CA2892128C - Method and apparatus for establishing injection into a cased bore hole using a time delay toe injection apparatus - Google Patents

Abstract

An apparatus and method for providing a time delay in injection of pressured fluid into a geologic formation. In one aspect the invention is a toe valve activated by fluid pressure that opens ports after a predetermined time interval to allow fluid to pass from a well casing to a formation, providing a time delay before fluid is passed through the ports. This time delay allows multiple valves to be used in the same well casing and provides a focused jetting action to better penetrate a concrete casing lining.

Description

, Method and Apparatus for Establishing Injection into a Cased Bore Hole using a Time Delay Toe Injection Apparatus Field [0001] An apparatus and method for providing a time delay in injection of pressured fluid into a geologic formation. More specifically, it is a toe valve apparatus activated by fluid pressure that opens ports after a predetermined time interval to allow fluid to pass from a well casing to a formation.
Background

[0002] It has become a common practice to install a pressure responsive opening device at the bottom or toe of a casing string within horizontal well bores and is some vertical bores. These devices make up and run as an integral part of the casing string.
After the casing has been cemented and allowed to solidify, the applied surface pressure is combined with the hydrostatic pressure and a pressure responsive valve is opened.
The combination of hydrostatic and applied pressure is customarily used to overcome a number of shear pins or to overcome a precision rupture disc. Once communication with the well bore [i.e., area outside of the casing] is achieved, the well can be hydraulically fractured or the valve can be used as an injection port to pump down additional wire line perforating guns, plugs or other conveyance means such as well tractors. Other known methods of establishing communication with the cemented and cased well include tubing conveyed or coil tubing conveyed perforators. These are all common methods to achieve an injection point but require increased time and money.

[0003] The present invention provides an improved apparatus and method that provides a time delay in fluid injection through the casing.
Summary [00134] This invention is an apparatus that allows a time delay in the injection of fluid through a section of oil and/or gas well casing to perforate a geologic formation (hydrofracturing). It does so by providing a sliding sleeve that uncovers ports in the apparatus in a time controlled manner. Controlled opening of the ports by a sliding sleeve also results in a jetting action that improves perforation of the formation. It is, in one broad aspect, an apparatus and method to provide time-delayed injection of pressurized fluid from a well casing to a geological formation, the apparatus comprising:
a housing with port openings that can communicate through the walls of the housing to a formation;
a movable piston or pistons capable of covering and uncovering the opening(s);
means for moving the piston to a position leaving the opening(s) uncovered;
and means for activation of the movement of the piston.
[0005] The invention is also a method, in one broad aspect, for the use and activation of the apparatus as described.

[0006] An apparatus an method to provide time-delayed injection of pressurized fluid from a well casing to a geological formation, the apparatus comprising:
a housing with openings that can communicate through the walls of the housing to a formation;
a movable piston or pistons capable of covering and sealing the opening(s);
means for moving the piston to a position leaving the opening(s) uncovered;
and means for activation of the movement of the piston.
[0007] The method in one broad aspect is the use and activation of the apparatus as described.
Description of Drawings [0008] Figure IA is a plan view of an apparatus of an embodiment of the invention.
[0009] Figure iB is a plan view of a cross section of an apparatus of an embodiment of the invention.
[Dow] Figure 2 is an exploded section view of the apparatus displayed in Figure IA and iB in which the ports are closed.
[0011] Figure 3 is an exploded section view of the apparatus displayed in Figure IA and iB in which the ports are open.
[0012]Figure 4 is a plan view of an apparatus of an embodiment of the invention.
[0013]Figure 5 is an exploded section view AE of a section of the apparatus of an embodiment of the invention displayed in Figure 4.

