THE USE OF SEISMIC MODELLING WHEN DESIGNING ONSHORE 3D AND 4D SURVEYS

Abstract

There are many parameters to consider when designing acquisition geometries for onshore 3D and 4D seismic surveys. Plots of attributes, such as fold and offset distribution, are necessary in the design process but they are not always sufficient. For instance, they fail to predict the bandwidth and signal-to-noise ratios associated with various candidate designs. Properly crafted synthetic seismograms, however, can be used to yield these predictions. Downhole and surface seismic measurements are needed to drive this. The downhole measurements— primarily well logs—are used to create stratified earth models for input to ray trace calculations and reflectivity modelling. The surface seismic measurements-including finely sampled noise tests-are needed to derive intraarray statics distributions, ambient noise distributions, ground roll characterisations and other descriptions. These empower modelling routines to contaminate and perturb the synthetic signal in prospect-specific fashions. Results from Middle East studies typically show that survey designs that are best suited for addressing one particular issue might not be best for addressing others. Incorporation of digital group forming algorithms within the modelling process allows prediction of results that would be obtained from new high channel-count, singlesensor systems.