Tight sandstones have become important targets in the exploration of unconventional oil and gas reservoirs. However, due to low porosity, low permeabi

Clay minerals are the most abundant materials in shale. Their presence significantly influences the elastic behavior of reservoir rocks as a function of mineral type, volume, and distribution, and their orientation controls the shale’s intrinsic anisotropic behaviors. Thus, knowing the elastic properties of shale with different types of clay minerals is imperative for fully understanding the seismic properties of the reservoir. However, it is extremely difficult to measure the elastic properties of natural shale by means of a single variable (in this case, the type of clay), due to the influences of multiple factors, including water, total organic carbon content, complex mineral composition, and so on. Thus, we use quartz, clay (kaolinite, illite, and smectite), carbonate, and kerogen extract as the primary materials to construct synthetic shale with different types of clay. Ultrasonic experiments were conducted to study the anisotropy of velocity and mechanical properties (Young’s modulus and Poisson’s ratio) in dry synthetic shale samples as a function of applied axial stress. The results show that the velocity of samples increases with applied pressure and the rate of velocity increase is higher at low pressures. Similarly, the dynamic Young’s modulus and Poisson’s ratio increase with applied pressure; $E_{11}$ is always larger than $E_{33}$, but ${\nu }_{31}$ may be larger or smaller than ${\nu }_{12}$. Furthermore, velocity anisotropy and mechanical anisotropy decrease with the increase of stress and are sensitive to stress and lithology. The closure of large aspect-ratio pores (and/or microcracks) seems to be a dominant mechanism controlling the change of anisotropy. Finally, the changes in mechanical anisotropy under applied stress are larger compared with the changes in velocity anisotropy, indicating that mechanical properties are more sensitive to the changes in rock property.

Young’s modulus and Poisson’s ratio are important for reservoir characterization and rock brittleness prediction in unconventional resource exploration and development. Conventional methods can estimate Young’s modulus and Poisson’s ratio by indirect calculations and direct inversion using approximate expressions, which have cumulative errors and limited accuracy of the estimated results, especially at large incident angles. In this study, we derived a new form of the Zoeppritz equation and P-to-P wave reflection coefficient in terms of density and Young’s modulus, Poisson’s ratio. It has the same accuracy as the original Zoeppritz equation over a wide range of incident angles. A robust non-linear inversion method based on the iteratively regularized Levenberg Marquardt (IRLM) algorithm, is used to invert all three parameters based on the new equation directly and simultaneously. Synthetic data and field data are used to test and verify the proposed direct inversion method, ensuring the feasibility and effectiveness of the proposed method and the high accuracy and stability of the inversion results. This study has a great potential and valuable guidance for “sweet spot” evaluation and subsequent horizontal well deployment and hydraulic fracturing.

Shale oil reservoirs usually have various lithofacies with complex spatial patterns. Seismic reflections usually reveal the combination of sets of thin mud shales with various lithofacies. The seismic response characteristics of the lithofacies and the differences in seismic response of different lithofacies are still unclear, making the reservoir description difficult. The complex tectonic structures, diverse lithofacies, thin interlayers, fractures with various length scales, and various fracture development zones in the shale oil reservoir have placed very high demands on the design and construction method during the physical modeling of the shale oil reservoir. Facing these challenges, a physical modeling study on shale oil reservoirs with complex lithofacies and meter-scale structures is conducted. The target is the shale oil reservoir of the ES4s subsegment in the Jiyang depression. The complex physical model of a shale oil reservoir, with the thin stratigraphic layers and the complicated lithofacies and fracture patterns to date, has been designed and constructed in a laboratory. In total, 25 combinations of materials have been developed to simulate various lithofacies with different elastic parameters, and the error of the wave velocity simulation is less than 2.35%. The simulation of 1 m thick interlayers and the construction method for seismic physical models with meter-scale geologic structures has been realized. The quality control analysis finds that the simulation accuracy of small-scale geologic structure, complex lithofacies, and fractures is relatively reliable. Based on the physical model of the shale oil reservoir, high-density and wide-azimuth seismic data are acquired. Preliminary data processing and analysis find that the model layers have clear reflection characteristics, providing reliable data for the next step of seismic characteristics analysis of complex lithofacies shale oil reservoirs. The methodology has improved the capacity of seismic physical modeling to simulate complex oil and gas reservoirs, enabling the seismic physical simulation method to be applied in analyzing the commonly observed complex lithofacies, fractures, and meter-scale structures in unconventional oil and gas reservoirs.