Applying the two-point paraxial ray tracing, we develop a technique for relative location of microseismic events. Our technique assumes the availability of a perforation shot or an already located microseismic event, termed the master, for which the paraxial ray tracing has been performed. The ray-tracing output for the master makes it possible to compute the relative locations of adjacent microseismic events, as many as a data set contains, with an efficient algorithm that requires no additional ray tracing and reduces to solving a series of simple, low-dimensional and well-behaved optimization problems. The relative event-location approach discussed in our paper is especially well suited for surface microseismic monitoring because the high accuracy of the paraxial ray approximation in the directions orthogonal to the reference rays, typically spanning the stimulated horizons for surface microseismic geometries, ensures the calculation of precise event hypocenters at appreciable distances from the master. Also, since our computations operate with differences of the recorded times of microseismic events rather than with the times themselves, inaccuracies in static corrections for surface receiver stations are largely eliminated. We test the relative location technique on synthetic and field microseismic data to demonstrate its accuracy, computational efficiency, and insensitivity to velocity errors.

Reducing noise is paramount when doing surface microseismic monitoring as the signal-to-noise ratio is usually lower than one. In fact denoising can significantly improve results since there are many more small microseismic events rather than large ones. It is shown here that efficient denoising can be obtained during the acquisition phase by deploying the geophones into small, dense arrays called patches. The patches ensure a 20dB noise reduction in all of the directions, while the traditional radial-shaped designs suppress noise only in the inline direction. This is particularly important as many noise sources are present in the monitored area, not only at the fraccing pumps whose noise is present only on about 1% of the network. Moreover, the patches are independent arrays. This indicates that non-permit areas can easily be avoided, and also that low-noise areas can be chosen in order to deploy the patches. This, combined with their intrinsic denoising capabilities, suggests that the overall signal-tonoise ratio can be greatly enhanced.

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