4-D seismic technologies: intersurvey calibration

Abstract

seismic data sets at different times in the production life of a reservoir, calibrating, then comparing the data sets and interpreting intersurvey differences in terms of fluid change or movement. In practice 4-D (time-lapse) analysis is typically applied to data sets not originally designed for time-lapse monitoring. Optimal results require data to be very carefully normalized for acquisition differences and processed in a sufficiently uniform manner. The seismic image can change in many ways from survey to survey. Intersurvey differences include geometry differences, time shifting of reflectors, frequency content variations, differing amplitude range/magnitudes, and phase character differences. These discrepancies between data sets can result from both production related changes in reservoir properties and non-production related differences in acquisition and processing. It is necessary to calibrate the data in a manner which minimizes the differences not associated with production and focuses on those which are. The major objective of the research is to test the application and design of intersurvey calibration with two very different data sets. Calibration involves the normalization of data in regards to space and time, frequency, phase, and amplitude. This allows for an assessment of the capabilities and limitations of 4-D analysis and the calibration involved, and tests the feasibility of application to a specific reservoir and data sets.