A quantitative evaluation for the sealing capability of caprock in CO2 storage

Abstract

The aim of CGS is to inject collected CO2 into deep geologic formation to reduce CO2 amount emitted to the atmosphere There are several mechanisms trapping CO2 such as structural trapping residual trapping solubility trapping and mineral trapping The sealing capacity of cap rock is the key of success for CGS Y site is a potential CGS site and located at northwest Taiwan with a sedimentary environment In this study indicator kriging is used for 11 borehole data to analyze the geological continuity of cap rock The shale lithiface can be categorized as rock type 1 while other lithiface can be categorized as rock type 2 The results show that the range of the cap rock in the horizontal direction is 150 m at most and the range in vertical direction is around 2 m Three scenarios are assumed in this study The first is with a range of 150 m and a nugget of 0 056 in horizontal direction Second one is with a range of 5 m and a nugget of 0 056 in horizontal direction Third one is with a range of 150 m without nugget in horizontal direction All scenarios are with a range of 2 m and a nugget of 0 056 in vertical direction TOUGH2-ECO2N is used to perform numerical modeling to study the effect of spatial continuity on CO2 migration The results show that if the threshold of dissolved CO2 mass fraction is assigned to be 0 056 at top of cap rock scenarios 2 takes the shortest time to penetrate the cap rock No significant difference in the dissolved CO2 migration If the threshold of supercritical CO2 saturation is assigned to be 0 17 at top of cap rock scenario1 2 and 3 take 448 years 400 years and 491 years respectively The difference in the supercritical CO2 is significant Moreover supercritical CO2 forms locally high saturation zones when migrates to the rock type 2 The pressure difference for each mesh in the cap rock will dramatically rise up due to the pressure propagation and drop down and then rise up again because of entry of supercritical CO2 The far the mesh of location is the changes of pressure are sharper and earlier

Date of Award	2016 Jul 27
Original language	English
Supervisor	Kuo-Chin Hsu (Supervisor)