Drilling slim hole

More rapid drilling (slim holes, optimised bit choice, good hydraulics and mud design) reduces shale exposure time. Since all of the diffusive processes are time-dependent, instability is less commonly observed, and slim holes are inherently easier to drill. However, the hydraulic system must be studies to insure adequate hole cleaning without excessive flow pressure effects (called equivalent circulating density effects in the oil industry). 

However, coiled tubing drilling is limited to slim holes, and the reliability of some of the drill string components such as downhole motors needs further improvement. Presently, the cost of building a new customised CTD rig limits the wider application of this emerging technology. 

Drilling Lines—Coring and Slim-Hole Rotary Rigs Shallow %, 1 Intemierliaie li 1 (22, 26) (26, 29) 6x26 WS. PF, RL, IPS or EIPS, IWRC 6x 19 S or 6x26 WS. PF. RL. IPS or EJPS, IWRC... 

Air and natural gas have also been used as drilling fluids in slim-hole-drilling mining operations, special large-diameter boreholes for nuclear weapons tests, and, more recently, in geothermal drilling operations. 

Core holes can be drilled to depth of more than a thousand feet. A slim-hole rig of 6-7 inches in diameter can yield a continuous core at a smaller cost than a conventional coring rig. It relative cost has resulted in its application in drilling for production wells in some areas. 

In 2003, carbon fiber drilling rod was applied in industrial tests. It was successfully used in a horizontal gas well of 422.15 m deep in Oklahoma. This kind of drilling rod can greatly decrease material cost and increase wear-resistance, which can provide technical support for slim-hole drilling. 

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