Drill collar length

The wellbore, drill string and drilling fluid data from the previous example are used. Casing depth is 4,000 ft. Assuming a drill pipe length of 5,000 ft and a drill collar length of 500 ft, find the friction pressure losses. 

The term drill collar originally derives from the short sub originally used to connect the bit to the drill pipe. Modern drill collars are each about 30 ft in length, and the total length of the string of drill collars may range from about 100 to 700 ft and more. 

Basically, the purpose of drill collars is to furnish weight on bit. However, both size and length of drill collars have an effect on bit performance, hole deviation, and drill pipe service life. Drill collars may be classified according to the shape of their cross-sections as round drill collars (conventional drill collars), square drill collars, or spiral drill collars (drill collars with spiral grooves). 

Drill Collar Number Outside Dia, D Bore, +A -0 i Length, ft, 6 in. L Bevel Dia. A D, Bending Strength Ratio... 

Drill Collar Yield Tensile With Gage length... 

The length of the drill collar string should be as short as possible, but adequate to create the desired weight on bit. Ordinary drill pipe must never be used for exerting bit weight. 

The required length of drill collars can he obtained from... 

Determine the required length of 7 by 2 -J- -iu, drill Collars if desired yreighi op bit,is W.= ,4<) fluid,density, ==.100 Ib/gal, and hole.deviation... 

The closed length, based on SQ-ift collars, is 390 ft or 13 joints of drill collars. 

Find the magnitude of the weight on bit and corresponding length of drill collars that result in second order of buckling. Drill collars 6 in. x 2 ft, mud density =12 Ib/gal. 

If the total length of drill collar string would be, for example, 330 ft, then the number 232 ft would indicate the distance from the bit to the neutral point. 

Unit weight of Hevi-Wate drill pipe = (41)(0.847) = 34.72 Ib/ft. Part of weight on bit that may be created using drill collars = (93.18)(330)(cos 40) = 23,555 lb. Required length of Hevi-Wate > drill pipe is... 

Normally, based on hole diameter, the designer can select drill collar diameter and drill pipe diameter. Next, specific pipe is chosen the maximum length of that pipe must be determined based on condition 1. For this purpose, the following equation is used ... 

Select 21 Joints of 7 f x 2 - in. drill collars that give the length of 630 ft. 

VC = annulus volume capacity opposite the drill collars in bbl/ft = length of drill collar in ft... 

Equation 4-297 is applicable if the kick length is shorter than the drill collars while Equation 4-298 is used if the kick fluid column is longer than the drill collars. 

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