Background of the invention

The invention relates to a drill bit comprising a metallic body and separately-formed cutting elements mounted fixedly to the body. The drill bit is designed for rotary drilling and is intended for boring vertical or sub stantially vertical holes to earth or soil. The drill bit may be used in drilling subterranean wells for oil and gas production .

The invention further relates to a method of manu facturing the earth-boring drill bit.

The field of the invention is defined more specif ically in the preambles of the independent claims.

Vertical drill holes are drilled for forming sub terranean formations such as wells required in oil and nat ural gas production. Rotary drilling is typically utilized in well drilling. In the rotary drilling a drill bit is located at a lowermost end of drilling equipment and the drill bit is rotated by means of a rotary drilling machine around longitudinal axis of the equipment and is simulta neously pushed i.e. fed against the drilled surface. The earth-boring drilling requires durable drill bits, since during the drilling the drill bits are subjected to hard wearing and also to impacts, yet no impacts are directed in the rotary drilling from the drilling machine to drilling tools. The drill bit, like in US-2013146366-A1, comprises a body and several cutting elements fixed to the body. The body is typically formed of metal-matrix composites and endures therefore well wear and high temperatures. However, the known drill bits have shown to contain some disad vantages especially regarding their mechanical properties.

Brief description of the invention

An object of the invention is to provide a novel and improved earth-boring drill bit for rotary drilling and a method for manufacturing the same. The drill bit according to the invention is charac terized by the characterizing features of the independent apparatus claim.

The method according to the invention is character ized by the charactering features and steps of the inde pendent method claim.

An idea of the disclosed solution is that the drill bit is intended for earth-boring utilizing rotary drilling technique without the use of impacts generated by any ham mering or striking device. By means of the disclosed drill bit subterranean well bores are formed, whereby the drilling is executed vertically or substantially vertically. The drill bit comprises a bit body which is made of steel ma terial and the body comprises a crown i.e. a drilling head with a drilling face facing towards a drilling direction. The crown is provided with several blades, which protrude in the drilling direction. An opposite rear end portion of the body is provided with an integral shank comprising ex ternal connecting threads for connecting the drill bit to a distal end of drilling equipment. The mentioned blades of the crown are provided with several cutting elements, which are separately-formed hard objects and are fixedly connected so that they are immovable relative to the bit body during the use of the drill bit. The crown is also provided with several flushing openings for discharging drilling fluid into the borehole being drilled.

Furthermore, the bit body is a unitary piece which is made of carbon steel material. The unitary structure means that the crown and the integral shank are of the same material. The bit body is first machined into desired shape and dimensions, and is thereafter surface hardened for cre ating desired surface properties. The surface hardening generates a thin surface layer of harder metal at the outer surface of the bit body and leaves a soft core deeper un derneath the harder surface. In other words, the surface and the core of the drill bit have different properties even though they are made of the same material. Thus, the drill bit is subjected to selective hardening effect.

An advantage of the disclosed solution is that the drill bit can be shaped in a relative easy and effective manner by means of chip removing machining techniques, and it provides the needed hard surface properties only after the shaping is finished. Heat treatment process of the sur face hardening is relatively gentle so that dimensional accuracy of the machined finished piece remains at good level. One benefit is that the bit body may be formed of relatively inexpensive material which is also well availa ble. In addition to the advantages of the manufacturing measures, the disclosed solution provides improved proper ties for the drill bit. The hard outer surface protects the drill bit effectively against wear caused by rock material detached from the drilled surface and rubbing against the crown during the drilling. On the other hand, the softer core of the drill bit endures well against impacts and strong forces, which typically occur during the drilling. In other words, the softer inner material is not sensitive to formation of cracks, whereby the drill bit is mechani cally durable. The drill bit has thereby a great combination of hardness and mechanical durability.

According to an embodiment, the cutting elements comprise polycrystalline diamond compact (PDC) material at least on their cutting head. The entire cutting element may be made of the PDC, or alternatively, only an outermost head portion of the cutting element is made of PDC material and a frame portion of the element is made of another material suitable for the purpose.

