US2191652A - Method of sealing earth formations - Google Patents

Description

v tintsz 5 -T oFr-ic METHOD OF SEALHN'G EARTH FORMATIONS Andrew C. Hamilton, in, Dallas, Tex assignor to v United States Gypsum Company, corporation of Illinois Chicago, 111., a

' No Drawing. Application August 12, 1938,

Serial No. 224,637

6 Claims.

The present invention relates to improved methods for treating holes bored into the earth, as well as to the provision of footings and the like in earth-filled dams.

The present application is a continuation in part of my previously filed application Serial No. 203,815, filed April 23, 1938.

One of the principal objects of the present invention is a method for sealing ofi caves, holes, water, and soft crumbly formations in the earth which may be encountered as aresult of drilling holes into the earth, as for example when drilling I particular applicability to the overcoming of the difficulty known in the industry as loss of circulation of the drilling mud used in the lubrication of the drilling instruments, which mud also serves the function of bringing the drillings up out of the bore hole.-

As is well known, when drilling a well it has become customary to employ a special type of defiocculated mud which usually contains a weighting agent such as barium sulfate, this mudbeing pumped down intojthe well, particularly when using rotary drilling tools. The mud serves three functions: first,'to lubricate the drill; sec- 0nd, by reason of its weight, to keep back gas pressure and water pressure; and, third, to bring the cuttings and debris produced by the drilling iii) to the surface. As the mud emerges to the top of the hole being drilled it is usually sent to sumps or small lakes, where the drillings, etc. settle out, whereafter the" remaining clarified mud is pumped back into the'hole. operating, everything will work satisfactorily provided there is a solid bottom to the hole so that the mud can be pumped down into it, surrounding the drilling tool, the excess flowing back out of the hole at the top. However, if, when drillg; a cavity in the earth is encountered, u1nculties may ensue. This is also true if a porous layer should be reached, through which the mud can escape. In any event, the mud fails to come back to the surface, preventing further operation and causing financial loss. layer of gravel or similar porousmaterial is encountered, the mud will'seep out through it or even flow rapidly, depending uponthe porosity of thestructure. I! there is ground water and is under pressure, this water y work up- When thus If, for example, a.

wardly. through the bore hole and may even reach the surface, or may form a definite level therein, depending. upon the pressure under which it is found; If there is much gas in the well, it may cause the water to be ejected with considerable force. practice, when encountering such dificulties,-to sink a special casing in an attempt to get past or through the porous cavity, so that drilling can then be continued. This however requires the use of a narrower casing, so that this can be lowcred down inside the one already there. Obviously the further drillingof the hole would have to be with a smaller gauge. With .the present invention, however, it is not necessary to employ a smaller casing, because the cavity is sealed off by means of a cementitious material the setting time of which can accurately becontrolled, but which is of such a nature that it is capable of forming a readily pumpableslurry, readily introducible into the casing, so that it may flow out of the bottom of the casing and into the surrounding porous structure, setting at that point and plug-' It'has formerly been the ging up the openings or pores in the structure.

It has been proposed in the .past to lower bags because the oil wouldprevent' the setting of the cement, which would simply pass out of the porous structureand be irretrievably lost. The same thing is true if specialtypes' of cement are used in such a manner.

The specific embodiment of the present invention, so far as it relates to oil wells, therefore differs from previous proposals in pumping into the wellfla sort of liquid slug or stopper consisting.

oia slurry of cementitious material which physically pushes water or other liquid ahead or it until it reaches the structure wherein it sets.

