US3600040A

US3600040A - Roof bolting and column building for solution mining

Info

Publication number: US3600040A
Application number: US866873A
Authority: US
Inventors: Donald W Dareing
Original assignee: Cities Service Oil Co
Current assignee: Cities Service Oil Co
Priority date: 1969-10-16
Filing date: 1969-10-16
Publication date: 1971-08-17
Anticipated expiration: 1988-08-17

Abstract

A well is drilled down to the mineral deposit to be mined. The mineral deposit is penetrated by the drill bit so that about 10 percent of the total thickness of the mineral deposit is exposed to the wellbore. A given volume, the size of a required cap for the roof bolt, is washed out about the wellbore and hanging wall of the mineral deposit. The cap and bolt are formed by introducing casing and cementing it and the washed out area to the roof of the soluble material. After the bolt has been set, the cap is drilled through and solution mining progressed. The mineral is washed away from the cement cap leaving a capped roof bolt to inhibit roof slouching. Columns may be formed by washing a cylindrical area to the foot wall by progressive lowering of the washing tube into the mineral deposit and sealing a perforated liner to the footwall. A permeable cement or an impermeable cement which is subsequently perforated may be used as the sealant so that fluid may flow freely from the wellbore to the mineral deposit. The mineral is then washed by introduction of washing fluid through the perforated liner and permeable column into the mineral formation.

Description

United States Patent [72] Inventor Donald W. Dareing Fayetteville, Ark. [21] Appl. No. 866,873 [22] Filed Oct. 16, 1969 [45] Patented Aug. 17, I971 [73] Assignee Cities Service Oil Company 54] ROOF BOLTING AND COLUMN BUILDING FOR SOLUTION MINING 10 Claims, 3 Drawing Figs.

[52] US. Cl 299/5, 299/1 1 [51] Int. Cl E21b 43/28 [50] Field otSearch ..299/5, 4, ll

[56] References Cited UNITED STATES PATENTS 2,038,757 4/1936 O'Donnell 299/5 3,018,095 1/1962 Redlinger Primary ExaminerErnest R. Purser Attorney-J. Richard Geaman ABSTRACT: A well is drilled down to the mineral deposit to be mined. The mineral deposit is penetrated by the drill bit so that about 10 percent of the total thickness of the mineral deposit is exposed to the wellbore. A given volume, the size of a required cap for the roof bolt, is washed out about the wellbore and hanging wall of the mineral deposit. The cap and bolt are formed by introducing casing and cementing it and the washed out area to the roof of the soluble material. After the bolt has been set, the cap is drilled through and solution mining progressed. The mineral is washed away from the cement cap leaving a capped roof bolt to inhibit roof slouching. Columns may be formed by washing a cylindrical area to the foot wall by progressive lowering of the washing tube into the mineral deposit and sealing a perforated liner to the footwall. A permeable cement or an impermeable cement which is subsequently perforated may be used as the sealant so that fluid may flow freely from the wellbore to the mineral deposit. The mineral is then washed by introduction of washing fluid through the perforated liner and permeable column into the mineral formation.

PATENTEU AUG 1 7 IQYI FIGURE I FIGURE 2 FIGURE 3 D.w. DARE 1 N6 INVENTOR.

- ROOF BOLTING AND COLUMN BUILDING FOR SOLUTION MINING BACKGROUND OF THE INVENTION This invention relates to the supporting of overburden strata during solution mining of soluble materials in subterranean formations. More particularly, it relates to a novel method working the forming of a roof bolt and column firm which the overburden may be supported during solution mining of mineral deposits from subterranean formations.

In solution mining of mineral deposits the hanging wall (roof) and footwall (floor) of the seam of mineral may consist of firm and coherent rocks. The working area need not be supported and will remain firm throughout the solution mining operation. More often, however, the roof rocks are not rigid and will cave or warp from the pressure of the exposed overburden. Support is then required to prohibit roof caving and premature breaking down of the mineral seam. Some rocks maintain themselves over a large area for long times and then cave suddenly and unexpectedly. Others are elastic and sink gradually and regularly. Still others are plastic or loose and sink quickly when undermined. In all cases it is necessary to provide the proper support to sustain a competent solution mining operation.

