Summary
In the oilfield industry, microseismic monitoring is widely applied to
determine induced fracture network geometry and stress changes in reservoirs.
The basic result is usually a map of the distribution of the microseismic
events describing the area influenced by injection/production of reservoir
fluids (e.g., hydraulic fracturing). As every microearthquake event (i.e.,
"dot" on the map) is processed individually, it has its own level of location
accuracy. To prevent any misinterpretations based on events with low accuracy,
quality-control (QC) reports can provide important information regarding
location accuracy and other attributes that help in the overall interpretation
of the maps, in addition to the standard event location. However, much of the
information needed to assess the quality of the data is very specialized and
technical, therefore, the figures presented in the QC reports often appear
complicated and are not easy to read for the nonspecialist. By introducing
easy-to-read figures that summarize the essential information, these reports
have become more useful to the occasional user.
Introduction
Microseismic monitoring has become a widely applied technology in hydraulic
fracture treatments and reservoir monitoring to determine the extent and
geometry of fracture networks and stress redistributions in reservoirs
(Warpinski 1994; Warpinski et al. 1996; Wright et al. 2002; Maxwell et al.
2003; Maxwell et al. 2002). The creation and reactivation of fractures in the
rock produces elastic waves that are recorded and located using nearby geophone
arrays. The result is a map showing the distribution and timeline of the
microseismic events correlated to injection pressure or other well
parameters.
Often, the distribution of the induced seismicity forms "clouds" that
consist of hundreds to thousands of individual events. Each event has its own
level of accuracy depending on its signal strength, accuracy of travel time
pick, applied velocity model, and other factors. In a standard map of the event
distribution, the differences in location accuracy are not visible, which might
lead to an incorrect engineering interpretation based on events with a
low-location confidence. As a result, it has become clear that some methodology
is required to provide meaningful information on the quality of the data and
the confidence in the results. An obvious solution is for the microseismic
processing company to provide a QC report that gives a summary of such
information.
The overall objective of a QC report is to help the user visualize the
accuracy of each single event as well as the accuracy of the overall event
distribution to minimize misinterpretations based on poor data. The QC
information can be very technical and only meaningful to a specialist who
understands microseismic theory and analysis techniques. However, with a basic
understanding of the localization process and by focusing on a few meaningful
figures, the nonspecialist can identify potential problems and avoid any
serious misinterpretations of the results. The philosophy of the QC reports
described in this paper provides detailed information of the quality of the raw
data and processed attributes so that anyone interpreting the microseismic
images has enough information to understand the limitations and confidence of
the data and resulting images.
© 2009. Society of Petroleum Engineers
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History
- Original manuscript received:
1 August 2007
- Meeting paper published:
11 November 2007
- Revised manuscript received:
11 June 2008
- Manuscript approved:
21 June 2008
- Published online:
2 July 2009
- Version of record:
22 December 2009
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