US3339978A - Prevention of floor erosion of a solution mining cavity - Google Patents

Description

Sept.. 5, 1967 E. P. HELVENSTON 3,339,978

PREVENTION OF FLOOR EROSION OF A SOLUTION MINING CAVITY Filed May 14, 1965 s Sheets-Sheet 1 2'\- EFFLUE'NT sou/aw ROCK, SHALE, ETC.

PRODuoT MINERALS EFF LUE NT SOLVENT PRoOuc'r MINERALS IN VEN TOR EDWARD B {151. VENSTU/V @h-swh ATTOR NEYJ 'NON- Peoouo-r MINERALQ Sept. 5, 1967 E. P. HELVENSTON 3,339,978

PREVENTION OF FLOOR EROSION OF A SOLUTION MINING CAVITY Filed May 14, 1965 5 Sheets-Sheet 2 vSOLVENT EFFLUENT RO K, SHALE, ETC.

PRO DU CT ROCK, SHALE, are.

PEQDU cT MINERALS IN VENTOR NON- PzoDucT MINERALS row/area BHELVENSTON (914M33 g m ATTORNEY P 1967 E. P. HELVENSTON 3,339,978

PREVENTION OF FLOOR EROSION CF A SOLUTION MINING CAVITY Filed May 14, 1965 5 Sheets-Sheet 5 goclc, SHALE,'ETC.

PRODUCT MINERALS NON- PaonucT MINERALS FIG. 5

INVENTOR EDWARD R HELVENSTON BY flaw SW ATTORNEYS United States atet fifiee 3,339,978, Patented Sept. 5, 1967 ABSTRACT OF THE DISCLOSURE Inert particulate material such as gravel is introduced to a solution mining cavity to form a protective layer on the floor of the cavity. The layer serves to insulate the floor from extraction by cavity solution.

This invention relates to a novel method of solution mining. It more particularly relates to guarding against extraction of the floor of a solution mining cavity.

In the solution mining of a soluble, techniques are employed whereby one or more cased bore holes are provided through the earth to communicate with a soluble deposit. The deposit typically comprises product minerals, i.e., minerals which it is desired to recover. Solvent of the mineable or product materials is passed through a bore hole into the deposit to extract soluble materials contained therein. The resulting solutions are withdrawn through a conduit to the surface of the earth thereby establishing a cavity in the deposit. These techniques have been employed, for example, in solution mining sodium chloride, potassium chloride, sylvinite, trona, borax, sulphur, and similar extractable materials.

Product mineral deposits are often disposed adjacent extractable non-product materials. Very often the floor of a solution mining cavity contains extractable non-product minerals. For example, potassium chloride-rich deposits are often disposed above and adjacent sodium chloride deposits lean in potassium chloride. The economics of a commercial solution mining operation in such a KCl-rich stratum are adversely affected by undue extraction of the KCl-lean deposit adjacent the cavity floor. Extraction along the cavity floor produces effluents from the cavity which contain an undesirably high proportion of NaCl to KCl.

According to the instant invention, undue extraction of the floor of a solution mining cavity is inhibited, typically substantially reduced, often essentially eliminated in a very simple manner. Thus, in accordance with the present invention, inert particulate material is introduced to the cavity to form an insulating layer on the floor thereof. Sufficient particulate material is introduced to the cavity to provide a physical barrier between the pool of solution in the cavity and the cavity floor. Thus, the cavity floor beneath the inert particulate material is protected from the extracting action of the solution in the cavity. It is unnecessary for the improvement of this invention that the entire floor be covered with a layer of inert particulate material. The improvement results when a relatively small percentage, sometimes no more than about 5 percent of the flgor is so covered. In small cavities a higher percentage, e. g., -50 percent is preferable.

The particulate inert materials contemplated by the instant invention include any solid material in particulate, granular, comminuted or other divided form which is substantially inert to and more dense that the solution in the cavity. Relatively coarse materials are generally effective because they are unlikely to wash from position due to currents within the pool of cavity solution. The specific gravity of the materials employed in the practice 'of this invention need not be appreciably greater than the cavity solution although heavy materials are preferred. In solution mining operations wherein the cavity solution typically has a density of between about 1.1 and 1.25 grams per cubic centimeter, particulate materials with specific gravities of between about 2 and about 5 are generally employable. Heavier materials are even better.

