Experimental Investigations of Composite Halite Core with a Hard Rock Creep Behavior

Abstract

ABSTRACT: Rock salt, mainly comprised of NaCl, exhibits inherent softness and has a good rheology property, resulting in complex creep patterns and fracture evolution for wellbore stability. They are, even coming from underground, facing weathering and dissolution & precipitation process, which makes the rock salt outcrop structure probably different from halite core. In this paper, physical property and chemical composition comparisons were conducted first to determine the difference between conventional rock salt outcrop and the halite core. The creep behavior of rock salt, shale, and halite core was investigated respectively by creep tests and DIC analysis. The results show that shale creeps are accompanied by fluctuation and the sample is compressive in both axial and radial. The fine grain rock salt has a smooth strain & time relation and the sample has a negative (tensile) volumetric strain as well as radial strain. However, the composite halite core creeps in a pattern between "soft rock" (rock salt) and "hard rock" (shale). Creeping with fluctuation, the sample dilates in radial while the volume is compressive. DIC analysis shows that the high strain area is concentrated at the boundary between different components. 1. INTRODUCTION Halite or rock salt formation is considered to be an ideal location for gas storage due to its perfect tightness, and the pre-salt area has shown great exploration potential and prospects nowadays (Formigli, J. M. et al. (2009); de Almeida, A. S.et al. (2010); Jones*, C. M. et al. (2015); França, D. et al. (2021)). Since the salt has a rheological property, it leaves tremendous challenges to drilling safety, as well as wellbore integrity. Therefore, there is of great necessity and meaning to investigate the creep behavior of rock salt. In Tarim basin, northwest of China, the salt composition is not as simple as that in, for example, the Brazilian coastal region. Since the salt formation is bedded, mud, quartz, and other impurities may exist between salt layers. Therefore, the creep behavior of this type of rock salt remains uncertain.