PRACTICAS CONTABLES SIGNIFICATIVAS

Schlumberger utilizes 2 types of gauge inserts in steel bodied bits. The first type consists of a cylindrical piece of hot pressed tungsten carbide with fluted sides to improve retention. The second type is like the first but also contains surface-set cube diamonds, orientated to their crystallographic optimum, to provided enhanced abrasion resistance. Reed-Hycalog holds a patent on using this technique for providing diamond gauge protection in a steel bodied bit. Schlumberger gauge inserts are manufactured with a radius on the outside face so when they are assembled in the bit gauge, they will be flush with the steel surface.

IMPREGS

Gauge Protection

Gauge Protection

PDC Nozzles

Schlumberger uses a variety of interchangeable nozzle types and sizes. The choice of nozzle type is based on many factors, including the size of the bit and the recommended hydraulic program. All nozzles are manufactured from tungsten carbide, which provides the necessary erosion resistance. They are screwed into the bit using custom nozzle wrenches and all have rubber "O" rings to hydraulically seal the threads. Because the nozzles are threaded, they may be removed from the bit body and changed should the hydraulics need to be adjusted.

Gauge Protection

PDC Bit Designs

The design of a PDC drill bit is largely a matter of compromise, as various factors, which may be in conflict, are considered against a tight framework of fundamental constraints. Features that prove extremely beneficial under one set of circumstances may be less than optimal under another. Consider that a PDC bit is a mechanical device designed to transmit energy for the purpose of drilling rock. Despite its small size, it must be designed to transfer more energy than is generated in a high performance race car engine.

Cone

The cone of the bit provides a degree of stability when the bit is drilling, due to the resultant cutting forces from the PDC set within the cone generally urging the bit to rotate about its central axes. The resulting central cone of rock further enhances this stabilizing effect, as it helps prevent the bit from shifting the location of the central axis. The cone of the bit is usually lighter set than elsewhere on the bit face as the rock cone is unconfined and

consequently less force is required to remove it. Also less rock per

revolution of the drill bit is removed towards the central region of the bit.

Nose

The nose of the bit is that region of the face that is the furthest from the pin end. It is, therefore, the first part of the bit to encounter any change in

formation when drilling a vertical or near vertical hole. Because of this, it is desirable to have a relatively large number of cutters set on the nose to prevent overloading during the transition to a harder formation.

Taper

The taper (or flank) of the bit is the section between the nose and the gauge. It may provide a degree of stability and its length is usually governed by the cutter density requirement. A bit designed for tough applications, which needs a large number of cutters, would tend to have a more extended taper than a product for drilling a soft formation. However, an alternative way to

Outer Diameter Radius

The Outer Diameter Radius (ODR) refers to that region of the bit profile where the radius at the end of the flank leads into the gauge of the bit. This region of a bit is extremely important, especially in motor or turbine

applications where rotating speeds are high. The cutters must withstand the effects of high velocity due to their radial position on the face of the bit. Although the angular velocity of cutters at the bit gauge is identical to that of cutters within the cone, the tangential velocity is greater since it is a function of radial location.

PDC Cutters

The number of cutters used on a PDC bit is a primary determinant of how the bit performs. In an ideal situation, a PDC bit would be designed so it would:

- drill a broad range of formations including hard and abrasive stringers - provide a consistently high rate of penetration

- have a long bit life - can be built at a low cost

Unfortunately, there are performance and cost tradeoffs in varying cutter count. Using more cutters allows a bit to drill harder, more abrasive formations and generally results in a longer bit life. However, a higher cutter count also makes a bit more costly (particularly since PDC

components constitute a high percentage of the total bit cost) and, in general, causes the bit to drill at a slower rate of penetration. As the number of

cutters is reduced, the direction of the tradeoff reverses.

Cutters of 8 mm diameter have been used on products designed for harder formations. In fact, the first PDC manufactured was this size. 13 mm cutters are the industry standard size. They are most suitable for cutting medium to medium-hard formations as well as abrasive rock. Generally associated with fast drilling, 19 mm cutters are most suitable for drilling soft to medium formations when mounted in high bladed style bits. Because larger cutters produce large cuttings in the right application, they are extremely useful when drilling with oil based mud or water based mud in a hydratable formation.

