Summary
This paper compares height, length, width, and pressure data from a
laboratory experiment to predictions from a three-dimensional (3D) planar
hydraulic fracture model for the case of a fracture propagating in a
lower-stress payzone region bounded by two symmetric higher-stress barrier
regions. A laboratory method that creates step-like stress changes on an
interface between two transparent polymethylmethacrylate (PMMA) blocks is
described. A fracture is propagated along this interface while measuring
fracture geometry and full-field fracture width (opening) by analysis of the
light intensity in images of the growing fracture. The fracture grew in overall
height to 1.7 times the pay height and in half-length to 3 times the pay
height. Results from a planar 3D numerical model closely matched the
experimental data for overall fracture shape, length, height growth, and
injection pressure. The data are presented so other numerical models can be
compared with these detailed measurements.
Introduction
The development of hydraulic fracturing models that are able to account for
height growth started with the introduction of the pseudo 3D approach in the
late 1970s (Settari and Cleary 1984) and has continued ever since. Simonson et
al. (1978) analyzed height growth by considering a uniformly pressurized
fracture cross section growing into symmetrical stress barriers. Stress
barriers are recognized to have a strong effect on hydraulic fracture height
growth (Warpinski et al. 1982a; Warpinski et al. 1982b; Nolte and Smith 1981).
Hydraulic fracture models must be able to demonstrate accurate prediction of
fracture height and length evolution, and this paper provides one detailed data
set for such verification. An equivalent detailed data set for fracture height
growth into stress barriers does not exist in the literature.
Overview of the Method
Laboratory experiments allow for control of the problem parameters to a
degree not possible in full-size field experiments. By controlling the
parameters, the effect on fracture growth of one aspect of the problem, such as
stress contrasts in this experiment, can be studied in detail. The experimental
data can then be compared to theoretical and/or numerical predictions to
provide the validation of those predictions.
The laboratory method relies on creating step-like stress changes on an
interface between two polymethylmethacrylate (PMMA) blocks. The stress
variations along the interface are produced by machining one surface of one
block with a prescribed profile designed so a step in the interface contact
stress is produced when this surface is pressed tightly against another, flat,
block surface. Results obtained by propagating a fracture along the interface
in this lower-stress payzone region bounded by two symmetric higher-stress
regions are presented in this paper.
© 2009. Society of Petroleum Engineers
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History
- Original manuscript received:
19 November 2006
- Meeting paper published:
29 January 2007
- Revised manuscript received:
11 July 2008
- Manuscript approved:
29 July 2008
- Published online:
2 July 2009
- Version of record:
28 September 2009
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