An investigation of permeability and porosity evolution of Kansas chalk under in-situ conditions

Abstract

Injections of brine into the chalk can leads to compaction. The chemical impacts of water injection on the mechanical strength of chalk have been investigating for several years. Also, porosity and permeability evolution resulted by compaction is a debate among scientists for many years. In this study we investigate the link between the observed compaction and the permeability evolution. The link between compaction and permeability evolution is studied both via theoretical modeling in combination with experimental work in laboratory. We have also studied the impact of different fluids (NaCl solution 1.833 M, synthetic sea water and distilled water) on mechanical strength of Kansas chalk under high pressure (20 MPa) and high temperature (130 °C). We observed that flooding SSW did not have a significant impact on the mechanical strength of chalk. However, injecting DW contributed to an increase in the creep strain of the Kansas core. In addition, chemical analysis is conducted employing Ionic Chromatography (IC) method. The IC results enlighten that Magnesium-bearing minerals are precipitating inside the core and calcium-bearing minerals produced in the effluent. However, we have not observed a noteworthy change in concentration of sulfate ions. We have also suggested the volumetric strain as 2.5 order of magnitude of the axial strain. In addition, permeability and porosity evolution is concluded to be affected by the chemical alterations. Accordingly, mechanical factors are not the only issues responsible for permeability and porosity evolution.