Unconventional rocks elastic properties profile and geomechanical characterization

Abstract This study investigates the relationship between Young's modulus (static (Es) and dynamic (Ed)) generated from triaxial test and its reduced form (E*) derived from impulse hammer measurements. The sensitivity of E* to sample weight, length, diameter, and lithology were also documented. A total of 100 core plugs covering over 800 ft of Paleozoic tight sands interval and shale reservoirs were analyzed using well-established geochemical and mechanical methods. Strong correlations were observed between the E* and other mechanical properties measured. However, compared to Es and Ed derived from triaxial test, E* from impulse hammer reveals detailed geomechanical heterogeneity and anisotropy. Sample mineralogy and grain size variabilities considerably influence the E*. For a better upscaling of the reservoir model parameters, we generated a continuous geomechanical profile from the laboratory measurements. The results show marked contrasts in rock mechanical facies, consistent with mechanical/energy barrier mechanism. We documented toughness/modulus and interface barriers within the studied Paleozoic tight sands and shale reservoirs. These mechanical facies are important considerations for drilling and stimulation designs. They can cause wellbore instability and behave as barriers to hydraulic fracture height growth. The knowledge of elastic properties of rocks is crucial to geomechanical modeling throughout the life cycle of an asset. As such, the findings of this paper will potentially help to resolve the difficulties that are associated with geomechanical characterization and model calibration of highly laminated unconventional reservoirs using laboratory-generated data. In such vertically discontinuous reservoirs, the relative thickness of intercalated stiff and weak mechanical layers in conjuction with the stress barriers determine how far the hydraulic fracture propagation will grow in height.