Research on Mechanical Properties and Failure Mode of Conglomerate Based on Discrete Element Method

Abstract

Conglomerate reservoir is an important part of unconventional oil and gas resources, which has great developmental potential. However, its sedimentary environment and structural background are complex, and its cementation types, gravel volume fraction and shape are quite different, which leads to its strong heterogeneity. When developing a conglomerate reservoir, it is extremely difficult to drill because of its strong heterogeneity. It is difficult to obtain the mechanical properties and laws of the conglomerate through physical experiments, which further restricts the development process of conglomerate reservoirs. In order to study its failure law, a three-dimensional numerical model of a conglomerate is built based on the discrete element method, and the effects of cementation strength and gravel characteristics on the mechanical properties of the conglomerate are emphatically studied. The results show that the elastic modulus and uniaxial compressive strength of the conglomerate decrease obviously with the decrease in cementation strength. With the increase in cementation strength, the normal contact force of the conglomerate model increases significantly, the distribution of normal contact force changes from cylinder to sphere, and the heterogeneity of the conglomerate decreases. There is a threshold value for the influence of cementation strength on mechanical properties of the conglomerate, and when the threshold is exceeded, the mechanical properties of the conglomerate no longer change obviously. With the increase in gravel content, the uniaxial compressive strength of the conglomerate decreases at first and then increases, the phenomenon of penetrating gravels and bypassing gravels increases, and the single diagonal crack changes into diagonal cross cracks; the cementation strength and gravel content of gravel jointly affect the mechanical properties and fracture morphology of the conglomerate, and its stress–strain relationship is the external macroscopic expression of normal contact force of internal particles.