Issue 42

J.-f. He et alii, Frattura ed Integrità Strutturale, 42 (2017) 263-271; DOI: 10.3221/IGF-ESIS.42.28 264 hydraulic hammer with a fluidic amplifier has also been regarded as the most efficient drilling tool in hard rock or complicated formations [3-5]. With the rapid development of drilling technology, the application of hydraulic hammers with a fluidic amplifier has been extended to horizontal directional well drilling in recent years, which contributes to the development of trenchless drilling technology of oil-gas pipeline construction in hard rock and complicated formations. Unlike the conventional vertical hole drilling with hydraulic hammers, horizontal directional well drilling demands the anvil horizontally impact the drill bit while the hydraulic DTH hammer is in operation, which aggravates the abrasion of hydraulic hammer and leads to the reduction of service life of hydraulic DTH hammers. In order to improve the penetration rate and drilling cost of hard rock formations, the hydraulic hammer has been initially proposed and designed in Former Soviet Union, and a proven efficiency of 40% has been achieved with new generation of hydraulic hammer. Afterwards, Yuri and Andrei conducted relevant field tests to improve the efficiency of the hammer in US, which leads to the development of hydraulic hammer [6]. Allowing for the cost reduction and technological advantages in deep or medium-to-hard rock formations, D. Pixton and D. Hall have proposed the advanced mud hammer system, and the prototype of the hammer system have also been developed and reported [7]. However, no extra introduction of this mud-actuated hammer has been reported with respect to the field application results and service life time. Therefore, the new type of hydraulic DTH hammer with a horizontal oriented slider has been urgently designed and applied to horizontal directional well drilling in order to improve the service life of hydraulic DTH hammers. Moreover, the abrasion property of hydraulic DTH hammers with horizontal oriented sliders should be intensively studied with respect to the application of hydraulic DTH hammers to horizontal directional well drilling. While in horizontal directional well drilling with hydraulic DTH hammers, the piston is actuated by powered muds, which drives the hammers horizontally and reciprocally impact the drill bit. However, the service life of hydraulic DTH hammers is unsatisfactory due to the reciprocating motion of anvil with high frequency, which deteriorates the performance of hydraulic DTH hammers in horizontal directional oil-gas well drilling [8]. In order to improve the service life of hydraulic DTH hammers in horizontal directional well drilling, a specialized anvil with horizontal oriented sliders has been designed, as shown in Fig. 1. The material of slider has been optimized, and totally 6 sliders are embedded into the anvil, which contributes to reducing the abrasion of hydraulic DTH hammer. Furthermore, the abrasion property of horizontal oriented slider has numerically analyzed by Finite Element Analysis, which indicates the design and optimization of hydraulic hammers in horizontal directional well drilling. Figure 1 : Structure of hydraulic DTH hammers with horizontal oriented slider. In previous studies, the service life of a hydraulic DTH hammer has been analyzed by drilling crews and researchers while in vertical or up-down drilling. C.W. Li has analyzed the effect of material property of hydraulic hammer on its service life time in 2002, and numerical models of damage mechanism are established [9]. Ding Daipo has improved the service life of hydraulic DTH hammers up to 120h while in oil-gas well drilling [10]. Meanwhile, series of experiments on abrasion property of hydraulic DTH hammers in vertical well drilling have been conducted by He Liu in 2014 on the basis of Finite Element Analysis (FEA), which numerically and practically contributes to improving the service life of hydraulic DTH hammers [4]. In addition, the abrasion process of abrasive particle is numerically analyzed by Wu Jinghua et al., which could theoretically illustrate the behavior of abrasive impacting [11]. Furthermore, Li Weitao has optimized the hydraulic DTH hammer by numerical analysis on the fluidic amplifier in order to improve the service life of hydraulic DTH hammers [10]. Some other related work has been finished with different experiments and apparatus in order to improve the service life of hydraulic hammers in various drilling conditions [13, 14].