No abstract

Taking a practical project as an example, based on the computational fluid dynamics (CFD), standard k-ε model and finite element method, a mathematical model for the diffusion due to liquefied natural gas (LNG) pipeline leakage in a tunnel was established, and the diffusion process was numerically simulated for three LNG leakage cases. From the simulation results, the variation of CH4 concentration field and explosive gas cloud with time within the tunnel, and the influence of leakage location on the diffusion was analyzed for the three cases. It was shown that the variation of CH4 concentration field had a similar trend for the three cases, but the CH4 explosive gas cloud length increased rapidly with the LNG leakage intensity so that dangerous situations would occur for the medium and large leakages, and a leak location closer to air inlet would lead to a more dangerous situation. When the amount of LNG leakage in the tunnel is large, the effect of mechanical ventilation is obviously weakened. Furthermore, a nitrogen seal precaution was proposed for the situations.

The single-cone bit has become the first choice for slim hole sidetracking and deep well drilling with its unique rock breaking method and high ROP (Rate Of Penetration), with its main failure mode being of early excessive wear of the cutting teeth. In order to improve the adaptability of single-cone bits to hard and highly abrasive formations, a spherical single-cone Polycrystalline Diamond Compact (PDC) compound bit is designed. According to the characteristics of the tooth profile, the way of tooth arrangement and the way of contact between the cutting teeth and the rock, the acceleration equation to the cutting teeth of the spherical single-cone PDC compound bit is established. The acceleration of the single-cone bit is verified by numerical simulation experiment of rock-breaking. The shaft inclination angle of the cone, the position and height of the PDC teeth, the radius of the PDC teeth, the lateral rotation angle and the front inclination angle on the acceleration are studied. The results show that as the shaft inclination angle increases, the bit transmission ratio gradually increases, and the harder the rock formation, the larger the transmission ratio of the single-cone bit; the shaft inclination angle and the position of the PDC tooth have a greater influence on the acceleration of the PDC tooth, and the radius, lateral rotation angle and front inclination angle of the PDC tooth have a small influence on the acceleration of the PDC tooth; rock properties have an impact on the acceleration of the cutting teeth, with the acceleration of the cutting teeth in hard rock formations being higher than that in soft rock formations; near the top of the cone, the absolute acceleration of the cutting teeth will fluctuate sharply and cause severe wear of the cutting teeth, so the tooth distribution in this area should be strengthened; on the premise that the bearing life of the single-cone bit is allowed, the value of the shaft inclination angle β can be approached to 70°. The relative error between the theoretical analysis results of the acceleration of the PDC cutter and the rock-breaking simulation experiment results is between −0.95% and −2.24%. This research lays a theoretical foundation for the dynamic research of spherical single-cone PDC compound bit.

The single‐cone bit has become the first choice for slim hole sidetracking and deep well drilling with its unique rock breaking method and high ROP (rate of penetration). The single‐cone bits currently used in the oil field all use cemented carbide inserts, with its main failure mode being of early excessive wear of the cutting teeth. In order to improve the adaptability of single‐cone bits to hard and highly abrasive formations, a single‐cone PDC composite bit is designed. According to the characteristics of the tooth profile, the way of tooth arrangement and the way of contact between the cutting teeth and the rock, the acceleration equation to the cutting teeth of the single‐cone PDC composite bit is established. The shaft inclination angle of the cone, the position and height of the PDC teeth, the radius of the PDC teeth, the lateral rotation angle, and the front inclination angle on the acceleration are studied. The acceleration of the single‐cone bit is verified by numerical simulation and drilling experiment of rock‐breaking. Rock formation properties have an impact on the acceleration of the cutting teeth, with the acceleration of the cutting teeth in hard rock formations being higher than that in soft rock formations. On the premise that the bearing life of the single‐cone bit is allowed, the value of the shaft inclination angle β can be approached to 70°. This research lays a theoretical foundation for the dynamic research and wear analysis of single‐cone PDC composite bit.