Pressure compensated downhole actuation mechanism

Abstract

A pressure-compensated downhole actuation mechanism includes an actuator housing with a pressure compensation chamber and a gas charge chamber separated by a partition. The pressure compensation chamber has a port allowing pressure equalization with an external environment. The partition includes a booster piston port with a sealing surface and a radial seal isolated from wellbore fluids. A booster piston is disposed within the gas charge chamber, with a piston shaft extending through the port and having a contact surface at an upper distal end. The booster piston translates upward when the gas charge pressure exceeds the chamber pressure, enabling the piston shaft to apply force to a power spring mandrel above. The mechanism also allows downward translation to disengage the piston shaft from the mandrel. The design facilitates reliable actuation under varying downhole pressure conditions and can incorporate features for gas injection, inert pressurization, and protective fluid circulation.

Description

PRESSURE COMPENSATED DOWNHOLE ACTUATION MECHANISM CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of, or priority to, U.S. Provisional Patent Application Serial Number 63 / 673,114, filed on July 18, 2024, which is hereby incorporated by reference in its entirety for all purposes. BACKGROUND OF THE INVENTION

[0002] Actuators are critical components used in downhole flow control devices. While actuators are integral to many inflow and outflow control devices, surface-controlled subsurface safety valves (“SSSVs”) present one of the most demanding applications, requiring robust performance under high pressures and high temperatures over extended periods of time. An SSSV is a fail-safe device that is designed to controllably permit the flow of production fluids to the surface during normal operations and prevent the uncontrolled release of production fluids during emergencies and other contingencies, thereby safeguarding personnel, equipment, and the environment.

[0003] Conventional SSSVs require the affirmative application of hydraulic actuation pressure from a pump on the surface to open a closure mechanism, such as a flapper, ball, poppet, or other closure device, against a spring-loaded actuation mechanism, whose operation is influenced by the pressure environment in which it is disposed. When sufficient hydraulic actuation pressure is applied, the actuation mechanism compresses a power spring that causes the closure mechanism to open, enabling controlled flow of production fluids through the valve to the surface. If the hydraulic actuation pressure is lost, intentionally or due to an emergency or other contingency, the spring-loaded actuation mechanism should overcome the hydrostatic head pressure in the control line, causing the closure device of the closure mechanism to automatically close, preventing any further production flow through the valve.

[0004] Conventional SSSVs are typically categorized as tubing-retrievable safety valves or wireline-retrievable safety valves. Tubing-retrievable safety valves are typically run- in as part of the production tubing string during completion. The control line, which provides the hydraulic actuation pressure from the surface, is disposed in the annulus between the production tubing and the casing. Because tubing-retrievable safety valves are run-in with production tubing during completion, they typically provide the largest inner diameter that maximizes production flow. In contrast, wireline-retrievable safety valves are run-in with a wireline or slickline after completion. As such, wireline-retrievable safety valves must be landed in a profile or hydraulic landing nipple that is disposed within the production tubing and therefore have a smaller inner diameter that restricts production flow as compared to tubing-retrievable safety valves. Notwithstanding, wireline-retrievable safety valves advantageously can be installed or retrieved without having to pull the entire production tubing string. Typically, wireline- retrievable safety valves are preferred when an SSSV was not installed as part of the production tubing during completion or in cases where a tubing-retrievable SSSV was installed as part of the production tubing during completion but fails and requires remediation. BRIEF SUMMARY OF THE INVENTION

[0005] According to one aspect of one or more embodiments of the present invention, a pressure compensated downhole actuation mechanism includes an actuator housing having a pressure compensation chamber including a pressure communication port that permits an interior pressure of the pressure compensation chamber to substantially equalize with an exterior pressure, a gas charge chamber disposed below the pressure compensation chamber, and a partition separating the pressure compensation chamber from the gas charge chamber. The partition includes a booster piston port hole, a sealing surface formed within the booster piston port hole, and a radial seal disposed within the sealing surface, where the radial seal is isolated from wellbore fluids in the pressure compensation chamber, and a booster piston including a catch end disposed within the gas charge chamber and a piston shaft at least partially extending through the booster piston port hole. The piston shaft includes a contact surface on an upper distal end. The booster piston axially translates upward when the interior pressure of the pressure compensation chamber is less than a gas charge pressure in the gas charge chamber such that the contact surface of the piston shaft provides an upward boost to a contact surface of a power spring mandrel at least partially disposed in the pressure communication chamber above the booster piston.

