Continuous rock drillability measurements using scratch tests

The traditional drillability measurement using micro-drilling test has the limitations of time-consuming data acquisition and low utilization efficiency of core samples. Moreover, it cannot provide continuous drillability measurements and test results are highly influenced by the heterogeneity of the rock, because the micro-drilling test is single-point test. To overcome these shortcomings, a new technique for continuous drillability measurements using scratch test is introduced in this paper. The new technique is proposed based on correlating the Specific Energy measured from the scratch tests and the micro-drilling tests with PDC bits. This technique can provide continuous and high-resolution drillability measurement, with relatively simple test procedure and high utilization efficiency of core samples compared with the micro-drilling tests. Furthermore, the new technique can capture the effect of the intrinsic heterogeneity of rock on drillability. Finally, a case study is performed using core samples from Songnan oilfield in northeast China. Drillability of these core samples are determined using the newly proposed technique and compared with the measurements of micro-drill tests. The comparison results demonstrate that the new technique based on scratch test can offer continuous drillability measurement with sufficient accuracy.