The coherence of the overburden depends upon rock pressure, the roof pressure, and the areal extent of the proposed solution mining operation. As roof pressure manifests itself only after a short interval of time, this length of time is dependent upon the degree of fissuring and loosening of the rock. The excavation must be supported immediately after the roof area is washed to prevent the development of stresses which will eventually cave the overburden.

A variety of methods have been employed in which roof bolts and columns are used in subsurface mining. These techniques, however, are normally constructed by mine workers working underground to prevent slouching and cave-ins for the protection of the miners. Conventional supporting techniques consist of pillars of unmined rocks, timbering props, cribs, forepoling, stowing and various and sundry other methods. Conventional supporting techniques, however, are not practical for solution mining operations as they require mining personnel to construct them in the subsurface. Many mineral deposits of economic value exist at depths which are impractical for conventional mechanical mining, for example sulfur, phosphates, uranium and metallic salts, but solution and recovery of which will result in caving of overburden without proper support.

It is an object of my invention, therefore, to provide a novel method for the supporting of underground structures.

It is another object of my invention to provide for a method of roof bolting the overburden formation during solution mining operations.

Another object of my invention is to provide for a method of supporting the overburden by columns during solution mining operations.

It is still a further object of my invention to provide for a method of roof bolting and column supporting overburden during solution mining operation, whereby the economic recovery of the mineral is afforded over a greater extent of the deposit than by use of conventional unsupported solution min- SUMMARY OF THE INVENTION The present invention comprises a method of construction for the supporting of overburdened rock during mining of subterranean mineral deposits. Initially a well is drilled into the mineral deposit. Generally percent of the total thickness of the mineral deposit will be a sufficient penetration. The area about the well exposed to the mineral deposit is then washed until a sufficient volume of material, the size of the required roof bolt cap, is removed. Casing is then introduced into the well and cavity so as to form an annulus between the well wall and casing. The annulus is then filled with sealant to form a roof bolt which will support the overburdened rock from caving or slouching during the subsequent mining'operation.

With these and other objects in mind the invention will be apparent from the drawings and description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional elevation view of the well drilled slightly into the mineral deposit depicting the washing process for the area of the roof bolt.

FIG. 2 is a cross-sectional elevation view of theroof bolt, cap and the continued washing of the mineral deposit to form the column cavity.

FIG. 3 is a cross-sectional elevation view of the column encasing in the perforated liner with the commencement of the washing of the surrounding mineral deposit.

DETAILED DESCRIPTION OF THE INVENTION The present invention is particularly applicable to solution mining of mineral deposits which are overburdened with an unconsolidated formation. The bed of mineral to be solution mined is shown in FIG. 1 with a shortened view of the prevalent overburden 107. The mineral deposit may, in effect, be a very thin formation as compared with the thickness of the overburden 107. The thickness and weight of the overburden are necessary considerations in the determination of the size of roof bolt and column to be employed but do not represent a restriction upon any embodiment of this invention.

The solution mining operation is effected by drilling to and slightly into the mineral deposit 105. The extent of penetration of the mineral deposit is dependent upon the size of the roof bolt required. Generally, penetration of 10 percent of the mineral deposit by the drill bit will allow adequate exposure of the mineral deposit from which material may be removed. The washing process is begun by introduction of a string of tubing 104 into the drilled cavity in the mineral deposit 105. A predetermined amount of material is then washed about the exposed casing and tubing string. An appropriate volume of material is removed from about the roof and the surrounding area of the tubing string 104 to form a cavity 106 in the mineral deposit 105. Casing is then introduced into the cavity and cemented to the roof, the mineral deposit 105 and wellbore 101. The tubing string 104 is withdrawn after introduction of the cement.

