Under the effect of bit weight on bit and rotary column winding, the teeth eat into the rock after crushing, and at the same time, some sliding occurs to shear the rock. When it rolls at the bottom of the well, its upper teeth will successively impact and press into the formation. This effect can crush a part of the rock at the bottom of the well. At the same time, depending on its sliding, the shear effect will weaken the remaining rocks between the teeth, so that the rock at the bottom of the well is completely broken and the well hole can be extended.
The impact force and static pressure caused by its longitudinal oscillation all lead to the impact and crushing effect of teeth on the land, forming a volume crushing pit.
Crushing action of cone bit
The radial and tangential movement of its teeth makes it possible to shear the rock between teeth.
Erosion effect of jet flow on cone bit
The rapid jet from the nozzle has an impact effect on the rock under the well, assisting in the fragmentation of the rock.
Due to the different lithology and hardness of the strata, and the different rock crushing mechanism, the failure forms of rock bit are also different. The physical and mechanical properties of the common formation lithology in the drilling of oil fields in China have been determined. Based on The formation lithology and lithology per meter shall be recorded during drilling, the hardness, plasticity, brittleness, abrasiveness and drillability of formation rocks shall be analyzed, and the selection and use of cone bits shall be confirmed to be reasonable according to the failure mode of cone bits.
The mechanical properties of rocks in different positions in the earth's crust vary greatly. The deep buried rock is in the state of multi-directional compressive stress, which reduces the porosity and increases the strength of the rock. The upper well section generally has loose rock cementation; Soft, high rotary speed and low WOB of cone bit. The rock in the lower well section is generally hard and abrasive, and the rotary speed of the cone bit is low, the WOB is high, and the service time is long. Analyze the stratum according to the collected well section position and the drilling time record of lithology per meter According to the hardness, plasticity, brittleness, abrasiveness and drillability of the rock and the failure mode of the cone bit, confirm whether the selection and use of the cone bit are reasonable.