Summary
Results of a temperature transient analysis of data from Shell’s diatomite
steamdrive pilots are used to image hydraulic injection fracture lengths,
angles, and heat injectivities into the low-permeability formation. The Phase I
pilot is a limited-interval injection test. In Phase II, steam is injected into
two 350-ft upper and lower zones through separate hydraulic fractures.
Temperature response of both pilots is monitored with 16 logging-observation
wells.
A perturbation analysis of the nonlinear pressure diffusion and
heat-transport equations indicates that at a permeability of approximately 0.1
md or less, heat transport in the diatomite tends to be dominated by thermal
diffusivity, and pressure diffusion is dominated by the ratio of thermal
expansion to fluid compressibility. Under these conditions, the temperature
observed at a logging-observation well is governed by a dimensionless quantity
that depends on the perpendicular distance between the observation well and the
hydraulic fracture divided by the square root of time. Using this dependence, a
novel method is developed for imaging hydraulic-fracture geometry and relative
heat injectivity from the temperature history of the pilot.
The azimuth of the Phase I hydraulic fracture is determined to be 14° ± 2
N-NE. The azimuth of the Phase II upper hydraulic fracture is determined to be
16° ± 2 N-NE in the northern half of the pilot, and estimated to increase to
21° ± 2 in the southern half of the pilot. The azimuth of the lower hydraulic
fracture averages 19° ± 4. The hydraulic fractures are found to be symmetric
around both injectors, with an estimated length of 200 ft.
Increased steam injection after the first year of pilot operations caused
what is interpreted to be horizontal fractures toward the west in the G cycle
and the east in the M cycle. These features are imaged to be at least 100 and
160 ft, respectively, along the hydraulic fracture azimuth.
These conclusions are compared to tiltmeter data, microseismic data, and a
simulation history match of pilot performance. Microseismic events recorded in
the pilot are apparently not diagnostic of heat delivery to the formation.
© 2009. Society of Petroleum Engineers
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History
- Original manuscript received:
18 January 2007
- Revised manuscript received:
5 February 2008
- Manuscript approved:
1 March 2008
- Published online:
16 March 2009
- Version of record:
1 March 2009
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