Real-time 4D Monitoring and Control

Time-lapse (4D) acquisition

The WesternGeco seismic fleet uses a suite of proprietary tools to plan, control, monitor, and evaluate 4D acquisition. Baseline and repeat surveys are meticulously planned and evaluated to ensure optimum acquisition in terms of efficiency and data quality.

Real-time monitoring of the source and receiver repeatability, in addition to vessel and CMP position comparison between baseline and monitor survey, is conducted while the vessel is acquiring the repeat survey. The example (right) shows the repeat CMPs (with the near groups highlighted in red) acquired on a 4D undershoot, overlaid on the baseline CMPs, which are shown in green.

In addition to 3D binning, 4D binning is used whereby coverage is only generated if there are hits for both a baseline and a monitor line for the same offset interval and azimuth interval in the same bin (based on the offset and azimuth threshold values entered). Two simulated examples of 4D binning are shown below. In the second display, there is less source and feather repeatability and the effect on the 4D coverage can be seen.

REPEAT is a software package, developed by WesternGeco, to facilitate planning 4D (time-lapse) surveys and the evaluation of 4D data acquisition. It enables line-by-line and survey-wide evaluation of repeat and baseline surveys. Onboard analysis against specifications, base surveys, and planned positions enables conducting the entire operation in the most efficient manner and implementation of immediate decisions and plans in real time. Attribute positioning maps enable evaluation of separations and differences between passes on a survey-wide basis for optimal survey acquisition.