A tri-cone bit is a drill bit that comprises three cones, each fitted with teeth of varying shapes and hardness. As the drill bit turns, these teeth effectively break rocks, enabling the drilling process into the formation. Tri-cone bits offer the benefits of a straightforward design, easy to use, prolonged durability, and rapid drilling speeds. Consequently, they find extensive application in oil drilling projects, establishing themselves as the most prevalent and widely utilized roller cone bits at home and abroad.
Tri-cone bit consists of more than 20 parts such as cutting structure, bearing structure, locking element, oil storage sealing device, and nozzle device. Its distinctive design enables it to proficiently execute drilling operations across diverse geological conditions.
Structure Composition
Shirttail
Shirttail is the main part of roller cone bit. A drill bit consists of three pieces of shirttails assembled and welded together. It has a connecting thread on the upper part, which is connected with rock drilling tools, and the lower part has a certain inclination journal, which forms a bearing pair with the inner hole of shirttail. Shirttail has a water hole runner and is also fitted with an oil storage pressure compensation device. Journal bears the load and needs high wear resistance and hardness, while the inner part of the matrix needs to have sufficient strength and impact resistance toughness.
Cutting structure: cone and carbide
The cone is a cone equipped with carbide, there are two types single cone and compound cone. The single cone is composed of main cone and back cone. The movement of single cone is pure rolling at the bottom of the well, which is suitable for drilling in hard strata. The compound cone consists of the main cone, the second cone, and the back cone. This kind of cone works in the bottom of the well not only by rolling but also by sliding and is used for drilling in softer formations.
There are two types of carbide on the cone: insert bit and steel tooth bit. The rows of teeth on the tri-cone bit mesh with each other, which can effectively and completely break the bottom rock without repetition and prevent alveolar mud bagging. The shape, size, quantity, and length of the carbide of drill bit depending on the hardness of the formation being drilled. The softer the formation, the larger, sharper, and the smaller the number of carbide. Conversely, the harder the formation, the smaller, shorter, and the greater the number of carbide.
Bearing structure
Roller cone bit bearing consists of the inner hole of cone, the journal of shirttail, the locking element, and so on.
① Bearing pair has large, medium, and small shafts and thrust surfaces, etc. The large and small bearings are subjected to radial loads, the middle shaft is mainly used for locking and positioning, and the thrust surface bears axial loads.
② According to the structure of bearing pair, the drill bit bearings are generally divided into two categories of rolling bearings and sliding bearings. According to the sealing of bearings, it can be divided into sealed and non-sealed.
③ To ensure that cone and shirttail are assembled securely, the cone must be locked. The locking methods mainly include steel ball locking and circlip locking.
④ The sealing methods of bearings are divided into metal seals, O ring seals, floating seals, etc.
Oil storage pressure compensation system
This device is composed of a bearing sealing ring, oil storage capsule, protection cup, gland, plug, retaining ring, and other parts. Its function is to balance the pressure difference inside and outside the bearing cavity when the cone is working so that the bearing sealing ring can work normally for a long time under the small difference between inside and outside, preventing drilling fluid from entering the bearing cavity and avoid the loss of lubricating grease, and can store enough grease to continuously replenish the bearing cavity so that the drill bit bearing is in a sealed state and works under good lubrication conditions.
Nozzle
Nozzle shape structure is divided into standard type and protective cover type. The standard type has a simple structure, low manufacturing cost, no tab protection, is easy to load and unload, and is often used for low abrasive soft ground steel tooth drill bits. It is often used for steel tooth drill bits in low abrasive soft formations. The protective cap type is protected by a tab on the top, which can reduce the erosion effect of abrasive materials on the locking retaining ring. All sliding bearing drill bits adopt the protective cover type, which can work for a long time under the condition of high-pressure injection in the well and is safe and reliable.
Precautions for use
Before using a tri-cone bit, you should check whether its structure is intact, whether the teeth are sharp, whether the bearings are operating normally, etc.
When drilling, maintain appropriate drilling pressure and rotational speed to avoid excessive impact force and low rotational speed, which may cause tooth wear or loss.
During use, regularly check the wear of bearings and seals and replace damaged parts in time.
When out of service, drill bits should be cleaned and coated with a rust inhibitor to prevent rust and damage.
During transportation and storage, avoid collision and extrusion to prevent damage and deformation.
The structure of the tri-cone bit is intricate and finely crafted. The design and manufacturing quality of each component plays a crucial role in determining the drill bit’s overall performance. During usage, it is essential to be attentive to inspections and maintenance to guarantee proper operation and prolong service life. Concurrently, thanks to the ongoing progress and innovation in science and technology, the structure and performance of tri-cone bits are continuously advancing and being enhanced. This evolution contributes to better support and services for the development of oil drilling projects.
