Two-dimensional Discrete Element Simulation of Negative Inversion Deformation Process

Abstract:

Inversion structure is an essential superimposed structure pattern, which can significantly influence the development of structural traps in hydrocarbon basins. Numerous previous researches present the dynamic process of positive inversion by numerical models and sandbox, while the study of negative inversion structure is relatively absent. Some simple theoretical models and physical sandbox simulation experiments have been established to study negative inversion structure, but the numerical simulation experiments are relatively scarce. This work presents discrete element numerical experiments of negative structural inversion in 2D, and aims at understanding of factors which controlling the negative inversion deformation process. The models are designed as pre-existing faults initially developing with a syn-sedimentary sequence. The experiment is mainly divided into two stages, i.e., the early compress stage and the late extension stage. The model is subjected to unidirectional or bidirectional stress. In both stages of the model, the amount of extrusion and the amount of extension are 25%. During the experiment, one layer was deposited every 5% of the deformation. Each layer was of equal thickness, and a total of 9 layers were deposited. The total of ten models of negative inversion have been conducted varying (i) geometric shape of pre-existing faults (i.e., listric fault, single tabular fault, step faults, ramp faults), and (ii) applying different dip angle of pre-existing fault (i.e.,30°,45°,60°). Research shows that (i) Changes in geometric shape of pre-existing faults lead to important variations in structural styles and fault displacement. Formation of conjugate faults can be seen during the experiments of ramp faults, (ii) The higher angle of the existing fault, the lower angle it intersects with the newly formed normal fault in the later tensile stage. When the angle of pre-existing fault is 60°, the normal fault formed in the later period is basically coincident with it. Next step we will also take thickness ratio of the syn-sedimentary strata to the original strata into consideration. And numerical models will be compared to Linhe Depression in China, and the relationship between them will help to explain the structural evolution process and benefit hydrocarbon exploration in this area.