Typical of the materials contemplated by this invention are sand, gravel, pebbles, slag, cinders, crushed rock, or admixtures of these materials. Ungraded materials generally provide a less porous layer. Thus, the coarser particles tend to entrap the finer particles in the interstices between the coarse particles thereby holding them in place. Even if a large quantity of fines or slimes is introduced along with the particulate materials contemplated by this invention, the coarser particles tend to settle to the bottom of the cavity. The slimes frequently flush away and are removed with the efiluent from the cavity.

The invention is more readily understood with reference to the accompanying drawings. FIGURE 1 represents a typical solution mining cavity communicating with a concentric system of conduits extending through a single bore hole. FIGURE 2 represents a similar cavity in which the floor is protected in accordance with this invention. FIGURE 3 illustrates a cavity communicating with a plurality of bore holes. FIGURES 4 and 5 represent preferred embodiments.

Referring to FIGURE 1 of the drawings, there is depicted a solution mining cavity 8 in a mineable or product deposit. Solvent is introduced through the annulus between casing 1 and pipe 2. Efliuent is withdrawn through pipe 2. Oil pad 6 floats on top of the solution in the cavity to insulate the roof of the cavity from undue vertical extraction. In this fashion, horizontal development of the cavity is encouraged. The floor of cavity 8 contacts extractable non-product minerals. Due to the relatively rapid rate of fluid flow in the cavity adjacent efiluent pipe 2, a portion 10 of the floor tends to be extracted. Extraction of the floor is normally deleterious to the quality of the efiluent.

In the practice of this invention, as illustrated by FIG- URE 2, particulate material is introduced to the cavity to provide a pile or layer 3 on the floor of the cavity. Sometimes sufiicient inert particulate material is introduced so that insulating layer 3 covers the entire floor of the cavity. Layer 3 should contain sufiicient material to significantly inhibit extraction of the cavity floor by the cavity solution. Usually a layer covering only a portion, typically as little as about 5 percent, of the cavity floor enhances the quality of the efliuent from the cavity. The precise amount of materials necessary to form an adequate protective layer depends upon a variety of factors such as the size distribution of the particulate materials, the porosity of the layer, the flow rates of the currents in the pool of cavity solution, the chemical and physical properties of the deposit, etc. Usually, a depth of as little as about A to about 6 inches of the insulating materials contemplated by this invention effectively inhibits extraction of the cavity floor.

This invention includes within its scope providing any effective amount of particulate materials to the cavity to establish and maintain a significant insulating layer. The term effective amount includes any amount sufiicient to desirably enhance the quality of the efliuent recovered from a cavity. Although the entire cavity floor need not be covered, it is desirable to cover a substantial portion of the cavity floor surrounding the axes of the bore holes communicating therewith. Thus, according to a preferred embodiment of this invention, sufiicient material is introduced to establish an effective insulating layer extending in all horizontal directions from the axes of the bore holes to a distance of from about 5 to about 30 feet, preferably at least about feet. It is particularly desirable to provide such a layer on the cavity floor beneath conduits which terminate close to the cavity fioor. Thus, in a typical solution mining cavity, it is particularly desirable to insulate the floor beneath the effluent conduits.

Referring to FIGURE 3, an embodiment of the instant invention is illustrated wherein a cavity 18 communicates with a plurality of bore holes. Insulating layer 13 is provided beneath infiuent casing 11 and layer 14 is provided beneath effluent casing 12. Oil pad 16 insulates the roof of the cavity from extraction. The particulate materials of this invention are readily introduced to a cavity through one or more conduits communicating therewith. According to a preferred embodiment, insulating materials are introduced through all communicating bore holes to facilitate good distribution over the cavity fioor.

