The existence of a large number of abandoned underground salt caverns poses seriously potential threats to safety and geological environments. Some of these caverns, defined as abandoned caverns under adverse geological conditions (AGC), are expected to store hydrocarbon energies (mainly natural gas or oil) to reduce the risk of potential disasters and simultaneously to support the national strategic energy reserve of China.
To achieve this target, a series of investigations primarily related with tightness and suitability of the caverns under AGC are initiated in this paper. Laboratory measurements to determine physical and mechanical properties as well as porosity and permeability of bedded salt cores from near target caverns are implemented to determine the petro-mechanical properties and basic parameters for further study.
The results show that the mechanical properties of the bedded rock salts are satisfactory for the cavern’s stability. The mechanical properties of interface between salt and interlayers behave in between those of rock salt and interlayers, and in particular, the interface is not a weak zone. The silty mudstone interlayers have relatively high porosity and permeability, probably due to their low content of clay minerals and the presence of halite-filled cracks. Conditions for evaluating the tightness and suitability of the cavern for storing hydrocarbons are proposed, including “No tensile stress”, “Factor of Safety” and “Threshold of leakage amount”. 3D numerical geomechanical models are developed to indicate how gas seepage evolves around the caverns.
Results show that the permeability of the interlayers is a key factor to influence the gas seepage in the vicinity of the caverns, and interlayers form primary channels for gas migration. By evaluating the fluid seepage around the cavern by the above Conditions, the upper threshold permeability of the interlayers is suggested to be no more than 10-16 ~ 10-17 m2 to guarantee the tightness when storing natural gas, and no more than 10-16 m2 when storing oil.
This study provides references for alternate uses of abandoned caverns for hydrocarbons storage under adverse geological conditions.
Liu Wei 1,2,3, Chen Jie1,2,3 , Jiang Deyi1,2, Shi Xilin 3, Li Yinping1,3, J.J.K. Daemen4, Yang Chunhe1,3.Show Affiliations
- State Key Laboratory of Coal Mine Disaster and Control, Chongqing University, Chongqing 400044, China.
- College of Resources and Environmental Sciences, Chongqing University, Chongqing 400044, China.
- State Key Laboratory of Rock and Soil Mechanics and Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan 430071, China.
- Mackay School of Earth Sciences and Engineering, University of Nevada, Reno, NV, USA.
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