[0006] According to one aspect of one or more embodiments of the present invention, a modular power spring module includes a power spring housing having an upper threaded connection end including an upper power spring mandrel port hole, a protection fluid chamber, and a lower threaded connection end comprising a lower power spring mandrel port hole, a power spring mandrel including a stop collar disposed within the protection fluid chamber, an upper mandrel shaft portion above the stop collar that at least partially extends through the upper power spring mandrel porthole, and a lower mandrel shaft portion below the stop collar that at least partially extends through the lower power spring mandrel port hole, and a power spring disposed around the lower mandrel shaft portion below the stop collar within the protection fluid chamber.

[0007] According to one aspect of one or more embodiments of the present invention, a subsurface safety valve including a closure mechanism having a closure device, at least one modular power spring module disposed below the closure mechanism, and a pressure compensated downhole actuation mechanism disposed below the at least one modular power spring module. The application of hydraulic actuation pressure compresses a power spring of the at least one modular power spring module causing the closure device to open enabling fluids to flow through the valve toward the surface and the absence of sufficient hydraulic actuation pressure causes the closure device to close under normal formation or tubing pressure. The pressure compensated downhole actuation mechanism provides an upward boost to the power spring of the at least one modular power spring module when the formation or tubing pressure is less than a gas charge pressure in a gas charge chamber of the actuation mechanism.

[0008] Other aspects of the present invention will be apparent from the following description and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1A shows the conventional use of a subsurface safety valve in a producing offshore well.

[0010] FIG. 1B shows the forces acting on a conventional subsurface safety valve at a predetermined setting depth.

[0011] FIG. 2A shows a cross-sectional view of a subsurface safety valve equipped with a pressure compensated downhole actuation mechanism operating in a gas-pressure- unassisted mode with the valve in the open position in accordance with one or more embodiments of the present invention.

[0012] FIG.2B shows a cross-sectional view of a subsurface safety valve equipped with a pressure compensated downhole actuation mechanism operating in a gas-pressure- unassisted-mode with the valve in the closed position in accordance with one or more embodiments of the present invention.

[0013] FIG. 3A shows a cross-sectional view of a subsurface safety valve equipped with a pressure compensated downhole actuation mechanism operating in a gas-pressure-assisted-mode with the valve in the open position in accordance with one or more embodiments of the present invention.

[0014] FIG.3B shows a cross-sectional view of a subsurface safety valve equipped with a pressure compensated downhole actuation mechanism in a gas-pressure-assisted-mode with the valve in the closed position in accordance with one or more embodiments of the present invention.

[0015] FIG. 4A shows a detailed view of a closure mechanism of a subsurface safety valve in accordance with one or more embodiments of the present.

[0016] FIG. 4B shows a detailed view of a modular spring module of a subsurface safety valve in accordance with one or more embodiments of the present.

[0017] FIG. 4C shows a detailed view of a pressure compensated downhole actuation mechanism of a subsurface safety valve in accordance with one or more embodiments of the present.

[0018] FIG. 5 shows a functional setting depth window of a subsurface safety valve equipped with a pressure compensated downhole actuation mechanism in accordance with one or more embodiments of the present invention.

[0019] FIG. 6 shows a wireline-retrievable subsurface safety valve equipped with a pressure compensated downhole actuation mechanism in accordance with one or more embodiments of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] One or more embodiments of the present invention are described in detail with reference to the accompanying figures. For consistency, like elements in the various figures are denoted by like reference numerals. In the following detailed description of the present invention, specific details are described to provide a thorough understanding of the present invention. In other instances, aspects that are well-known to those of ordinary skill in the art are not described to avoid obscuring the description of the present invention. For purposes of clarity, “top” or “upper” refer to a portion or side that is closer, whether directly or in reference to another component, to the surface above a wellbore and “bottom” or “lower” refer to a portion or side that is closer, whether directly or in reference to another component, to the bottom of the wellbore.

