Abstract
To fully utilize the abandoned salt cavern resources and to increase the total amount of the fossil energy reserve of China, reconstructing some of these salt caverns for underground gas storage (UGS) or strategic petroleum reserve (SPR) would be an effective method. The salt resources in China mainly are bedded salt, which brings great challenges for the cavern construction and safety evaluation. In this paper, the investigations are presented to evaluate the tightness of the UGS and SPR salt cavern facilities, located in the bedded rock of Jintan, China. Microcosmic analysis, and permeability and porosity tests of the surrounding rock are carried out to determine their properties, which provide the basic data for the tightness assessment. A 3-D numerical model is developed based on the test results and the geological features of the target formation. The numerical simulation results show that the seepage velocity, seepage range and loss rate of leakage of the SPR salt caverns are much smaller than those of UGS salt caverns. The cavern's pillar width with a pillar to diameter ratio (P/D) of 1.5 can satisfy the tightness requirement of SPR salt caverns, but it cannot meet the requirement of UGS caverns. This indicates that some existing abandoned salt caverns in Jintan which are unsuitable for UGS due to their small pillar width have the potential to be rebuilt for SPR. This would help to increase the storage capacity of crude oil in China. The results can also provide a reference for the implementation of similar projects in other bedded salt districts.
Highlights
Energy has always been considered as the engine and fundamental impetus of social-economic development
According to the data from the National Energy Administration of China [7], as shown in FIGURE 1 (a), the total amount of crude oil reserves is 3.773×107 t by the end of 2017, about 29 days of the annual consumption, far less than the 90 days proposed by the International Energy Agency (IEA)
The study on the gas/oil seepage in the interlayer should be the focus during the design of underground gas storage (UGS)/strategic petroleum reserve (SPR) salt cavern in bedded rock salt to eliminate its negative effects on the cavern and pillar safety
Summary
Energy has always been considered as the engine and fundamental impetus of social-economic development. The seepage pressures and the penetration distances in the interlayers are much larger than those in the rock salt This Indicates that the interlayers serve as the main channels for the natural gas or crude oil to seep through, which is consistent with the results of permeability and porosity tests. The study on the gas/oil seepage in the interlayer should be the focus during the design of UGS/SPR salt cavern in bedded rock salt to eliminate its negative effects on the cavern and pillar safety. After operating for 15 years, as shown in FIGURE 7 (c), the seepage areas of the UGS salt caverns in the interlayers begin to join together, and the pore pressure in the middle of the pillar becomes higher with time increasing. The loss rate of the leakage during the natural gas storage period can be calculated as gas leakage
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