GB2330164A - Method of controlling downhole hydraulic activation circuits - Google Patents

Abstract

A method of controlling a hydraulic activation circuit (fig 1, 16) within a string of well tools comprises, providing a valve 10 between upper and lower parts of the hydraulic circuit. The valve is arranged to be urged shut by well pressure, but is held open by a frangible member 84. A detonating cord 104 passes close to the frangible member, and when a detonation wave, passing down the cord, to fire a perforating tool (fig 1, 18b) below the valve, passes the frangible member, the member breaks, allowing the valve to close, preserving the integrity of the upper part of the hydraulic circuit.

Description

METHODS OF CONTROLLING DOWNHOLE HYDRAULIC ACTIVATION CIRCUITS Background of the Invention This invention relates to methods of controlling downhole activation circuits.

In completing a product recovery well, such as in the oil and gas industry, several downhole tasks or functions must generally be performed with tools lowered through the well pipe or casing. These tools include, depending on the required tasks to be performed, perforating guns that ballistically produce holes in the well pipe wall to enable access to a target formation, setting tools that install well-sealing bridge plugs at a desired depth within the pipe, packer-setting tools that create a temporary seal about the tool and valves that are opened or closed.

Several tools can be configured as a single tool string lowered on the end of a long, hollow tube filled with fluid, the tools being hydraulically activatable in sequence by pressurizing either the fluid in the tube or the interior of the well casing.

Such a configuration of tools has included perforating guns carefully arranged to perforate the well casing without damaging the internal hydraulic activation circuit of the string.

Within these tool strings, explosive-based firing heads are frequently employed to trigger the detonation of associated downhole perforating guns or other tools. Due to safety issues understood by those familiar with well completion techniques, the detonation of a gun by a firing head is typically accomplished by a series of linked detonations that effectively transfer a detonation from the firing head to the gun across separable joints in the tool string in an assembly that enables the armed firing head to be assembled to the gun at the last possible moment. The firing head is generally separated from the gun by a spacer of sufficient length that when the firing head is finally assembled to the tool string by workers on a rig platform, the associated gun, already lowered into the well casing, is safely below the platform. A detonating cord, sometimes called primacord, typically extends down an internal bore of the spacer between the firing head and its associated gun to link the firing head to the gun.

Summary of the Invention According to the present invention, a method is provided for controlling a hydraulic activation circuit within a string of tools in a well. The method comprises providing a valve, containing a piston and a frangible element, disposed between the uphole and down hole parts. The piston is arranged to move under well pressure forces from a first position to a second position to desirably alter the hydraulic circuit, and is supported in the first position by the frangible element. The method also comprises exposing the piston to well pressure forces, and shattering the frangible element to enable the piston to move to the second position to alter the circuit when desired.

In some implementations the well pressure forces bias the piston toward a closed position to isolate an uphole part of the circuit from a downhole part of the circuit upon the shattering of the frangible element.

In a particularly useful implementation, the piston is exposed to well pressure of at least 2000 psi (13.8 MPa) and effectively alters the circuit in less than about 10 milliseconds after the frangible element is shattered.

In some particularly advantageous implementations, the present invention maintains the integrity of the intemal activating hydraulic system of a tubingconveyed string of detonatable tools during sequential detonation of the tools, advantageously enabling the sequential firing of perforating guns or other tools having intemal hydraulic lines that tend to be damaged when the tools are operated.

In this manner, a string containing middle-positioned guns may be lowered into the well and operated in a bottom-up sequence, as particularly advantageous in certain conditions, one at a time when desired.

In other implementations, the valve of the invention controllably alters a hydraulic activation circuit within a string of tools in a well by opening in response to a detonation wave passing through the frangible member, thereby enabling the subsequent hydraulic activation of a tool in the string.

Brief Description of the Drawings Fig. 1 illustrates a downhole tool string containing a valve used in the implementation of the invention; Fig. 2 schematically illustrates the function of a shutoff valve within a tool string section; Fig. 3 is a cross-section of a presently preferred embodiment of the shutoff valve in an open condition; Fig. 4 is a cross-section of the shutoff valve of Fig. 3 in a closed condition; and Fig. 5 illustrates a perforating gun with an array of charges and an extemal hydraulic line.

Description of the Preferred Embodiment Referring to Fig. 1, a shutoff valve 10 according to a preferred embodiment of the invention is part of a string 12 of tools which is lowered into a well casing 14 on a length of tubing 15 to perform desired downhole functions, typically related to well completion. In this particular embodiment, string 12 consists of an upper functional section A, a middle functional section B, and a lower functional section C, each containing a hydraulically-activated firing head 16 that detonates an associated tool (18a in Section A, 18b in Section B, and 18c in Section C) to perfonn a respective function.