[0014]Figure 6 is an exploded section view AC of a section displayed in Figure

4.
[0015] Figure 7 is an exploded section view AD of an embodiment of the invention of the apparatus displayed in Figure 4.
[0016] Figure 8 is a graphic representation of results of a test of the operation of an apparatus of an embodiment of the invention.
Detailed Description [0017] The present invention is an improved "toe valve" apparatus and method to allow fluid to be pressured through ports in an oil or gas well casing wall section (and casing cement) into a geologic formation in a time delayed manner.
[0018] The apparatus, in one broad aspect, provides time-delayed injection of pressurized fluid through openings in a well casing section to a geological formation comprising:
a housing with openings that can communicate through ports in the walls of the apparatus housing to a formation;
a movable piston or pistons capable of moving into position covering and sealing the port(s) and to a position where the ports are uncovered;
means for moving the piston to a final position leaving the port(s) uncovered;
and means for activating the movement of the piston.
[0019]The present invention represents several improvements over conventional pressure responsive devices ¨ improvements that will be appreciated by those of ordinary skill in the art of the well completions. The greatest limitation of current devices is that the sleeve or power piston of the device that allows fluid to flow from the casing to a formation (through opening or ports in the apparatus wall) opens immediately after the actuation pressure is reached. This limits the test time at pressure and in many situations precludes the operator from ever reaching the desired casing test pressure. The present invention overcomes that limitation by providing a hydraulic delay to afford adequate time to test the casing at the required pressure and duration before allowing fluid communication with the well bore and geologic formation.
This is accomplished by slowly releasing a trapped volume of fluid through a hydraulic metering chamber that allows a piston covering the ports to move to a position where the ports are uncovered. This feature will become even more advantageous as federal and state regulators mandate the duration of dwell time of the casing test pressure. The metering time can be increased or tailored to a specific test requirement through manipulation of the fluid type, fluid volume, by altering the flow rate of the hydraulic liquid flow restrictor and by appropriate placement and setting of pressure valves on either or both sides of the flow restrictor.
[0020] A
second advantage of this invention is that two or more valves can be installed (run) as part of the same casing installation. This optional configuration of running two or more valves is made possible by the delay time that allows all of the valves to start metering before any of the valves are opened. The feature and option to run two or more valves in a single casing string increases the likelihood that the first , stage of the well can be fracture stimulated without any well intervention whatsoever.
Other known devices do not allow more than a single valve to operate in the same well since no further actuation pressure can be applied or increased after the first valve is opened.
[0021]A third significant advantage is that in the operation of the valve, the ports are opened slowly so that as the ports are opened (uncovered) the liquid is injected to the cement on the outside of the casing in a high pressure jet (resulting from the initial small opening of the ports), thus establishing better connection to the formation. As the ports are uncovered the fluid first jets as a highly effective pinpoint cutting jet and enlarges as the ports are opened to produce an effect of a guide-hole that is then enlarged.
[0022]
Referring to the Figures, Figure IA represents and inner mandrel, 10, that is inserted directly into the casing string and shows an overall external view of an embodiment of the apparatus of the invention. Item 28 represents slotted ports through which fluid will be transported into the geologic formation surrounding the casing.
Figure 18 shows a cross section view of the apparatus of Figure IA. The integral one-piece design of the mandrel carries all of the tensile, compressional and torsional loads encountered by the apparatus. The entire toe valve apparatus is piped into the casing string as an integral part of the string and positioned where perforation of the formation and fluid injection into a formation is desired. The apparatus may be installed in either direction with no change in its function.

