Abstract
The existing statistical evaluation methods of caprock sealing ability in CO2 sequestration engineering only take into account the sealing ability of caprocks before sequestration but cannot reflect the retained sealing ability of caprock after hydrochemical reactions. A microscopic sealing evaluation method of caprock was established based on the microscopic mechanism of chemical reaction and the breakthrough pressure of caprock which, changes with the time of CO2 sequestration, was taken as the dynamic evaluation index. The results show that the change of microstructure parameters such as the average pore radius after dissolution is the essential reason that affects the variation of the caprock microscopic sealing property. Dissolution or precipitation of different caprock minerals during the chemical reaction process is the key factor that determines the decrease or increase of caprock microscopic sealing property. The evaluation method can reflect the change of microscopic sealing property of the caprocks in different areas as the sealing time goes and provides an efficient and practical quantitative evaluation method for the initial formation site selection and safety sealing in the later stage.
Highlights
CCUS technology is widely used in major oilfields as a significant method of energy conservation and pollution emission reduction combined with the displacement of reservoir oil
The mudstone caprock of the second layer of this oilfield is selected as an example, and the above evaluation method is used to dynamically evaluate the impact of CO2 storage on its microscopic sealing property
A microscopic sealing evaluation method of caprock under CO2 sequestration is established and the following insights are obtained: (1) The essential change of the caprock microscopic sealing ability caused by CO2 fluid is the change of microstructure, such as the rock pore radius
Summary
CCUS (carbon capture, utilization, and storage) technology is widely used in major oilfields as a significant method of energy conservation and pollution emission reduction combined with the displacement of reservoir oil. In the above evaluation methods of the caprock sealing capacity, the evaluation criteria obtained by laboratory experiments are not in line with the actual strata numerically This is due to the significant difference between the actual formation states and the laboratory conditions, which is mainly reflected in the following two aspects: first, the rock skeleton is stressed by the overlying strata, and most of the pores are in a compressed state; second, the temperature environment of the formation will change with the temperature system of each layer, and the temperature at different depths varies greatly; liquid viscosity and gas phase will change with the temperature. The change of breakthrough pressure with time is taken as the dynamic evaluation index, and the microsealing evaluation method is established based on the microscopic mechanism of caprock chemical reactions. The caprock microscopic sealing property of an oilfield is analyzed and evaluated by using the actual data of CO2 flooding and sequestration project with this method
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