Sensitivity measurements for locating microseismic events

John C. Bancroft, Joe Wong, Lejia (Lilly) Han

The first arrival clock-times from a number of receivers are used to estimate the clock-time and location of a microseismic event. The 3D solution is based on a 2D source location scheme based on the Apollonius method. This 3D solution requires four receivers that are non-coplanar or non-collinear. These restrictions are typically violated when receivers are placed in a large grid on the surface or in a linear array in a well. Non Apollonius solutions are presented for these restricted cases along with an analysis that relates the accuracy of the estimated source location to clock-times at the receivers. It is anticipated that these methods will be part of a larger system where these analytic solutions can be used with data extracted from the large arrays.