[0023] Figure 2 (a section of Figure 113) shows an exploded view of details of the apparatus of an embodiment of the invention. Item 23 is a pressure activated opening device (preferably a Reverse Acting Disc but conventional rupture discs may be used).
Since the rupture disc is in place in the casing string during cementing it is very advantageous to have a reverse acting rupture disc that will not be easily clogged and not require extra cleaning effort. The valve mandrel is machined to accept the opening device item 23 (such as rupture discs) that ultimately controls actuation of piston 5. The opening piston 5 is sealed by elastomeric seals (16, 18 and 20 in Figure 2 and 45, 47 and 49 in Figure 6) to cover the inner and outer ports, 25-27 and 28, in the apparatus.
[0024] The openings 25-27 (and a forth port not shown) shown in Figures 2 and 3 are open ports. In one embodiment the ports 25-27 (and other inside ports) will have means to restrict the rate of flow such as baffles (50 in Figure 5) as, for example, with a baffle plate consisting of restrictive ports or a threaded and tortuous pathway 50. This will impede rapid influx of well bore fluids through the rupture discs, 23 in Figure 2 and 52 in Figure 7 into the piston chamber 32. In Figure 5, item 54 is the mandrel housing corresponding to item 5 in Figure 2 and 52 is the rupture disc that corresponds to 23 in Figure 2. Item 51 is the mandrel housing and is the same as item 6.
[0025] In one embodiment, the piston 5, has dual diameters Figure 6 shows the piston 5 (46 and 48), with one section 46, having a smaller diameter at one end than at the other end 48. This stepped diameter piston design will reduce the internal pressure required to balance out the pressure across the piston when the piston is subjected to casing pressure. This pressure reduction will increase the total delay time afforded by a specific restrictor. The resistance to flow of a particular restrictor is affected by the differential pressure across the component. By reducing the differential across the component, the rate of flow can be skillfully and predictably manipulated.
This design provides increased delay and pressure test intervals without adding a larger fluid chamber to the apparatus. The dual diameter piston allows the pressure in the fluid chamber to be lowered. This has several advantages; in particular the delay time will be increased by virtue of the fact that the differential pressure across a given restrictor or metering device will be reduced. With a balanced piston area, the pressure in the fluid chamber will be at or near the well bore pressure. With the lower end of the piston 46 smaller and the piston are adjacent to the fluid chamber 48, larger the forces will balance with a lower pressure in the fluid chamber. In this way it will be easy to reduce the fluid chamber pressure by 25% or more.
[0026] A series of outer sections 4, 6 and 8 in Figures IA, fB and 2 are threadedly connected to form the fluid and pressure chambers of the apparatus. The tandem 3, not only couples item 4 and 5 but also houses a hydraulic restrictor 22. The area 32, to the left of the piston 5 is a fluid chamber and the area to the left of item 3 is the low pressure chamber that accommodates the fluid volume as it traverses across the hydraulic restrictor. The chambers are both capped by the item 8 upper cap.
[0027] The rupture disc 23 (52) is the activation device that sets the valve opening operation into play. When ready to operate (i.e., open the piston), the casing pressure is increased to a test pressure condition. This increased pressure ruptures the rupture disc 23 (52) and fluid at casing pressure (hydrostatic, applied or any combination) enters the chamber immediately below and adjacent to the piston 5 (in Figure 2 this is shown at the right end of piston 5 and to the left of valve 14). This entry of fluid causes the piston to begin moving (to the left in the drawings). This fluid movement allows the piston to move inexorably closer to an open position. In actual lab and field tests a piston movement of about 4.5 inches begins to uncover the inner openings 25-27 and the other openings 28. These openings are initially closed or sealed off from the casing fluid by the piston 5. As piston 5 moves toward the open and final position, slots 28, are uncovered allowing fluid to flow through openings 25, 26 and 27 through slots 28. Thus, the restrained movement of the piston allows a time delay from the time the disc 23 (52) is ruptured until the slots are uncovered for fluid to pass. This movement continues until the piston has moved to a position where the ports are fully opened. Piston 5 surrounds the inter wall of the apparatus 29. As fluid pressure increases through port 14 it moves piston 5 into the fluid chamber 32. Hydraulic fluid in the fluid chamber restrains the movement of the piston. There is a hydraulic flow restrictor 22 that allows fluid to pass from chamber 32 to lower pressure chamber 34 and thereby controls the speed of the movement of the piston as it moves to the full open position. Items 28 are the slots in the apparatus mandrel that will be the passageway for fluid from the casing to the formation. Figure 3 shows the position of piston 5 when "opened" (moved into chamber 32). Initially, this movement increases pressure in the fluid chamber to a value that closely reflects the hydrostatic plus applied casing pressure. There is considerable predetermined control over the delay time by learned manipulation of the fluid type, fluid volume, initial charging pressure of the low pressure chamber and the variable flow rate through the hydraulic restrictor. The time delay can be set as desired but generally will be about 5 to 6o minutes. Any hydraulic fluid will be suitable if capable of withstanding the pressure and temperature conditions that exist in the well bore. Those skilled in the art will easily be able to select suitable fluids such as Skydrol 500B-4.
[0028] The rupture disc 23 (52) is the activation device that sets the valve opening operation into play. When ready to operate (i.e., open the piston), the casing pressure is increased to a test pressure condition. This increased pressure ruptures the rupture disc 23 (52) and fluid at casing pressure (hydrostatic, applied or any combination) enters the chamber immediately below and adjacent to the piston 5 (in Figure 2 this is shown at the right end of piston 5 and to the left of valve 14). This entry of fluid causes the piston to begin moving (to the left in the drawings). This fluid movement allows the piston to move inexorably closer to an open position. In actual lab and field tests a piston movement of about 4.5 inches begins to uncover the inner openings 25-27 and the other openings 28. These openings are initially closed or sealed off from the casing fluid by the piston 5. As piston 5 moves toward the open and final position, slots 28, are uncovered allowing fluid to flow through openings 25, 26 and 27 through slots 28. Thus, the restrained movement of the piston allows a time delay from the time the disc 23 (52) is ruptured until the slots are uncovered for fluid to pass. This movement continues until the piston has moved to a position where the ports are fully opened. Piston 5 surrounds the inter wall of the apparatus 29. As fluid pressure increases through port 14 it moves piston 5 into the fluid chamber 32. Hydraulic fluid in the fluid chamber restrains the movement of the piston. There is a hydraulic flow restrictor 22 that allows fluid to pass from chamber 32 to lower pressure chamber 34 and thereby controls the speed of the movement of the piston as it moves to the full open position. Items 28 are the slots in the apparatus mandrel that will be the passageway for fluid from the casing to the formation. Figure 3 shows the position of piston 5 when "opened" (moved into chamber 32). Initially, this movement increases pressure in the fluid chamber to a value that closely reflects the hydrostatic plus applied casing pressure. There is considerable predetermined control over the delay time by learned manipulation of the fluid type, fluid volume, initial charging pressure of the low pressure chamber and the variable flow rate through the hydraulic restrictor. The time delay can be set as desired but generally will be about 5 to 6o minutes. Any hydraulic fluid will be suitable if capable of withstanding the pressure and temperature conditions that exist in the well bore. Those skilled in the art will easily be able to select suitable fluids such as Skydrol 5ooB4TM.
[0029] In another embodiment there are added controls on the flow of fluid from the piston chamber 32 to the low pressure chamber 34 to more precisely regulate the speed at which the piston moves to open the ports. As illustrated in Figure 5 (a sectional enlarged view of the section of the tool housing the flow restrictor that allows fluid to flow from the piston chamber 32 to the lower pressure chamber 34) there is a back pressure valve or pressure relief valve 42 placed downstream of the flow metering section 22 to maintain a predetermined pressure in the fluid chamber. This improves tool reliability by reducing the differential pressure that exists between the fluid chamber 34 and the well bore pressure in the piston chamber 32. This back pressure valve or pressure relief valve 42 may be selected based on the anticipated hydrostatic pressure. Back pressure valve(s) may also be placed in series to increase the trapped pressure. Another back pressure valve or pressure relief valve 44 may be placed downstream of the fluid metering section 22 to ensure that only a minimum fluid volume can migrate from the Fluid Metering Section 22 to the Low Pressure Chamber 34 during transport, when deployed in a horizontal well bore or when inverted for an extended period of time. By selecting the appropriate pressure setting of these back pressure valves "slamming" (forceful opening by sudden onrush of pressurized fluid) of the flow control valve is reduced.
[00301 In operation an apparatus of the invention will be piped into a casing string at a location that will allow fluid injection in the formation where desired. The apparatus may be inserted into the string in either direction. An advantage of the present invention is that two or more of the valves of the invention may be used in the string. They will, as explained above, open to allow injection of fluid at multiple locations in the formation. It can also be appreciated by those skilled in the art how two or more valves of the invention may be used and programmed at different time delays to open during different stages of well operations as desired (e.g. one or more at 5 minute delay and one or more at 20 minutes delay). For example, the apparatus may be configured so that an operator may open one or more valves (activating the sliding closure) after a five minute delay, fracture the zone at the point of the open valves, then have one or more valves and continue to fractures the zone.
[0031] In general the apparatus will be constructed out of steel having properties similar to the well casing.
[0032] Figure 2 shows an exploded view of details of the hydraulic flow restriction apparatus of an embodiment of the invention ¨ the embodiment shown in Figures IA
and iB. Item 23 is a pressure activated opening device (preferably a reverse acting disc that resists plugging during the cementing operations, but conventional rupture discs may be used). Since the rupture disc is in place in the casing string during cementing it is very advantageous to have a reverse acting rupture disc that will not be easily clogged and not require extra cleaning effort. The valve mandrel is machined to accept the opening device item 23 (such as rupture discs) that ultimately controls actuation of piston 5. The opening piston 5 is sealed by elastomeric seals (16, 18 and 20) to cover the inner and outer ports, 25-27 and 28, in the apparatus. A series of outer parts, items 4, 6, and 8 are threadedly combined to form the fluid and pressure chambers for the tool.
The tandem 3 not only couples item 4 and 5 but also houses the hydraulic restrictor 22.
The area above the piston is a fluid chamber and the area above item 3 is the low pressure chamber that accommodates the fluid volume as it traverses across the hydraulic restrictor. The chambers are both capped by the item 8 upper cap.