When the cement is hardened the well is repenetrated by the drill bit and the well is continued by drilling through the cap of the roof bolt. The respective roof bolt is formed, consisting of casing 202, liner 203 and cap 208 as shown in FIG. 2. The washing of the mineral deposit 205 is continued by re-entering the tubing string 204 through the drilled roof bolt cap 208. The washing may continue to the point that no further economic recovery of material can be obtained.

It may become necessary in the solution mining of large seams of material with weak overburden structures to provide more support than can be derived from the use of the roof bolt type supporter. Under these conditions the extended cavity 209 in FlG. 2 washed out by the solution mining process is controlled so as to form a cylindrical cavity from the roof to the floor of the mineral deposit 205. The cylindrical cavity is formed by the progressive lowering of the tubing string during the washing process so that an evenly washed volume is removed from the roof to the floor of the mineral deposit 205. A casing 310 having

perforations

313 and 314 as shown in FIG. 3 is then set from a point somewhat above the roof of the A preferred embodiment of the invention is to construct the cement column 311 of a permeable cement, such as gravelbased mix, which will allow injection and removal of the washing fluid used in the subsequent solution mining operation. Another preferred embodiment of the invention is to force the washing fluid or some other fluid through the perforations in the casing as the sealant is setting to leave perforations in the column 311, thus enhancing the further solution mining process. Still another preferred embodiment of the present invention is to perforate the hardened sealant by chemical, explosive or mechanical means before continuation of the solution mining process so as to provide an unrestricted area for the flow of washing fluid and recovered material to and from the wellbore.

After the column has been constructed tubing string is reintroduced and packed off or segregated by isolation means 312 at a given interval in the mineral deposit. Use of a packing gland would represent a typical means of isolating the tubing string. Washing fluid is then introduced through the perforated casing 310 and column 311 as shown by the flow lines in FIG. 3 and solution mining of the surrounding area 305 is begun.

The solution mining operation is conducted by introducing washing fluid into the tubing string 304 at the surface. The washing fluid exits at the well bottom and is forced through the lower perforations 314 in casing 310. Washing fluid is restricted from directly returning through the well annulus by isolation means 312. The washing fluid, therefore, flows outwardly through column 311 either due to the permeability of the sealant material or induced perforations as previously discussed. The washing fluid then contacts the mineral deposit thereby dislodging it from the seam of material. Both washing fluid and "mineral return through the upper portion of column 311 and perforations 313 to wellbore 301 and continue of the annulus to the surface where the mineral is separated from the washing fluid.

lt will be understood and appreciated by those familiar in the art that the solution mining may be accomplished by either roof bolting, column building or a combination of both as described herein. The novelty of the present invention, however, is the method of construction and use of the roof bolts and columns to enhance the solution mining operation. The actual method of solution mining of the mineral deposit to be mined, such as interwell washing, is not a criteria of the invention.

When the present invention is applied to the art of solution mining it provides for an effective means for the supporting of overburden in order that a large areal extent of mineral deposit may be recovered. The invention enhances the art of solution mining by allowing a cheap and facilemethod for mining mineral deposits from subterranean mineral deposits.

The present invention as has been described herein with respect to the particular embodiment thereof will be appreciated by those skilled in the art, however, various changes and modifications can be made without departing from the scope of the appended claims.

Therefore, I claim:

1. In a method of construction for the supporting of overburdened rock during mining of subterranean mineral deposits in which a well is drilled into the mineral deposit and a cavity is washed in said mineral deposit through which casing is introduced into the well, thereby forming an annulus between the wall of the well and the casing and filling said cavity and annulus with a sealant, thereby sealing said casing to the wall of the well and overburdened rock forming a support in the form of a roof bolt, the improvement which comprises:

a. drilling through the cap of the roof bolt; b. washing a cylindrical cavity from the support to the floor of the mineral deposit; c. introducing easing into said cavity; and d. filling the annulus fonned between said cylindrical cavity and said casing with a sealant, thereby forming a column to support further mineral recovery operations. 2. The method of claim 1 in which said sealant for sealing said casing is cement.

3. The method of claim 1 in which:

a. said casing is perforated; and

b. said sealant for sealing said casing is a permeable cement so that further mining may be conducted through the support well.

