ABSTRACT:

Underground gas storage using salt cavern is becoming popular due to the rising problem of the seasonal gas demand peaking. The salt cavern stability analysis is an indispensable part of the salt cavern design. The aim of the research is to study the stability of the two-well-horizontal caverns and establish the universal similarity criteria controlling the creep of the cavern. The WIPP-Drucker model is investigated. The mechanical properties of the formation generally follow the geo data from Pingding Mountain. The creep simulation is performed over a period of 30 years under different and cycling cavern gas pressures simulating the gas demand peak over the whole year. The similarity criteria regarding salt cavern stability are established based on dimensional analysis. The dimensional relationships between surface subsidence, cavern volume reduction, in-situ stress, cavern gas pressure, steady-state creep rate, creep time and characteristic length of the cavern are founded. Results show that the simulated cavern volume reduction due to creep corresponds to the measured real cavern volume change over years. The results also show that a total of 9 dimensional physical quantities control the whole creep system. There are 4 simple criteria and 2 composed criteria, which correspond to 6 scaling criterions. The numerical simulation results verify the accuracy of the scaling criterions. The study provides guidance to the salt cavern design and operation process in the term of the mechanical stability of the cavern.

1. Introduction

Underground gas storage is generally placed in salt rock, non-permeable rock formations and porous rock formations. At present, there are four types of underground gas storage reservoirs used worldwide: depleted gas reservoirs, aquifer gas reservoirs, salt cavern gas storage reservoirs, and abandoned coal-gas reservoirs (Yin et al., 2006). The salt formation is believed to be the ideal medium for the underground gas storage due to the following reasons: firstly, the salt has low permeability; secondly, the underground-gas-storage salt cavern is structurally stable, which makes it possible to run under different pressure.

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