[0021] FIG. 1A illustrates a conventional use of a subsurface safety valve in a producing offshore well. Production well 100 includes a wellbore 105 drilled into the subsea surface 110, with a series of casings 115 cemented into place to stabilize wellbore 105, prevent formation collapse, and isolate one or more production zones 120. In high-pressure or deepwater environments, well 100 may be completed with one or more liners or packers 125 disposed above the active production zone 120. During completion, production tubing string 130 may be installed inside the cased wellbore 105, extending through packers 125, to provide a conduit for hydrocarbons (not shown) to flow from the production zone 120 to the surface. A tubing-retrievable SSSV 135 may be run into the well 105 as part of the distal end of the production tubing string 130. An annulus 140 is defined between the outer wall of production tubing string 130 and the inner wall of casing 115. A control line 145 for hydraulically actuating the tubing-retrievable SSSV 135 may be disposed in the annulus 140.

[0022] During production, the tubing-retrievable SSSV 135 may be hydraulically actuated into the open, or producing, state by a surface-based pump that communicates hydraulic actuation pressure via control line 145 to tubing-retrievable SSSV 135 disposed downhole. The hydraulic actuation pressure bears on the actuation mechanism (not independently illustrated) and compresses a power spring (not independently illustrated) causing the closure mechanism (not independently illustrated) to open, allowing production fluids (not shown) to flow through the valve 135 toward the surface. In the absence of sufficient hydraulic actuation pressure, the power spring (not independently illustrated) expands causing the closure device (not independently illustrated) of the closure mechanism (not independently illustrated) to close the valve 135, thereby preventing production fluids (not shown) from flowing through the valve 135 toward the surface. As such, SSSV 135 requires the affirmative application of hydraulic actuation pressure to open the valve 135 to produce formation fluids and is designed to automatically close the valve 135 whenever the hydraulic actuation is removed or substantially reduced, whether intentionally or due to an emergency or other contingency.

[0023] Conventional SSSVs 135 suffer from a number of issues that complicate their operation and use. In order to fully close the valve 135, the spring-loaded actuation mechanism (not independently illustrated) must store sufficient energy to overcome the hydrostatic head pressure in control line 145 that extends from the surface to the valve’s 135 setting depth. At significant depths, the static column of fluid exerts substantial pressure on the actuation mechanism (not independently illustrated). To reliably force the closure device (not independently illustrated) of the closure mechanism (not independently illustrated) into the fully closed position, the actuation mechanism (not independently illustrated) must generate an opposing force that exceeds the hydrostatichead pressure. By optimal design, this ensures that, in the event of a loss of hydraulic actuation pressure or an emergency shutdown, the actuation mechanism (not independently illustrated) automatically forces the closure device (not independently illustrated) of the closure mechanism (not independently illustrated) to fully close the valve 135. However, this is not always the case as described in more detail herein.

[0024] While the description provided above has been in reference to a tubing-retrievable SSSV 135 depicted in the figure, one of ordinary skill in the art will appreciate that it applies with equal force to wireline-retrievable SSSVs (not shown) that are disposed within the production tubing string 130, and sometimes within a failed tubing- retrievable SSSVs (e.g., 135) as well as with other downhole components that use actuators including, but not limited to, inflow control devices and outflow control devices.

[0025] Continuing, FIG. 1B illustrates the forces acting on a conventional subsurface safety valve 135 at a predetermined setting depth. The setting depth refers to the downhole depth at which SSSV 135 is installed within wellbore 105. While regulatory guidelines define minimum installation depths, an SSSV 135 is typically positioned significantly deeper, below the packer 145 and above the production zone (e.g., 120 of FIG. 1), to ensure effective isolation of the reservoir in emergency conditions. Prior to deployment, engineers calculate the fail-safe setting depth through careful analysis of well parameters and other variables, in a process well known in the art. A key factor in this calculation is the hydrostatic head pressure in control line 145, which increases with depth due to the weight of the fluid column. The actuation mechanism 150 of SSSV 135 must be able to overcome the hydrostatic head pressure in the control line 145 at the setting depth to reliably shift the closure device (not shown) of closure mechanism 155. Accordingly, the fail-safe setting depth is selected to ensure that the hydraulic actuation pressure is capable of causing the actuation mechanism to fully open the valve 135 and, in the absence of sufficient hydraulic actuation pressure, fully close the valve 135.

