Ideally, the global natural gas consumption has been on the rise owing to population increase and stringent laws on other petroleum products of more injurious nature to the environment. Specifically, in China, where in 2015, 210 billion cubic meters of natural gas was consumed, and these figures are expected to shoot up to around 300 billion M3. Since demand for gas vary with time and season, there is need to have large storage facilities that can satisfy the demand at peak time. Constructing storage tanks is a viable solution but at exorbitant costs which would be translated to higher natural gas costs. Therefore, natural storage systems such as the use of underground salt caverns has been highly sought after. However, in China, the underlying salt stratum are quite thin thereby inhibiting formation of large caverns. Presently, single-well-vertical caverns are the most popular but their implementation encounter serious problems in the thinly-bedded salt rocks of China. In simple terms, the volume of caverns forgeable using this technique to not provide adequate capacity for natural gas storage in many regions of the country.
Chongqing University researchers developed an alternative technique that would aid expand the existing single-well-vertical (SWV) caverns, thereby increasing their effective natural gas storage capacity. In this quest, they proposed the two-well-horizontal (TWH) caverns where existing single-well-vertical caverns could be co-joined thus almost doubling their capacity. Their work is published in the research journal, Energy.
The research technique employed commenced with the thorough evaluation of the comprehensive feasibility of the two-well-vertical-caverns as gas storage facilities. Next, the frame-work and criteria of feasibility evaluation of gas storage salt caverns were determined. The researchers then determined the construction process and shapes of TWH-cavern by physical simulation tests, from which an optimum cavern shape was obtained by numerical simulation. Lastly, the effects of mudstone inter-beds, cyclic operating modes on the serviceability and safety of TWH-cavern were investigated.
From the geo-conditions and the physical simulation results, 3-D numerical models of TWH-cavern were established. The authors observed that, based on the model generated, the cavern shape was optimized. Additionally, they noted that the inter-beds could well constrain the deformation of the salt layers and reinforce the cavern’s safety. As a consequence, both the volume loss rate and wall rock displacement of the TWH-cavern were seen to be significantly decreased.
In conclusion, Wei Liu and colleagues study successfully modeled the TWH-caverns to replace the SWV-cavern in the thinly bedded salt rocks of China. By carrying out a series of tests, they confirmed the adoptability of the TWH caverns as gas storage facilities. In general, they observed that as a gas storage facility, TWH-cavern had a higher serviceability, greater safety, and much better flexibility for operation than SWV-cavern. Altogether, TWH-caverns have desirable feasibility as natural gas storage facilities in thinly-bedded salt rocks of China. Furthermore, as an added advantage, they also have great potential for crude oil storage, compressed air energy storage or hydrogen storage.
Wei Liu, Deyi Jiang, Jie Chen, J.J.K. Daemen, Kang Tang, Fei Wu. Comprehensive feasibility study of two-well-horizontal caverns for natural gas storage in thinly-bedded salt rocks in China. . Energy, volume 143 (2018) page 1006-1019Go To Energy