Method and means for injecting well treatment fluid

Abstract

A column of high density well treatment composition in liquid or solid form is stored in the bottom portion of the well bore of a producing fluid well and is subjected to fluid pressure from the well fluid. The flow of production fluid is used to create a pressure differential between the treatment composition and a treatment fluid injection outlet, thereby causing the treatment fluid to flow through the injection outlet. By locating the outlet in the flow of production fluid, the resulting flowing pressure drop creates the necessary differential pressure. The rate of flow of treatment fluid is metered by a capillary tube at the outlet or by a flow-actuated positive displacement pump. In all but one of the embodiments, the inlet of the conduit is at the bottom of a column of treatment liquid and at the top of a column of treatment solids. In another embodiment formation, fluid percolates up through a bed of solid treatment particles and into the well bore.

Description

FIELD OF THE INVENTION

This invention relates broadly to the introduction of treatment fluid into a well bore. More particularly, it relates to a method and means for utilizing the energy of production of the well to cause treatment fluid to be injected into the well bore.

BACKGROUND OF THE INVENTION

It is often necessary to introduce treatment chemicals into fluid producing wells in order to correct or prevent certain undesirable conditions. Corrosion or scale inhibitors, for example, have been introduced in a variety of ways in both solid and liquid form. One method of introduction involves pumping or pouring chemicals in liquid form down the tubing string or the production string, or through separate strings of tubing inserted into the well bore for that purpose. Although chemicals in liquid form can be readily mixed with the flow of production fluids and can be readily pumped or poured at controlled rates, there are serious disadvantages to the use of these treatment methods. The use of additional strings of tubing is expensive and runs the risk of interfering with other operations of the well, while the pumping or pouring of liquid chemicals from the surface down into the well can require an excess of chemicals to be introduced, at a correspondingly higher cost, in order to ensure adequate distribution throughout the well.

Both solid and liquid treatment compositions have also been introduced from containers which are filled with chemicals on the surface and lowered into the well. A number of ways have been suggested for introducing chemicals into the production fluid from containers, one of which is through use of containers which are degradable by the treatment composition or by the well fluid. While overcoming some of the objections to the continuous pumping or pouring of liquid chemicals referred to above, there are distinct disadvantages to this approach as well. Some methods of introducing the containers and releasing the chemicals require temporary interruption of well production, while most methods of chemical release are not able to continuously inject controlled amounts of treatment chemicals into the production fluid over an extended period of time. The result has been the introduction of chemicals basically in the form of a batch treatment process of short duration, with less control over the operation than desired. Moreover, the amount of chemicals which can be introduced by containers is limited to the size container that can fit into the lubricator.

Another way of introducing liquid treatment chemicals involves the use of containers which incorporate various types of mechanical arrangements for causing the release of chemicals carried by the containers. For example, pistons, bellows, pumps and the like have been incorporated in containers for injecting or pumping treatment liquid into the well. While enabling some control over the rate at which the liquid is introduced, these mechanical arrangements are generally relatively complicated in design, resulting in costly containers, a higher probability of failure than desired and a relatively short operating life.

It would be desirable to be able to introduce chemical treatment fluids into a well bore in a simpler, less complicated manner which does not have the objectionable characteristics mentioned above and yet which is accurate, reliable, and inexpensive to install and operate. It would also be desirable to be able to introduce chemicals from a container or chamber having far greater storage capacity than that of conventional containers. Further, it would be highly desirable to be able to accomplish the foregoing objects of the invention with a system which can introduce treatment fluids over a relatively long period of time.

SUMMARY OF THE INVENTION

This invention provides a method and means for utilizing the energy of production of a fluid well to inject treatment fluid into a well bore containing production perforations. It also utilizes the unused volume at the bottom of the well bore to store the treatment composition prior to injection. To accomplish this, treatment composition having a density greater than the density of the well fluid is introduced into the lower portion of the well bore to form a column of the composition beneath the lowermost production perforation in the well bore. The treatment composition is connected by a fluid path to an outlet located in the well bore. By exerting sufficient fluid pressure on the column of treatment composition, the pressure drop at the outlet of the fluid path caused by the flow of production fluid creates a pressure differential between the outlet and the inlet of sufficient magnitude to cause the flow of treatment fluid through the fluid path. The flow is metered to control the rate at which treatment fluid is injected into the production stream.