[0026] In normal operation, the application of hydraulic actuation pressure from the surface via control line 145 bears on actuation mechanism 150, typically resulting in the compression of a power spring (not shown) that causes an actuator or shaft (not shown) to axially translate down that, in combination with the hydrostatic head pressure 160 above closure mechanism 155, causes the closing device (not shown) of closure mechanism 155 to open, thereby enabling the flow of production fluids 165 throughvalve 135 toward the surface. In the absence of sufficient hydraulic actuation pressure, whether intentionally or due to an emergency or other contingency, SSSV 135 is designed to automatically and fully close, preventing production fluids 165 from flowing toward the surface. As hydraulic actuation pressure is removed, the compressed power spring (not shown) of actuation mechanism 150 starts to decompress causing an upward force that is bolstered by the upward force provided by production fluids 165 that in combination cause the closing device (not shown) of closure mechanism 155 to close. In normal operation, this upward force is sufficient to overcome the hydrostatic head pressure 160 above the closing device (not shown) of the closure mechanism 155, resulting in the automatic closure of the valve 135.

[0027] However, as SSSVs are being set deeper and deeper, the hydrostatic head pressure in control line 145 is greater than the power spring (not shown) of actuation mechanism 150 can overcome. This motivated the incorporation of a gas charge to provide a boost to actuation mechanism 150, as described in U.S. Patent 7,392,839 (the “‘839 Patent”). The gas charge is typically disposed below an actuator piston (not shown) that provides an upward boost to the power spring (not shown), assisting it to overcome the hydrostatic head pressure in control line 145, when the energy stored in the power spring (not shown) alone in not sufficient. The gas charge is housed in a sealed chamber (not shown) within actuation mechanism 150 and is charged with a pressurized inert gas, typically nitrogen. As a closed system, the gas charge remains contained within actuation mechanism 150. The gas charge in the sealed chamber (not shown) is pressurized prior to deployment of the valve 135 to a specific level, often hundreds or thousands of pounds per square inch (“psi”), and this stored energy acts like a compressed spring, ready to release force when needed. The incorporation of this gas charge enabled, for the first time, substantially deeper setting depths, as are commonly required in offshore wells. However, the ‘839 patent disclosed two distinct actuators, each capable of operating the valve separately and independently of one another. If one failed, the other was brought online. While this innovation enabled substantially deeper setting depths, it presents a number of implementation challenges as well as difficult problems.

[0028] A significant challenge in the design of SSSVs is determining the appropriate charge pressure for the gas charge chamber, typically filled with an inert gas such as nitrogen, to ensure reliable operation at the subsurface setting depth. The gas charge is set at the surface under ambient temperature conditions but must function effectivelyunder varying downhole temperatures, ranging from approximately 40°F in shut-in conditions (e.g., ocean temperatures in deepwater wells) to 300°F or higher during production, as dictated by flowing bottomhole temperatures. These temperature variations, governed by Boyle’s and Charles’ laws, cause the gas charge pressure to increase with rising temperatures, affecting the boost force provided by the gas charge chamber. Consequently, the surface charge pressure must be precisely calculated to account for these changes, resulting in a narrow operational window where the SSSV can be set and expected to perform reliably in accordance with API Specification 14A, highlighting the need for improved actuator designs to enhance operational stability.

[0029] A significant challenge in the deployment of SSSVs is determining the optimal setting depth within the narrow operational window to ensure reliable performance in accordance with API Specification 14A. The setting depth, typically ranging from a few hundred feet to 1000 feet below the subsea wellhead in offshore wells, is selected to minimize the adverse effects of depth, such as increased hydrostatic pressure and temperature variations, while maintaining accessibility. However, deeper settings may be required to avoid zones prone to asphaltene or scale deposition, which can impair valve operation. Greater depths necessitate higher gas charge pressures to actuate the closure mechanism effectively, complicating the design and calibration of the gas charge chamber. Once the SSSV is installed as part of the production tubing string, its depth and gas charge pressure are fixed, limiting in-situ adjustments and underscoring the need for advanced actuation mechanisms to enhance operational reliability across diverse well conditions.