According to an embodiment, the cutting elements are substantially cylindrical pieces which are formed sep arately relative to the unitary bit body made of steel. The cylindrical element may be easily and firmly mounted to a mounting recess having also cylindrical configuration. The mounting recess is fast and simple to manufacture by drill ing techniques, for example.

According to an embodiment, the cutting elements comprise a cutting head portion and a body portion, wherein the cutting head is made of PDC material and the body por tion is made of material other than the cutting head.

According to an embodiment, as an alternative to the mentioned PDC material any other suitable super-abra sive material may be used on the cutting head of the cutting element .

According to an embodiment, each blade of the crown comprises several mounting recesses which are shaped and dimensioned according to the cutting elements and are con figured to receive the cutting elements partly inside them. The mounting recess provides the cutting element with proper support and shape locking against forces trying to remove it from the blade, and the brazing or corresponding fas tening of the cutting element completes the immovable mount ing .

According to an embodiment, the mounting recesses are machined by using chip removing machining techniques and have thereby accurate shape and dimensions correspond ing to those of the cutting elements. When the shapes and dimensions of the mounting recesses match with those of cutting elements, rigid and fastening is achieved.

According to an embodiment, the cutting elements are secured to the blades by brazing after the bit body is heat treated.

According to an embodiment, the brazing of the cut ting elements is done by using silver solder material.

According to an embodiment, hardness of the hard surface layer of the bit body is 50 - 63 HRC, and hardness of the softer core is 35 - 45 HRC.

According to an embodiment, thickness of the hard surface layer of the bit body is 1 - 3 mm. Thus, a relatively thin protective exterior shell may provide sufficient wear protection for the drill bit for harsh conditions.

According to an embodiment, the crown comprises sev eral flushing openings which are provided with inner threads and are capable to receive nozzle pieces provided with outer threads corresponding to the mentioned inner threads. Since the nozzle pieces are screw-mounted to the flushing open ings, their mounting is easy and fast. Further, it is rel atively easy to drill the flushing openings and to execute thereafter thread cutting measures for providing them with the threads .

According to an embodiment, one or more of the blades are provided with one or more wear inserts, which are separately-formed pieces made of wear-resistant mate rial. Thanks to the use of the wear inserts service life of the drill bit may be increased. The wear inserts may be positioned on surface locations wherein problematic wearing tendency is notified. Fastening recesses for the wear in serts can be done fast and effectively when the bit body is machined in a machining center, for example.

According to an embodiment, the drill bit comprises several wear inserts facing towards the drilling direction. The wear inserts may protect the drilling face of the bit body against wear.

According to an embodiment, the drill bit comprises several wear inserts facing towards the radial direction of the drill bit. The wear inserts may protect the side sur faces of the bit body against wear.

According to an embodiment, the wear inserts dis closed above may be made of PDC material. The wear inserts may be placed to mounting space formed to the bit body and the mounting may be secured by brazing. Thus, the mounting principle of the wear inserts may the same as with the cutting elements.

According to an embodiment, the bit body is coated at least partly with a hard-facing material layer, which is affixed on the bit body after the heat treatment. This way the bit body is well protected against wear since it has two protective exterior layers, namely the surface hardened layer and the hard coating layer.

According to an embodiment, manufacturing an earth boring rotary drill bit comprises principally three main phases, forming by machining a bit body of blank steel material, surface hardening bit body having the desired shapes and dimensions, and finally assembling the drill bit by mounting several separately-formed cutting elements to the bit body together with possible wear inserts and flush ing nozzles. This way, a unitary steel body is shaped and hardened utilizing known basic workshop techniques and de vices, and after that the bit body is equipped with the needed drilling components.

According to an embodiment, the machined bit body, which is made of unitary carbon steel blank piece is surface hardened in a furnace by utilizing carburizing technique. Then the bit body is placed into the furnace inside which is arranged carbon-rich environment and elevated tempera ture. The bit body is kept in the furnace for pre-determined time, and is there after quenched^ This type of surface hardening process is relatively easy to manage.

According to an embodiment, the above mentioned carburizing of the bit body is executed by utilizing gas carburizing method, wherein the drill bit is placed in a furnace maintained with a carbon-rich interior. The furnace may then be equipped with gas feeding means for filling the furnace with carbon-gas. The process is well adjustable and stable .

