METHOD FOR INCOMPETENT MUD SHALE BED PENETRATION DURING DRILLING OPERATION Russian patent published in 2005 - IPC

FIELD: oil and gas well drilling, particularly to penetrate incompetent mud shale bed.

SUBSTANCE: method involves performing subdrilling by chisel within the boundaried of bed consisting of incompetent mud shale with the use of visco-plastic drill fluid circulating in annular well bore cavity. Drill fluid flow is within laminar regime. To provide guaranteed laminar drill fluid flow and, therefore, to provide penetration of above bed without well wall caving the selected flow rate of drill fluid Q is 20-30% less than critical flow rate Q_cr corresponding to transition from laminar regime to turbulent one. The selected visco-plastic drill fluid must have minimal possible filtration efficiency.

EFFECT: prevent well erosion and well wall caving during incompetent mud shale bed drilling.