Tri-Cone Drill Bit: Application Insights

1) The basic structure of a tricone drill bits. The drill bit body: There are three pieces of teeth that are assembled and welded together, and there are connecting threads on the upper part. Gear: a cone-shaped metal body composed of gear body and teeth. Teeth are divided into two types: milled teeth and insert teeth, bearings and their oil storage sealing device nozzles.

2) Working principle of the roller cone bit When the roller cone bit works at the bottom of the well, the entire drill bit rotates around the axis of the drill bit, which is called revolution, and the three cones roll at the bottom of the well according to their own axes, which is called rotation. The drilling pressure endured by the drill bit acts on the rock through the teeth, causing the rock to break (crushing effect). During the rolling process, the cone alternately contacts the bottom of the well with single teeth and double teeth, and the position of the center of the cone fluctuates, causing the drill bit to vibrate longitudinally. This longitudinal vibration causes the drill string to continuously compress and stretch. The lower drill string converts this periodically changing elastic deformation energy into impact force on the formation through the teeth to break the rock. This impact and crushing effect is the main way for the roller cone drill bit to break rocks.

In addition to impacting and crushing the rock at the bottom of the well, the roller cone bit also produces shearing effects on the rock at the bottom of the well. While the cone rolls at the bottom of the well, it also causes the teeth to slide against the bottom of the well. The sliding of the teeth creates a shearing effect on the rock at the bottom of the well, scraping the bottom of the well like a scraper bit. The sliding of teeth is mainly caused by the over-top, auxiliary cone and shifting arrangement of the gear wheel. The over-top arrangement of the cone cone causes sliding in the tangential direction, and the shift arrangement of the cone causes sliding in the axial direction. Generally, drill bits for drilling soft to medium-hard formations are designed with over-top, compound cone and shifting shafts; drill bits for drilling medium-hard to hard formations are designed with over-top and compound cones; drill bits for drilling extremely hard and highly abrasive formations are designed with over-top and compound cones. Drill bits often use single cone cones, which do not overshoot or move the axis.

3) Classification and Selection of Roller Bits There are many manufacturers of roller bits, and these drill bit manufacturers provide drill bits of various types and structures. In order to facilitate the selection and use of roller cone bits, the International Institute of Drilling Contractors (IADC) has developed a unified classification standard and numbering method for roller cone bits around the world. IADC stipulates that each type of drill bit is represented by a three-digit number, and the meaning of each number is as follows:

• The first digit indicates the type of tooth and the formation suitable for drilling: 1- milling tooth, soft formation; 2- milling tooth, medium to medium-hard formation; 3- milling tooth, hard, abrasive or semi-abrasive formation; 4- spare; 5-Tooth, soft to medium formation; 6-Tooth, medium-hard formation; 7-Tooth, hard, abrasive or semi-abrasive formation; 8-Tooth, extremely hard, highly abrasive formation.
• The second digit indicates that the drilled formation is subdivided into four hardness grades: 1, 2, 3, and 4.
• The third digit indicates the structural characteristics of the drill bit: 1- Unsealed rolling bearing; 2- T-shaped outer row of teeth for diameter protection; 3- Insert teeth for diameter protection on the gauge diameter; 4- Sealed rolling bearing; 5- Sealed rolling bearing on the gauge diameter There are inserts and gauges; 6- sealed sliding bearings; 7- sealed sliding bearings with inserts and gauges on the gauge; 8- directional well deflection bits; 9- others.

Features and advantages of roller cone drill bits:

• 1. Rock breaking with dual effects of impact and shear, both impact of teeth and shear caused by sliding, resulting in high rock breaking efficiency.
• 2. It is adaptable to a wide range of strata and is suitable for drilling in all strata.
• 3. The drill bit has good self-cleaning effect and is not easy to get muddy.
• 4. Drill bit cost is lower.