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The MultiStudio QC Suite is a group of tools which collect and analyse navigation, performance and seismic attributes. Along with the more commonly used 3D analysis tools, MultiStudio also has many routines and displays designed specifically for 4D surveys and techniques.

Due to the nature of 4D survey techniques a comprehensive understanding of local conditions and the data quality of the baseline survey is vital to the success of 4D acquisition. MultiStudio QC Suite provides the tools to perform these tasks.

Most 4D projects begin with a full pre-survey analysis of a baseline survey which can be performed by EPI. A MultiStudio attribute database is constructed and examined to check attributes such as feathers, offsets, separations, depths and crab. This baseline database would normally be pre-installed on our field systems for use during acquisition. This also allows assessment of the 4D preplots, to verify they have not been over-filtered and to check that any preplots which result from merging of several baseline sequences are both valid and achievable with the select survey equipment. The suite also includes tools for creating a 'perfect preplot', this allows comparison of different vintages of a 4D to a common denominator.

Feather differences
The difference in feather between the monitor and baseline surveys is displayed in either time-series, or as a spatial plot. On the plot the feather from the monitor is red, the green is streamer feather, Feth-D is the difference, and Feath-purple is the baseline. Because the baseline is entered to the QC database, the link between monitor and base for the display is achieved automatically.

Source Position Differences/Repeatability
The position difference for the source is also entered to the database as an attribute and can be displayed as either a time-series or spatial plot. On this plot only one array of a dual source has been selected for display, and the chart shows the difference in cross and along line between acquired and baseline.

Track Plots and Closest Point of Approach (CPA)
MultiPLOT also has tools to examine (at shot level) the positions for any of a number of nodes. This allows investigation of preplots against offshore installations (to determine CPAs for example), 4D preplots against the baseline P1/90 (to investigate how much smoothing had taken place in producing the preplot), acquired position verses preplot or baseline for 4D.

The example track plot shows the track of a preplot (dark gray) verses a baseline (pale blue). The baseline had been acquired prior to the existence of the platform which the preplot had to steer around.

Streamer Receiver Position Differences/Repeatability
With other systems it can be more difficult to present receiver repeatability without producing too many plots to allow easy assimilation of the information. With MultiStudio we take three offsets on each streamer of the baseline survey (or perfect preplot if no baseline is available), these will be at the Front / Mid and Tail and for each shot of the survey these positions are entered into the database.

Using this database, MultiStudio takes the acquired receiver positions and searches for the nearest receiver at each of the offsets, no matter which streamer it belongs to. We also take the streamer number which was the nearest and create this as an attribute. In conditions where feather match between monitor and base is poor it is possible for the same monitor streamer to be the nearest to all baseline streamers. These differences can be displayed as time-series as with many of the attributes stored within the MultiStudio database.

Azimuth Plots
For 4D surveys where the azimuth from source receiver is of interest, we can compute the azimuths for a baseline, a perfect preplot and a monitor, then display them as a ShotPLOT. The data can be merged across all streamers on a sequence so that there is just one plot per sequence (instead of one per sequence per streamer), and these can be displayed on a single web-page in geographical order to allow assessing azimuth repeatability across an entire survey on a single page.