, [0033] The rupture disc 23 is the activation device that sets the valve opening operation into play. When ready to operate (i.e., open the piston), the casing pressure is increased to a test pressure condition. This pressurization process ruptures the rupture disc 23 and fluid at casing pressure (hydrostatic, applied or any combination) enters the chamber immediately below and adjacent to the piston. This entry of fluid causes the piston 5 to begin moving. This fluid movement allows the piston to move inexorably closer to an open position. In actual lab and field tests the piston movement of about 4.5 inches begins to uncover the openings 25-27 and 28. These openings are closed or sealed off from the casing fluid by the piston 5. As piston 5 moves toward the open and final position, slots 28, are uncovered allowing fluid to flow through openings 25, 26 and 27 through slots 28. Thus, the restrained movement of the piston allows a time delay from the time the disc is ruptured until the slots are uncovered for fluid to pass. This movement continues until the piston has fully opened. As fluid pressure increases through port 14 it moves piston 5 into the fluid chamber 32. Piston 5 surrounds the inter wall of the apparatus 29. Hydraulic fluid in the fluid chamber restrains the movement of the piston. There is a hydraulic flow restrictor 22 that allows fluid to pass from chamber 32 to lower pressure chamber 34. This flow restrictor controls the rate of flow of fluid from chamber 32 to chamber and thereby the speed of the movement of the piston as it moves to the full open position. Items 28 are the slots in the apparatus mandrel that will be the passageway for fluid from the casing to the formation. Figure 3 shows the position of piston 5 when "opened" by moving into chamber 32. Initially, this movement increases pressure in the fluid chamber to a value that closely reflects the hydrostatic plus applied casing pressure. There is considerable predetermined control over the delay time by learned manipulation of the fluid type, fluid volume, initial charging pressure of the low pressure chamber and the variable flow rate through the hydraulic restrictor.
The time delay can be set as desired but generally will be about 5 to 6o minutes. Any hydraulic fluid will be suitable if capable of withstanding the pressure and temperature conditions that exist in the well bore. Those skilled in the art will easily be able to select suitable fluids such as Skydrol 5ooB4TM. In operation an apparatus of the invention will be piped into a casing string at a location that will allow fluid injection into the formation where desired. The apparatus may be inserted into the string in either direction. An advantage of the present invention is that two or more of the toe values of the invention may be used in the string. They will, as explained above, open to allow fluid penetration at multiple locations in the formation.
[0034] In general the apparatus will be constructed out of tool steel of about the same type as is used for the casing.
[0035] A prototype apparatus had the general dimensions of about 60 inches in length, with a nominal outside diameter of 6.5 inches and inside diameter of 3.75 inches.
Other dimensions as appropriate for the well and operation in which the apparatus is intended to be used are intended to be included in the invention and may easily be determined by those of ordinary skill in the art.

