US2363269A - Method for sealing borehole casings - Google Patents

Description

Nov. 2l, 1944- M. SCHI UMBLTRGEF` 2,363,269

METHOD FOR SEALING BORE HOLE CASINGS Filed July 26, 1940 5 Sheets-Sheet vl 27 71M j'g-Z f4@ will Ill INVENTOR ATTORNEYS 3 Sheets-Sheet 2 INVENTOR ATi Filed Jlly 26, 1940 M. SCHLUMBERGER METHOD FOR SEALING BORE HOLE CASINGS Nov. 2l, 1944.

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Nov. 21, 1944. M SCHLUMBERGER 2,363,269

METHOD FOR SEALING BoRE HOLE cAsINGs Filed July 26, 1940 5 SheetS-Sheet 3 INVENTOR ATTORNEYS A n n muil...

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Patented Nov. 21, 1944 METHOD FOR S CA poration of Delaware ALING BOBEHOLE S Marcel Schlumberger, Paris, France, assigner, by mesne assignments, to Schlumberger Well Surveying Corporation, Houston, Tex., a cor-Y Application July 26, 1940, Serial No. 347,647 In France July 29, 1939 3 Claims.

The present invention relates to methods for sealing off the space between the wall of a bore hole and its casing for the purpose of preventing the iiow therealong of fluids such as gas or water, for example.

It is the current oil-well practice, after a well has been lined with a casing and plugged at the bottom with cement, to seal oil the space between the wall of the well and the casing at the upperand lower boundaries of an oil sand which is to be exploited, in order to prevent water or gas from other formations from having access thereto.

Heretofore this has been accomplished by perforating the casing in the vicinity of the formation to be exploited and by forcing liquid cement through the perforations in the casing into the space between it and the wall of the bore hole. For a number of reasons this method has not been found to be entirely satisfactory.

For one thing, the cement mixture must be pumped long distances through supply piping, and in order that it may have vthe proper consistency to enable this to be done, it must contain water in a proportion very much higher than is required for good setting and hardening properties, so that the seal obtained is not always satisfactory.

Moreover, the fluid cement mixture, after it has been injected through the perforations in the casing, tends to follow the line of least resistance in a longitudinal direction along the casing, without spreading laterally. Hence, the cement mixture tends to accumulate only in those portions of the space between the casing and the wall of the borev holes Where the resistance to its flow is low. This phenomenon is known in the art as channeling and it produces an unsatisfactory seal.

It is an object of the invention to provide a new and improved method for sealing ofi the space between the wall of a bore hole and its casing which is free from the above noted defects of the prior art and which enables a highly satisfactory seal to be obtained.

Another object of the invention is to provide a novel method of the above character whereby the .extent of flow of the sealing material longitudinally of the casing is limited so that it tends to spread laterally to the end that channeling may be effectively prevented.

A further object of the invention is to provide a novel method of the above character wherein the extent of iiow of the sealing material longitudinally of the casing is controlled by the influence of a physical field in the bore hole.

' The objectsof the invention are attained by creating at a given level in the bore hole, a physical eld which is capable of retaining the sealing material injected into the space between the wall of the bore hole and the casing between predetermined longitudinal limits, so that it will tend to spread laterally in the space between these limits, thereby constituting an eii'ective sealing ring between the casing and the wall of the bore hole.

In a preferred embodiment of the invention, a sealing material comprising a substance which is normally solid at the temperature of the formations at the depth where the seal is to be formed, is injected in the molten state into the space between the wall of the bore hole and the casing at that depth. Meanwhile, a predetermined length of the casing and the surrounding formations in the vicinity of the point of injection of 'the sealing material are maintained at a temperature above the melting point of the sealing material.

It will be readily apparent that after the sealing material has been injected through the perforations in the casing, it will remain in the molten state and will continue to ow until it passes beyond the limits of the thermal field where the temperature is lower. Here it solidiiles, causing the still molten material to spread laterally until the entire space between the bore hole and its` casing is effectively sealed between the limits imposed by the thermal field.