The basic principle of the invention is based upon the fact that-it ispossible a ccurateiyto control the setting of a slurry of calcinedgypsum or plaster of Paris, or similar calcium sulfate type of cement.- It will readily be reliance were placed merely uponfthe slurry to obturate physically the openings in the structure, this alone would lead to no result, becauseunless the cement could be caused to set at the exact time when setting ,was' desired. no. plug would term; at all. This been the .great'difficulty has with the attempts to use Portland cement for understood that ii this purpose. It takes entirely too long for Portland cement to set, and furthermore the slurries made therewith are so heavy that they are not readily pumpable and certainly cannot be used in the manner in which the present invention is carried out. 4

Calcium sulfate, CaS04.2H2O, by itself is not a setting substance, but when it is heated to a suitable temperature it will lose some of its water, forming the hemihydrate, CaSOdHzO, which is a setting substance known in the industry under a number of names such as plaster of Paris, stucco, cement plaster, calcined plaster, gypsum plaster, etc. Ordinarily calcium sulfate hemihydrate when mixed with water will set very rapidly, say, on the order of from 4 to 5 minutes. It has therefore been customary to add to the calcined gypsum plasters various nitrogenous organic materials known as retarder, which retard the setting for a predetermined period. It is possible so to retard the setting of plaster of this kind that itwill not set for many hours after being put in place, and the setting time can be controlled with great accuracy. Such retarders have been in use for many years and can be found described in textbooks on plasters, as, for I example, Eckels Cements, Limes 8: Plas'ters, and'in the patents to Melvin B. Church, No. 255,937, in which glue is described as a retarding material, and to George R. King, No. 368,594, in which glue is employed. Hydrolyzed keratinous materials such as hoofs and hair also have been widely used. Particularly applicable in the practice of the present invention is the setstabilizing composition described by Alfred H. Gallagher in his Patent No. 1,683,539, in which waste animal hair is hydrolyzed with caustic soda under steam pressure, followed by the addition of lime, Gallagher also employing crystal-forming calcium sulfate accelerating material to balance the retarding effect of the hydrolyzed nitrogenous material so asto produce a plaster having a predeterminable time offset. More recent patents along the same lines' describing set-stabilized plasters having predetermined times of set are the patents to George D. King, Nos. 1,989,641; 2,078,198; 2,078,199 and 2,078,200.

In accordance with the present invention, a properly retarded 'calcium sulfate hemihydrate is employed. Let it be assumed that in the drilling of an oil well, for example let us'say, for purposes of illustration, at a 1000-ft. level, difiiculties are encountered by reaching a porous stratum or a cavity. Let it also be assumed that water tends to flow into the bottom of the well being drilled. When this condition is encountered, the present invention is brought into practice by an'operation which is substantially as follows: The first thing that is done is to remove the drilling tools from thecasing.- Thereafter,

by means of suitable pumps, water is rapidly pumped into the hole at such a rate that it will get into the hole faster than it will leave through the porous structure; so that the hole becomes filled up with water. In the meantime there has been prepared a slurry of calcium sulfate hemihydrate and water, say in the proportion of 100 parts by weight of the calcium sulfate hemihy-- drate and 30 to parts by weight'of water, which mixture forms a pumpable slurry. Knowing the length of time that it will take the slurry to get to the 1000-ft. level, sufficient retarder is mixed with the plaster before the water is added to retard it for about. the time that it will take the prepared calcium sulfate slurry to reach the porous stratum. Let it be assumed for purposes of illustrationthat it has been determined that it will take 45 minutes to do this. The plaster is, therefore retarded so that it will begin to setabout 45 minutes after it has first been mixed with water. The prepared calcium sulfate slurry having been made, the pumping of water is stopped, whereupon the water starts sinking into the bore hole. As this happens, the prepared slurry is introduced into the hole by pumps or other means, so that there will then be a column or slug of calcium sulfate hemihydrate slurry which follows the receding water down into the bore hole. Because this prepared slurry is properly retarded, it remains liquid; and when a sufficient amount of. this slurry has been pumped in to form a plugof the predetermined size or the estimated size, water or mudis then pumped on top of the prepared slurry, forming another column on top of it. The force of this column continues to force down the slug or liquid plug of prepared slurry which then follows the water receding from the bottom of. the bore hole until the prepared slurry arrives at the level of the porous stratum. Let it be assumedthat 40 or 45 minutes have elapsed and that the prepared slurry is at the level of the porous stratum. Because of the retarder which has been calculated to cause setting at the end of 45 minutes, the pre viously liquid prepared slurry will now begin to set. At first'it acts something like a starch gel and hence will notfiow as freely as water, and as it gets into the small interstices of the porous stratum it will begin to obturate these porosities and within a few minutes will set to a solid. As soon as this takes place the pressure in the pipes through which the water or mud is pumped on top of the prepared slurry will greatly increase,

