What geological conditions are tricone drill bits suitable for
The roller cone bits can be classified into milled tooth (steel tooth) roller cone bits and inserted tooth (hard alloy teeth are inserted on the roller cones) roller cone bits according to the tooth type. Different types of roller cone bits are suitable for different geological conditions, as follows:
Steel Tooth Roller Cone Bits
Clay and Mudstone Strata: The hardness of clay and mudstone is relatively low, and the steel teeth can easily cut into and break the rock. The shape of the steel teeth can be designed to be suitable for scraping and shearing. During the rotation of the bit, it scrapes off the soft rock like a shovel. Moreover, in such strata, the bit is subjected to less impact force, and the steel teeth can give full play to their breaking function without excessive tooth wear. Soft Sandy Strata: For some soft sandy strata with fine particles and poor cementation, the steel tooth roller cone bits can also work effectively. In such strata, the rolling of the roller cones and the shearing action of the teeth can loosen the sand grains, which are then carried out of the wellbore by the drilling fluid. However, due to the presence of sand grains, there may be a certain degree of wear on the bit teeth, so it is necessary to select an appropriate bit type according to the specific situation of the sand.
Inserted Tooth Roller Cone Bits
Sandstone Strata: For sandstone with general cementation degree and moderate hardness, the inserted tooth roller cone bits are a better choice. The hard alloy teeth can withstand the wear and impact of the sandstone on the teeth, and break the sandstone through the rolling of the roller cones and the impact and crushing action of the teeth. At the same time, the drilling fluid is ejected through the water holes, which can cool the bit and carry away the broken sandstone particles to ensure the normal operation of the bit. Limestone Strata: Limestone has a certain hardness, but it is not as difficult to break as some extremely hard rocks, and the inserted tooth roller cone bits are also applicable. The hard alloy teeth can use the compound movement of the roller cones to break the limestone by means of impact and crushing. Moreover, during the drilling process, the drilling fluid can cool the bit to prevent damage to the bit caused by the high temperature generated by friction, and at the same time carry away the broken limestone debris from the wellbore. Hard Shale Strata: For some hard shale strata, the inserted tooth sealed bearing tricone bits can play a role. The hard alloy teeth of this kind of bit can effectively break the shale, and the sealed bearing can prevent the solid particles in the drilling fluid from entering the bearing, ensuring the stable operation of the bit under high pressure and impact force. Some Hard Sandstone Strata: In some hard sandstone strata with relatively high hardness but not reaching the extremely hard level, the inserted tooth tricone bits can also be used for drilling with appropriate drilling parameters (such as rotational speed, drilling pressure, etc.). However, as the hardness of the sandstone increases, the breaking efficiency of the bit will gradually decrease, and the tooth wear will also intensify. Gravel and Cobble Strata: Gravel and cobble strata usually have poor bonding force, and the cobbles are hard and have smooth surfaces, which are prone to problems such as wellbore deviation. When using a roller cone bit for drilling, the roller cones of the tricone bit can press down on the large cobbles and roll and pound on them. As long as a reasonable drilling pressure can be applied, the cobbles will be quickly crushed into surface breakage and fatigue breakage, thus improving the drilling efficiency.
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