Microseismicity: Beyond dots in a box — Introduction

Abstract

This special section of Geophysics is a consequence of a very successful SEG workshop titled Microseismicity: Beyond dots in a box. The workshop was held 22 October 2010, following the SEG Annual Meeting that was held in Denver. More than 120 people attended the meeting, and nine oral papers and 22 posters were presented. Small microseismic events, or acoustic emissions, occur naturally and a result of anthropogenic influences in reservoirs. Sudden stress release leads to elastic rock failure, which serves as an effective seismic source. These microearthquakes may be the result of production or hydraulic stimulation, but they also may be a consequence of natural tectonic activity. They are usually detectable using only sensitive sensors and after careful data processing. Such passive seismic monitoring has been used in mining settings for more than 100 years, but its application in petroleum setting is relatively new. As such, it is a rapidly advancing field of technology, where the challenges are manifold and span issues associated with data acquisition, processing, and interpretation. Much can be learned from methods and case studies developed for microseismic monitoring in volcanological, geothermal, and mining settings, but one of the key advantages in oilfield monitoring is that a great deal is ordinarily already known about the reservoir. Comparatively good velocity models exist, and production or injection information is available — the same is obviously not true for a volcano. The microearthquake or microseismic event location is useful in itself. Clusters of events delineate faults and fracturing, highlighting reactivation or the generation of new zones of failure. This has been very effective in helping assess the efficacy of hydraulic stimulation (i.e., frac monitoring). Longer term monitoring will no doubt provide an early warning system for detecting top seal leakage and fault reactivation in CO 2 sequestration projects, for example. Until …