Further objects and advantages of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings in which:

Figure 1 illustrates a cased bore hole together with the apparatus for sealing ,off the space between it and the wall of the bore hole according tothe invention;

Figure 2 illustrates the manner in which the` seal is formed in accordance with the method of the invention;

Figure 3 illustrates a modled form of the invention in which the method is carried out between a pair of spaced apart plugs in the bore hole;

Figure 4 shows the manner in which the seal is formed by the apparatus shown in Figure 3;

Figures 5 and 6 illustrate a modified form of the invention utilizing a ladle for loweringl the sealing material to the desired level in the bore hole;

Figures l and 8 illustrate a further modication in which a ladle is employed in conjunction with a pair of spaced apart plugs to practice the invention;

Figure 9 is a view in vertical section illustrating diagrammatically apparatus for determining the level of the sulfur in the bore hole.

Considering Figure 1, a bore hole I is shown in vertical section, containing the liquid or mud II. The bore hole I0 is lined with a metallic casing I2 which is slightly smaller in diameter than the diameter of the bore hole I0, forming an annular space I3 therebetween. For the sake of convenience, it will be assumed that it is desired to seal ofi the space between the wall of the bore hole I0 and the casing I2 in the vicinity of an oil sand I4 which is known to exist at a given depth in the bore hole III.

First of all, a plug I5 which may be of metal, foi` example, is placed in position inthe casing I2 a short distance below the lower boundary of the oil sand I4. This may be accomplished in any known manner as, for example, byy pumping it down the casing I2 in the usual fashion. A plurality of holes I6 are then bored in the casing I2 a short distance below the lower boundary of the formation I4, by meansy of a gun perforator of the type disclosed in prior Patent No. 2,141,827, for example.

Pressure is then applied to the column of liquid II in the bore hole IU to force it through the holes I6 and up through the space I3 between the casing I2 and the bore hole I0, for the purpose of removing any mud which may have collected in the space I3 adjoining the oil sand I4.

For this purpose, the casing I2 is provided with a cover plate I'I which communicates with a pump I8 whose function it is to supply liquid II under pressure to the bore hole within'the bore hole casing I2. The cover plate I1 is also provided with a conventional type liquid pressure gauge I9 which serves to provide indications of the actual pressure of the liquid II within the casing I2.

After the cleaning operation has been completed, sealing material in the fluid state may be injected through the holes IB into the space I3 between the casing I2 and the bore hole I0 for the purpose of sealing it o as indicated above.

In the embodiments employing a thermal eld, which are illustrated in Figures 1-9 of the drawings, the sealing material should comprise preff erably a substance having the following characteristics:

(a) It should have a melting point which is higher than the normal temperature of the earth formations at the place where it is to be used.

(b) Its melting point should be lower than the vaporization point of the liquid contained in the bore hole at the pressure encountered at the depth where it is to be injected.

(c) It should have maximum fluidity in the molten state in order that it may flow readily through the perforations in the casing and into the space between the casing and the wall of the well.

(d) It should have relatively high mechanical strength in the solid state.

(e) It should be insoluble or only slightly soluble in water or oil.

Substances like sulfur and low melting point alloys, particularly lead base alloys such as mixtures of lead and tin have been found satisfactory for the purpose. Bitumen may also be used, but care should be exercised tov prevent it from coming into contact with oil. Of these substances, sulfur is preferred for use in the method,

since it is readily available. inexpensive and because it melts at a temperature considerably higher than the normal temperature of the formation surrounding a bore hole without requiring excessive quantities of heat.

It desired, the sealing material, sulfur, for example, may be lowered to the desired level in the bore hole IU and there kmelted by the application of heat as shown in Figure 1. To this end an assembly 20 is lowered into the bore hole I0, which comprises a conducting plate 2I which is adapted to rest upon the metal plug I5 and which has secured to the central portion thereof a conventional type heating element 22, capable of dissipating about 10 kw. in the form of heat.

Seated on the plate 2I are a plurality of sulfur disks 23, each of which is provided with a central aperture 24 of greater diameter than the outside diameter of the heater 22, forming a, cylindrical passage in the lower portion of which the latter is disposed. The entire assembly 2li is supported on a cable 25 which passes up through a packed bushing 26 in the cover plate I1 to suitable apparatus located at the surface of the earth (not shown) for raising and lowering the assembly 2U in the bore hole I0.

The electrical heater 22 is connected at its lower end to the metal plate 2| which is in contact with the metal plug I5 in the bore hole I0, and its wpfper end is connected through the single conductor in the cable 25 to one terminal of a generator 21 located at the surface of the earthv the other terminal of which is grounded to the casing at the point 28.

