Prediction of dispersion and attenuation on elastic wave velocities in partially saturated rock based on the fluid distribution obtained from three-dimensional (3D) micro-CT images

Elastic wave attenuation in partially saturated porous rock is primarily due to wave-induced fluid flow, which arises from the contrast in compressibility between air and water and is influenced by the water distribution within the rock. We propose a method for constructing a numerical model that predicts mesoscopic dispersion and attenuation. Initially, we use fluid distribution data sourced from 3D X-ray Computed Tomography images to construct the numerical model, utilizing Biot’s poroelastic equations as the governing equations. Subsequently, we implement the finite element method to derive solutions for the numerical model. Our focus is centered on two key challenges: 1) reducing memory cost, and 2) efficiently handling element intersection during the meshing process. The solutions illustrate the evolution of fluid pressure distribution and the frequency-dependent advancement of the elastic moduli, coupled with their corresponding attenuation. Ultimately, we compare these numerical predictions with previously published experimental data from a study on partially saturated Indiana limestone. The considerable agreement between our numerical results and the experimental data confirms the validity of our method, which crucially incorporates the actual fluid distribution (captured from 3D CT images) as a vital input

Reservoir fluid substitution effects on seismic profile interpretation : a physical modeling experiment

P-wave seismic surveys are performed on realistic physical models of a reservoir formed of interbedded sand and shale layers and filled with gas, water, and oil. They show characteristic behaviour which can be used to distinguish between fluids, with significant implications for the interpretation of time-lapse experiments. Discontinuous reflections originate in gas-filled reservoirs, with widely varying amplitude compared to oil- or water-filled reservoirs. Anomalous changes in seismic amplitude difference attributes for reflections within the reservoir are seen for gas/oil substitution. Oil/water substitution results in only weak variations of reservoir elastic properties, thus amplitude difference attributes may be unsuitable for monitoring changes in oil/water saturation. However, direct differences between the time traces are strong. On time-lapse sections, strong amplitude difference anomalies do not necessarily correspond to the region where the fluid variations occur; this is significant for monitoring oil field development by water injection

Three-Dimensional Ultrasonic Imaging and Acoustic Emission Monitoring of Hydraulic Fractures in Tight Sandstone

Hydraulic fracturing is an important means for the development of tight oil and gas reservoirs. Laboratory rock mechanics experiments can be used to better understand the mechanism of hydraulic fracture. Therefore, in this study we carried out hydraulic fracturing experiments on Triassic Yanchang Formation tight sandstone from the Ordos Basin, China. Sparse tomography was used to obtain ultrasonic velocity images of the sample during hydraulic fracturing. Then, combining the changes in rock mechanics parameters, acoustic emission activities, and their spatial position, we analyzed the hydraulic fracturing process of tight sandstone under high differential stress in detail. The experimental results illuminate the fracture evolution processes of hydraulic fracturing. The competition between stress-induced dilatancy and fluid flow was observed during water injection. Moreover, the results prove that the “seismic pump” mode occurs in the dry region, while the “dilation hardening” and “seismic pump” modes occur simultaneously in the partially saturated region; that is to say, the hydraulic conditions dominate the failure mode of the rock

Effect of Pore Collapse and Grain Crushing on the Frequency Dependence of Elastic Wave Velocities in a Porous Sandstone

International audienceA saturated Bleurswiller sandstone, of 25% porosity, was compacted by increasing the confning pressure over the critical pressure P* which characterizes the onset of pore collapse and grain crushing. The frequency-dependence of Young’s moduli were measured before and after the compaction using forced-oscillation method in a triaxial cell. For the intact and compacted samples, we observed one dispersive transition within the seismic band (0.01–100 Hz). The dispersion is consistent with crack-to-pore squirt fow, making the transition from the relaxed to the unrelaxed fuid-fow regime. The induced compaction shifted the critical frequency of the squirt-fow dispersion towards higher frequencies, thus moving it out of the seismic band and allowing Biot-Gassmann to fully apply. This result is a consequence of an increase in the crack aspect ratio after compaction. In addition, the dispersion of elastic modulus after compaction increases from about 25 to 30%, related to the increase of crack fractio

Energy management strategy of dual planetary hybrid electric vehicle based on optimal transmission efficiency

A power split hybrid electric vehicle with dual planetary gear sets is studied in this paper. Firstly, the power split and circulation phenomenon are further described by analyzing a speed and torque relationship between the engine, motors and the output shaft based on the lever analogy. The transmission efficiency and the electric power ratio are then obtained. The working modes of the hybrid electric vehicle (HEV) are divided according to the system operation mechanism. On this basis, the engine optimal operating line (OOL) control strategy and the mechanical point (MP) control strategy are designed. Furthermore, a fuzzy controller is designed to realize the optimal torque distribution of the engine and the motors in the MP control strategy. Simulation results demonstrate that the MP control strategy can guarantee a higher efficiency of the transmission system, which also shows good performance in improving fuel economy of the HEV by adjusting the engine operating point