Известия Томского политехнического университета: Инжиниринг георесурсов (May 2019)
Analysis of anisotropic rock destruction with cone bits
Abstract
Relevance of work is caused by the need to solve the problem of controlling well direction when drilling. The main aim of the study is to obtain the analytical dependences for calculation of an overturning moment arising at rock destruction by anisotropic mountain. The moment destabilizes the work of a roller cone bits; and to determine the analytical relation of bit design features with the size of this power factor. The methods used in the study: the analysis of results of experimental works on mechanics of anisotropic rocks destruction by boring bits and indentors of various forms, analytical researches of rock destruction, comparison and analysis of convergence of the obtained data and formulas. The results. It was ascertained that one of the major power factors causing a curvature of wells at destruction of anisotropic rocks is the occurrence of the overturning moment caused by an inequality of elastic and strength properties of rocks. The size of the moment is determined by the size of axial effort, the size and the form of rock cutting elements, as well as by the parameters of anisotropy of physic-mechanical properties of rock and by the boring tool and rock layers angle of incidence. The avlue of the overturning moment at anisotropic rock destruction by a roller cone bit changes for one turn of a chisel rotation on a face. The number of the maximum and minimum values as well as their fluctuation amplitude depends on a number of roller cone bits and a tilt angle of cone roller rotation axes in relation to a well face. The mentioned feature of the overturning moment size fluctuation can be used when designing configurations of a boring column to minimize the influence of the overturning moment on a curvature of wells, drilling in anisotropic rocks. Well curving in anisotropic breeds drilled with roller cone bits, is defined by the mechanism of rock destruction and its features. The dual nature of rock cutting action - rock crush by axial force and rock crushing by slanting by a blow at an angle to a face is included into the process and also some design features of arms of bits. A form and sizes of rock cutting inserts, an angle of their sharpening as well as the scheme of rock cutting inserts installation in wreaths of roller cone bits can be referred to the features of arms of the roller cone bits influencing the destruction of anisotropic rock and occurrence of the overturning moment.