A number of different ways of applying fluid pressure to the treatment composition and achieving an adequate pressure drop may be used. In addition, the treatment composition may be liquid or solid, as long as it has a high enough density to enable it to settle down to the bottom portion of the well bore. This feature of the invention allows large quantities of treatment composition to be stored for long periods of time prior to being injected into the production stream in the manner broadly described above.

Other features and aspects of the invention, as well as its various benefits, will be ascertained from the more detailed description of the invention which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial longitudinal sectional view schematically showing a fluid well incorporating one embodiment of the present invention for injecting treatment fluid into the well bore;

FIG. 2 is an enlarged partial longitudinal sectional view showing a modified form of injection head;

FIG. 3 is a view similar to that of FIG. 1, but showing another embodiment of the invention for use with a solid treatment composition;

FIG. 4 is an enlarged partial longitudinal sectional view showing the components of the fluid conduit in greater detail;

FIG. 5 is a view similar to that of FIG. 1, but showing another embodiment of the invention;

FIG. 6 is a view similar to that of FIG. 1, but showing a further embodiment of the invention;

FIG. 7 is a view similar to that of FIG. 1, but showing still another embodiment of the invention; and

FIG. 8 is a view similar to that of FIG. 1, but showing yet another embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a well bore 10 includes a casing 12 containing production perforations 14 through which fluid from the surrounding formation F can flow. A packer 16 located above the perforations 14 supports the tubing string 18 and seals the annular space between the casing 12 and the tubing string 18. Although not shown, it will be understood that the tubing string and casing extend up to the well head and that other equipment common to well bore installations would be connected above the well head to effect the production of fluids such as oil or gas.

A packer 20 is provided in the bottom portion of the well bore spaced any desired distance above the bottom 22 of the well. Treatment liquid L is supported in the well bore by the packer 20, although it should be understood that the packer 20 can be dispensed with if the well bottom is sealed and the treatment liquid is supported directly thereon.

Other perforations 24 are provided in the casing 12 a distance below the production perforations 14 and the casing is sealed by packer 26 located between the perforations 14 and 24. A capillary tube 28 extends upwardly from the packer 26 so that the upper outlet 30 of the tube, which functions as the injection outlet of the treatment liquid L, is positioned within the flow of the production fluid entering the casing through the production perforations 14. The capillary tube is connected at the bottom thereof to a drop tube 32 which extends down to the bottom of the well bore where it is held in place at that level by a suitable weight 34. The inside diameter of the drop tube may be of any convenient desired size as long as it allows ready flow of the treatment fluid under the differential pressure to which the fluid is exposed. Obviously it should be substantially greater than the size of the capillary. A tube having an inside diameter of 1/4", for example, should function properly, while a capillary tube having an inside diameter of about 1 mm would be a representative size.

In operation, the treatment liquid L is introduced into the well bore by any suitable conventional means, such as by bucket, until the well bore has been filled to the desired level just below the perforations 24. Because the liquid is of greater density than the well fluid it will settle by gravity in the storage space. Any desired treatment liquid may be used, such as corrosion or scale inhibitors, as long as its density is sufficiently high so as to remain at the bottom of the well bore and not mix with the well fluid above it. Treatment liquid having a specific gravity of 1.4 is an example of a liquid that would function in this manner.

As production fluid flows from the perforations 14 up through the well bore toward the tubing 18, the resulting pressure drop across the perforations 14 causes the pressure adjacent the injection outlet 30 to be less than the pressure at the bottom of the drop tube 32. This pressure differential causes treatment fluid to flow up the drop tube 32 and through the outlet 30 of the capillary tube where it is mixed with the production fluid. The rate of flow of the treatment fluid is directly proportional to the differential pressure and the radius of the capillary, and inversely proportional to the length of the capillary and the viscosity of the treatment liquid. Therefore the rate of flow can be predetermined through selection of the treatment liquid and selection of the parameters of the capillary tube.

Fluid entering the well bore through the perforations 24 will be at substantially static formation pressure and will replace the treatment liquid as it is used so that the level of the interface I between the treatment liquid and the formation fluid will continually drop during flow conditions. Because the available storage volume of the well bore is so large, however, ranging from at least 50 feet to more than 100 feet, the initial amount of treatment liquid introduced should supply the well for quite lengthy periods up to several months duration.

