The quality of drill bit, the type of drill bit and the adaptability of formation lithology play an important role in accelerating drilling speed and improving the footage of a single drill bit. Usually, multiple drill bits with different sizes are used to drill an oil and gas well. When drilling the upper stratum, use a bit with larger diameter, because the stratum drilled by the bit is soft.
A single drill bit has many footage and short service time, so a drill bit can generally reuse several wells; However, when drilling a lower formation, it is necessary to use a bit with a smaller diameter. Because the formation is hard and the footage of a single bit is small, it is generally necessary to use multiple bits.
Extended data:
The rock-breaking function of diamond bit is completed by diamond particles. In order to know the rock-breaking effect of a drill, it is necessary to know the rock-breaking effect of a single diamond. In hard strata, under the action of WOB, a single diamond makes the rock in a very high stress state (about 4,200-5,700 MPa, and some data think it can reach 6300MPa), which makes the rock change from brittleness to plasticity.
When a single diamond eats into the stratum, it cuts the rock under the action of torque, and the cutting depth is basically equal to that of diamond particles. This process, like "ploughing", is called the ploughing action of diamond bit.
In some brittle rocks (such as sandstone and limestone). ), under the simultaneous action of WOB torque, the volume of broken rock is much larger than the eating and rotating volume of diamond particles. When the pressure is not high, small grooves can only be formed along the direction of diamond movement, while increasing the pressure will break the rocks in the depth and on both sides of the small grooves, exceeding the cross-sectional size of diamond particles.
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