not accounted for in conventional
production data analysis.
Clarkson et al. (2011) modified the pseudovariables used for analyzing gas
reservoirs in production data analysis to account for slippage. They
demonstrated that if the effect of slippage is not considered, it leads to
noticeable errors in reservoir characterization. Clarkson et al. (2011) also
mentioned that even after using the modified pseudovariables, the values for
permeability and fracture half-length do not exactly match the input data to
simulation. In this paper, a methodology to properly analyze the production
data from a fractured well in a tight/shale gas reservoir producing under a
constant flowing pressure in the presence of desorption and slippage is
presented. This method uses a new pseudotime definition instead of the
conventional pseudotime currently being used in production data analysis. The
method is validated using a number of numerically simulated cases. It is found
that the newly developed analytical method results in a more reliable estimate
of fracture half-length or contacted matrix surface area, if permeability is
known.
© 2012. Society of Petroleum Engineers
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History
- Original manuscript received:
27 July 2011
- Meeting paper published:
21 September 2011
- Revised manuscript received:
6 February 2012
- Manuscript approved:
8 March 2012
- Published online:
31 May 2012
- Version of record:
12 June 2012
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