For downhole microseismic monitoring of hydraulic fracturing, the acquisition is performed using a set of three-component (3C) seismic receivers attached firmly to the borehole wall by a clamping mechanism. Such an acquisition cannot be repeated, and it is focused on recording weak signals. Thus, proper installation of the receivers is especially crucial for microseismic applications. We have developed a case study of using a seismic-interferometry approach for assessing the receiver's installation quality from ambient-noise records. Crosscorrelation of one vertical receiver noise records with the others allows us to retrieve the direct body wave propagating along the receiver array. Our observations indicate that the inability to retrieve the direct body wave is an indicator of clamping issues. Our case study does not support the emergence-frequency hypothesis reported in the literature (that higher frequencies present in the retrieved body-wave spectrum imply better clamping quality). Another conclusion is that seismic-interferometry processing provides a stable assessment of the clamping quality only for the vertical receivers. Thus, one gets only partial diagnostics of the clamping quality for the 3C downhole tool. This is important because the horizontal components may be affected more by the clamping issues compared with the vertical components. The overall conclusion is that seismic-interferometry processing of noise records is recommended for the assessment of the downhole receiver installation prior to microseismic monitoring. It does not provide complete diagnostics but comes for free (does not need any additional technological operations or extra time).
- downhole receivers
- tube wave