CLASSES OF LOST CIRCULATION (Mud Losses)

Lost circulation or mud losses when oil gas drilling can be grouped into four classes:

1. Seepage losses: From 1-10 bbl/hr and lost while circulating at the normal drilling circulateng rate

2. Partial losses: From 10-50 bbl/hr and lost while circulating at the normal drilling circulating rate

3. Severe losses: Greater than 50 bbl/hr and lost while circulating at the normal drilling circulating rate. In some cases, no losses may be seen if pumping stops indicating that the ECD is the cause of lost circulation.

4. Total losses: When the mud level in the annulus can not be seen or the hole can not be filled

through the annulus. Total losses usually occur in cavernous formations.