切削具的“后部效应”对岩石破碎的影响

本文通过一个光弹实验和静压卸载实验,着重讨论了钻井中做回转运动的切削具后部的岩石表面上出现张裂纹和卸载破坏的问题。光弹实验表明,运动的切削具(如金刚石颗粒)在其后部的岩石中诱发出一个张应力区,最大张应力是在岩石表面上,在此表面上极易形成微小张裂纹。卸载实验表明,对某些脆性岩石(如花岗岩),载荷只要达到其压碎载荷的60％以上,就可以通过卸载方式破坏岩石。

THE INFLUENCE OF THE BACK EFFECTS OF DRILLING CUTTERS ON THE FRACTURE OF ROCKS

This article discusses, through a photoelastic experiment and a static- pressing unloading experiment, the possibly appearing tensile cracks and unloading fractures on the rock surface behind the moving cutters in drilling process. The analysis of the photoelastic experiment shows that the moving cutters, such as diamond grits on bit, induce a tensile stress field in the rock behind the cutters. The largest tensile stress appears on the rock surface, and tensile micro-cracks are easily formed on the surface. The moving cutters exert alternative loads on the rock surface. The unloading experiment shows that as long as the load imposed on some brittle rocks, such as granite, reaches over 60 percent of the fracture load, the rocks, might be fractured through unloading.