Zimmer U.,Pinnacle Halliburton Service
74th European Association of Geoscientists and Engineers Conference and Exhibition 2012 Incorporating SPE EUROPEC 2012: Responsibly Securing Natural Resources | Year: 2012
Microseismic event locations are most often represented by individual points in space. Depending on the quantity and quality of input data and the localization algorithm applied each of these locations has an individual uncertainty space. This uncertainty space is often approximated by error bars. The approximated space is often interpreted as the volume where the event is located with 100% certainty. For most calculations of the uncertainty space this is not true. This paper suggests a method where the different input parameters, e.g. traveltime or hodogram information, can be translated into probability density functions (PDFs) which then allow the calculation of intervals of different confidence levels. The resulting space describes the volume where the event is located with the provided level of confidence. For most applications the 95% or 99% confidence interval is a reasonable definition of the error space but any other level of confidence can be specified. The resulting confidence interval does not have to be continuous as it is suggested by standard error bars. Comparing localization algorithms that use only a single phase arrival, e.g. P-waves, with multiple phase arrival algorithms shows the order of magnitude difference in the location accuracy.
Wilson S.A.,Pinnacle Halliburton Service |
Dando B.,Pinnacle Halliburton Service |
Chambers K.,Pinnacle Halliburton Service
4th EAGE Passive Seismic Workshop | Year: 2013
The use of microseismic event locations to define the locus of stress/strain changes in hydrocarbon reservoirs is now an established technique and represents one of several key technologies in enabling the economic development of unconventional resources. Within the literature relating to this applied technology there is an unfortunate yet consistent and arguably systematic mis-understanding of the differences between precision, accuracy and error. Such misunderstandings have a direct impact on how we interpret microseismic locations in an engineering context. Even the use of the term uncertainty is used by different authors in several different ways and is arguably uncertain itself. The use of both imaging and inversion methods for event location and source characterization adds further complexity to the semantics of separating bias from the random component of error. In this paper, • We attempt to clarify the meaning of uncertainty, precision, accuracy and error for different location methodologies using the scientific literature, and discuss the issues of precision bias and other logical fallacies • We describe a set of monitoring scenarios, then compare event accuracy obtained using (i) an imaging method based on a surface network geometry and (ii) an inversion method based on a down-hole wireline tool geometry . We show for each scenario which method offers the better solution. By doing so we provide some general guidelines on which monitoring scenarios are best suited to which monitoring objectives In conclusion we recommend that all parties are vigilant in using appropriate terminology and consider the objectives of any monitoring project, prior to deciding upon the network geometry. We advise that any decision to carry out a monitoring project is considered in the light of the nature of the sub-surface velocity field and the extent of our knowledge of this velocity field. With such consideration in mind one can decide whether this knowledge is likely to be sufficient to answer the project objectives in a constrained and meaningful fashion.