A noteworthy characteristic of the instant invention is the beneficial protection of substantially the entire cavity floor provided by an insulating layer which covers a relatively small portion thereof. Although the mechanism of this improvement is not fully understood, and while it is not intended to limit this invention to any particular theory, the following is offered by way of a possible explanation. As solvent extracts minerals from a deposit, it usually becomes more dense. The dense solution tends to settle to the bottom of the cavity filling any low spots. Thus, dense solution settles into exposed floor areas or pockets formed in the floor by extractive action such as those designated 5 in FIGURE 2 and in FIGURE 3. Solution in these pockets is thought to be relatively undisturbed by currents in the cavity. It thus eventually reaches equilibrium with the materials in the cavity floor, i.e., it becomes incapable of extracting further material from the floor. Similarly concentrated solution becomes entrapped in the interstices of the inert layers 3, 13 and 14, thereby further inhibiting extraction through these layers. In the absence of these layers, particularly in the vicinity of the withdrawal pipes, the high flow rates in that region would cause a continual disturbance and/or removal of this dense solution.

In practice, the exact distribution of insulating materials on the floor of a cavity is difficult to determine directly. The specific depths and areas disclosed herein and recited in the accompanying claims are based on a physical model wherein the materials introduced to a cavity assume their characteristic angle of repose. This angle of repose is readily determined empirically for large heavy particles by allowing the selected material to drop freely through a restricted area into a substantial pool of solution. The solution should have approximately the composition of the effluent from the cavity. Thus, the approximate area and depth of material in contact with the cavity floor can be calculated from the weight of material charged to the cavity.

It is recognized that the actual configuration of the insulating layer in the cavity may differ substantially from the assumed model. The distribution of sand, for example, which is the preferred material, will depend more on the variable path of descent through the cavity solution and the depth of the cavity than on the angle of repose, The model is nevertheless useful if it is desired to introduce the minimum required amount of particulate materials to the cavity. Due to the low cost and general availability of the insulating materials contemplated by this invention, it is often more convenient to simply charge substantial quantities, for example, several tons, of inert particulate materials through one or more conduits communicating with the cavity. Liquid, typically solvent or cavity solution, may then be introduced through the same conduit or conduits at flow rates substantially higher than the normal flow rates employed in the operation of the cavity. In this manner, the insulating material is flushed out away from the conduit or conduits.

A suitable insulating layer is thus distributed over substantial portions, often the entire cavity floor. The procedure can be repeated as often as necessary to achieve the desired results.

FIGURES 4 and 5 illustrate two embodiments of this invention whereby the lateral distribution of the insulating materials is increased. According to the embodiment of FIGURE 4, a deflecting cone 7 is attached to a pipe 22 and inserted through casing 21 to a cavity 28. Insulating material, for example, ungraded sand is introduced through pipe 22. FIGURE 5 shows the same arrangement with rotating right angle nozzles 9 replacing the deflecting cone 7. The particulate materials may be introduced to pipe 22 in dry form or in a fiuid vehicle. It is often advantageous to introduce these materials under substantial pressure to enhance the scattering effect of the inclined surface 7 or the nozzles 9. Of course, numerous other scattering techniques will become apparent to the skilled art.

Sometimes when high flow rates are employed, some of the particulate inerts may flush out of the cavity with the efiluent. In that event, it is often advantageous to introduce a compensating amount of particulate inerts with the infiuent.

The following example further illustrates the manner in which this invention may be practiced.

Example A solution mining operation similar to that illustrated by FIGURE 3 of the drawings is conducted in a sodium chloride deposit. The deposit consists of a plurality of strata of varying compositions. The mineable stratum contains in excess of about 15 percent potassium chloride based upon the total weight of potassium chloride and sodium chloride in the stratum. The combined Weights of potassium chloride and sodium chloride in the entire deposit are in excess of percent of the weight of the deposit. Disposed beneath the mineable stratum is a sodium chloride-rich potassium chloride-lean stratum which contains less than about 10 percent potassium chloride. The area of the cavity floor is calculated according to well known sonar techniques to be about 8,000 square feet. The cavity is initially operated in accordance with accepted solution mining practice. The effiuent from the cavity is analyzed. It is found that the weight ratio of KCl to NaCl in the efiiuent is less than the corresponding ratio which exists in the mineable stratum. Approximately 10 tons of ungraded sand are introduced to the influent casing. Approximately 10 tons of the same material are introduced to the effluent casing. The bulk density of the sand is approximately 90 pounds per cubic foot. The specific gravity of the densest solution in the cavity is approximately 1.23. The sand has approximately the following size distribution:

