Time Lapse

4D feasibility studies and intelligent survey planning are essential to ensure the success of time-lapse reservoir and/or overburden monitoring. The main objective of the analysis is to determine the magnitude of the expected “4D difference” in the time frame of the surveillance and to determine if this difference is discernible from the “4D noise”.

This requires two main phases:

1) 4D feasibility

2) 4D survey planning

The 4D feasibility study involves determining the expected changes in reservoir velocity and density due to changes in fluid type, saturation and/or pressure. These changes can then be modelled as either simple two-layer AVO synthetics or 3D Acoustic/Elastic Finite Difference synthetics with the legacy and planned acquisition parameters. Comparisons of modelled data to legacy seismic data are then used to predict expected NRMS levels.

4D survey planning investigates the survey technique and optimal parameters to provide the required seismic data quality; while ensuring that the survey is as repeatable as possible. This is not trivial given expected environmental changes such as: weather, currents and water temperature for Marine surveys; and vegetation growth and soil moisture for Land surveys to name a few. These differences introduce many sources of 4D noise, such as source and receiver positioning errors, travel time errors, source and receiver coupling differences. Other source of 4D noise include changes in source and receiver technology, additional infrastructure, HSE, and cultural noise. Planning also involves analysis of the useability of legacy surveys not acquired as “baseline” surveys.

Contact Jon at PHASE GEO for your 4D feasibility and 4D survey design requirements (jon@phasegeo.com).