- which is an indication that the setting is taking place, whereafter the pumping can be stopped. Several hours are then allowed to elapse to insure the thorough setting and hardening of the plaster of the prepared slurry. Thereafter, the' rotary drilling tools or other equipment are lowered into the, well, and the drilling is resumed. As calcium sulfate when set .is a soft and easily cut substance, it will take but a short time for the drills tu find their way to the bottom of the hole; and as this is'now surrounded by a set plug of gypsum or calcium sulfate plaster, there will be no loss of the mud, and the drilling can go on without further interruptions. If, later on, further porous strata should be encountered, the same procedure is repeated. In case merely an opening has been found, it may be necessary to estimate its approximate size. It may be only a small cavity, say a few hundred cubic feet. which causes the tool suddenly to drop and the mud to escape. If water is pumped into the hole amount of slurry corresponding in volume to the volume of the opening may be simply poured or pumped down into the hole until it extends to within a short distance from the bottom of the cavity and up into the casing. Afterenough; time has elapsed for the setting of the raterial, which time can be calculatedin advance, the drilling operation may be resumed. because then the cavity will have been filled up with the set calcium sulfate plaster.

The invention is of particular utility in connection with porous strata filled with gas, water,

enemas at the exact time required, and therefore the cement slurry merely found its way out throughthe openings in the surrounding earth and was lost. This was sometimes overcome by pumping in enormous quantities of cement, which ohviously is a very expensive expedient. However,

with the present invention, by causing the setting of a slug of calcium sulfate hemihydrate slurry, only a small amount thereof is needed, and yet the hole is efiectively shut off so that drilling may rapidly be recommenced.

In addition to being useful for the sealing on of oil wells, as just described, the invention is also applicable to the sealing of other holes which may have been drilled into the ground for other purposes. For example, recourse is often had to the drilling of holes into the earth for the purpose of reaching a stope in a mine for the purpose of ventilation. When drilling a hole for that purpose it often happens that ground water is encountered, which of course prevents further drilling of the hole or, ifdrilling were continued, would cause thewater to be diverted into the mine. Obviously, therefore, it becomes necessary to shut off this groundwater. This is accomplished in accordance with the teachings of the present invention in substantially the same way as described in connection with the sealing ofi of an oil well. In other words, advantage is taken of the fact that it has been found possible to produce a liquid pumpable slug of a potentially quickly setting substance such as calcium sulfate hemihydrate, which is pumped into the hole in the form of a slurry, the time of setting of the slurry being so controlled that the setting will take place about the time that the slug reaches the predetermined point in the hole.

In connection with oil-well sealing it is mentioned that calcium sulfate hemihydrate may be retarded to set in a predetermined time, but it should also be understood that in place of the retarders it may be advisable under some conditions to use set-accelerating salts or substances to speed the set of the gypsum. Such substances, well known in the art, are, for example, seed crystals of calcium sulfate dihydrate (either naturally or synthetically produced by metathesis frbm suitable salts), aluminum sulfate, sodium chloride, etc. Thus, for example, a plaster which has been retarded in manufacture may be found to be too slow setting, in which case accelerators may be added in suitable amounts; in fact, both.

accelerators and retarders may be used in order to produce predeterminedsetting time. Alternatively, it is possible to start with a set-stabilized plaster-'which is well known in'the art andcan be purchased in the open market-having a setting time which has been predetermined by the manufacturer by the admixture with the plaster of both accelerating and retarding materials.

gravel, gas, etc.