Percent retained Screen size, No.: (cumulative) 4 2 8 15 16 35 3O 55 5O 79 97 After introduction of the sand to the cavity, the operation of the cavity is commenced. After a period of ten days, effiuent is again collected and analyzed. It is found that the ratio of KCl to NaCl in the efiiuent has increased.

While the instant invention has been described with reference to specific details of certain preferred embodiments thereof, it is not intended thereby to limit the scope of the invention except insofar as specific details are recited in the appended claims.

I claim:

1. The method of inhibiting extraction of solubles adjacent the floor of a solution mining cavity which comprises introducing to the cavity sufiicient particulate substantially inert materials more dense than the cavity solution to form a protective layer on the floor of the cavity.

2. The method of protecting the extractable floor of a solution mining cavity from extraction by the cavity solu tion which comprises establishing an insulating layer on the floor of the cavity by introducing to the cavity an effective amount of substantially inert particulate material more dense than the cavity solution.

3. The method of claim 2 wherein the particulate material is ungraded sand.

4. The method of inhibiting extraction of the extractable floor of a solution mining cavity which comprises providing to an efiluent conduit communicating with the cavity suflicient inert particulate material more dense than the cavity solution to form an insulating layer of said material extending in all horizontal directions trom the aXis of the conduit for a distance of at least 5 feet.

5. The method of claim 4 wherein suflicient inert particulate material is provided to all bore holes communicating with the cavity to establish an insulating layer extending all horizontal directions from the axes of said bore holes fora distance of at least 5 feet.

6. The method of inhibiting extraction of the extractable fioor of a solution mining cavity which comprises providing to the cavity sufiicient inert particulate material more dense than the cavity solution to establish an insulating layer adjacent at least about 5 percent of the area of the floor.

7. The method of claim 6 wherein after the said layer is established, suflicient additional particulate inert material is introduced with the influent to the cavity to maintain said insulating layer adjacent at least about 5 percent of the area of the cavity floor.

8. A method of increasing the ratio of product minerals to non-product minerals in the eflluent from a solution mining cavity disposed adjacent a mineable deposit and above a extractable non-product stratum which comprises introducing inert particulate material more dense than the cavity solution to the cavity to insulate the cavity floor from extraction.

9. The method of claim 8 wherein the product mineral is potassium chloride.

10. The method of claim 9 wherein the non-product stratum is rich in NaCl and lean in KCl.

References Cited UNITED STATES PATENTS 2,822,15 8 2/1958 Brinton 299-4 2,890,755 6/1959 Eurenius et a1 2995 X 3,088,717 5/1963 Myers 299-5 ERNEST R. PURSER, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,339,978 September 5, 1967 Edward Phelps Helvenston pears in the above numbered pat- It is hereby certified that error ap Patent should read as ent requiring correction and that the said Letters corrected below.

Column 5, line 22, before "all" insert 1n Signed and sealed this 5th day of November 1968.

(SEAL) Attest:

EDWARD J. BRENNER Edward M. Fletcher, Jr.

Attesting Officer Commissioner of Patents

Claims (1)

1. THE METHOD OF INHIBITING EXTRACTION OF SOLUBLES ADJACENT THE FLOOR OF A SOLUTION MINING CAVITY WHICH COMPRISES INTRODUCING TO THE CAVITY SUFFICIENT PARTICULATE SUBSTANTIALLY INERT MATERIALS MORE DENSE THAN THE CAVITY SOLUTION TO FORM A PROTECTIVE LAYER ON THE FLOOR OF THE CAVITY.

Images