The Computer Simulation of the Interaction Between Roller Bit and Rock

Abstract

Abstract In this paper, the surface of each tooth of roller bits is represented by scores of points, whose 3-D compound coordinates are used to reflect the shape and size of the tooth. Thus, the cutting structure of the bit together with their movement is represented by the time-sequence of the coordinates of the several thousand points. Hence, the computer simulates the roller bit. In the simulation, the bottom hole that changes with drilling is represented, according to the sequence of time, as a series of time points. And the bottom hole at each time point is represented, according to space, as tens of thousands of points, whose 3-D compound coordinates are used to express the shape and size of the bottom hole at an arbitrary time. The changes of the bottom hole with drilling are described by a recurrence model made up of the bottom hole at each time point. Hence the reproduction of the bottom hole is on computer. The well bore is dealt with the same principle as the bottom hole. The interaction between the roller bit and the rock is represented by the balance model of the vertical and the lateral interactions. The index, inclination, the shape and size of rock fragile breakage by a contacting tooth at any time are calculated by the fragile criterion model and the rock breakage model. The craters with various shapes are formed by the rock fragile breakage and the amount of the rock occupied by the tooth directly. BRIAS, the simulation software thus set up, can be used to analyse all the interactions in the process of drilling. Detailed experiment data have proved that the simulation software is able to well reflect the effects of the subtle differences of bit structure, WOB and rock properties upon the rotation rate and the torque of the bit. Introduction The content of the interaction between a roller bit and bottom rock is very extensive. This paper mainly deals with two major issues: how the bottom rock is smashed upon the force of the bit; How the roller bit moves under the action of the drilling string and the reaction of the bottom rock. The key problem here is the relative movement and the interaction between the tooth and the bottom hole. In fact, the movement of the bit can be analysed if the pressures upon the bit are available; the smashing of the rock can be studied if the pressures upon the rock are clear. P. 309