- where there mines, the operation. of stopping ofi water and loose sand, gravel, etc., is commonly known as grouting. In the past, this has been attempted by the use of comparatively slow-setting hydraulic cements such as Portland cement; but as the setting time of these cements cannot be accurately controlled, they are often washed away by the water or escape through the loose formations without doing any good. By employing the present invention, however, a slug or liquid plug of calcium sulfate hemihydrate is forced into the hole under such conditions that, just about the time it reaches the point where it is desired to haveit set, it will very rapidly set, thus sealing the hole at that point against water, loose sand,

hole may be drilled through it of the same size as the hole that is being drilled, whereafter the drilling may be resumed, continuing either until the desired stope has been reached or until further caves, water, gravel, etc., are encountered, when the invention can again be availed of.

,A further utilisation of the invention lies in the field of acidizing wells. As is well known, the acidizing of wells consists in pouring into the well, or forcing into it under pressure, a strong solution of an acid capable of dissolving the earthy formation at the bottomof the well, so as to open up the formation to permit oil from the surrounding earth forrnation to flow into the hole. An acid commonly used for that purpose is mu- ,riatic acid. However, if the bottom of the hole is very porous, such acid may work straight down without spreading out suficiently to do any good in the area immediately surrounding the bottom of the hole. It has already been proposed to pour heavy liquids into the well for the purpose of producing afoot, which prevents the downward penetration of. the acid, but such liquids are expensive and in many cases are quite inefilcacious. However, a liquid slurry of calcined gypsum having a predetermined set can be forced into the well with the assurance that about the time it reaches the bottom of the well it will set and become hard. Some of it will also penetrate into the surrounding sand, particularly are crevices; and the operation can be so controlled that when acid is subsequently poured into the well it will tend to spread out laterally and act upon those earth formations which it is particularly intended to attack.

After the material has set, a.

The present invention also has another very useful object, and that is its utilization in the sealing off of seepage flow under an earth-filled.

dam, levee, or dike. As is well known, dams are very often made merely by earth fill. Usually, such dams are based upon bedrock, upon which there is heaped a sufficiently high mass of earth, which is usually progressively narrowed toward the top. While this effectively stops water from flowing down a valley, it very often happens that water, will, under the pressure of the water head accumulated behind the dam, force its way be tween the bedrock and the dam, despite the weight of the earthy matter lying on the bedrock. Such seepage can become quite serious and has been knownto cause rupture of the .dam. It

has therefore been the practice in the past toattempt to place concrete or cement at the junction line between the earthy matter of the dam and the bedrock foundation thereof. It however water is already seeping, this procedure is ineffective, because the cement, which is applied in the form of a slurry, will be washed away by such water. The present invention howevw -water well or oil well.

solves this problem very effectively in the following manner:

Suitable holes are drilled vertically, or at an angle, through the dam until bedrock is reached. There is then pumped into the holespreferably under pressure, although if the holes are deep the pressure occasioned by the head of liquid may be sufficient-a thick slurry or slug of calcium sulfate hemihydrate, the setting time of which has been so adjusted as to cause it to set substantially at the time when it penetrates from the bottom of the holes to some distance around the holes, at a point where the seepage is either taking place or is expected. This slurry upon setting will therefore form a roughly circular mass at the surface of the rock foundation, whereafter it will be possible, if desired, to force ordinary cement in upon the wall of set gypsum, where it can then have ample time to harden without danger of being washed away by seepage water. This procedure may be advisable, because calcium sulfate itself is not completely insoluble in water; and if itwere used as the sole plugging means, it might be effective only for a number of years, because the water might wash it away. However, the Portland cement behind it is not subject to being washed away by water, and by the time the set gypsum will have been washed away the concrete or cement will long since have reached its maximum hardness and strength. In other words, the invention is used in such a manner that calcium sulfate hemihydrate of predetermined setting time is forced into the interface between the earth-filled dam or dike and the bedrock between which it lies, to form a temporary bridge or dam at that point, serving as a retaining wall for subsequently applied ordinary Portland cement.

