Mechanism of Flow and Controlled Dissolution of Salt in Solution Mining

Abstract

A washing technique has been developed to form a spherical cavity in massive salt. The technique is, basically, a process of controlling the fluid motion in the cavity, the concentration distribution of brine, the rate of dissolution at the walls of the cavity, and the particular settings of the wash pipe, or pipes (inlet and outlet pipe) employed. For a particular arrangement of tubing and casing, fresh water enters from the casing annulus at a position above the bottom of the tubing, and the dissolved material leaves the cavity through the tubing near the bottom of the projected hole, The initial configuration of the cavity is cylindrical representing the drilled hole situated at the axis of the projected cavity. As washing progresses the original hole is enlarged radially (any direction perpendicular to the axis of the hole). An inert fluid (generally a hydrocarbon, natural gas, or air) which serves as a blanket is injected through the annular space between the original hole and the casing. The controlled downward motion of this blanket maintains the upper edge of the brine region that is expanding on the surface of the projected sphere.A large spherical glass container and a radial model were used to investigate the flow patterns and the concentration distribution of brine occurring during the progress of solution of the salt. Aluminum flakes and dye were injected and flow patterns were observed and recorded on motion picture film. Based on the results of these model studies and other work carried out in this laboratory, the controlled washing technique was formulated. Introduction Underground cavities leached in salt beds and salt domes have been used extensively for storing hydrocarbons. Little attention has been focused on the shape of the cavities as long as large volumes were obtained and the cavities were structurally stable. The general process involves circulating fresh water and removing brine. Two distinctly different circulating systems can be employed, each of which yields characteristically different shapes. By far the most generally accepted method of washing storage caverns in salt domes is the direct circulation system. Water is introduced through the innermost pipe of a concentric pipe system, and brine is withdrawn through the annulus. In the reverse-circulation method, water enters through the annulus and is discharged through the smallest tubing string. The size of the operation, and hence the size of tubing and casing used, depends on such factors as cavity volume, length of hole, availability of water, disposal of brine and power requirements. Underground caverns are from 100 to 1,000 ft or more in length, and when completed vary from 40 to 100 ft in diameter, providing storage of 100,000 bbl or more. The volumes of water required per volume of salt removed vary from 6 to 7 for the reverse circulation method to 10 to 11 for the direct circulation method. Up to 80,000 BWPD are often circulated.In the direct circulation method, because water enters near the bottom of the projected cavity, solution of salt is greatest at this point, particularly in view of the fact that when the washing is begun turbulent flow undoubtedly exists in the immediate vicinity of the discharge of the inlet water. As the diameter of the hole increases, flow rates also are increased, so perhaps the condition of fluid turbulence is maintained for some time. During the later stages of leaching, when capacity of equipment may be the limiting factor in maintaining flow rates, there may still exist some turbulence adjacent to the point of influx; however, for the most part laminar flow conditions prevail. There appears, therefore, rather good evidence to indicate that the state of fluid motion is responsible for the typically shaped cavity which results from such washing - namely a cylindrical form, generally somewhat larger at the bottom than at the top. SPEJ P. 317^

Salinity-Based Pump-and-Dump Strategy for Drilling Salt With Supersaturated Fluids

“…Jessen (1964a, 1964b) and Kazemi and Jessen (1964) performed numerous experimental studies of salt leaching and developed mathematical models to simulate the salt-leaching process. Their interests were mainly associated with the leaching of salt bodies to create storage caverns.…”

Salinity-Based Pump & Dump Strategy for Drilling Salt with Supersaturated Fluids

“…Hessen (June 1964, September 1964) and Kazemi and Jessen (1964) performed numerous experiments into salt leaching and developed mathematical models to simulate the salt leaching process. Their interests were mainly associated with the leaching of salt bodies to create storage caverns.…”

Physical models of underground salt leaching

“…As remarked by Kulle [i] and Kazemi and Jessen [7], the solution rate constant k is independent of the solution concentration; for free convection conditions it is a function only of temperature and of the angle of inclination of the dissolving surface to the horizontal.…”

“…Such small linear velocities in the current washing the salt wall cannot have any appreciable influence on the rate of solution of the salt. According to the experimental results of Kazemi and Jessen [7], an increase in the linear flow velocity by a factor of more than ten from 0.5.10 -2 m/see to 7-10 -~ m/sec only increased the rate of salt solution from 0.3" 10 -5 to 0.4-I0 -s m/sec. Thus it is obvious that hydrodynamic similarity criteria cannot haves decisive influence on the process of brine formation in leaching chambers, and therefore must be eliminated from the overall criterial equation representing this process.…”

“…In the case of working an open block of untouched ore, it is recommended [7] that its surface area should be reduced to the equivalent vertical area by multiplying it by the factor 1.5. The value of Pz enables us to determine the productivity for a given stage height, or vice versa.…”