Influence of Stress Anisotropy on Petrophysical Parameters of Deep and Ultradeep Tight Sandstone

Abstract

Rock mechanics parameters control the distribution of in situ stress and natural fractures, which is the key to sweet spot evaluation in reservoir engineering. Combined with the distribution of in situ stress, an experimental scheme of stress on rock physical parameters was designed. The results show that rock sonic velocity is extremely sensitive to water saturation under overburden pressure. At ultrasonic frequencies, when the water saturation increases from 0% to 80%, the P-wave velocity increases first and then decreases. When the water saturation continues to increase to 100%, the P-wave velocity increases. This is due to the effect of water saturation on the shear modulus. Saturation is negatively correlated with shear wave velocity and resistivity. Different minerals have different control effects on the rock P-S wave velocity ratio. Quartz content plays a dominant role, and the two are negatively correlated, followed by feldspar and clay, and the two are positively correlated with the P-S wave ratio. The confining pressure, axial compression, stress ratio and burial depth are positively correlated with the P-S wave and negatively correlated with the P-S wave ratio; in descending order, the influencing factors of stress on the petrophysical parameters are maximum stress ratio > confining pressure > axial pressure.

Mechanical Properties of Rocks under Complex Stress Conditions: Investigations Using Experimental and Numerical Methods

“…Bai et al [9] conducted a series of triaxial compression tests on coal samples and discussed the dynamic failure characteristics and mechanism of coal bursts under different mining-induced stress disturbances. Zhang et al [10] studied the influence of stress anisotropy on the petrophysical parameters of tight sandstone. Shi et al [11] conducted triaxial drained shear, loading-unloading, and standard consolidation tests on sandy gravel specimens and obtained stiffness parameters of the hardening soil based on a model of a sandy gravel stratum.…”

Fracture Toughness Testing of Brittle Laminated Geomaterials Using Hollow Double-Wing Slotted Specimens

“…At present, the proposed specimen configurations are mostly suitable for fracture toughness tests performed under normal temperature and pressure conditions. The mechanical properties of rock under deep in situ conditions differ significantly from those under normal temperature and pressure [11,12]. The burial depth of shale gas reservoirs in China generally exceeds 2000 m [13,14], and in situ stress can significantly affect crack propagation in shale gas reservoirs [15,16], which in turn affects the stimulation of shale gas reservoirs.…”