A still further embodiment of the invention comprises its utilization for the tamping of explosives in' the bottom of a well, as for example a Thus, for example, a charge of nitroglycerin or similar explosive, together with a thereto attached primer and time bomb, may be lowered into the bottom of a well; and thereafter a slug of calcium sulfate hemihydrate may be poured into the well, being so adjusted as to setting time that it will harden in the bore hole at the time it reaches the bottom of the well or nearly the bottom of the well and will then set and thoroughly plug the hole. As calcium sulfate hemihydrate slightly expands on setting, it is particularly-advantageous, because it insures a very tight tamping of the explosive.

There is thus little or no likelihood of the thus formed plug being blown or shot out of the hole. As the setting time can be controlled from thirty minutesto several hours, there will still be ample time to allow the calcium sulfate hemihydrate to set before the time bomb goes off. Time bombs Y are usually adjusted to set off the charge of explosive at the end of eight to ten hours. When the explosive explodes, its force will be extended radially and downwardly around the hole, and but little force will be exerted upwardly because of the resistance offered by the calcium sulfate dihydrate plug which resulted from the setting .of the gypsum. After the charge has exploded,

it is a simple matter to drill through the plug of calcium sulfate dihydrate, because this is a soft substance which is very rapidly drilled through.

Other applications of the present invention will readily be apparent to those skilled in the art of earth boring on the basis of the examples above given. While calcium sulfate has been described as the preferred setting material, the invention is not limited thereto, although it has been found that calcium sulfate hemihydrate is the most suitable, because it is easily controlled as to setting time, can be either accelerated or retarded,

or both, and is also relatively inexpensive.

I claim:

1. The method of sealing an opening in the earth which comprises forcing into it a liquid slug or columnof potentially hardenable calcined gypsum gauged with water and characterized by a definitely predetermined time of set until said slug reaches the point in the opening where it is desired to seal the same and where the slug will then rapidly set to effect sealing of the open- 2. The method of sealing of! an opening in the earth which comprises the steps of first filling it with water, then forcing into it a slug or column of potentially hardenable calcined gypsum gauged with water and characterized by a definitely predetermined time of set, permitting water to recede in the opening so as to cause the slug to travel downwardly in the opening until it reaches the point to be sealed, the time of setting of the calcined gypsum being so predetermined by admixture with sufiicient set-controlling substances as to cause it to set at about the time when the slug reaches the said point.

3. The method of preventing or minimizing seepage under an earth-filled dam, levee or dike which comprises drilling holes through the same until bedrock is reached, then forcing into the holes and causing laterally to spread around the bottom of the holes a slurry of calcined glypsum having its setting time so controlled as to set in a roughly circular mass around the bottom of the holes, and then forcing a slurry of Portland cement into the 'space between the mass of set gypsum and the bottom of the holes.

4. The process of sealing in or tamping an explosive in a hole in the earth which comprises lowering a slug of calcined gypsum having a predetermined time of set in admixture with water into the hole, whereupon the slug will set at a point between the explosive and the top or outlet of the hole. a

5. The method of cementing of! a-well which comprises forcing into it a liquid slug or column of potentially hardenable calcined gypsum gauged withwater and characterized by a definitely predetermined time of set until said slug reaches the point in the well where it is desired to seal the same and where the slug will then rapidly set to effect sealing of the well.

I 6. The method of sealing off a well which comprises the steps of first filling it-with water, then forcing into it a slug or column of potentially hardenable calcined gypsum gauged with 'water and characterized by a definitely predetermined time of set, permitting water to recede in the well so as to cause the slug to travel down the casing of the well until it reaches the point to be sealed, the time of setting ofthe calcined gypsum being so predetermined by admixture with sumcient retarderas to causeit to set at about the time when the slug reaches the said point.