Lag time and lag time distribution monitoring

A system for estimating a cuttings lag time or lag time distribution during a drilling operation, the system comprising:

• a plurality of colored magnetic markers configured for introduction into circulating drilling fluid on a drilling rig;
• a magnetic or electromagnetic trap configured to remove ones of the colored magnetic markers from the circulating drilling fluid at a surface location on the drilling rig;
• an optical sensor or digital camera;
• and
• a processor configured to receive measurements from the optical sensor or the digital camera, evaluate the measurements to identify the removed colored magnetic markers based upon a color thereof, and evaluate evaluating arrival times at the surface location of the detected colored magnetic markers to estimate the lag time or the distribution of lag times.

A method for estimating a cuttings lag time or lag time distribution during a drilling operation, the method comprising:

• circulating drilling fluid in a wellbore while drilling, the circulating drilling fluid traveling downhole through a drill string and uphole through a wellbore annulus, the circulating drilling fluid carrying drill cuttings generated by the drilling to a surface location;
• introducing first and second sets of colored magnetic markers into the circulating drilling fluid while drilling, the first and second sets of colored magnetic marker having corresponding first and second different colors;
• removing ones of the first set of colored magnetic markers and ones of the second set of colored magnetic markers from the circulating drilling fluid at the surface location using a magnetic or electromagnetic trap;
• detecting the removed ones of the first set of colored magnetic markers and the removed ones of the second set of colored magnetic markers using an optical sensor based upon the first and second different colors;
• and
• evaluating arrival times of the first set of colored magnetic markers to estimate a first lag time or a first distribution of lag times and arrival times of the second set of colored magnetic markers to estimate a second lag time or a second distribution of lag times.