[0036] Figure 8 represents the results of a test of a prototype of the apparatus. As shown, a 5 minute test shows constant pressure for 5 minutes while the piston movement uncovered openings in the apparatus.
[0037] In the foregoing specification, the invention has been described with reference to specific embodiments thereof. The scope of the invention should not be limited by the preferred embodiments set forth in the examples but should be given the broadest interpretation consistent with the description as a whole. The claims are not to be limited to the preferred or exemplified embodiments of the invention.

Claims (43)

Claims

1. An apparatus to provide time-delayed injection of pressurized fluid from a cemented well casing into a geological formation comprising:
a housing with openings that allows fluid to pass through the openings to the formation;
a mandrel, wherein the mandrel is a one piece design that is configured to carry all of the tensile, compressional and torsional loads of said apparatus;
a movable piston configured to cover the openings in a closed position;
means for moving the piston to an open position leaving the openings uncovered;
means for activating a movement of the piston from the closed position;
the activation means is a reverse acting rupture disc activated by pressure;
the reverse acting rupture disc is configured to resist blockage by concrete;
whereby, as the piston moves from the closed position into a high pressure chamber comprising a hydraulic fluid, the piston is restrained in movement by a passage of the hydraulic fluid from the high pressure chamber into a low pressure chamber through a liquid flow restrictor, and the movement of the piston from the closed position to the open position is delayed by a predetermined metering time.

