A Comparison of the Relationship between Dynamic and Static Rock Mechanical Parameters

Abstract

The rock’s mechanical properties play an important role in the whole process of conventional and unconventional oil and gas exploration and progression. At present, there are two approaches to determining the mechanical parameters. One is to measure the rock sample in the laboratory (i.e., static elastic modulus Es). The other is to obtain parameters by geophysical logging data (i.e., dynamic elastic modulus Ed). In general, static parameters can more accurately reflect the mechanical properties of rock under actual geo-stresses. At the same time, their determinations are difficult. Therefore, one of the best methods is to establish the correlation between the dynamic and static parameters. This paper investigates the relation between the dynamic and static parameters using different methods for various rocks in the literature. Based on the relationship of Es=aEd+b, a correction between a and b is proposed using the multinomial form a=0.67+0.101b−0.006b2+0.0001b3. It is found that the Es can be derived from the Ed just when the parameter b is known. In terms of different types of rocks, for igneous and metamorphic rocks, the best correlation between Es and Ed obeys the power-law correlation; for sedimentary rocks, there are linear and logarithmic correlations. Theoretically, the difference between dynamic and static elastic moduli can be attributed to microcracks and pores within rocks. This study can provide guidance for engineers to predict the desired static parameters precisely using logging or seismic data.

Keywords

• rock mechanics
• dynamic parameters
• static parameters
• elastic modulus
• Poisson’s ratio