G = heel row inserts on a tooth bit. Not all of tooth bits come with heel row
inserts. Typically it is included on the directional tooth bits and on the motor tooth bits. The G feature is standard on all insert bits, so it is not included as a part of the insert bit nomenclature.
The benefit of the G feature is that it helps maintain gauge. It is in contact with the borehole wall and it does help protect the gauge teeth on a mill tooth bit. It does have side cutting ability and it is diamond-compatible. The downside is that in some designs, it can reduce the total carbide on gauge. If the gauge row carbide were compromised in order to
accommodate the hole for the G feature, it probably would not be added. The applications would be any application where gauge rounding results in an under gauged hole or premature bearing failure. This feature will be used in bits that are for directional applications, or any tooth bits that are run in a motor application.
The next feature is TuffGage. There is no nomenclature for this feature at the present time. It is a different configuration of the heel pack inserts. Typically there is one row of large heel pack inserts going around the back face of the cutter. The TuffGage feature basically is two rows of inserts. Sometimes they line up one on top of each other. Sometimes they are staggered between each other. Sometimes they have skip spacing between
TuffGage in this heel pack configuration, give somewhere in the range of 20% to 40% more carbide on the back face of the cutter. That increase improves durability. It helps protect the gauge row inserts and helps increase the bit life.
The next features are shirttail and lug protection. There are 3 configurations of shirttail and lug protection used by Schlumberger Drill Bits:
- K, KP, DK, and DKP - KPR and DKPR - L and DL
“K”, “KP”,
K, KP, DK, and DKP are holes that are drilled into the shirttail where flattop tungsten carbide inserts are pressed into the drilled holes. There are standard patterns that are use for the K and KP shirttail protection. However, there is the flexibility to install any kind of design pattern as long as the pattern does not violate the specs in terms of the relationship of the inserts to each other, to the grease-loading hole, to the grease reservoir cap, and to the hard metal. This is an add-on feature. It can be done after the bit is built, either in the factory or at a machine shop that has been certified at a field location. The second type of protection is L, or DL, which stands for lug stabilizer pad. This is a piece of steel that is welded onto the shirttail and then machined. Once the piece of steel is machined to the proper diameter, holes are drilled and tungsten carbide inserts or diamond-coated inserts are pressed into the lug pad. The benefits of the lug pad are they stabilize the bit, they help to maintain gauge by reducing side loads, and they also reduce bit body wear. The downside is that sometimes the lug pads extend the gauge length of the bit. This can be a possible problem in a directional well with the overall length and steerability of the bit. So if the lug pads extend the gauge length and affect directional steerability, they will not be installed on the bit.
The third type of shirttail protection is KPR and DKPR. This is shirttail protection that is premium. The R stands for raised inserts that are rounded and protruding from the shirttail. This feature was introduced in 2000 and has become a very effective shirttail feature. This feature can also be
installed in both the factory and in the field. There is a new KPR insert that is just being introduced. It is called Mega KPR. This is an insert that is going to be used on the “Titan” product line. The difference between Mega KPR and the standard KPR, is that the standard KPR insert is 5/8" diameter and the Mega KPR inserts are 3/4" diameter. The applications for this is directional or any application where: 1) off-center wear or bit rotation is encountered, 2) bit stability could be a problem or be a limiting factor, or 3) in any application where a little more insurance is wanted. They can also be used in situations where a customer just wants to make sure that they do not have any shirttail damage or they just want a little extra protection.
These shirttail features do not cost very much and is a very effective tool to help ensure that you have a longer bit life. In a directional or off-center wear application, these features are very important because they do help protect the shirttail and protect the gauge row. In a directional situation, the bit is laying on the low side of the hole the majority of the time. The
shirttail and gauge row inserts are taking an abnormal amount of wear. Also, in a directional application, there are more opportunities for downhole vibrations, off-center wear, and gyrations. This shirttail protection, gives the bit added bit life when running in a directional application.
T = GageGuard. This is the insert that is located in between the gauge row
inserts as shown in the picture below.
This insert is typically a shorter, rounder protruding insert. It makes contact with the borehole wall which helps to protect the gauge inserts. This helps because it gives 3 points of contact with the borehole wall. There are the gauge row inserts, the GageGuard inserts, and the heel pack inserts, all in contact with the borehole at the same time. This transfers the load between the 3 inserts and helps protect the gauge row, which is the most vulnerable part of the bit. The benefits of the GageGuard feature are better gauge durability and better material selection. Diamond PDC-coated inserts can also be used with GageGuard. The downside is that there may be a
reduction in gauge count on some designs.
In order to make the space to drill the hole and press in the GageGuard
insert, some of the gauge row inserts would have to be moved or eliminated. In some designs, it is not worth sacrificing the gauge row inserts for the GageGuard feature. If the gauge row inserts are spread out too far, or the configuration is changed, the gauge row could be weakened. It is not
beneficial to weaken the gauge row by adding GageGuard. If it does cause a reduction in the gauge count for some designs, GageGuard would not be added. GageGuard is a factory-installed feature. It is not an add-on feature. The bit has to be designed with GageGuard on it from the beginning.
GageGuard does come standard on some Schlumberger products but is not available on all of the product lines. Most applications will see benefits of GageGuard unless there is a reduction in the gage count that limits the run.
JA = Jet Air. It is design differences that are used for durable bit geometry
for under-balanced drilling. It typically has a low offset, an open cutting structure, and has special nozzle ports. There are only two areas in the world that typically use jet air bits. They are used in the Northeast and in West Texas, U.S.A. The bit is only built in two sizes, 7-7/8" and 8-3/4". The applications are for under-balanced drilling using air, foam, or mist.
M = in the suffix represents Mudpick II hydraulics on HP bits. Normally if
a bit had Mudpick II hydraulics, it would be called EHP. In order for a bit to be an EHP, it had to have three things: 1) threaded ring, 2) Mudpick II
hydraulics, and 3) enhanced shirttail protection. In the 7-7/8" product line ball bearing are used instead of threaded rings. Since these bits do not have threaded ring, they cannot be called EHP. The way the Mudpick II
hydraulics are designated on the 7-7/8" product line is by the M. The benefits of Mudpick II hydraulics on HP bits are a faster ROP (Rate Of Penetration) and better cutter and bottom hole cleaning. Most importantly, it makes more efficient use of the available hydraulic energy. There are some downsides to using Mudpick II hydraulics. There may be some cutter shell erosion due to the high-energy zone directly at the corner. There have also been some cases of backwash on the shirttail. Mudpick II cannot be used effectively in all situations. It works well in most soft and medium
formations, especially where there is a tendency for bit balling. Any time there is low hydraulic energy or more efficient use of the hydraulic energy is
Diamond Features
With Schlumberger’s roller cone cutting structure and shirttail features, there is the opportunity to use diamond PDC-coated inserts. If a bit has diamond PDC-coated inserts, the following designations are used:
DA - Diamond Coating on All Inserts
DN - Diamond Coating on Nose Row Inserts DI - Diamond Coating on Inner Row Inserts DG - Diamond Coating on Gage Row Inserts DT - Diamond Coating on GageGuard Inserts DH - Diamond Coating on Heel Row Inserts DK - Diamond Coating on Shirttail Inserts
DKP - Diamond Coating on Premium Shirttail Inserts
DKPR - Diamond Coating on Premium Shirttail Raised Inserts DL - Diamond Coating on Lug Pad Inserts