Abstract: The precise acquisition of deep rock mechanical parameters is required for the safe and efficient development of deep rock engineering. In response to the problems of difficult and costly coring, little data from laboratory tests and large discreteness, a method based on mm-indentation tests is developed to accurately obtain the elastic modulus of tight sandstone. In this paper, five indenters commonly used in mm-indentation test are used. A large number of mm-indentation tests on tight sandstone in the Tarim oilfield are performed by controlling the maximal load and loading/unloading rate as test variables. The results show that Brinell spherical indenters can accurately measure the elastic modulus of tight sandstone based on the Oliver-Pharr theory. In addition, the influence of test conditions such as Brinell indenter diameter, loading/unloading rate, and maximal load on test results is analyzed, and the optimal test conditions are clarified. The stress distribution in the stressed area is analyzed using FEM software, and the applicabilities of representative volume element and Oliver Pharr theory under various test conditions is discussed. Compared with the traditional micro/nanoindentation test, the proposed method has the advantages of rapid testing speed, simple sample preparation, and low cost, and it can be applied to a large number of drill cuttings returned from drilling sites as well as core samples with fracture development that are difficult to make standard samples, providing strong support for the efficient development of deep resources and the safe construction of deep rock engineering.

Key words: mm-indentation test, tight sandstone, elastic modulus, Brinell indenter, Oliver-Pharr theory