Summary
Well Ba-E-1 was drilled in the Tompa prospect (now the Ba-IX Mining Plot) in
Hungary targeting the Miocene and Cretaceous formations between 2600 and 3500
mTVD. These are tight sandstones, and the expected permeabilities were in the
range of 0.001 to 0.5 md. Two hydraulic-fracture treatments were performed. The
first fracture treatment was in the lower part, and the second treatment was in
the upper part of the deepest interval. With no previous propped-fracturing
experience in this field, the first treatment was designed as a conventional
crosslinked-gel treatment to minimize the risk of a premature screenout.
Following the analysis of the data from the first zone, it became clear that
the average permeability was closer to the minimum expectation of 0.001 md.
Because of lower-than-expected stimulation effectiveness of the first fracture,
and the confirmation of the low permeability, the second fracture treatment was
changed to a water-fracture design. This formation clearly falls into the
unconventional category, and consequently was a good candidate for a water
fracture.
This paper describes the prefracture diagnostics, fracture execution, and
post-fracture production evaluation of this unconventional gas well. Special
emphasis is placed on the use of small-volume injection tests, or diagnostic
fracture injection tests (DFITs), to obtain an estimate of the in-situ kh
because it is impossible to perform prefracture welltests in such a formation.
The result of the DFIT analysis is then used to constrain the post-fracture
well-test analysis in a numerical-simulation model that includes
fracture-filtrate-cleanup modeling. Post-fracture analysis showed that the
initial proppant-pack damage is high and effective fracture length is much
smaller than the created length, especially with crosslinked gel. The
crosslinked-gel treatment was not able to clean up effectively, and therefore
showed limited stimulation effectiveness. The first-ever water fracture in a
gas reservoir performed in Europe showed a more significant production
improvement during the short post-fracture test. The results from this well
suggest that, as in North America, water fractures appear to have better
initial production than crosslinked-gel fractures because of better fracture
cleanup in European reservoirs with microdarcy permeability.
© 2012. Society of Petroleum Engineers
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History
- Original manuscript received:
30 January 2011
- Meeting paper published:
24 May 2011
- Revised manuscript received:
29 June 2011
- Manuscript approved:
22 September 2011
- Published online:
12 April 2012
- Version of record:
1 May 2012
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