Fixed cutter bits

Steel Tooth Bit Selection 783. Diamond Bits 789. lADC Fixed Cutter Bit Classification System 801. Downhole Tools 812. Shock Absorbers 813. Jars. Underreamers 819. Stabilizers 823. 

The lADC Drill Bits Subcommittee began work on a new classification method in 1985. It was determined from the outset that (1) a completely new approach was required, (2) the method must be simple enough to gain widespread acceptance and uniform application, yet provide sufficient detail to be useful, (3) emphasis should be placed on describing the form of the bit, i.e., paint a mental picture of the design , (4) no attempt should be made to describe the function of the bit, i.e., do not link the bit to a particular formation type or drilling technique since relatively little is certain yet about such factors for fixed cutter bits, (5) every bit should have a unique lADC code, and (6) the classification system should be so versatile that it will not be readily obsolete. 

The resultant four-character diamond bit classification code was formally presented to the lADC Drilling Technology Committee at the 1986 SPE/IADC Drilling Conference. It was subsequently approved by the lADC Board of Directors and designated to take effect concurrent with the 1987 SPE/IADC Drilling Conference. A description of the 1987 lADC Fixed Cutter Bit Classification Standard follows [54]. 

Four characters are utilized in a prescribed order (Figure 4-156) to indicate seven fixed cutter bit design features cutter type, body material, bit profile, fluid discharge, flow distribution, cutter size, and cutter density. These design traits were selected as being most descriptive of fixed cutter bit appearance. 

Each of the four characters in the lADC fixed cutter bit classification code are further described as follows ... 

Figure 4-156. Four-character classification code for fixed-cutter bits [54]. (Courtesy SPE.)...

The distinction of primary cutter types is made because fixed cutter bits often contain a variety of diamond materials. Typically one type of diamond is used as the primary cutting element while another type is used as backup material. 

The section describes the first lADC standardized system for dull grading natural diamond, PDC, and TSP (thermally stable polycrystalline diamond) bits, otherwise known as fixed cutter bits [55]. The new system is consistent with the recently revised dull grading system for roller bits. It describes the condition of the cutting structure, the primary (with location) and secondary dull characteristics, the gage condition, and the reason the bit was pulled. 

The format of the dull grading system is shown in Figure 4-165. For completeness, Figure 4-165 contains all of the codes needed to dull grade fixed cutter bits and roller bits. Those codes which apply to fixed cutter bits are in boldface. 

Eight factors about a worn fixed cutter bit can be recorded. The first four spaces are used to describe the cutting structure. In the first two spaces, the amount of cutting structure wear is recorded using the linear scale 0 to 8, based on the initial useable cutter height. This is consistent with grading tooth wear... 

The third space is used to describe the primary dull characteristic of the v/orn bit, i.e., the obvious physical change from its new condition. The dull characteristics which apply to fixed cutter bits are listed in Figure 4-165. 

The location of the primary dull characteristic is described in the fourth space. There are six choices cone, nose, taper, shoulder, gauge, and all areas. Figure 4-167 shows four possible fixed cutter bit profiles with the different areas labeled. It is recognized that there are profiles for which the exact boundaries between areas are debatable and for which certain areas may not even exist. Notice that in the bottom profile there is no taper area shown. However, using Figure 4-167 as a guide, it should be possible to clearly define the different areas on most profiles. 

The fifth space will always be an X for fixed cutter bits, since there are no bearings. This space can be used to distinguish dull grades for fixed cutter bits from dull grades for roller bits. 

Winters, W. J., and H. H. Doiron, The 1987 lADC fixed cutter bit classification system, SPE/IADC 1642, Proc. 1987 SPE/IADC Drilling Conference, New Orleans, March 15-18, 1987, pp. 807-817. 

---