According to an embodiment, one or more selected areas of the bit body are protected during the carburizing process so that the carbon-rich gas has no influence on them. The protection can be done by arranging removable shield material on the desired areas. Paint, for example, can be used as the shield material. It is possible to pro tect threads of mounting places of the flushing nozzles by means of a removable shield paint or plugs. The connecting thread of the shank may also be protected against the sur face-hardening, if so desired.

According to an embodiment, the machining process of the steel body may comprise cutting a blank from a hot rolled steel bar and machining the blank into its final shape in a machining center by using lathe, drilling and milling techniques.

The above disclosed embodiments may be combined in order to form suitable solutions having those of the above features that are needed.

Brief description of the figures

Some embodiments are described in more detail in the accompanying drawings, in which

Figure 1 is a schematic side view of a drill bit comprising several blades with cutting elements arranged in one row,

Figure 2 is a schematic side view of another drill bit, wherein every other blade of the crown comprises cut ting elements in a single row and every other blade com prises cutting elements in a double row system,

Figure 3 is a schematic and sectional side view of a steel body of the drill bit and its surface hardened outer layer, and

Figure 4 is a schematic diagram showing manufactur ing principle and possible steps for forming the disclosed drill bit.

For the sake of clarity, the figures show some em bodiments of the disclosed solution in a simplified manner. In the figures, like reference numerals identify like ele ments . Detailed description of some embodiments

Figure 1 shows a drill bit 1 comprising a bit body 2. The bit body 2 has a crown 3 facing towards a drilling direction D. At an opposite rear end of the drill bit 2 is a shank 4. The body 2 is a unitary piece wherein the crown 3 and the shank 4 are integrated parts of the body 2. The shank 4 comprises connecting threads 5 for connecting the drill bit 1 to drilling equipment. The crown 3 comprises several blades 6 protruding from the crown 4 and being equipped with several cutting elements 7. The cutting ele ments 7 may be made at least partly of PDC material or corresponding extremely hard material, and they are fastened immovably to mounting recesses 8, which are formed to the blades 6. The blades 6 may also comprise several wear in serts 9, which may also be made of PDC material. Mounting of the cutting elements 7 and the wear inserts 9 may com prise brazing. Further, at the crown 4 may be several flush ing openings 10 for feeding flushing agent into the hole being drilled and to thereby flushing the drilling cuttings away. The bit body 2 is made of carbon steel material. Shapes and features of the steel-body 2 are formed by uti lizing chip-removing machining, wherefore it has dimen sional accuracy.

In Figure 1 the cutting elements 7 are arranged in one row in each of the blades 6. Figure 2 discloses an alternative solution wherein every other blade 6a of the crown 4 comprises cutting elements 7 in a single row and every other blade 6b comprises cutting elements 7 in a double row arrangement. Other basic features of the solution of Figure 1 apply to the solution of Figure 2. It should be noted, that there may be other alternative ways for posi tioning the cutting elements 7 at the crown.

Figure 3 shows in a highly simplified manner basic principles of the steel body 2 comprising a relatively thin and hard surface layer SL and a softer core C. The surface hardening may extend to 1 - 3 mm deep and may create Rockwell hardness 50 - 63 HRC for the surface layer SL. The core C may remain softer and may have Rockwell hardness 35 - 45 HRC. Figure 3 also shows that the bit 2 may comprise flush ing channels 11 extending from the rear part of the body to the drilling face. The crown 3 comprises flushing openings 10 which may be configured to receive flushing nozzles 12. Between the nozzles 12 and the openings 10 may be threads for screw mounting purpose. During drilling operations, drilling fluid or mud may be pumped down into the hole and through the nozzles 12 to facilitate drilling and to carry away formation cuttings which have been cut away by the cutting elements. Cutting elements and their mounting re cesses, nor wear inserts are disclosed in Figure for clarity reasons .

Figure 4 illustrates steps and features of the manufacturing process of the disclosed drill bit. These features are discussed already above in this patent appli cation .

The drawings and the related description are only intended to illustrate the idea of the invention. In its details, the invention may vary within the scope of the claims .