Imaging Geometry And Growth Rate Of A Hydraulic Fracture Zone By Locating Induced Microearthquakes
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1995.6 Li_Cheng.pdf
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Author(s)
Li, Yingping
Cheng, C. H.
Date Issued
1995
Publisher
Massachusetts Institute of Technology. Earth Resources Laboratory
Series/Report no.
Earth Resources Laboratory Industry Consortia Annual Report;1995-06
Abstract
The hydraulic fracturing technique has become an important tool in the enhancement
of hydrocarbons recovery, geothermal energy extraction, and solid waste disposal. The
characterization of geometry parameters and growth rate of a hydraulic fracture zone
is an important task for monitoring and assessing subsurface cracks. In this paper,
we develop a location approach to determine the precise hypocenter locations for a
cluster of seismic events induced by hydraulic fracturing. Two techniques were used
in our location scheme: waveform correlation and grid search methods. The waveform
correlation method allows us to obtain more accurate differential arrival times among
events within in a cluster.. The grid search method is suitable when dealing with a
nonlinear location problem.
We applied our method to seismic waveform data from a hydraulic fracturing experiment
at the Los Alamos Hot Dry Rock geothermal site and determined hypocenter
locations for 157 induced microearthquakes. The maximum absolute and relative location
errors were estimated to be 30-39 meters and 3-9 meters, respectively. Among the
157 events, 147 microearthquakes occurred in a tight cluster of a dimension of 40 meters,
roughly defining a vertical hydraulic fracture zone. The length, height, and width
of the hydraulic fracture zone were measured to be 40, 35 and 5 meters, respectively.
The orientation of the fracture zone is estimated at about N400W. Analysis of the
temporal-spatial pattern of the induced microseismicity revealed that the fracture zone
grows significantly in a two-hour period during the hydraulic injection. Using seismicity
distribution in time and space in this period, we determined that the fracture zone
grows toward the northwest along the fracture zone strike with a growth rate of 0.1-0.2
meters per minute.
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