Drill collar

The drill string, consisting of a drill bit, drill collars, drill pipe, and kelly, is assembled and lowered into the conductor pipe. Drilling fluid, better known as drilling mud, is circulated through the kelly and... 

Drill Collar 716. Drill Pipe 735. Tool Joints 748. Heavy-Weight Drill Pipe 749. Fatigue Damage of Drill Pipe 763. Drill String Design 765. 

Since no excess weight for drill collars need be considered. Equation 4-30 becomes... 

Figure 4-80. Effective weight of drill collars in drilling fluid [11].

Kelly Tool Joint Tool Joint Dnti Collar Drill Collar Swivel Sub... 

Tool Joint Tool Joint Drill Collar Drill Collar... 

The drill string is defined here as a drill pipe with tool joints and drill collars. The drill stem consists of the drill string and other components of the drilling assembly that includes the kelly, subs, stabilizers, reamers as well as shock absorbers, and junk baskets or drilling jars used in certain drilling conditions. The drill stem (1) transmits power by rotary motion from the surface to a rock bit, (2) conveys drilling fluid to the rock bit, (3) produces the weight on bit for efficient rock destruction by the bit, and (4) provides control of borehole direction. 

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). 

Square drill collars are used to increase the stiffness of the drill string and are recommended for drilling in crooked hole areas. The spiral type of drill collar is used for drilling formations in which the differential pressure can cause sticking of drill collars. The spiral grooves on the drill collar side reduce the area of contact between drill collar and wall, which considerably reduces the sticking force. 

Conventional drill collars are made with uniform outside diameter and with slip and elevator recesses. Slip and elevator recesses are designed to reduce drill collar handling time while tripping by eliminating lift subs and safety clamps. However, the risk of drill collar failure for such a design is increased. The slip and elevator recesses may be used together or separately. 

Dimensions, physical properties, and unit weight of new, conventional drill collars are specified in Tables 4-71, 4-72, and 4-73, respectively. Technical data on square and spiral drill collars are available from manufacturers. 

Selection of the proper outside and inside diameter of drill collars is usually a difficult task. Perhaps the best way to select drill collar size is to study results obtained from offset wells previously drilled under similar conditions. 

The most important factors in selecting drill collar size are ... 

To avoid an abrupt change in hole deviation (which may make it difficult or even impossible to run casing) when drilling in crooked hole areas with an unstabilized bit and drill collars, the required outside diameter of the drill collar placed right above the bit can be found from the following formula [38] ... 

The casing string for a certain well is to consist of 13-f-in. casing with coupling outside diameter of 14.375 in. Determine the required outside diameter of the drill collar in order to avoid possible problems with running casing if the borehole diameter is assumed to be 17- in. 

Being aware of standardized drill collar sizes, an 11 or 12-in. drill collar should be selected. To avoid such large drill collar OD, a stabilizer or a proper-sized square drill collar (or a combination of the two) should be placed above the... 

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... 

NOTE 2 Tensile specimens from drill collars shall be taken vithin S feet of the end of the drill collar in a longitudinal direction, having the centerline of the tensile specimen 1 inch from the outMe surface or midwall, whichever is less. 

Drill Collar Weight (Steel) [51] (pounds per foot)... 

NOTE 1 Refer to API Spec 7, Table 6.1 for API standard drill collar dimensions. 

NOTE 2 For special configurations of drill collars, consult manufacturer for reduction in weight... 

In general, if the optimal drilling programs require large drill collars, the operator should not hesitate to use them. 

Typical hole and drill collar sizes used in soft and hard formations are listed in Table 4-74. 

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. 

Drill collar programs are the same as [or the next reduced hole size. 

In highly deviated holes, an excessive torque is encountered with conventional drill collars therefore, a heavy wall drill pipe can he used to supply pan of the required weight. 

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

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