In order to prevent heat from being carried away by convection currents through the liquid I I contained within the casing I2, it may be desirable to provide a washer plug 29 on top of the uppermost sulfur disk 23. The washer plug 29 may be of rubber or any other suitable material and it should preferably be somewhat larger in diameter than the inside diameter of the casing I2 and acts as a plug. As a further precaution, mud of r/elatively high viscosity might be deposited in any suitable manner above the plug I5 prior to the insertion of the assembly 20 therein for the purpose of reducing convection losses through the bore hole liquid II. Obviously, the density of the viscous mud so deposited should be less than the density of the molten sulfur, or whatever other substance is used as the sealing material.

In operation, electrical energy is supplied to the heater 22 from the source 21 for a sufficient length of time to melt the sulfur surrounding it and to produce a thermal field in the adjoining part of the casing I2 and the surrounding formations, in which the temperature is above the melting point of the sulfur. The boundaries of this field are indicated generally by the. vdotted lines 30 in Fig. 2. Inasmuch as the density of the melted sulfur is greater than that of the liquid Il Within the casing I2, the former will tend to displace the liquid Il and accumulate above the plug I5.

When the desired quantity of sulfur has been melted and the desired thermal field has been produced, the pump I8 is operated to increase the pressure of the liquid I I above the washer 29, thereby forcing the melted sulfur through the holes I8 and into the space I3 between the wall of the bore hole I0 and the casing I2. The sulfur thus injected into the space I3 will flow upwardly and downwardly therein until it reaches the upper and lower limits of the heated zone.

' as indicated by the dotted line 30. where i-t will solidify. The sulfur which is still in the molten state will then tend to spread laterally until finally upper and lower sealing rings 32 and 3|, respectively, oi' solid sulfur are formed.

It will be noted that if any channeling" occurs initially, it will continue only until the sulfur has reached one of the limits indicated by the dotted line 38. When these limits are reached, the sulfur will solidify, thus preventing.

any further longitudinal flow and forcing the molten sulfur behind to ilow laterally. In, this fashion continuous sealing rings may be obtained which are effective and entirely satisfactory.

When the solid sulfur sealing rings 3| and 32 have been formed, it will be impossible to inject further quantities of melted sulfur through the holes I6 into the space I3, and this will be indicated by an increased reading of the pressure gauge I 9. At this point the operation can lbe regarded as terminated and the assembly 28 may be raised to the surface of the earth.

However, in certain cases, it may be advantageous to continue the heating operation by means of the heater 22 after the sealing rings 3| and 32 have been formed. In this fashion, further quantities of sulfur may be melted within the casing I2 as well as part of the sulfur comprislng the sealing rings 3| and 32. When this occurs, additional quantities of melted sulfur may be forced through the holesI I6 into the space I3, pushing before it the remelted sulfur therein, until the latter again passes beyond the limits of the thermal eld set up by the heater 22, thereby effecting the operation in successive steps.

In certain cases, particularly in deep holes, the pressure required/to force the sulfur into the space I3, together with the normal head of the liquid Il contained within the casing, may be excessive and may damage the casing I2. 'I'hls difliculty may be avoided by applying the pressure t0 the sulfur between a pair of spaced apart plugs in the bore hole I0. as indicated in Figures 3 and 4.

In this modification, the plug I5 will be placed in position, the holes I6 perforated in the casing I2 and the space I3l cleaned out in the same manner as indicated above in connection with Figs.

l and 2. A second plug 33, secured to a hollow rod 34 is then lowered into the casing I2. The plug 33 has a plurality of sulfur disks 23 secured to its lower face by means of the cables 35, which disks are provided with centrally located apertures 24 forming a cylindrical passage within which the heater 22 may be disposed.

In operation, electrical energy is supplied from the source 21 at the surface of the earth to the heater 22 in the same manner as described above in connection with Figs. 1 and 2. When the requisite amount of sulfur has been melted, the pump I8 is connected to the hollow rod 34 and is operated to force liquid under pressure therethrough to the space between the plugs 33 and I5 in the bore hole, thereby forcing the melted sulfur through the openings I8 into the space I3 between the bore hole I0 and the casing I2. This operation is continued until the formation of the sealing rings 3| and 32 has been completed as indicated above in connection with Figs. 1 and 2.

In certain cases it may be advantageous to drill a plurality of openings -36 in the casing at a position above the plug 33 to permit the mud displaced by the injection of the sulfur into the space I 3 to re-enter the casing I2.

