Drilling advances ///
Lost circulation. Lost circulation is the loss of returned mud from the annulus of a conventionally circulated well. From a hydraulic standpoint, it means that the mud column equivalent circulation density (ECD) exceeds the ability of the formation to resist injection. The reasons are numerous: naturally fractured formations or vugular porosity in which the formation pore pressure is the only resistance to mud loss (i.e., formation pore pressure equals “fracture” pressure), high-porosity/ high-permeability formations, leaks to upper intervals of various kinds (behind pipe, at a bad shoe and up a fault plane), induced fractures (stimulations or waterflooding at high pressures) and other types of induced interwell communications (gas zones, fluidized beds, shale planes, etc.).
In his book Field Guide to Lost Circulation, author Bill Murchison refers to lost circulation as “...the number one problem in drilling...” Bill could not be more correct.
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