PDC cutters of up to 48 mm diameter have been used in soft formation bits. However, Reed-Hycalog's experience is that the incremental advantage does not outweigh the inherent problem of redundancy limitations. Space is limited on the bit face and by using such large cutters there is only sufficient room to mount the minimum number of cutters to cut a full bore hole. If one cutter were to fail, the bit would be unable to proceed. Additionally, as very large cutters wear, the very large wear flats produce considerable heat that can cause catastrophic damage to the diamond layer.

Cutters are distributed across the bit face in such a way as to satisfy various requirements. Naturally the cutter layout must result in a full gauge hole being cut as the bit is rotated. As with most bits, satisfying one condition may well be at the cost of another. Judgments based on experience must be used to produce an optimized bit design.

Cutter Wear

It is desirable to get even wear across all the cutters of the bit. If one cutter wears appreciably more than the others, it could result in a weak spot. Additionally, even wear results in the efficient utilization of the PDC.

Cutter Placement

The cutters are arranged across the bit in such a way as to provide maximum bit life and to take into account expected rates of penetration and product cost.

Cutter Balance

The lateral imbalance force, resulting from the vectorial addition of all the cutting forces as the bit is drilling, is calculated at the design stage. Certain types of anti-whirl drill bits utilize this force in conjunction with a cutter devoid area and a low friction zone at the gauge to reduce the incidence of backward whirling, a detrimental motion of the bit which can occur under certain conditions. On most products, however, it is desirable to minimize this lateral force and the cutters are positioned accordingly.

Cutter Redundancy

Depending on the target formation, Schlumberger bits may have

considerable cutter redundancy built into the design. This is especially true on the flank and Outer Diameter Radius. If the bit is designed for tough, abrasive formations, the work performed per cutter, in these expected high wear regions, is minimized. This reduced work per cutter results in longer product life and reduced risk of premature failure.

Schlumberger PDC Cutter Technology

There are performance steps that are followed in the development of cutter technology. First, the best performing cutters in the industry are identified. Currently, Schlumberger primarily utilizes in-house cutters but will also use five outside vendors as suppliers. Whenever a new cutter design is

developed, it is tested to assure consistent quality and reliability. Currently, only between 10 and 15% of cutters evaluated actually meet the test criteria. Schlumberger continually evaluates it’s own standard cutters to make sure they are all up to the standards.

Here are some interesting facts about diamond. Diamond is in fact 10 times harder than steel. It is also twice as hard as tungsten carbide. Remember, tungsten carbide is the substrate that is used in the PDC cutters. Diamond is 10 times more wear resistant than tungsten carbide. In compression,

diamond is 20 times stronger than granite, which is probably one of the hardest rocks. Diamonds also have the lowest coefficient of friction of any known material. Friction of course creates heat. Convection cooling is not as efficient in maintaining low temperatures as reducing friction. Diamonds are one of the best thermal conductors known. This means if heat is

transmitted to the cutter it will soon spread throughout the diamond layer. Diamond also turns to graphite at approximately 1,300 degrees Centigrade at ambient pressure, and in the presence of oxygen will burn at 800 degrees Celsius. Diamond is non-wettable which means it must be combined with another material in order to bond. What Schlumberger uses is cobalt to bond the diamond. Unfortunately at 700 degrees C, the cobalt will actually force the diamond apart. Therefore the challenge is to mix the diamond grit with the cobalt and the tungsten carbide to develop a superior PDC cutter.

In the manufacture of PDC cutters, Schlumberger uses a diamond press. This is a huge piece of equipment 12 feet high, 27 tons in weight, and all that is used just to compress a two-inch square cube. The pressures involved are 1 million psi and temperatures up to 1,400 degrees Celsius. The

diamond press is used not only to manufacture the standard cutters but is also used to test out new designs for research and development. In the manufacturing process two cutters are manufactured at one press.

Salt is used as an excellent thermal conductor and will not deform under the massive pressures. As the pressure and heat is applied the cobalt is driven down from the substrate by a concentration gradient into the diamond grit. Once it mergers with the diamond grit it then bonds it together, and also bonds the diamond layer to the tungsten carbide substrate.

Unfortunately, the tungsten carbide and diamond have different thermal expansion rates. As the cutter cools down the tungsten carbide is wishing to expand while the diamond is wishing to contract. This creates incredible stresses at the interface between the diamond layer and the tungsten carbide substrate. The thickness of diamond layer that can be manufactured is limited by several factors. Primarily, it is the cobalt diffusion. If diamond layer is too thick, not enough cobalt will actually get into the PDC cutter that will result in a very weak outer edge. Also there are stresses induced by

Cobalt