Referring to FIG. 2, instead of injecting treatment fluid from a relatively small capillary tube unassociated with other related equipment, it may be desirable to provide a larger injection head 36. The injection head 36 is illustrated as being of cylindrical shape surrounding the capillary tube 28 and being supported by a rigid tube 38 extending up from the packer 26 of FIG. 1. The capillary tube would thus be sheathed in the tube 38. Although the injection head may take any desired shape or size other than that illustrated in FIG. 2, it should be of sufficient size to substantially restrict the flow of production fluid as it moves up the well bore from the perforations 14. This produces a pressure drop greater than that produced by the flow of production fluid alone and could be utilized if it is determined that the pressure differential should be increased.

Referring to FIG. 3, where like reference numerals denote like elements to those in FIG. 1, a related arrangement to that of FIG. 1 also utilizes perforations 14 and 24 with a packer 26 therebetween supporting an upwardly extending capillary tube 28. Instead of filling the lower portion of the well bore with treatment liquid, however, it is filled with a treatment composition in the form of water soluble particles P, such as granules or crystals. As in the previous case the treatment composition has a greater density than that of the formation fluid entering the perforations 24. Due to the presence of water in the formation fluid, saturated inhibitor solution would exist at the top of the column of treatment particles. Therefore the drop tube 40 need extend only to the top of the column. It will be understood that as the treatment particles are dissolved, the top of the column will gradually move down to the bottom of the well bore, necessitating a drop tube having a length sufficient to eventually reach down to the bottom of the well bore. The drop tube 40 will follow the gradual reduction in height of the column of solid treatment particles due to the weight 42 maintaining a constant downward pull on the tube. The saturated inhibitor solution at the top of the column will flow up through the drop tube 40 and out the injection outlet 30 in the manner of the treatment liquid in the arrangement of FIG. 1.

As shown in FIG. 4, the capillary tube 28 may extend through an aperture in the sealing packer 26 and the lower end may be received in the socket 44 in the upper end of the drop tube 40. If necessary the connection between the tubes may be made more secure by any suitable means such as clamp 46. The tube 40 may be secured to the weight 42 by any suitable means, such as by collar or clamp 48. Preferably, flanges 50 or other suitable support means are provided at the bottom of the weight to hold a filter 52 in place for the purpose of preventing undissolved particles of treatment composition which may flake off from the top of the column from clogging the drop tube 40 or the capillary tube 28. The filter may be any suitable type, such as a simple mesh screen, so long as it is formed of a material which will not corrode away when exposed to the well fluid over the duration of the column dissolving process.

Referring now to FIG. 5, another means of providing adequate pressure to the stored treatment liquid is shown. Again, in connection with this and subsequently described embodiments, like reference numerals to those used in previously described embodiments denote like elements. In this arrangement, instead of utilizing the sealing packer 26 and the perforations 24 of FIG. 1, a permeable packer 54 is provided a substantial distance, such as 50 feet, below the production perforations 14. Apertures 56 in the packer 54 subject the treatment liquid to the pressure of the production fluid and also permit well fluid to enter the storage chamber below the packer in a nonturbulent manner so that mixing of the well fluid and the treatment liquid does not occur. The device operates on the same principle as the previously described arrangements, whereby the flowing pressure drop at the injection outlet 30 causes a pressure differential between the treatment liquid at the entry end of the drop tube 32 and the production fluid at the injection outlet, resulting in the injection of treatment liquid into the stream of production fluid. Although for purposes of illustration the injection outlet 30 is shown as being similar to that of FIG. 1, it is quite likely that this arrangement would require an injection head of the type shown in FIG. 2 in order to increase the pressure drop. As in the previously described embodiments, the parameters of the capillary tube can be selected to control the rate of injection.

Another arrangement which makes use of the energy of the flowing well to cause the injection of treatment fluid but which does so in a still different manner is illustrated in FIG. 6. As in the arrangement of FIG. 5, production perforations 14 are located above the packer 58, with no perforations below the packer. Instead of a capillary tube for controlling the rate of injection of treatment fluid, however, a positive displacement pump 60 is positioned above the packer 58. Any suitable support means may be employed to hold the pump in place, such as the rigid tube 62 which itself is supported in the packer 58 and extends below the packer to communicate with the chamber beneath it. A turbine or propeller 64 connected to the operating mechanism of the pump extends into the flow path of the production fluid so that it is rotated by the fluid flow. Any type of positive displacement pump capable of being actuated by the flow of the production fluid can be used, an example being a reciprocating piston in a cylinder with suitable check valves, the design of which is readily known to one skilled in the art. It should be understood, however, that the specific design of the pump and propeller may vary according to well conditions. An injection tube 66, also supported by the packer 58, communicates at one end with the drop tube 32 and is open at the other end to function as an injection port.

