Analytical and Experimental Study of the Mechanisms of Diamond Bits Interaction with Rocks in the Wellbore During Sinking Processes

摘要

This paper presents the classification of the existing methods to determine the diamond number (diamond size) in contact with the wellbore during deepening or sinking processes. The classification is based on two principles, according to which there are a group of theoretical (estimation) and a group of empirical (practical) methods. The theoretical methods are subdivided to two subgroups, which are based on deterministic and probabilistic methods. Generally, in the theoretical methods the number of diamonds involved in the destruction of the rock, are determined using the calculation methods. In this paper, we also considered empirical methods based on the indentation (fingerprint) method. Laboratory conditions were met in this research by using rock simulators in which Plexiglas plates were used, with contours of the bit on them. The Bench method was also used in this research during the wellbore drilling processes. Based on the measurements of the height of protrusion of the diamond from the matrix-type bits A4DP, the average (diamond size) number of diamond in contact with the wellbore was calculated depending on the depth of the diamond's intrusion. In doing so, the surface of the wellbore was considered smooth but rough for the bit. Analysis of the calculated results show that at the initial time the wellbore was in contacted with a limited diamond number (diamond size), i. e., not exceeding 20% of the total diamond size. With an increment in the penetration depth of the diamond in the rock, the (size of diamonds) number of diamonds in contact can reach 80-100%. The following assumptions were made in this study: 1. The study mechanism of the diamonds contact with the wellbore, bottom profiles and matrix bits are treated as a flat body. 2. Both the deterministic and probabilistic calculation methods are not supported by experimental studies of (size of diamonds) number of diamond in contact with the wellbore. These shortcomings introduce significant inaccuracy in the calculations of the diamonds number in contact with the borehole bottom, and hence increases the inaccuracy in the calculation of the contact space volume of a pair of "diamond bit-rock". However, it should be noted that the essential novelty in these studies is to determine the number of active diamonds using drillability index values K_d.