Ii' desired, exo-thermic chemical reactions might -be utilized instead of the electrical heater 22 for the purpose of heating the sulfur in the bore hole I2. In this connection, mixtures of.

`the type used in alumina-thermal technique may be employed to advantage. In particular," the sulfur might be melted by igniting a vmixture of sulfur and iron filings in a closed vessel within the casing, thereby releasing a quantity of heat sumcient to eilect the melting of the sulfur mass.

Instead of melting the sulfur mass in situ within the tubing, it might be melted at the surface of the earth and thereafter lowered to the desired level in the casing by any suitable means, such as, for example, a ladle or bucket, preferably heat proofed, as illustrated in Figs. 5, 6, '1 and 8.

Referring to Fig. 5, the ladle or bucket l31 may be of any conventional type and it is provided with a lower valve 38 seated in a port 39 and an upper valve 48 seated in a port 4|, the valves 38 and 48 being connected by a common actuating rod 42. The rod 42 is provided with a downwardly extending portion 43 which is adapted to be thrust against the plug I 5 when the ladle 31 is lowered in the bore hole I2, to open the valves 38 and 48 and permit the sulfur contained therein to pour out.

The valves 38 and 40 are normally maintained in the closed position by means of a spring 44 which is seated vbetween the upperface of the valve 40 and a bearing element 45 formed upona bail 46 by meansof which the ladle 31 is suspended in the bore hole I2. A pair of inwardly extending springs 41 and 48 are secured to the ladle 31 adjacent the lower port 89 which are adapted to cooperate with the valve 38 to maintain it and the valve 40 in the open position once they have been opened.

In operation, the ladle 31 is lowered into the bore hole upon the cable 49 until the downwardly extending portion 43 on the rod 42 comes into contact with the plug I5. At this point the valves 38 and 48 open and are thereafter maintained open by the springs 41 and 48. This permits the sulfur contained in the ladle 31 to flow into the casing above the plug I5, where it may remain for a sufficient length of time to heat the surrounding portion of the casing I2 and formations -in the manner described above.

If desired, the ladle 31 may -be provided with a heating resistance 58 in its outer wall which will prevent the loss of heat and the solidiilcation of the sulfur contained in the ladle 31 during the period of its descent within the casing I2. The heating resistance'50 may at the same time serve to heat the casing I2 and the surrounding formations when the ladle has come to rest on the plug l5. in such fashion as to produce the requisite thermal field for limiting the flow of the sulfur.

The heating resistance 58 is grounded at its lower end to the ladle 31 and its upper end is connected to a conductor in the cable 49, the upper end of which is connected to the source of electrical energy 21 at the surface.

As a modification, the valves 38 and 43 might be dispensed with and the ports 39 and 4| temporarily closed by suitable fuses adapted to be melted electrically after the ladle 31 has been lowered to the desired level in the bore hole I2.

In the embodiment illustrated in Figs. '7 and 8,

the ladle 31 is secured to the hollow rod 34 on which the upper plug 33 is fitted. In this modication, the ladle 31 is lowered into the casing I2 in the usual manner until the downwardly extending portion 43 of the rod 42 comes into contact with the plug I5, thereby opening the valves 38 and 40 and permitting the sulfur contained within the ladle 31 to pour into the casing I2 above the plug 3l.

The plug 33 is then secured to the casing in any conventional manner and the pump I8 is operated to force water under pressure into the hollow rod 34, thereby injecting the sulfur above the plug I in the casing I2 through the holes I6 into the space I3 between the wall of the bore hole I0 and the casing I2. From this point on,

the operations are exactly the same as indicated above in connection with the other modifications in the invention.

If desired, after the valves 38 and 40 in the ladle 31 have been opened, the ladle 31 may be raised until all of the sulfur contained therein has been emptied into the casing I2 above the plug I5, whereupon the plug 33 may be secured to the casing I2 at any desired height in the conventional manner.

Obviously any other suitable means may be employed for increasing the pressure between the plugs I5 and 33. For example, a container of gas under pressure might be lowered with the ladle 31 into the bore hole I2 and gas might be released therefrom after the plugs I5 and 33 are locked in position in the casing I2, for the purpose of forcing the sulfur through the holes I6 into the space I3.

In order to avoid a plurality of raising and lowering operations, the requisite plugs, suitable perforating mechanism for boring the holes I6 in the casing I2 and the ladle 31 containing the melted sulfur, might be combined into a unitary assembly adapted to be lowered into the bore hole.