In operation, the treatment liquid stored in the chamber beneath the packer 58 is subjected to the pressure of the production fluid, and as production fluid is pumped into the storage chamber in measured amounts a like volume of treatment liquid is displaced through the drop tube and the injection tube. The interface between the well fluid and the treatment liquid will remain well defined due to the difference in densities of the fluids and the low rate of dispersion in the stagnate storage volume. The rate of injection in this case is proportional to the production rate through the production perforations 14 and is determined by the design of the pump and turbine.

In the embodiment shown in FIG. 7, a capillary tube arrangement is provided in connection with a column of solid treatment particles similar to the arrangement shown in FIG. 3. Instead of perforations located below the packer 26 as in FIG. 3, perforations 68 are provided in the casing 12 in the bottom portion of the well bore just above the bottom packer 20. In this manner the pressure of the fluid entering the perforations 68 is sufficiently greater than the reduced pressure at the injection outlet 30, causing treatment fluid at the top of the column of treatment particles to flow through the drop tube 40 and the capillary tube 28. This method would preferably be used in connection with solid treatment particles of relatively high chemical concentration, so that treatment fluid at the top of the column, produced by formation water percolating up through the bed of solid particles and thereby becoming saturated with treatment material, will be of sufficient concentration to provide the desired treatment.

Another method of introducing treatment fluid into the well bore may be employed in accordance with the embodiment shown in FIG. 8, wherein a column of water soluble solid treatment particles P are supported in the bottom portion of the casing 12 by a packer 70. The top of the column of particles is located below the lowermost perforation 24 in the production area of the well bore, and the packer 70 is located above perforations 72 in the bottom portion of the casing. The packer 70 contains a capillary 74 which extends through the packer so as to provide a fluid conduit connecting the space in the well bore beneath the packer 70 to the particles above it. The capillary may be of any suitable construction, being either integrally formed with the packer or comprising a capillary tube extending through the packer in the manner of the arrangement shown in FIG. 4.

In operation, formation fluid entering the well bore through the perforations 72 flows up through the capillary 74 at a rate determined by the parameters of the capillary and percolates up through the bed of treatment particles P. By the time it reaches the top of the column of particles the formation fluid will have become saturated with treatment material and will then mix with and be carried upwardly by the fluid flowing through the perforations 24. Thus the top of the column of particles in this case comprises the outlet of the fluid path of the treatment fluid.

It should now be clear that the invention provides a simple method of injecting treatment fluid into the production stream of a flowing well. The devices contemplated by the invention do not require complicated injection mechanisms for their operation, instead utilizing the energy of the production of the well to cause injection to take place. Further, the invention makes use of the storage capacity of the well bore to store enough treatment composition to last for a period of months.

In general, the embodiments shown as utilizing treatment liquid can also function with solid treatment particles, and the embodiments showing solid particles can also function with treatment liquid, except for the arrangements of FIGS. 7 and 8. In these cases the presence of perforations at the bottom of the well bore would not be suitable for use with treatment liquid of normal concentration because the upward flow of formation fluid would cause undesirable dilution of the treatment liquid. It should be understood that except for the embodiment of FIG. 8 an injection head may be used in any of the embodiments that use capillary tubes, regardless of whether the system utilizes liquids or solids.

It should now be obvious that although preferred embodiments of the invention have been described, changes to certain of the specific details of the embodiments may be made without departing from the spirit and scope of the invention, as defined in the appended claims.

Claims

1. A method of injecting treatment fluid into the well bore of a fluid producing well, the well bore including a casing containing perforations through which production fluid from a surrounding formation may flow, the method comprising the steps of:

filling the casing with a treatment composition having a greater density than the density of the well fluid to form a column of treatment composition bounded on the sides thereof by the casing:

the entire column of treatment composition being located beneath the lowermost production perforation in the casing;

providing a fluid conduit within the casing, the conduit having an outlet located in the path of flow of the production fluid and an inlet in contact with the treatment composition;

exerting fluid pressure on the column of treatment composition so that the pressure exerted adjacent the inlet of the fluid conduit is greater than the pressure of the production fluid adjacent the outlet of the fluid conduit whereby a pressure differential between the outlet and inlet of the fluid conduit exists which is sufficient to cause treatment fluid from the treatment composition to flow through the conduit and into the well bore; and

metering the flow of the treatment fluid by a capillary tube included in the fluid conduit.

