Patent Application
20160160626
Leached storage caverns in salt formations typically have a relatively flat roof. Large diameter flat roofs in a salt cavern can be unstable due to the low tensile strength of the salt, salt movement, fractured salt or low pressure in the cavern. The stability of the roof may be increased by leaching a modified dome shape in the roof.
The leaching of storage caverns in salt formations is typically performed under a blanket of liquid hydrocarbons. Some storage applications may require very clean or ultra pure caverns, where residual hydrocarbons could contaminate the stored product. To prevent these contamination issues, ultra pure salt caverns can be leached under an inert gas blanket. This invention claims that to increase the overall stability of the roof of a leached salt cavern, a domed roof is leached using in an inert gas blanket
This method includes a solution mined underground salt cavern, wherein the salt cavern has a main body with a mean diameter of DN, and an upper portion comprising an inert gas pad, a stream of leaching water which is injected below the inert gas pad with a velocity V, thereby leaching an Nth tier adjacent to the upper portion having a height H1 and a mean diameter DN+1 that is smaller than DN by a ratio R raising the inert gas pad by an amount A1, providing a stream of leaching water which is injected below the inert gas pad with a velocity V, thereby leaching a N+1th tier adjacent to the Nth tier having a height H2 and a to a mean diameter DN+2 that is smaller than DN+1 by a ratio R, and repeating steps c and d a number of times T, thereby forming a stable roof.
For a further understanding of the nature and objects for the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein:
Illustrative embodiments of the invention are described below. While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.
This invention claims that to increase the overall stability of the roof of a leached salt cavern, a domed roof 204 is leached using in an inert gas blanket 102, which could be nitrogen, helium, argon or methane. The inert gas blanket is injected into the outer annulus string 106 of a salt cavern 101. The blanket pressure is maintained at a pressure above the water injection pressure but less than the maximum pressure for the cavern as defined by the depth of the final cemented casing shoe and the maximum pressure gradient for the cavern.
The blanket depth may be controlled by monitoring the blanket gas pressure and by verification of the blanket depth may be by wire line density measurement for the gas-brine interface. Inert gas depth may be raised in increments of between 20 to 40 ft at a time. The cavern roof may be leached to a diameter 20 to 30 percent less than the old essentially flat roof. Once the new roof is leached to the smaller diameter, the inert gas blanket is raised another 20 to 40 ft and the cavern roof is leached to a diameter 20 to 30 percent less than the old roof. This process continues until the final geometry of the cavern approximates a dome. Geometry of the roof is verified by through pipe sonar.
It is further claimed that the geometry of the storage cavern roof may be controlled by the flow of water 103 into the cavern. The water injection flow into the cavern may be maintained between the minimum flow rate of 5 ft/sec velocity and the maximum flow rate of 8 ft/sec. Ideal cavern roof geometry is achieved by flowing at a constant flow rate of approximately between 6 and 7 ft/sec.
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The inert gas pad has a pressure, and a depth defined by the interface between the inert gas and a brine/water mixture produced by the solution mining, and the inert gas pad depth may be determined by monitoring the gas pad pressure. The inert gas pad depth may be verified by wire line density measurement at the interface.
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This application claims the benefit of priority under 35 U.S.C. §119 (a) and (b) to U.S. Provisional Patent Application No. 62/089,564 filed Dec. 9, 2014, the entire contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62089564 | Dec 2014 | US |
