Werner M. Heigl

Uncertainties in passive seismic monitoring

The use of passive seismic techniques to monitor oil- field completion and production processes is on the rise. Stress changes induced by such reservoir activities as hydraulic fracturing, water injection, or fluid extraction will often result in failure of the rocks with a concurrent release of seismic energy in the form of compressional (P) and shear (S) waves. Passive seismic monitoring is based on recording these emitted waves and then using their arrival times to estimate the location of the failure events.

Computing Gaussian derivative waveforms of any order

The first and second derivatives of a Gaussian, also known as Ricker wavelets, are often used as source waveforms in forward modeling of seismic and electromagnetic wavefields. In applications such as borehole acoustics, the source waveform has more cycles than traditional Ricker wavelets. For such sources, the higher-order derivatives of a Gaussian are a more accurate representation. Such a source waveform can be computed as the product of a Hermite polynomial and the Gaussian; taking the required derivative is not necessary. Explicit expressions for these polynomials are not required because they satisfy a recurrence relation and thus can be computed from the two lowest-order polynomials. The Gaussian is formulated in terms of the dominant frequency of the derivative order of the desired source waveform. Strictly causal waveforms are not possible with a Gaussian because of its infinite length. However, the computed waveform can be made (pseudo-) causal by shifting it along the positive time axis until i...

Microseismic monitoring — Introduction

Most papers the readers find in this special section were presented at the First International Workshop on Microseismic Technology held in Asheville, North Carolina, USA, on 17–22 August 2014. The workshop’s organizing and technical program committee consisted of Werner Heigl (Apache Corporation), Vladimir Grechka (Marathon Oil), Leo Eisner (IRSM Academy of Sciences of the Czech Republic), Christophe Maisons (Magnitude), Serge Shapiro (Freie University, Berlin), Julie Shemeta (MEQ Geo), and Stephen Wilson (Seismogenic). The workshop, designed to facilitate sharing of microseismic expertise and the key observations and findings, was organized with special attention to balancing the needs of industry and academia. To encourage participation from the industry, only brief abstracts of papers were requested and no recording was permitted at the workshop; to attract academic contributions, the special section in Geophysics was offered to authors who would be willing to develop their workshop presentations into full-scale papers. The workshop, attended by 80 geophysicists and engineers from 11 countries, was enthusiastically supported by operating and service companies, with sponsorship from ITASCA, Magnitude, Marathon Oil, Pinnacle, Read, Sigma 3 , and …