Crossflow checks are used to determine the fluid status in a wellbore during shut-in temperature passes and can also be used as the primary survey method in wells with rates to slow to log with conventional methods. Crossflow checks should always be run in conjunction with any fluid movent logging method where shut-in temperatures are run.
Slugs of radioactive material are ejected between zones of interest and then timed runs are made with the chart recorder on depth drive. The shots should be approximately 30 to 50 feet apart to prevent material diffusion from allowing the slugs to grow together as they are being logged.
A fluid velocity can be calculated by timing the travel interval from peak to peak as in the velocity profile method used on production logs.
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