2. The apparatus of claim 1 configured and sized to mate with the well casing.

3. A method of injecting pressured fluid from a cemented well casing to a geological formation, comprising:
providing a housing with openings that allows fluid to pass through the openings to the formation;
providing a movable piston configured to cover openings in a closed position;
providing means for moving the piston to an open position leaving the openings uncovered;
providing means for activating a movement of the piston from the closed position with a reverse acting rupture disk;
and whereby, as the piston moves from the closed position into a high pressure chamber comprising a hydraulic fluid, the piston is restrained in movement by a passage of the hydraulic fluid from the high pressure chamber into a low pressure chamber through a liquid flow restrictor, and the movement of the piston from the closed position to the open position is delayed by a predetermined metering time;
injecting the pressured fluid in the well casing to a desired pressure;
activating the piston to move from the closed position;
delaying the time of the piston movement to the open position for the predetermined metering time, uncovering the openings in the housing; and maintaining pressure on the pressured fluid to force the pressured fluid into the formation.

4. The method of claim 3 wherein the movable piston surrounds an inner circumference of the housing.

5. The method of claim 3 wherein the rupture disc is burst by pressure above the desired working pressure of the fluid in the well casing, releasing pressure on one end of the piston to move the piston from the closed position into the high pressure chamber and wherein the piston movement displaces the hydraulic fluid from the high pressure chamber.

6. The method of claim 3 wherein at least two of the apparatuses are placed in the well casing.

7. The method of claim 3 wherein the predetermined metering time is chosen such that movement of the piston creates a high pressure jet through the casing and a cement sheathe surrounding the casing; said high pressure jet is created by substantially slowly moving the piston to uncover the openings.

8. The apparatus of claim 1 wherein the predetermined metering time is 5 minutes.

9. The apparatus of claim 1 wherein the predetermined metering time ranges from 5 minutes to 60 minutes.

10. The apparatus of claim 1 wherein a length of the apparatus is 60 inches.

11.The apparatus of claim 1 wherein an outside diameter of the apparatus is 6.5 inches.

12. The apparatus of claim 1 wherein an inside diameter of the apparatus is 3.75 inches.

13. The apparatus of claim 1 wherein the apparatus is made from tool steel.

14. The apparatus of claim 1 wherein the predetermined metering time is controlled by the hydraulic fluid type.

15. The apparatus of claim 1 wherein the predetermined metering time is controlled by the hydraulic fluid volume.

16. The apparatus of claim 1 wherein the predetermined metering time is controlled by a flow rate in the hydraulic flow restrictor.

17. The method of claim 3 wherein the apparatus is placed in the well casing in either direction.

18. The method of claim 6 wherein a first stage in the well casing is fracture stimulated by at least one of said apparatus.

19. The method of claim 3 wherein the predetermined metering time is controlled by the hydraulic fluid type.

20. The method of claim 3 wherein the predetermined metering time is controlled by the hydraulic fluid volume.

21. The method of claim 3 wherein the predetermined metering time is controlled by a flow rate in the hydraulic flow restrictor.

22. An apparatus to provide injection of pressurized fluid from a cemented well casing into a geological formation comprising:
a housing with openings that allows fluid to pass through the openings to the formation;
a movable piston configured to cover the openings in a first closed position;
means for moving the piston to a second open position leaving the openings uncovered;
means for activating a movement of the piston from the first closed position with a reverse acting rupture disk;
whereby, when the piston moves from the first closed position into a high pressure chamber comprising a hydraulic fluid, the piston is restrained in movement by a passage of the hydraulic fluid from the high pressure chamber into a low pressure chamber through a liquid flow restrictor, and the movement of the piston from the first closed position to the second open position is delayed by a predetermined metering time; and whereby the openings are opened substantially slowly so that as the openings are opened, the fluid is injected to the formation in a high pressure jet.

23. The apparatus of claim 22 wherein the high pressure jet begins as a pinpoint cutting jet and enlarges as the openings are opened to produce the effect of a guide hole with no flow restriction.