4. The method of claim 1 in which said casing is perforated and said sealant is cement which has been previously perforated in a manner that the well and mineral deposit are in direct communication through said perforated casing and said cement column so that further mining can be conducted through the support well.

5. The method of claim 4 in which;

a. the well was drilled into the mineral deposit so that about 10 percent of the total thickness of the said deposit exposed to the wellbore; and

b. the cavity washed is hemispherical in shape with the spherical portion thereof extending downwardly from the roof of said mineral deposit so that the subsequent filling of said cavity and annulus with sealant forms a cap and roof bolt which will support further mineral recovery operations for the washing of the cylindrical cavity from the cap of the roof bolt to the floor of the mineral deposit.

6. A method of construction for the supporting of overburdened rock during mining of subterranean mineral deposits comprising:

a. drilling a well to the floor of the mineral deposit;

b. washing a cavity from the roof to the floor of the mineral deposit;

c. introducing casing into the well, thereby forming an annulus between the well wall and the casing and the wall of the cavity and the casing; and

d. filling the cavity and annulus with sealant, thereby sealing the casing to the well wall and overburdened rock forming a support so that continued mining is enhanced in that no caving or slouching of the overburdened rock will occur as further mineral deposit is recovered.

7. The method of claim 6 in which:

a. said casing is perforated; and

b. said cement for sealing said casing is a permeable cement so that further mining can be conducted through the support well.

8. The method of claim 6 in which said casing is perforated and said cement has been previously perforated in a manner that the well and mineral deposit are in direct communication through said perforated casing and column so that further mining can be conducted through the support well.

9. The method ofclaim 6 in which the sealant for sealing the casing is cement.

10. The method of claim 6 in which the cavity washed is cylindrical.

Claims

1. In a method of construction for the supporting of overburdened rock during mining of subterranean mineral deposits in which a well is drilled into the mineral deposit and a cavity is washed in said mineral deposit through which casing is introduced into the well, thereby forming an annulus between the wall of the well and the casing and filling said cavity and annulus with a sealant, thereby sealing said casing to the wall of the well and overburdened rock forming a support in the form of a roof bolt, the improvement which comprises: a. drilling through the cap of the roof bolt; b. washing a cylindrical cavity from the support to the floor of the mineral deposit; c. introducing casing into said cavity; and d. filling the annulus formed between said cylindrical cavity and said casing with a sealant, thereby forming a column to support further mineral recovery operations.

2. The method of claim 1 in which said sealant for sealing said casing is cement.

3. The method of claim 1 in which: a. said casing is perforated; and b. said sealant for sealing said casing is a permeable cement so that further mining may be conducted through the support well.

5. The method of claim 4 in which; a. the well was drilled into the mineral deposit so that about 10 percent of the total thickness of the said deposit exposed to the wellbore; and b. the cavity washed is hemispherical in shape with the spherical portion thereof extending downwardly from the roof of said mineral deposit so that the subsequent filling of said cavity and annulus with sealant forms a cap and roof bolt which will support further mineral recovery operations for the washing of the cylindrical cavity from the cap of the roof bolt to the floor of the mineral deposit.

6. A method of construction for the supporting of overburdened rock during mining of subterranean mineral deposits comprising: a. drilling a well to the floor of the mineral deposit; b. washing a cavity from the roof to the floor of the mineral deposit; c. introducing casing into the well, thereby forming an annulus between the well wall and the casing and the wall of the cavity and the casing; and d. filling the cavity and annulus with sealant, thereby sealing the casing to the well wall and overburdened rock forming a support so that continued mining is enhanced in that no caving or slouching of the overburdened rock will occur as further mineral deposit is recovered.

7. The method of claim 6 in which: a. said casing is perforated; and b. said cement for sealing said casing is a permeable cement so that further mining can be conducted through the support well.

9. The method of claiM 6 in which the sealant for sealing the casing is cement.

10. The method of claim 6 in which the cavity washed is cylindrical.