PSI - Issue 68

Sair Kahraman et al. / Procedia Structural Integrity 68 (2025) 722–726 Sair Kahraman and Abdalrahim A.M. Malakni / Structural Integrity Procedia 00 (2025) 000–000

723

2

Nomenclature PR

penetration rate (cm/min) weight on bit (kN) round per minute P-wave velocity (km/s)

W N V p

including operating parameters and rock properties. These studies were conducted only on mudstone, mudstone, conglomerate and sandstone. It is not possible to apply these equations when drilling other rocks (especially igneous rocks). Another PR equation that considers both operational parameters and rock properties was developed by Ersoy and Waller (1995). This study was conducted on sedimentary rocks (mudstone, sandstone, siltstone and limestone), and therefore the derived equations cannot be expected to be particularly valid for igneous rocks. Therefore, there are no models available in the literature that consider both operational parameters and rock properties to estimate the PR in diamond drilling of igneous rocks. The aim of this study is to investigate the drillability of igneous rocks such as granite, basalt and andesite with a diamond core bit considering operational parameters and P-wave velocity, and to develop an estimation equation for PR. The P-wave velocity of intact rocks is a measure of microfractures (Zinke, 1999; Wang et al., 2015; Chenga et al, 2019). A low P-wave velocity value is an indicator of high microfractures. With the increase of microfractures, P wave velocity decreases and PR increases. 2. Experimental studies 2.1. Drilling tests Three andesites, one granite, and one diabase samples were used in the drilling tests. The drilling tests were performed using the instrumented diamond core drilling machine (Fig. 1a). Diamond core bits used in the tests are indicated in Fig. 1b. The drilling machine has an electrical engine with a power of 11 kW. The rotational speed and the thrust capacity of the drilling machine is 5000 rpm and 5 kN, respectively. Forty-two drilling tests were conducted in the laboratory using different operational variables. Two different thrust (weight on bit) values were applied, 1 and 4 kN. Rotational speed values were changed to 1000, 1500, 2000, 2500 and 3000 rpm for each thrust value. During the drilling tests, drilling times and hole lengths (core lengths) were recorded and PR values were calculated in cm/min. The test results are shown in Table 1.

a

b

Fig. 1. (a) Instrumented diamond core drilling machine; (b) Diamond core bits.