Pinlu Cao

Analytical and experimental study of a reverse circulation drill bit with an annular slit

A new type of drill bit designed with an annular slit was developed to enhance the reverse circulation effect of the down-the-hole hammer drilling technology. A computational fluid dynamics code, Fluent, was used to simulate the flow phenomena inside the drill bit. The simulation results show that the air flowing through the annular slit moves upward along the wall of the central passage of the annular drill bit and that there is no interference phenomenon similar to the normal drill bit, which is beneficial for the formation of reverse circulation. Meanwhile, the new drill bit with the annular slit was produced and tested in the laboratory. The results show that for the annular drill bit with the flushing nozzles closed, the mass flow rate of the sucked air is approximately 63.78 g/s, which is 1.76 times that of the normal drill bit, while it is about 2.46 times if the flushing nozzles are opened. In addition, many factors can affect the reverse circulation effect of the annular drill bit, including the slit width, the distance between the annular slit and the working surface of the drill bit, and the flow direction of the gas ejected from the annular slit.

Low-molecular-weight, fatty-acid esters as potential low-temperature drilling fluids for ice coring

Abstract A challenge for future deep-ice coring in central Antarctica is to identify an appropriate inert drilling fluid with no undesirable physical or chemical characteristics. The drilling fluids currently in use (kerosene-based fluids with density-increasing additives, ethanol and n-butyl acetate) are not intelligent choices for the future from safety, environmental and some technological standpoints. Recently proposed drilling fluids based upon ESTISOL™ have high viscosity at low temperatures, which severely limits their application in cold environments. This paper presents our research into the application of low-molecular-weight, fatty-acid esters (FAEs), substances commonly used in the fragrance and flavoring industries. According to available data, selected FAEs are not hazardous to human health. Considering density requirements alone, ethyl butyrate and n-propyl propionate best meet our present needs. The viscosities of these two chemicals are also the lowest among studied FAEs, not exceeding 4 mPas at temperatures down to −60°C. Both compounds are highly volatile, and insoluble in water. Such properties are attractive, but the applicability of FAEs to deep, cold, ice drilling can be evaluated only after field-based, practical experiments in test boreholes.

Anti-torque systems of electromechanical cable-suspended drills and test results

Abstract To prevent spinning of the upper non-rotated part of the electromechanical drill, an ‘anti-torque system’ has to be included in the downhole unit. At the same time, the anti-torque must allow the drill to move up and down the borehole during drilling and tripping operations. Usually the anti-torque system has a blade form of various designs that engages with the borehole wall and counteracts the torque from the stator of the driving motor. This paper presents a review of the different anti-torque systems and test results with selected designs (leaf spring, skate and U-shaped anti-torque systems). Experiments showed that the skate anti-torque system can provide the maximal holding torque between 67 and 267 Nm−1 depending on the skates’ outer diameter and ice temperature, while the leaf spring anti-torque system can provide only 2.5–40 N m−1 (in case of straight contact between the ice and the leaf springs). The total resistance force to axial movement of the skate anti-torque system lies in the range 209–454N if the system is vibrating. For the leaf spring anti-torque system, the total axial resistance force is far less (19–243 N).