[0030] A significant challenge in the operation of SSSVs is the impact of changing well conditions over time, which can compromise the valve’s narrow operational window and lead to critical failure. In new wells, bottomhole pressures typically range from 10,000 to 20,000 psi, with some reaching 25,000 psi, and bottomhole temperatures span 225°F to 350°F, occasionally exceeding 500°F. As wells age and hydrocarbons are produced, both pressure and temperature naturally decline due to reservoir depletion. Additionally, artificial lift techniques, such as water injection in approximately one- third of wells, further reduce downhole temperatures by introducing cooler surface fluids. These reductions in bottomhole pressure and temperature can disrupt the balance of forces required for reliable valve actuation, particularly the closing force provided by the gas charge chamber and power spring, which must overcome the hydrostatic head pressure in the tubing. In severe cases, insufficient closing force results in the valvefailing in an open state, allowing uncontrolled flow of production fluids to the surface, or in a closed state, halting production. These dynamic well conditions underscore the need for advanced actuation mechanisms to maintain reliable fail-safe operation across the well’s lifecycle, in compliance with API Specification 14A.

[0031] The industry faces additional challenges with deep-set gas-charged SSSVs, due to mechanical failures stemming from prolonged exposure to harsh downhole environments. While early generations of these valves were designed for an anticipated service life of 20 years, many deployed over 30 years ago continue to operate in prolific wells, increasing the likelihood of mechanical failure. Common failure modes include seal degradation, flow tube movement restriction, closure mechanism leakage, and control line failures. With respect to seal degradation, long-term exposure to corrosive wellbore fluids, such as those containing H2S or CO2, degrades seals within the actuation mechanism, including those in the gas charge chamber. Seal failure can lead to loss of the gas charge, eliminating the boost force needed for fail-safe closure, causing the valve to remain open, or preventing hydraulic actuation from the surface resulting in permanent closure. With respect to flow tube movement restriction, accumulation of asphaltene, scale, or sand around the flow tube or closure mechanism restricts axial movement, causing the valve to fail in its current state, either open or closed, disrupting the production or safety function. With respect to closure mechanism leakage, flappers or other closure devices may leak during periodic API 14B testing due to weak springs that rely on well pressure to seal effectively, compromising the valve’s ability to isolate the wellbore. With respect to control line failures, loss of integrity in the control line prevents hydraulic actuation, causing the valve to close permanently.

[0032] Failures of SSSVs have significant operational, safety, and economic consequences, particularly in deepwater and ultra-deepwater wells. A failure in the closed state halts production, which can range from 10,000 to 30,000 barrels per day or equivalent gas volumes, resulting in substantial revenue losses. Conversely, failure in the open state necessitates immediate well shut-in to prevent uncontrolled flow, compromising safety and requiring costly interventions. In shallow-water wells with dry trees, wireline-retrievable SSSVs can be deployed inside a failed tubing-retrievable SSSVs to restore functionality, a well-known practice referred to as intervention. However, in deepwater and ultra-deepwater environments, interventions are more complex and costly, often requiring floating specialized vessels or rigs to pull and replace the entire production tubing string. Such operations incur significant expensesand extended downtime, particularly in deepwater and ultra-deepwater settings where equipment lead times and logistical challenges further exacerbate costs. These issues highlight the critical need for an advanced actuation mechanism that enhances reliability, minimizes failure risks, and reduces the need for invasive interventions, in compliance with API Specification 14A.

[0033] Conventional deep-set gas-charged SSSVs enable deployment at increased setting depths to meet operational requirements, but they are limited by their inability to adapt to changing downhole conditions, particularly declining formation pressure. These gas- charge chambers of these valves are charged at the surface with an inert gas, such as nitrogen, to a pressure calibrated for the expected formation pressure at the time of deployment. However, as the well produces and formation pressure decreases, the upward force from formation pressure that aids valve closure diminishes, reducing the effectiveness of the gas charge chamber and power spring, namely, their ability to fully close the valve. This results in a narrow operational window where the SSSV can reliably close, as required by API Specification 14A. Over time, pressure in the wellbore significantly declines and can eliminate this window, causing the valve to fail in an open state, which allows uncontrolled flow of production fluids to the surface—a critical safety and operational concern. These limitations highlight the need for advanced actuation mechanisms that maintain reliable fail-safe closure across a wide range of downhole conditions.

