Imaging Hydraulic Fractures: Source Location Uncertainty Analysis At The UPRC Carthage Test Site
Name
1996.15 Li et al.pdf
Size
1.13 MB
Format
Adobe PDF
Checksum (MD5)
3011cf4525b83ca7fa7242165a12771f
Author(s)
Li, Yingping
Zhu, Xianhuai
Cheng, Arthur C. H.
Toksoz, M. Nafi
Date Issued
1996
Publisher
Massachusetts Institute of Technology. Earth Resources Laboratory
Series/Report no.
Earth Resources Laboratory Industry Consortia Annual Report;1996-15
Abstract
Hydraulic fracturing is a useful tool for enhancing gas and oil production. High-resolution seismic imaging of the fracture geometry and fracture growth process is the key in determining optimal spacing and location of wells and in improving reservoir performance for increased production rate. In this paper, we address how accurately the
sources along a fracture zone at different depths can be determined for given velocity
models, geophone array geometry configurations, and location of monitor wells. We apply
a theory of uncertainty analysis to estimate microearthquake location uncertainties
in both relative and absolute senses. To estimate the location uncertainties, we used
the velocity models, two geophone arrays in two monitor wells, and the location of the
fracture well, and an assumed fracture orientation of an upcoming hydraulic fracturing
experiment by Union Pacific Resources Company (UPRC) and its partners at Carthage Field, Panola, Texas.
We calculated the 95% confidence regions, in both absolute and relative senses, for
five hypothetical sources along an assumed strike of a target fracture zone at three
different depths. The semimajor and semiminor axes of the relative error ellipses for
these epicenters are typically estimated to be 12 and 5 ft, respectively, and the relative depth uncertainty is derived at about 6 ft. The absolute location uncertainties are at least 3 to 10 times larger than the relative location uncertainties. The high-precision relative source locations result in a relative measurement error about 4-15% in measuring the fracture length. The location ambiguity from two-station locations is discussed and arrival azimuthals is proposed to to be used for removing such location ambiguity. The location uncertainty analysis is expected to be generalized as a practical tool in optimal designing of a two-well seismic monitoring system for high-resolution imaging of hydraulic fractures.
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