Characterization of Rock Mechanical Properties Using Lab Tests and Numerical Interpretation Model of Well Logs

Abstract

The tight gas reservoir in the fifth member of the Xujiahe formation contains heterogeneous interlayers of sandstone and shale that are low in both porosity and permeability. Elastic characteristics of sandstone and shale are analyzed in this study based on petrophysics tests. The tests indicate that sandstone and mudstone samples have different stress-strain relationships. The rock tends to exhibit elastic-plastic deformation. The compressive strength correlates with confinement pressure and elastic modulus. The results based on thin-bed log interpretation match dynamic Young’s modulus and Poisson’s ratio predicted by theory. The compressive strength is calculated from density, elastic impedance, and clay contents. The tensile strength is calibrated using compressive strength. Shear strength is calculated with an empirical formula. Finally, log interpretation of rock mechanical properties is performed on the fifth member of the Xujiahe formation. Natural fractures in downhole cores and rock microscopic failure in the samples in the cross section demonstrate that tensile fractures were primarily observed in sandstone, and shear fractures can be observed in both mudstone and sandstone. Based on different elasticity and plasticity of different rocks, as well as the characteristics of natural fractures, a fracture propagation model was built.

Comparative Characterization of Petrophysical and Mechanical Properties of Siliciclastic Reservoir Rocks within a compressional structure of the Teapot Dome Oilfield, Wyoming, USA

“…According to Bentley and Zhang (2005), Poisson's ratio is known to be between the ranges of 0 -0.5. The higher the value the more likely the rock will change shape under stress (Xu, et al, 2016). Brittleness Index has no definite definition but has been used to classify shale into brittle or ductile shale, it is observed that the presence of quartz increases the brittleness index while the presence of clay significantly reduces the brittleness index (Fjaer et al, 2008).…”

“…However, the static methods are difficult, expensive, and time-consuming (Fei et al, 2016). Dynamic methods on the other hand, make use of correlations and calculations of compressional wave velocities (Vp) and shear wave velocities (Vs), which can be obtained from well logs or the laboratory (Xu, et al, 2016). Acoustic well logging is one of the methods used to obtain or estimate dynamic mechanical properties of rocks as it is used to measure the acoustic wave velocities which can be used together with density to obtain dynamic Elastic modulus and dynamic Poisson ratio.…”

Exposure Time Impact on the Geomechanical Characteristics of Sandstone Formation during Horizontal Drilling

“…Rock Young's modulus and Poisson's ratio are necessary for stress evaluation [14]. Many studies utilized the dynamic moduli to estimate the static moduli to be used as inputs for the modeling purposes as the case of reservoir simulation and earth modeling [14,15]. The rock unconfined compressive strength (UCS) is the most significant parameter among these properties for evaluating rock geomechanical behavior [16], and the strength is controlled by many rock parameters such as rock porosity, internal friction angle, grains particle size, and the cohesive forces [17].…”

Investigating the Effects of Mechanical Properties of Rocks on Specific Energy and Penetration Rate of Borehole Drilling

“…The mechanical properties of rocks play important role in drilling operation such as prediction of fracture zone, well stability and other engineering techniques (Xu et al 2016). Kahraman et al (2003) stated that the specific energy (SE), the unconfined compressive strength (UCS), the Brazilian tensile strength, the point load strength and the Schmidt hammer rebound test values are the significant rock properties that influence the penetration rate in drilling operations.…”