[0034] Accordingly, in one or more embodiments of the present invention, a pressure compensated downhole actuation mechanism enhances fail-safe closure by autonomously adapting to changing formation pressures. Advantageously, a gas charge boost is provided, when needed, and in the right amount, to ensure fail-safe closure in response to changing formation pressures. The actuator housing includes a pressure compensation chamber with a pressure communication port whose internal pressure substantially equalizes with the pressure outside the actuator housing, a gas charge chamber disposed below the pressure compensation chamber, and a partition separating the pressure compensation chamber from the gas charge chamber. The partition includes a booster piston port hole, a sealing surface formed within the booster piston port hole, and a radial seal disposed within the sealing surface. The radial seal is isolated from wellbore fluids in the pressure compensation chamber. The booster piston includes a catch end disposed within the gas charge chamber and a piston shaft at least partially extending through the booster piston port hole. The piston shaft includes acontact surface on an upper distal end. The booster piston axially translates upward when the interior pressure of the pressure compensation chamber is less than a gas charge pressure in the gas charge chamber such that the contact surface of the piston shaft provides an upward boost to a contact surface of a power spring mandrel at least partially disposed in the pressure communication chamber above the booster piston.

[0035] FIG. 2A shows a cross-sectional view of a subsurface safety valve 600 equipped with a pressure compensated downhole actuation mechanism 400 operating in a gas- pressure-unassisted mode with the valve in the open position in accordance with one or more embodiments of the present invention. Subsurface safety valve 600 may include a closure mechanism 200, one or more modular power spring modules 300, and pressure compensated downhole actuation mechanism 400.

[0036] Closure mechanism 200 controllably opens valve 600 to enable production fluids to flow toward the surface and is designed to automatically close valve 600 during emergencies and other contingencies. Closure mechanism 200 includes a closure housing 210 having a hydraulic chamber 220, a hydraulic communication port 230 that is in fluid communication with a control line (e.g., 145 of FIG. 1) that communicates hydraulic actuation pressure from the surface to hydraulic chamber 220, and a protection fluid chamber 240. Closure piston 290 is at least partially disposed within hydraulic chamber 220 and protection fluid chamber 240, within closure housing 210. Closure piston 290 includes a shoulder 270 having a radial seal 280 that prevents fluid communication between hydraulic chamber 220 and protection fluid chamber 240. Flow tube 260 includes a radial seal 285 that, in combination with radial seal 280, establishes the sealed volume of hydraulic chamber 220. Flow tube 260 moves and mechanically engages a closure device (not shown) disposed above flow tube 260. The closure device (not shown) may be a flapper, ball valve, poppet valve, or other closure device well known in the art that is configured to open based on the downward movement of flow tube 260 and close or enable automatic closure based on the upward movement of flow tube 260. Closure piston 290 is at least partially disposed within protection fluid chamber 240 and at least partially extends through closure port hole 295. Closure housing 210 may also include an upper protection fluid port 250 that fluidly communicates protective fluids through protection fluid chamber 240. Closure housing 210 may also include a lower threaded connection end 297 to removably attach closure mechanism 200 to a modular power spring module 300a.

[0037] Modular power spring module 300a includes a power spring 350a that compresses during hydraulic actuation to store energy and facilitate opening the closure device (not shown) of closure mechanism 200, to enable production fluids to flow toward the surface and, in the absence of sufficient hydraulic actuation, releases the stored energy to provide an upward force that facilitates, at least in part, closing or enabling the closure of the closure device (not shown) of closure mechanism 200. Modular power spring module 300a may be removably disposed below closure mechanism 200. Modular power spring module 300a may include a power spring housing 305a comprising an upper threaded connection end 310a having an upper power spring mandrel port hole 315a, a protection fluid chamber 240, and a lower threaded connection end 320a having a lower power spring mandrel port hole 325a. A power spring mandrel 330a may include a stop collar 335a disposed within protection fluid chamber 240 of power spring housing 305a and a lower mandrel shaft portion 345a below stop collar 335a that at least partially extends through the lower power spring mandrel port hole 325a, having a contact surface 355a on a distal end. Power spring 350a may be disposed around the lower mandrel shaft portion 345a below stop collar 335a within protection fluid chamber 240. Upper threaded connection end 310a of modular power spring module 300a may be removably attached to lower threaded connection end 297 of, for example, closure mechanism 200. In certain embodiments, lower threaded connection end 310a of modular power spring module 300a may be removably attached to pressure compensated downhole actuation mechanism 400 (e.g., single power spring module 300 embodiment not shown). In other embodiments, lower threaded connection end 310a of modular power spring module 300a may be removably attached to an additional modular power spring module 300 (e.g., dual power spring embodiment with 300b depicted in the figure). In still other embodiments, a plurality of modular power spring modules (e.g., 300) may be arranged in series (e.g., plurality of power spring modules 300 embodiment not shown), where the number of modular power spring modules 300 deployed may be based on the opposing force required to overcome the anticipated hydrostatic head pressure in the control line (e.g., 145 of FIG.1) from the surface to valve 600 at its anticipated setting depth.

