Impact of distance-dependent location dispersion error on interpretation of microseismic event distributions

Abstract

Along with horizontal drilling and hydraulic fracturing technology, monitoring-induced microseismic activity during hydraulic fracturing has played a significant role in the economic development of today's prolific tight-gas and shale resource plays. Many microseismic fracture monitoring papers in the current literature discuss the equipment, how to acquire and process microseismic data, and how to determine an appropriate velocity model. Unfortunately, for an operating company's completion engineers and geophysicists charged with interpreting these data and integrating them with other data sets, only a few papers discuss the impact of artifacts and location uncertainties on the interpretation. While microseismic data have been very useful in the economic development of resource plays, there are a number of significant pitfalls and interpretational issues that, if not understood, will potentially lead to erroneous interpretations. This is especially important for any real-time decisions during a hydraulic fracture treatment.

Hydraulic Fracturing, Microseismic Magnitudes, and Stress Evolution in the Barnett Shale, Texas, USA

“…However, the routine residual error in the location of a single event is on the order of tens to a hundred or more feet (Maxwell, 2009;Kidney et al, 2010), which in many cases approaches the lateral or vertical dimensions of the reservoir into which the fluid is being injected. The uncertainty in event location, combined with systematic errors from the estimate of the velocity structure, makes precise mapping of the induced fracture network highly uncertain.…”

Integration of hydraulically induced microseismic event locations with active seismic attributes: A North Texas Barnett Shale case study

“…Angular uncertainty for a vertical monitoring well decreases as 1∕ p n, where n is equal the number of geophones (Warpinski, 2009). Eisner et al (2010) and Kidney et al (2010) find that the vertical uncertainty for a borehole single vertical array, such as the array used to acquire our data set, increases with distance from the borehole. At 152 m distance, vertical error can be on the order of 15 m, depending upon the velocity model and other parameters (Eisner et al, 2010;Kidney et al, 2010), but increases up to 46 m of vertical uncertainty at 610 m (Kidney et al, 2010).…”

“…Eisner et al (2010) and Kidney et al (2010) find that the vertical uncertainty for a borehole single vertical array, such as the array used to acquire our data set, increases with distance from the borehole. At 152 m distance, vertical error can be on the order of 15 m, depending upon the velocity model and other parameters (Eisner et al, 2010;Kidney et al, 2010), but increases up to 46 m of vertical uncertainty at 610 m (Kidney et al, 2010). At 152 m distance, horizontal uncertainty is between 15 and 30 m, and increases to 60-107 m at a distance of 610 m (Eisner et al, 2010;Kidney et al, 2010).…”

“…At 152 m distance, vertical error can be on the order of 15 m, depending upon the velocity model and other parameters (Eisner et al, 2010;Kidney et al, 2010), but increases up to 46 m of vertical uncertainty at 610 m (Kidney et al, 2010). At 152 m distance, horizontal uncertainty is between 15 and 30 m, and increases to 60-107 m at a distance of 610 m (Eisner et al, 2010;Kidney et al, 2010). Our microseismic data were acquired in 2003 and 2005, and processed prior to our study.…”

“…Microseismic data sets recorded with downhole tools exhibit a distance-dependent uncertainty (location dispersion error), which causes systematic spreading of events as the distance between source and receiver increases (Warpinski, 2009;Eisner et al, 2010;Kidney et al, 2010). Moving away from the source also decreases recorded amplitudes by 1∕distance through geometrical spreading, and thus lowers the signal-to-noise ratio (S/N).…”