It will be understood, of course, that where a heat proofed ladle is used, the heating elements thereof may be utilized to supply heat to the sulfur and to maintain the requisite thermal field in the surrounding formations.

As an alternative, molten sulfur might be poured into the space between the plugs I5 and 33 through the hollow rod 34. In such case, a heating conductor should be disposed therein and supplied with current in order to prevent the sulfur from solidifying and cooling in its passage from the surface of the earth to the place where it is to be used.

In Fig. 9 is shown apparatus for providing indications of the level of the molten sulfur within the casing I2. The apparatus comprises a single conductor cable 5I having a steel braid 52 which is connected to one end of the heater element 22, the other end of which is connected to the conductor 53 in the cable 5I. At the junction point between the conductor 53 and the heater element 22 are connected a pair of electrodes 54 and 55 which define the desired lower and upper levels, respectively, of the melted sulfur contained above the plug I5 in the casing I2, between which is interposed a series resistance 56.

The electrodes 54 and 55 are made of metal whose electropositive value is diierent from that of steel so that they form a voltaic cell with the braid 52 of the cable 5I and the muds II in the bore hole I0. During the heating operation, the source of electrical energy 21 is connected across the steel braid 52 and the conductor 53 of the cable 5I, but it is disconnected and replaced by the millivoltmeter 51, as shown in Fig. 9, when the sulfurlevel is to be ascertained.

The electrodes 54 and 55 may both be made of the same metal, copper for example, in which case the voltage indicated by the instrument 51 will have one value when the electrode 55 is in contact with the liquid II in the casing I2 and it will have a greater value when the lower electrode 54 is also in contact with the muds II.

If, however, the upper electrode 55 is made of copper and the lower electrode 54 is made of zinc and the resistance 56 is given a value of about ohms, the potential difference indicated by the instrument 51 will be of one sign when the electrode 55 is in Contact with the mud Il, and the opposite sign when the electrode 54 is also in contact with the mud I I.

At the beginning of the process, when both of the electrodes 54 and 55 are immersed in molten sulfur, the instrument 51 will give a zero reading. As the level of the sulfur decreases and the upper electrode 55 comes into contact with the mud II contained in the casing I2, the indicating instrument 51 will give a reading of one sign. When the sulfur level is below the electrode 54, the indicating instrument 51 will give a reading of opposite sign.

The purpose of the resistan 56 between the electrodes 54 and 55 is to make Ithe influence of the lower electrode 54 preponderant when they are both in contact with the mud II in the casing I2.

I claim:

l. A method of sealing oi the space between the wall of a bore hole and its casing at a position located intermediate the top and bottom of the bore hole, the bore hole having a column of liquid therein, comprising locating a plug at a predetermined depth in the casing in the vicinity of said position, perforating the casing at a position above said plug, lowering a quantity of solid sulfur and an electric heater to the level of the plug, blocking off the casing above the sulfur and the heater to reduce heat transfer by convection therefrom through the bore hole liquid, supplying elecrical energy to said heater for a suicient length of time to liquefy the sulfur and to create a thermal field in the adjoining part of the casing and its environs, in which the temperature is above the melting point of sulfur, applying pressure to the column of liquid in the casing to force the liquid sulfur through the perforations in the casing into the space between the wall of'the bore hole and the casing, and continuing the application of pressure to the liquid in the bore hole until effective seals have been formed by the solidication of the liquid sulfur in the Vicinity of the boundaries of said thermal iield.

2. The method of sealing off a portion of the space between the bore hole and casing of a well at a desired level between the top and bottom thereof, the casing being provided at the desired level with perforations, comprising the steps of positioning a plug in the casing below said perforations, lowering a quantity of fusible material, and a cooperating electric heater, to the zone of said perforations, energizing the heater to melt the fusible material, and forcing the molten mass outwardly through the perforations so that it passes out of range of the heater and solidiiies.

3. The method of sealing oil a portion of the space between the bore hole and casing of a well( at a desired level between the top; and bottom;-l

thereof, the casing being provided at the desired level with perforations, comprising the steps of positioning a plug in the casing below said perforations, lowering a quantity of sulfur, and a cooperating heater, to the zone of said perforations, energizing the heater to melt -the sulfur, and applying pressure to the molten sulfur for forcing it outwardly through the perforations Aso that it passes beyond the thermal range of the heater and solidies.

1 MARCEL scrmUMBERGER.

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