[0038] Pressure compensated downhole actuation mechanism 400 includes a gas charge chamber 425 and a booster piston 450 that provides additional upward force when pressure in a pressure compensation chamber 415 falls below a gas charge pressure within gas charge chamber 425. Advantageously, pressure compensated downholeactuation mechanism 400 provides additional upward force when and to the extent based on declining formation pressures. Pressure compensated downhole actuation mechanism 400 may be removably disposed below modular power spring module 300a or the lowest modular power spring module 300 in the stack when there is a plurality of modular power spring modules 300 deployed. Pressure compensated downhole actuation mechanism 400 may include an actuator housing 410 having a pressure compensation chamber 415 including a pressure communication port 420 that permits an interior pressure of pressure compensation chamber 415 to substantially equalize with an exterior pressure, a gas charge chamber 425 disposed below the pressure compensation chamber 415, and a partition 430 separating pressure compensation chamber 415 from gas charge chamber 425. Partition 430 may include a booster piston port hole 435, a sealing surface 440 formed within the booster piston port hole 435, and a radial seal 445 disposed within sealing surface 440. Radial seal 445 facilitates axial translation of booster piston 450 but is advantageously isolated from corrosive wellbore fluids. In certain embodiments, gas charge chamber 425 may be pressurized with inert gas. In other embodiments, gas charge chamber 425 may be pressurized with inert nitrogen, helium, or argon. In still other embodiments, gas charge chamber 425 may not be pressurized and is at atmospheric pressure or in a vacuum state. Pressure compensated downhole actuation mechanism 400 includes booster piston 450 comprising a catch end 455 disposed within gas charge chamber 425 and a piston shaft 460 at least partially extending through booster piston port hole 435. Piston shaft 460 may include a contact surface 465 on an upper distal end. Actuator housing 410 may include a threaded connection 470 on a top distal end for connecting to one or more modular power spring modules (e.g., 300b in the configured depicted in this figure). Actuator housing 410 may include a lower protection fluid port 475 for circulating protective fluids through pressure compensation chamber 415 as part of the protective fluid chamber 240. Actuator hosing 410 may include a gas injection port 480 for injecting gas into gas charge chamber 425.

[0039] For purposes of illustration, FIG. 2A depicts what is referred to as the gas- pressure-unassisted-mode of operation of valve 600. As previously discussed, pressure communication port 420 permits the interior pressure of pressure compensation chamber 415 to substantially equalize with the exterior pressure external to actuator housing 410. When the interior pressure of pressure compensation chamber 415 exceeds the gas charge pressure in gas charge chamber 425, the interior pressure bearson contact surface 465 of booster piston 450, causing booster piston to axially translate downward, such that contract surface 465 does not make contact with contact surface 355b of power spring mandrel 330b disposed above it, even when power spring mandrel 330b axially translates downward. In essence, booster piston 450 is parked and provides no upward force, despite the presence of the gas charge.

[0040] In this mode of operation, hydraulic communication port 230 fluidly communicates hydraulic actuation pressure from the surface via a control line (e.g., 145 of FIG. 1) to hydraulic chamber 220. The hydraulic actuation pressure in hydraulic chamber 220 bears down on a top side of shoulder 270, providing a downward force on flow tube 260. A bottom distal end of closure piston 290 of flow tube 260 provides downward force on shaft portion 340a of power spring mandrel 330a disposed below it, compressing power spring 350 and causing lower mandrel shaft portion 345a of power spring mandrel 330a to axially translate downward. In embodiments where more than one modular power spring module 300 is deployed, their respective power springs 350 are compressed causing their respective lower mandrel shaft portions 345 to axially translate downward. While not depicted, the downward axial translation of flow tube 260, causes or enables the closure device (not shown) to open, permitting the flow of production fluids toward the surface.

