Petrophysical characteristics of shale oil reservoirs in the Yanchang Formation,Ordos Basin

The mediate-low maturity continental shale oil reservoir in the 7th member of the Triassic Yanchang Formation is one of the main zones for shale oil exploration and development in Ordos Basin,China,but the seismic response mechanism of the reservoir remains unclear.Therefore,developing a new method for“sweet spot”seismic prediction combined with rock physics is necessary.To determine the petrophysical characteristics of continental shale in the 7th member of the Yanchang Formation in the study area,a series of tests,such as a systematic acoustic test on shale oil samples in the target segment,X-ray diffraction analyses,analysis of thin optical sections,and scanning electron microscopy,were conducted to summarize the patterns of seismic elastic property changes.Results show that the shale oil samples of the 7th member of the Yanchang Formation are primarily composed of lithic feldspar sandstone with feldspar dissolution and intergranular pores,widespread micron pores,and throats.Such composition indicates a positive correlation between porosity and permeability.The velocities of the samples are affected by their porosity and mineral composition.Velocity increases with the increase of the calcium content and decreases with the increase of the clay content,indicating a negative correlation with the porosity and total organic carbon(TOC)content on the condition of the same rock structure(quartz skeleton or clay skeleton).The elastic properties of the rock are horizontally isotropic(T1 medium),and the velocity is vertically anisotropic.In addition,the directional arrangement of clay controls the anisotropy of rock velocity.TOC is mainly distributed in the primary intergranular pores,and it has no contribution to the anisotropy of rock velocity.The results of this paper can provide a reference for the seismic prediction of continental shale oil reservoirs in the 7th member of the Yanchang Formation.

法国科学家正研制魔镜可预测人类未来长相

在《白雪公主》童话中，邪恶的王后拥有一面神奇的魔镜，可以预言谁是世界上最美丽的女人；而法国科学家正在发明一面真正的“魔镜”，可以精确“预言”你5年后的体型和面容。

A two-scale contact model for collisions between blocks in CDEM

Contact detection between interacting blocks is of great importance to discontinuity-based numerical methods, such as DDA, DEM, and NMM. A rigorous contact theory is a prerequisite to describing the interactions of multiple blocks. Currently, the penalty method, in which mathematical springs with high stiffness values are employed, is always used to calculate the contact forces. High stiffness values may cause numerical oscillations and limit the time step. Furthermore, their values are difficult to identify. The intention of this study is to present a two-scale contact model for the calculation of forces between colliding blocks. In this new model, a calculation step taken from the moment of contact will be divided into two time stages: the free motion time stage and the contact time stage. Actually, these two time stages correspond to two real physical processes. Based on this, we present a new numerical model that is intended to be more precise and useful in calculating the contact forces without mathematical springs. The propagation of the elastic wave during collision is of a characteristic length, which determines the volume of material involved in the contact force calculation. In conventional contact models, this range is always regarded as the length of one element, which may lead to an inaccurate calculation of contact forces. In fact, the real scale of this range is smaller than the length of a single element, and subdivided elements, which are refined according to the characteristic length and are presented in the new contact model.