Establishing the Influence of CaCl2 on the Vulnerability of Cement Slurries to Gas Migration Using the Modified Wellbore Simulation Chamber Apparatus

Abstract

Summary A modified wellbore simulation chamber (MWSC) apparatus was used to perform a series of gas migration tests to identify the vulnerability period of cement slurries containing three different percentages of CaCl2. In addition, the Virtual Cement and Concrete Testing Laboratory (VCCTL) software was used to establish a correlation between the vulnerability period and the fundamental properties of the hydrating slurry, such as the degree of hydration (DoH) and the volume fraction of hydration products. MWSC test results confirmed that as long as the slurry pressure is higher than the formation gas pressure, gas migration does not take place. However, once the slurry pressure drops below the formation gas pressure, gas migration can occur. The incorporation of CaCl2 affects the vulnerability period in two ways. First, CaCl2 increases the strength gain rate of the slurry, thus shortening the time for the slurry pressure to drop below the formation gas pressure. In addition, the incorporation of CaCl2 shortens the time needed for the slurry to develop sufficient rigidity to withstand gas migration. However, the effect of CaCl2 on the latter is significantly higher. The test results show that for the studied cement slurry, the incorporation of 2% CaCl2 reduces the vulnerability period by approximately 40%. It was also shown that regardless of the percentage of CaCl2, all three mixtures developed sufficient rigidity to withstand gas migration when they reached the DoH of approximately 25%. At this hydration stage, the sum of volume fraction of hydration products for all the mixtures was approximately 24%.