Low-permeability gas wells often produce less than predicted after a fracture treatment. One of the reasons
for this is that fracture lengths calculated after stimulation are often less than designed lengths. While
actual fracture lengths may be shorter due to fracture growth out of zone, improper proppant settling, or
proppant flowback, short calculated fracture lengths can also result from incorrect analysis techniques. It is
known that fracturing fluid that remains in the fracture and formation after a hydraulic fracture treatment
can decrease the productivity of a gas well by reducing the relative permeability to gas in the region
invaded by this fluid. However, the relationships between fracture fluid cleanup, effective fracture length,
and well productivity are not fully understood.
In this work I used reservoir simulation to determine the relationship between fracture conductivity,
fracture fluid production, effective fracture length, and well productivity. I simulated water saturation and
pressure profiles around a propped fracture, tracked gas production along the length of the propped
fracture, and quantified the effective fracture length (i.e., the fracture length under single-phase flow
conditions that gives similar performance as for multiphase flow conditions), the "cleanup" fracture length
(i.e., the fracture length corresponding to 90% cumulative gas flow rate into the fracture), and the
"apparent" fracture length (i.e., the fracture length where the ratio of multiphase to single-phase gas entry
rate profiles is unity).
This study shows that the proppant pack is generally cleaned up and the cleanup lengths are close to
designed lengths in relatively short times. Although gas is entering along entire fracture, fracturing fluid
remains in the formation near the fracture. The water saturation distribution affects the gas entry rate
profile, which determines the effective fracture length. Subtle changes in the gas rate entry profile can
result in significant changes in effective fracture length. The results I derived from this work are consistent
with prior work, namely that greater fracture conductivity results in more effective well cleanup and longer
effective fracture lengths versus time. This study provides better explanation of mechanisms that affect
fracturing fluid cleanup, effective fracture length, and well productivity than previous work.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/3050 |
| Date | 12 April 2006 |
| Creators | Lolon, Elyezer P. |
| Contributors | McVay, Duane A. |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | 5183612 bytes, electronic, application/pdf, born digital |
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