MONITORING OF MICROSEISMICITY IN DIATOMITES

Due to their high porosity (up to 60%) and other formation characteristics, the diatomites in Southern California offer a great opportunity to investigate possible limitations to microseismic monitoring. To investigate the potential for utilizing microseismic monitoring, a series of models were constructed to determine both microseismic event detectability and locatability. That modeling indicated that event signals would most likely be heavily attenuated and therefore event detectability would be limited to detecting only larger microseismic events, and that poor signal‑to‑noise ratios would constrain the ability to locate events using a single array (single phase events). Subsequently it has been demonstrated in the field that the dynamic range of a monitoring system can be increased and the potential for locating events improved by installing multiple arrays having overlapping radii of observation. Results show that both multi‑ and single‑phase events have been not only detected and located by these multiple arrays, but the observed detection limits and size distribution has far exceeded those originally predicted by the earlier formation modeling. Innovative system design, deployment techniques and operational procedures, plus advanced multi‑well processing strategies have all contributed to creating a growing data set that is providing unique insights into treatment and production operations and expanding on the causal relationship between shear wave dominated microseimic events, fracture growth and process zone fracturing complexity observed by Vinegar et. al. (1992).