24. The apparatus of claim 22 wherein there is a time delay to begin to open the openings.

25. The apparatus of claim 22 wherein the piston moves from the first closed position to the second open position instantaneously.

26. An apparatus to provide time-delayed injection of pressurized fluid from a cemented well casing into a geological formation comprising:
a housing with openings that allows fluid to pass through the openings to the formation;
a piston configured to cover the openings in a closed position;
a reverse acting rupture disk configured to be in pressure communication with the piston;
a restrictive means configured to be connected to the reverse acting rupture disk;
means for moving the piston to an open position leaving the openings uncovered;

whereby, when a pressure of the pressurized fluid activates the reverse acting rupture disk, the restrictive means substantially impedes a flow of the pressurized fluid that moves the piston, and as the piston moves from the closed position into a high pressure chamber comprising a hydraulic fluid, the piston is restrained in movement by a passage of the hydraulic fluid from the high pressure chamber into a low pressure chamber through a liquid flow restrictor, and the movement of the piston from the closed position to the open position is delayed by a predetermined metering time.

27. The apparatus of claim 26 wherein the restrictive means is a threaded pathway.

28. The apparatus of claim 26 wherein the restrictive means is a tortuous pathway.

29. The apparatus of claim 26 wherein the restrictive means is a baffle plate comprising restrictive ports.

30. The apparatus of claim 26 wherein the apparatus is integral to the well casing.

31. An apparatus to provide time-delayed injection of pressurized fluid from a cemented well casing into a geological formation comprising:
a housing with openings that allows fluid to pass through the openings to the formation;
a piston configured to cover the openings in a closed position;
a reverse acting rupture disk configured to be in pressure communication with the piston; and means for moving the piston to an open position leaving the openings uncovered;
wherein, the piston is configured with a first end and a second end; the first end is associated with a first diameter; the second end is associated with a second diameter;

the first end is in pressure communication with a high pressure chamber; the first diameter is greater than the second diameter; whereby, as the piston is activated, the first end of the piston moves from the closed position into a high pressure chamber comprising a hydraulic fluid, the piston is restrained in movement by a passage of the hydraulic fluid from the high pressure chamber into a low pressure chamber through a liquid flow restrictor, and the movement of the piston from the closed position to the open position is delayed by a predetermined metering time.

32. The apparatus of claim 31 wherein the predetermined metering time delay is substantially increased without increasing the high pressure chamber area to the apparatus.

33. The apparatus of claim 31 wherein the first diameter is configured to allow a pressure in the high pressure chamber to be lowered, whereby the predetermined metering time delay is substantially increased.

34. The apparatus of claim 31 wherein the predetermined metering time is increased by reducing the differential pressure across the given restrictor.

35. The apparatus of claim 31 wherein the first diameter and the second diameter are chosen such that the pressure in the high pressure chamber pressure is reduced by at least 25%.

36. The apparatus of claim 31 wherein the apparatus is integral to the well casing.

37. An apparatus to provide time-delayed injection of pressurized fluid from a cemented well casing into a geological formation comprising:

a) a housing with openings that allows fluid to pass through the openings to the formation;
b) a piston configured to cover the openings in a first closed position;
c) a reverse acting rupture disk configured to be in pressure communication with the piston;
d) a restriction valve configured to be in pressure communication with a liquid flow restrictor; and e) means for moving the piston to a second open position leaving the openings uncovered;
whereby, when the piston moves from the first closed position into a high pressure chamber comprising a hydraulic fluid, the piston is restrained in movement by a passage of the hydraulic fluid from the high pressure chamber into a low pressure chamber through the liquid flow restrictor and the restriction valve and, the movement of the piston from the first closed position to the second open position is delayed by a predetermined metering time.

38. The apparatus of claim 37 wherein the restriction valve reduces a differential pressure across the hydraulic flow restrictor.

39. The apparatus of claim 37 wherein the restriction valve is a back pressure valve.

40. The apparatus of claim 39 further comprises a second back pressure valve connected in series with the back pressure valve.

41. The apparatus of claim 37 wherein the movement of the piston is further restrained by the restriction valve.

42. The apparatus of claim 37 wherein further comprises a second restriction valve connected downstream to the hydraulic flow restrictor.

43. The apparatus of claim 37 wherein the apparatus is integral to the well casing.