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This paper presents an experimental investigation on the nonlinear nature of the dynamic geomechanical characteristics of a clastic rock (sandstone). Rock samples of 7.5 mm in diameter and 15.6 mm in length were prepared. Rock properties were identified. Firstly, the limits of the rock linear elasticity zone were defined during quasistatic loading and uniaxial compressive strength determination at the Tinius Hounsfield rig. Secondly, the small experimental custom-built rig was designed to study the nonlinear nature of the Young’s modulus in the zone of linear elasticity. At the rig the sample was stationary preloaded. The dynamic load was generated by a piezoelectric actuator powered with a signal generator. The displacement of rock sample surfaces was recorded by a laser sensor and an eddy current probe. The dynamic experiments were conducted at the load amplitude ranging from 50 to 250 N for each of frequencies of 25 Hz and 40 Hz. It was found that the dynamic Young’s modulus increased with amplitude for all the frequencies studied. The newly developed experimental rig allows to investigate elastic moduli dispersion of rocks at the strain up to 10-3 under vibrations with frequency up to 40 Hz.

Summary During the development of hydrocarbon fields geomechanical characteristics of rocks change under the effect of nonlinear dynamic loads. Elasticity modulus is one of the most important characteristics of mechanical properties of rocks used in engineering. It is known that the elasticity modulus of dry rocks does not depend on the frequency of the applied load. However, dispersion of elastic moduli in dry sedimentary rocks still exists. The mechanism, in accordance with which dispersion of the dynamic component of elastic modulus occurs, remains not fully disclosed. Studies on the dispersion of the dynamic component of the elasticity modulus under the influence of uniaxial dynamic loads are conducted on dry sandstone samples in the zone of linear elasticity. Physically substantiated relations are proposed. The nonlinear nature of the dynamic elasticity modulus under the influence of dynamic loads of given frequency and amplitude was confirmed. The obtained relations allow taking into account the influence of nonlinear dynamic loads on the elasticity modulus of the rock in the calculations when designing the development of hydrocarbon fields.

Under dynamic loading, the geomechanical properties of porous clastic rocks differ from those in quasistatic loading. A small experimental rig was built to directly assess the influence of vibrations on the uniaxial compressive strength (UCS), Young modulus, and Poisson&rsquo, s ratio. A piezoelectric actuator powered by a signal from an oscillator was used in the rig as a generator of vibrations. A laser sensor and eddy current probe measured the longitudinal and transverse deformation. Tinius Hounsfield and Instron Series 4483 installations were used to determine the geomechanical properties of new red sandstone in a quasistatic regime. The boundaries of elastic deformations determined in the quasistatic loading were implemented in the dynamic loading. To perform the experiments in the elastic zone (on the graph of stress (&sigma, )&ndash, strain (&epsilon, )), small samples with diameters ranging between 7.5 and 24.7 mm were manufactured. The investigation demonstrated that the Young&rsquo, s modulus of the sandstone increased with increasing values of the dynamic load and frequency.

This paper shows and analyzes causes of oil reservoir properties deterioration. It describes changes in rock sate of stress during well drilling and perforation and analyzes existing technologies for oil well perforation. It is shown that abrasive jet perforation is the most efficient gentle method for well perforation. Upgraded abrasive jet perforation technology is proposed. That takes into account speed of wearing out of nozzles made of composite materials under abrasive jet influence of sand carrier based on mathematical simulation of well conditions. Due to qualitative well perforation proposed technology increases well productivity and decreases energy consumption.