Summary
Diagnostic fracture injection testing (DFIT) is an invaluable tool for
evaluating reservoir properties in unconventional formations. The test
comprises injection of water over a very short time period, initiating a
fracture at the end of a well's horizontal section, followed by a long shut-in
period. Analysis of the falloff data with the G-function plot reveals the
fracture closure pressure, and the fracture pseudolinear-flow period leads to
the initial reservoir pressure.
In most tests, wellhead pressure (WHP) measurements are used because of cost
considerations. A wellbore heat transfer model is used to allow conversion of
WHP to bottomhole pressure (BHP) by accounting for changing fluid density and
compressibility along the wellbore. This model, in turn, allowed us to assess
the quality of solutions generated with the WHP data. For DFIT analysis, we
adapted the modified-Hall plot for the injection period, whereas both the
pressure-derivative and G-function plots were used for the analysis of falloff
data. The derivative signature of the modified-Hall plot allows unambiguous
estimation of the fracture breakdown pressure (pfb) during
the injection period. As expected, the pfb always turns out
to be higher than the fracture closure pressure (pfc),
estimated with the two methods during pressure falloff, thereby instilling
confidence in the solutions obtained.
A statistical design of experiments with coupled geomechanical/fluid-flow
simulation capabilities showed that the formation permeability is by far the
most important variable controlling the fracture closure time. Mechanical rock
properties, such as Young's modulus of elasticity and the Poisson's ratio, play
minor roles. In microdarcy formations, a longitudinal fracture takes much
longer to close than its transverse counterpart.
© 2012. Society of Petroleum Engineers
View full textPDF
(
638 KB
)
History
- Original manuscript received:
1 February 2012
- Meeting paper published:
6 June 2012
- Revised manuscript received:
23 June 2012
- Manuscript approved:
22 July 2012
- Published online:
11 October 2012
- Version of record:
30 October 2012
View Cart
