Development and Test of a New Device for Geomechanical Rock Properties

The strength of the rock has a crucial importance in drilling engineering as it can be used to predict the ROP, drill bit optimization and to avoid wellbore stability related issues. Unconfined Compressive Strength (UCS) is one of the most generally accepted parameters used to quantify the rock strength. Determining the UCS in a laboratory requires availability of rock samples, special techniques and treatment of the samples. Therefore, it represents a high cost and cannot be done on each well that is drilled. There are other ways to determine UCS, but they all have limitations. In this work, a novel device along with a methodology to determine UCS from rock cuttings is presented: the Rock Crusher. A series of initial tests were done using cement samples with different strengths taking the mean current of the device as an indicator of the strength. These tests showed a good correlation between the mean current and the UCS of the tested material. The concept of Specific Energy applied to rock cuttings was used, and the specific energy necessary to crush the rock was found to be a better indicator of the strength of the rock. Finally, a series of tests on rock samples with different strength were done showing a weaker correlation between the strength and the specific energy, compared to the one of the cement samples. However, after a careful analysis of the information generated it was observed that the parameter that better describes the crushing process of cuttings is the Cohesion of the rock.