How can I identify an inadvertent return and how can I fix it?

In the geotech surveys on most horizontal directional drilling (HDD) crossings, the soils being drilled are identified. So you can plan ahead with drilling programs best suited for the terrain you'll be drilling. With certain soils, you can almost expect inadvertent returns because you're pumping through sensitive areas at high pump rates.

Lower mud levels in the pits are one of the first signs of an inadvertent return along with reduced pressure readings in the drill cab. An easy way to identify an inadvertent return is if you see it fracture up into the the ground. Having Lost Circulation Material (LCM) products on location is a cost-effective way to remediate inadvertent returns and reduce downtime. Most LCMs are designed to be spotted/squeezed, and/or swept through "thief zones" at the onset of the inadvertent return.

Essentially, you're looking to seal unconsolidated and loose soils with the LCM. Knowing the calculations to spot the LCM pill in the exact location is paramount to the success of the spotting procedure, so, having a qualified Mud Engineer on location is highly advised.