Abstract
Thousands of caverns have been leached out from salt formations. They are used for storing a variety of fluid products ranging from compressed air and hydrogen to LPG, natural gas and crude oil, which requires that the caverns be tight. The main factors in the onset of well leakage and its prevention are discussed: fluid pressure distribution, geological environment, cementing workmanship and well architecture. The Mont Belvieu accident is described to illustrate the importance of periodic cavern testing. Test methods are discussed; apparent, corrected and actual leaks are distinguished. Factors contributing to apparent leaks are described, as are two actual in situ tests that use fuel oil and nitrogen as test fluids. It is proven that a thorough test analysis allows good estimations of actual leaks.
Highlights
Tightness is a fundamental prerequisite for many underground works where minimum product leakage is required
Natural gas is stored in depleted reservoirs or aquifers; LPG is stored in unlined galleries; and various hydrocarbons, from hydrogen and natural gas to crude oil, are stored in salt caverns
Part 4 proposes a mathematical theory for the “nitrogen leak test” and Part 5 describes an actual test aimed at validating this test method and the equations deduced in Part 4
Summary
Tightness is a fundamental prerequisite for many underground works where minimum product leakage is required. Natural gas, butane and propane are not poisonous from the perspective of underground-water protection: the leakage of sufficiently diluted natural gas into underground water has minor consequences for water quality. This would not apply to other products, such as crude oil. From the viewpoint of ground-surface protection, the most significant risk is the accumulation of flamable gas near the surface In this situation, gases that are heavier than air (propane, ethylene, propylene) are more dangerous than natural gas. We will focus on the tightness of salt caverns used for storing hydrocarbons. Part 4 proposes a mathematical theory for the “nitrogen leak test” and Part 5 describes an actual test aimed at validating this test method and the equations deduced in Part 4
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