The firing head 16 of each section is activated by a respectively selected elevated hydraulic pressure condition, preferably pressure conditions transmitted from the well surface through tubing 15, such as selected hydraulic pressures and/or selected durations of application of the pressures. An internal hydraulic path provided by internal ports and lines (not shown) transmits this activating pressure through upper sections A and B, such that in an initial state all three firing heads 16 are connected in parallel hydraulic communication to tubing 15. To enable the pressure inside tubing 15 to be elevated to activate firing heads 16, the internal hydraulic passages of sections A and B that allow hydraulic activation of section C must be sealed from casing annulus 20, such that substantially no flow occurs within tubing 15 during the activation process. In various embodiments, tools 18a, 18b and 1 8c include perforating guns, bridge plug-setting tools, and other downhole equipment, although the invention has particularly useful application if middle tool 18b is a tool that has the potential to destroy the integrity of the internal hydraulic activation system by opening an undesirable hydraulic path from tubing 15 to well casing annulus 20 when the tool is operated, such as is typical with a perforating gun.

Shutoff valve 10 is constructed as a valve along the internal hydraulic communication passage from firing head 16 to tool 18b in middle section B. Valve 10 is initially in an open position, enabling the transmission of activating pressure to firing head 16 of lower section C, which is arranged to fire in sequence before section B. As described in detail below, shutoff valve 10 is arranged to close when the firing head 16 of middle section B detonates tool 18b, thereby avoiding the possibility of a breach in the hydraulic activation system caused by the operation of tool 18b damaging intemal hydraulic lines. Once activated, valve 10 prevents the loss of hydraulic pressure within tubing 15 by isolating tubing 15 from all parts of the string lower than shutoff valve 10, thereby maintaining the operability of any firing heads 16 or other hydraulically operated downhole devices yet to be operated. In this manner, closing a shutoff valve 10 in a given functional section ensures the integrity of the hydraulic activation system for the operation of any functional sections arranged to fire later in sequence. Sections A and C are shown without shutoff valves 10 in the embodiment of Fig. 1 because tool 18c of the lowest section of a string is typically constructed without internal hydraulic lines, as there are no lower firing heads 16 to be hydraulically activated, and assuming that section A is the last section of the string to be operated, a breach in the hydraulic activation system occurring after it has been fired would be of little consequence. Other embodiments employ the shutoff valve of the invention in different arrangements, as required to maintain activating hydraulic circuit integrity.

Referring to Fig. 2, firing head 16 in a particular arrangement of section B of Fig. 1 detonates charges 30 within perforating gun 32. Located between firing head 16 and gun 32, the housing 47 of shutoff valve 10 contains a length of detonator cord 36 (primacord) connecting an upper receptor booster 38 and a lower transfer charge 40. When firing head 16 is activated, a firing pin 42 impacts a detonator 44 that subsequently explodes a transfer charge 46. The explosion of transfer charge 46 detonates booster 38, which ignites detonator cord 36. As the detonation wave propagates downward through detonator cord 36 toward charge 40, it passes, and causes to permanently close, a valve element 48 along a hydraulic passage 50 within shutoff valve 10. Once valve element 48 closes, it blocks any subsequent transfer of internal hydraulic flow or pressure from firing head 16 to gun 32 or backflow of well annulus fluids into line 51. As shaped charges 30 of gun 32 are subsequently fired, therefore, any physical damage that might otherwise consequentially occur to the internal hydraulic passages 52 within gun 32 does not affect the internal activating hydraulic system above valve element 48.

Referring to Fig. 3, in the presently preferred embodiment shutoff valve 10 comprises an upper housing assembly 60 and a lower housing assembly 62, joined at threaded joint 64. Both housing assemblies include several separable portions, not shown, to enable efficient manufacturing and assembly. Upper housing assembly 60 includes a stem 66. Disposed about stem 66 is an operating piston 68 with o-ring seals 70 and 72 that seal against a small bore 74 and a large bore 76 of upper housing assembly 60, respectively, and o-ring seals 80 that seal against an inner bore 82 of lower housing assembly 62. O-ring seals 78 about the lower end of stem 66 seal against an inner bore of the operating piston 68. In an open position, operating piston 68 is supported in an upper position, as shown, by a frangible member 84 between the piston and a support 86 of lower housing assembly 62. In the presently preferred configuration, frangible member 84 consists of a vertical stack of individual frangible elements 88 of gray-iron class 40 (spec number ASTM A48-76), otherwise more commonly known as grade 40 cast iron. The operating piston 68 is held downward against frangible member 84 by well pressure applied through ports 89 and acting on a differential area of the piston, the difference between areas bounded by the sealing diameters of o-ring seals 70 and 72.

Because o-ring seal 72 has a larger sealing diameter than o-ring seal 70, the net force of pressure applied through ports 89 always tends to force piston 68 downward. All other hydraulic loads acting on piston 68 are balanced, due to equal pressures acting against equal areas of opposing o-ring seals, opposed ring pairs 80 and 78; 70 and 73.

