Creep Characteristics Research of Ultra-deep Composite Rock Salt in Tarim Basin Based on 2D Image Contour Identification

Creep is a distinctive mechanical response observed in soft rocks like salt. Typically, there are three primary methods which have been widely applied in the investigation of salt creep within high-purity and thick formations: analytical solutions, triaxial experiments, and numerical simulations. However, for ultra-deep composite salt layers in the Tarim Basin, Xinjiang Uygur Autonomous Region, China, the intense tectonic movement has resulted in salt formations that exhibit distinct characteristics from conventional fine-grained rock salt. In addition, the presence of interlayers of clay minerals within the salt makes the creep behavior even more complex. The ultra-deep composite rock salt exhibits incompatible deformation phenomena which cannot be explained by continuum theory. In addition, the proportion of different components in the standardized sample is usually uncertain and that, doubtlessly, introduces an uncontrollable variable into the creep experiments. In simulation, the morphology of the interfaces is usually not considered. Sometimes they are treated as separate layers, leading to significant disparities between physical model and reality. Therefore, all these approaches have limitations. This paperwork introduces a comprehensive and novel approach for investigating rock salt creep behavior. Based on image identification, the contours of interface from real salt samples are first extracted and imported into finite element method (FEM) program for simulations. Verified by digital image correlation (DIC) experiments, it reveals that under uniaxial stress state, near the front edge of gypsum, the compression of composite salt rocks increases as creep progresses. Tensile strain tends to appear in the segments with angles greater than 45°, causing fissures of 0.01 µm width within NaCl. From electron microscopy, localized damage was observed, revealing micro-cracks of 1–2 µm width occurring predominantly at interfaces, where shear strain accumulates, especially in the junction area. In addition, shear strain tends to accumulate near segments with angles ranging from 0° to 35°. Through precise interface morphology description, the results of simulation could be much more practical and reliable. The methodology in this study can actually be adopted in the simulation of any types of rock.

Highlights

This paperwork introduces a comprehensive and novel approach for investigating rock salt creep behavior especially the composite.