4D seismic

Time-lapse (or 4D) seismic is a reservoir monitoring technology which has proven to be a reliable reservoir surveillance tool. By analysing differences of multiple seismic surveys acquired over a producing reservoir and by integration with conventional reservoir monitoring tools, 4D seismic data can provide valuable insight on dynamic reservoir properties such as fluid saturation, pressure and temperature. Although 4D technology is relatively mature, the Curtin Reservoir Geophysics Consortium is working in areas that can help extract even more value from the data.

For example, the effective application of 4D technology requires a well-calibrated rock physics model, which is essential for seismic modelling of the time-lapse seismic response in order to establish the feasibility of the method and to facilitate the interpretation of 4D data. A rock physics model is also essential for methods being developed to quantitatively estimate saturation and stress changes from 4D data. To support the application of rock physics modelling of 4D seismic processes, CRGC is working in the following areas:

  • seismic signatures of patchy saturation
  • modelling of attenuation and dispersion due to squirt flow in rocks saturated with viscous and viscoelastic fluid (especially applicable to monitoring heavy oil recovery)
  • modelling stress-dependent properties of rocks
  • broadband acoustic measurements, from seismic to ultrasonic frequencies
  • laboratory measurements of intrinsic and stress-induced anisotropy
  • experimental and theoretical study of partial saturation effect on elastic properties of sedimentary rocks

Most successful 4D seismic surveys have been acquired offshore. Onshore 4D surveys face significant data quality challenges. Land data, which are often dominated by ground roll and refractions, commonly have poorer repeatability than marine data, due to lateral and temporal variations in near-surface velocity and in source and receiver coupling. Back-scattered, source-generated noise can vary rapidly throughout the field. The CRGC is a pioneer in the onshore application of time-lapse seismic technology, particularly for Carbon Capture and Storage (CCS). Focused on acquisition and processing methods, current research includes:

  • surface and downhole (VSP) time-lapse seismic monitoring at the Otway CCS test site
  • time-lapse full waveform inversion of vertical seismic profiles
  • distributed acoustic sensing (DAS) for permanent monitoring at reduced cost
  • surface orbital vibrators for permanent seismic monitoring