With the operating piston 68 positioned as shown, hydraulic fluid is free to move through the length of the shutoff valve 10 between an inlet 90 and an outlet 92. The path of flow, from inlet to outlet, is as follows: down holes 94 in upper housing assembly 60, down annulus 96 about stem 66, outward through ports 98 in operating piston 68, down annulus 100, and down holes 102 in lower housing assembly 62. The hydraulic passages within the valve housings are of small size as there is very little hydraulic flow along this path even with the valve open, as the primary purpose of the hydraulic path in this embodiment is to transfer hydraulic pressure. In the open position shown, o-ring seals 78 at the lower end of stem 66 are below ports 98 in piston 68.

A detonating cord 104 (primacord) is disposed within a sealed bore that extends the length of the housings of shutoff valve 10, connecting a receptor booster 106 at the top of the shutoff valve with a trigger charge 108 at the bottom of the shutoff valve. Detonator cord 104 passes through the center of hollow frangible member 84. The primary function of detonator cord 104 is to transfer a detonation wave from receptor booster 106 to trigger charge 108, and in the process of transferring this detonation wave, detonator cord 104 is destroyed.

Referring also to Fig. 4, when the detonation wave propagating within detonator cord 104 passes through the center of frangible member 84, the individual frangible elements 88 will each shatter into a multitude of pieces due to the properties of the material (e.g. cast iron) of which they are made. When elements 88 shatter, the debris 110 from the frangible elements falls into annulus 112 of lower housing assembly 62, allowing operating piston 68 to move downward to a closed position (as shown) due to the force of well pressure applied through ports 89. The piston is in a closed position when ports 98 have been displaced a sufficient distance to be disposed below o-ring seals 78, with seals 78 thereby blocking any subsequent transfer of hydraulic pressure or flow between annulus 96 and ports 98.

Although cast iron is the presently preferred material of frangible elements 88, other materials may be employed. Suitable materials are selected and sized to be strong enough to support operating piston 68 in an unbroken condition, and brittle enough to shatter due to the propagation of the detonation wave down detonating cord 104. Certain ceramic materials, for instance, are suitable. In other embodiments, frangible member 86 is in the form of a single frangible plate member, or a supporting web. In other embodiments the frangible member is arranged to be loaded in tension rather than compression.

Piston 68 is constructed with a low inertia and a large differential pressure area, such that the piston is accelerated rapidly by biasing well pressure forces when the frangible member is shattered. Laboratory tests of prototypes have demonstrated that the piston moves fast enough to isolate the inlet and the outlet in less than about 10 milliseconds after the propagation of the detonation wave has commenced when the well pressure exceeds about 2000 psi (13.8 MPa).

The valve of the invention, configured to close in response to a detonation, is advantageously employed to enable the use of tool strings comprising several hydraulically activated firing heads that are arranged to be activated at different tubing pressures in a sequence from bottom up. This configuration is enabled by the function of the shutoff valve to reliably maintain the integrity of the activating hydraulic system, even when some hydraulic lines are damaged by the firing of nearby guns or other tools. The shutoff valve enables perforating guns of middle sections of a string of tools to be configured with intemal hydraulic lines that tend to be destroyed by the firing of the gun, or with helical charge pattems that tend to damage even external lines but are useful for perforating some zones. For example, Fig. 5 illustrates an elongated gun 120 with an array of outwardly-facing perforating charges 122, some of which (e.g. charge 122a) are oriented to rupture a nearby external hydraulic line 124 upon detonation.

In a particularly useful configuration, the invention is employed in combination with the inventors' hydraulically activated firing head with hydro-mechanical locks, as described in U.S. Patent Application Serial No 08/752,810 entitled "Device and Method for Performing Downhole Functions" filed November 20, 1996, corresponding to United Kingdom Patent Application No 9724575.7 (2 319 546), which is hereby incorporated by reference.

In other embodiments, the valve of the invention is configured to open in response to a detonation, employing a similar structure to that shown in Fig. 3 but arranged to open a port when a frangible member supporting a piston is shattered.

In this case, the opening of the valve enables, in some instances, the subsequent operation of a hydraulically activatable tool. The valve may also be employed elsewhere in a string of downhole tools as a means for otherwise controlling a hydraulic activation circuit.

Other embodiments and advantages of the invention will occur to those skilled in the art. For example, more than three functional sections may be included in a string, with shutoff valves in each middle section, for performing four or more discrete functions in sequence with one trip down a well.

Claims (3)

1. CLAIMS 1. A method of controlling a hydraulic activation circuit within a string of tools in a well, the method comprising: providing a valve disposed between uphole and downhole parts of the string of tools, said valve containing a piston and a frangible element, said piston being arranged to move under well pressure forces from a first position to a second position to desirably alter said hydraulic circuit and being supported in said first position by said frangible element; exposing said piston to well pressure forces; and shattering said frangible element to enable said piston to move to said second position to alter said circuit when desired.
2. 2. The method of claim 1, wherein said well pressure forces bias said piston toward a closed position to isolate an uphole part of said circuit from a down hole part of said circuit upon the shattering of said frangible element.
3. 3. The method of claim 1 or claim 2, wherein the piston is exposed to well pressure of at least 2000 psi (13.8 MPa) and effectively alters said circuit in less than about 10 milliseconds after said frangible element is shattered.