Modeling and Analysis of Salt-Cavern Natural-Gas Storage

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 164489, ’Modeling and Analysis of Salt-Cavern Natural-Gas Storage,’ by P. Barajas and F. Civan, SPE, University of Oklahoma, prepared for the 2013 SPE Production and Operations Symposium, Oklahoma City, Oklahoma, USA, 23-26 March. The paper has been peer reviewed and published in the February 2014 SPE Production & Operations journal. A rigorous modeling approach is developed for effective management and inventory analysis of natural-gas storage in underground salt caverns. Computational-fluid-dynamics and heat-transfer modeling approaches are implemented to simulate the strongly coupled fluid-mechanics and heat-transfer problems involving cavern gas storage. Accurate prediction of natural-gas storage performance and inventories made on the basis of the present comprehensive simulation approach can be instrumental in effective management and balancing of natural-gas supply and demand. Introduction Gas-storage caverns are typically developed through drilling of a wellbore to reach the salt formation and subsequently injecting and circulating hot water to dissolve and remove the salt and create a cavity intended for gas storage by a process known as solution mining. Gas-storage-cavern facilities consist of three subsystems: the wellbore that connects surface facilities with the cavern, the cavern itself, and the surrounding salt formation enclosing the cavern (Fig. 1). Accurate prediction of cavern-gas pressure is important for avoiding improper gas-storage-operation parameters and thus the fracturing and failure of the salt formation (and hence cavern-roof collapse, which can lead to catastrophic incidents where the stored gas migrates toward the ground surface and causes harm to field personnel and the nearby population or damage to surface facilities). On the other hand, loss of volume caused by creep closure can occur when the cavern-gas pressure drops below the minimum allowable cavern pressure. Effective management and inventory analyses of underground natural-gas storage are generally accomplished by modeling and simulation of the gas conditions in the storage media. The increasing popularity of salt caverns is attributed to their flexibility to switch quickly from gas injection to gas production. The void space of the cavern does not cause pressure loss from flow restrictions in contrast to depleted reservoirs or aquifers. Ideally, stored gas cannot leak into the surrounding naturally fractured salt formation because of the essentially negligible porosity and permeability of the formation. Thickness of salt formations can vary typically from a few meters in salt beds to thousands of meters in salt domes.