Abstract:
An apparatus and method for providing a time delay in injection of pressured fluid into a geologic formation. In one aspect the invention 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, allowing multiple valves to be used in the same well casing and providing a focused jetting action to better penetrate a concrete casing lining.

Description:
BACKGROUND 
       [0001]    1. Field 
         [0002]    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 activated by fluid pressure that opens ports after a predetermined time interval to allow fluid to pass from a well casing to a formation. 
         [0003]    2. Background 
         [0004]    It has become a common practice to install a pressure responsive opening device at the bottom or toe of a casing string within a horizontal well bore. These devices are made 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 the 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. 
       SUMMARY 
       [0005]    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 openings that can communicate through the walls of the housing to a formation;   a movable piston or pistons capable for covering and sealing the opening(s);   means for moving the piston to position leaving the opening(s) uncovered; and   means for activation of the movement of the piston.   
 
         [0010]    The method in broad aspect is the use and activation of the apparatus as described. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0011]      FIG. 1   a  is a plan view t of an apparatus of an embodiment of the invention. 
           [0012]      FIG. 1   b  is a plan view of a cross section of an apparatus of an embodiment of the invention. 
           [0013]      FIG. 2  is an exploded section view of the apparatus displayed in  FIGS. 1   a  and  1   b  in which the ports are closed. 
           [0014]      FIG. 3  is an exploded section view of the apparatus displayed in  FIGS. 1   a  and  1   b  in which the ports are open. 
           [0015]      FIG. 4  is a graphic representation of results of a test of the operation of an apparatus of an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    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 (and cement) into a geologic formation. 
         [0017]    The apparatus provides time-delayed injection of pressurized fluid through opening in a well casing to a geological formation comprising:
   a housing with opening that can communicate through the ports in the walls of the housing to a formation;   a movable piston or pistons capable of covering and sealing the port(s);   means for moving the piston to a final position leaving the port(s) uncovered; and   means for activation the movement of the piston.   
 
         [0022]    The present invention represents several improvements over conventional pressure responsive devices—improvements that will be appreciated by those of ordinary skills in the art of 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 openings or ports in the apparatus wall) opens immediately after the actuation pressure is reached. This limits the test time at pressure and in many cases 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 or 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 and by altering the flow rate of the hydraulic liquid flow restrictor. 
         [0023]    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. 
         [0024]    A third significant advantage is that in the operation the valve, the ports are opened slowly so that as the ports are opened the liquid is injected to the cement on the outside of the casing in a high pressure jet, thus establishing better connection to the foundation. The jet begins 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. 
         [0025]    Referring to the Figures,  FIG. 1   a  represents an Inner mandrel that attaches directly to the casing string and shows an overall external view an embodiment of the toe valve apparatus of the invention where item  28  are slot ports through which fluid will be transported into the geologic formation into which the casing is set.  FIG. 1   b  shows a cross section view of the apparatus of  FIG. 1   a.  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 is piped into the casing string as an integral part of the string and positioned where perforation and fluid injection into a formation is desired. The valve may be installed in either direction with no change to the tool function. 
         [0026]      FIG. 2  shows an exploded view of details of the hydraulic flow restriction apparatus of an embodiment of the invention—the embodiment shown in  FIGS. 1   a  and  1   b.  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 the piston,  5 . The opening piston,  5 , is sealed by elastomeric seals ( 16 ,  18  and  20 ) to cover the inner and outer ports,  28  and  25 - 27 , 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. 
         [0027]    The rupture disc  23  is the activation device that sets the valve opening operation in 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  5 . 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  27 - 29  and  28 . These openings are closed or sealed off from the casing fluid by the piston  28 . As piston  28  moves toward the open and final position, the 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 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  34  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.  FIG. 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 set as desired but generally will be about 5 to 60 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™. 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 an 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. 
         [0028]    In general the apparatus will be constructed of tool steel of about the same type used incasing. 
         [0029]    A prototype apparatus had the general dimensions of 60 inches in lengths, with a nominal outside diameter of 6.5 inches and an 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 skilled in the art. 
         [0030]      FIG. 4  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. 
         [0031]    In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes can be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification is, accordingly, to be regarded in an illustrative rather than a restrictive sense. Therefore, the scope of the invention should be limited only by the appended claims.