2. A method according to claim 1, wherein the treatment composition comprises a liquid and wherein the inlet of the fluid conduit is located in the bottom portion of the column of treatment liquid.

3. A method according to claim 1, wherein the treatment composition comprises solid particles which are soluble in the well fluid, and wherein the inlet of the fluid conduit is located adjacent the top of the column of solid treatment particles, whereby treatment fluid comprising a solution of treatment composition enters the inlet of the fluid conduit and flows through the fluid conduit.

4. A method according to claim 1, wherein fluid pressure is exerted on the column of treatment composition by sealing the well bore between the fluid conduit and the casing at a point which is above the column of treatment composition, below the outlet of the fluid conduit and below the lowermost production perforation in the casing, the method further including the step of providing an additional perforation in the casing between the point of the seal and the column of treatment composition, whereby fluid from the surrounding formation can enter the well bore through the additional perforation to replace the volume of treatment fluid flowing through the outlet of the fluid conduit.

5. A method according to claim 1, wherein fluid pressure is exerted on the column of treatment composition by exposing the column of treatment composition to the well fluid entering the well bore through the production perforations, whereby the well fluid replaces the volume of treatment fluid flowing through the outlet of the fluid conduit.

6. A method according to claim 3, wherein fluid pressure is exerted on the column of treatment particles by sealing the well bore between the fluid conduit and the casing at a point located above the column of treatment particles and below the lowermost production perforation and by perforating the casing at a point adjacent the lower portion of the column of treatment particles, whereby well fluid can enter the column of treatment particles through the perforation in the lower portion of the casing.

7. A method according to claim 1, including the step of restricting the flow of the production fluid adjacent the outlet of the fluid conduit to increase the rate of flow of production fluid adjacent the outlet and thus increase the pressure drop at the outlet.

8. Means for injecting treatment fluid into the well bore of a fluid well, the well bore including a casing containing production perforations through which production fluid from a surrounding formation may flow, said means comprising:

a column of treatment composition filling the casing and being located entirely beneath the lowermost production perforation, the treatment composition having a density greater than the density of well fluid from the surrounding formation;

a fluid conduit within the well bore having an inlet in contact with the treatment composition and an outlet located in the path of flow of the production fluid, said fluid conduit including a capillary tube therein for metering the flow of the treatment fluid into the well bore; and

means for exerting fluid pressure on the column of treatment composition so that the pressure exerted adjacent the inlet of the conduit is greater than the pressure of the production fluid adjacent the outlet of the conduit, thereby creating a pressure differential between the outlet and the inlet of the fluid conduit sufficient to cause treatment fluid from the treatment composition to flow through the fluid conduit and into the well bore.

9. Means for injecting treatment fluid into a well bore according to claim 8, wherein the means for exerting fluid pressure on the column of treatment composition includes means for sealing the well bore between the fluid conduit and the casing at a point which is above the column of treatment composition, below the outlet of the fluid conduit and below the lowermost production perforation, and further including an additional perforation in the casing between the sealing means and the column of treatment composition, whereby fluid from the surrounding formation can enter the well bore through the additional perforation to replace the volume of treatment fluid flowing through the outlet of the fluid conduit.

10. Means for injecting treatment fluid into a well bore according to claim 8, wherein the means for exerting fluid pressure on the column of treatment composition includes means for exposing the column of treatment composition to the well fluid entering the well bore through the production perforations, whereby the well fluid replaces the volume of treatment fluid flowing through the outlet of the fluid conduit.

11. Means for injecting treatment fluid into a well bore according to claim 8, wherein the treatment composition is a liquid and wherein the fluid conduit includes a drop tube having an end extending to substantially the bottom of the column of treatment liquid, the inlet of the fluid conduit corresponding to the end of the drop tube, whereby treatment liquid from the bottom of the column enters the inlet of the fluid conduit.

12. Means for injecting treatment fluid into a well bore according to claim 8, wherein the treatment composition comprises solid particles which are soluble in the well fluid and wherein the fluid conduit includes a drop tube having an end extending to the top of the column of treatment particles, the inlet of the fluid conduit corresponding to the end of the drop tube, whereby saturated treatment fluid at the top of the column enters the inlet of the conduit.