METHOD FOR DETERMINING THE PROFILE OF AN UNDERGROUND HYDROCARBON STORAGE CAVERN

摘要

Underground storage caverns are used for the bulk storage of hydrocarbon liquids, such as crude oil and gases, such as natural gas. The cavern is accessed through a bore hole which has casing and, for some bore holes, internal tubing with an annulus between the casing and tubing. The upper end of the cavern has a roughly cylindrical region termed the chimney. In order to check it for physical integrity, it is necessary to measure the profile of the chimney. This is also referred to as conducting a survey of the cavern. The cavern typically has hydrocarbon liquid above brine up to the surface. An inert gas can be injected above the hydrocarbon liquid to form an interface. The profile is conducted by driving the gas/liquid interface downward with gas pressure to a reference level determined by sequentially transmitting acoustic pulses to locate the reference level. Gas is injected to increase the pressure by a predetermined value and thereby drive down the interface by a known distance. The volume of the gas injected is used together with the known distance to determine a profile of the chimney. The process of injection of gas to increase the pressure by the predetermined value and measurement of the volume is repeated sequentially to determine the chimney profile at progressively lower regions, thereby producing an extended profile of the chimney.

主权项

1. A method for determining at least a portion of a chimney profile of a cavern which has a casing that extends from the surface down to the chimney and contains a hydrocarbon liquid, wherein the cross-sectional area of the chimney below the lower end of the casing is greater than that of the casing, comprising the steps of:
(a) injecting a gas into said casing at the surface to drive an interface between the gas and said liquid down to a first level within said chimney, (b) monitoring the pressure of said gas in the casing at the surface, (c) determining a first gas pressure in said casing at the surface when said interface is at said first level, (d) after said interface has reached said first level, injecting said gas into said casing at the surface to increase the gas pressure in the casing at the surface by a selected pressure value to drive said interface down to a second level, (e) determining the distance between said first level and said second level based on a gradient (pressure/distance) of said liquid and said selected pressure value, and (f) measuring the volume of said gas injected into said casing that moved said interface from said first level to said second level to determine the volume of said chimney between said first level and said second level.