The Impact of Environmental and Acquisition Variations for PRM 4D Processing - Snorre Case Study

Since going live in 2014, five permanent reservoir monitoring (PRM) surveys have been acquired over the Snorre field at regular intervals. The PRM installation itself is currently the largest in the world consisting of 57 cables containing ~10,000 multi-component (4C) buried receivers and covering an area of around 200km2. The processing effort of the early PRM surveys was dedicated to establishing and optimising a robust, repeatable sequence with the objective of providing fast turnaround, high quality 4D seismic data. For key processing steps such as geophone reorientation and PZ summation the high degree of receiver repeatability allows us to apply operators derived on the base to subsequent monitor datasets. However, variations in environmental and acquisition conditions between surveys are observed and can impact the 4D response (generating so-called 4D noise). The purpose of this abstract is to highlight some of these issues and how they are dealt with in the context of fast delivery Snorre PRM data. The topics summarised are those which have been especially important to the Snorre dataset: source layback, water velocity and shot coverage harmonization.