[0041] Continuing, FIG. 2B shows a cross-sectional view of subsurface safety valve 600 equipped with pressure compensated downhole actuation mechanism 400 operating in a gas-pressure-unassisted-mode with the valve in the closed position in accordance with one or more embodiments of the present invention. When sufficient hydraulic actuation pressure from the surface is not communicated to hydraulic chamber 220 of closure mechanism 200, whether intentionally or as part of an emergency or other contingency or failure mode, the energy stored in power spring 350a (and 350b in the example depicted and potentially other power springs 350 depending on the number of modular power spring modules 300 deployed) relaxes and provides upward force on a lower distal end of closure piston 290 that causes flow tube 260 to axially translate upward, which causes or enables the closure device (not shown) to close, thereby preventing production fluids from flowing toward the surface.

[0042] It is important to recognize that in the gas-pressure-unassisted-mode of operation, where the formation pressure exceeds the gas charge pressure, booster piston 450 is essentially parked and does not provide any upward force or assistance. In this situation, the hydraulic actuation pressure from the surface is sufficient to compress the one ormore power springs 350 of the one or more modular power spring modules 300 to cause or enable the closure device (not shown) of valve 600 to open and the energy stored in the one or more power springs 350 of the one or more modular power spring modules 300, with the assistance of the formation pressure, is sufficient to cause or enable the closure device (not shown) to fully close valve 600 against the hydrostatic head pressure in the control line (e.g., 145 of FIG. 1). Over time, as the well is produced, the formation pressure starts to decline and at a certain point, conventional valves (e.g., 135 of FIG. 2) fail because their actuation mechanism (e.g., 150 of FIG. 2) with the assistance of the now declining formation pressure, cannot overcome the hydrostatic head pressure in the control line (e.g., 145 of FIG. 2) and cause or enable the closure device (not shown) to automatically close the conventional valve (e.g., 135 of FIG. 2). However, it is in this very situation where conventional actuators and valves fail, that pressure compensated downhole actuation mechanism 400 becomes operative, providing a critically needed boost to ensure the ongoing operation of valve 600 in spite of declining formation pressure, as described in more detail herein.

[0043] FIG. 3A shows a cross-sectional view of subsurface safety valve 600 equipped with pressure compensated downhole actuation mechanism 400 operating in a gas- pressure-assisted-mode with the valve 600 in the open position in accordance with one or more embodiments of the present invention. As the formation pressure starts to decline, there comes a point where the combination of energy stored in the one or more power springs 350 of the one or more modular power spring modules 300 plus the formation pressure, cannot provide sufficient upward force to overcome the hydrostatic head pressure in the control line (e.g., 145 of FIG. 1) that bears on hydraulic chamber 220 of closure mechanism 200. However, as the interior pressure of pressure compensation chamber 415 starts declining, corresponding to a decline in formation pressure, such that the interior pressure of pressure compensation chamber 415 is less than the gas charge pressure present in chamber 425, booster piston 450 starts to axially translate upward. In the figure, a near equilibrium state is shown where any further decline in formation pressure will cause booster piston 450 to provide additional upward force to contact surface 355b of power spring mandrel 330b disposed above it.

[0044] Continuing, FIG. 3B shows a cross-sectional view of subsurface safety valve 600 equipped with pressure compensated downhole actuation mechanism 400 in a gas- pressure-assisted-mode with the valve 600 in the closed position in accordance with one or more embodiments of the present invention. As the formation pressure continues todecline, at the point that the gas charge pressure exceeds the interior pressure of pressure compensation chamber 415, contact surface 465 of booster piston 450 is in contact with contact surface 355b of power spring mandrel 330b and provides a boost of upward force to power spring 350b. In this gas-pressure-assisted-mode of operation, the combination of the upward force provided by the energy stored in the one or more power spring modules 300, the upward force provided by the formation pressure from bottom hole, and the boost of upward force provided by pressure compensated downhole actuation mechanism 400 is sufficient to overcome the hydrostatic head pressure in the control line (e.g., 145 of FIG.1) and close or enable the closure of valve 600.

[0045] Advantageously, pressure compensated downhole actuation mechanism 400 works under initial downhole conditions and continues to work after downhole conditions have changed, typically do to declining formation pressures. In so doing, pressure compensated downhole actuation mechanism 400 substantially widens the functional window of valve 600 and enhances long term reliability. For the first time, subsurface safety valves (e.g., 600) may be deployed with confidence that they will perform under initial and changing conditions over the long term.

[0046] FIG. 4A shows a detailed view of closure mechanism 200 of subsurface safety valve 600 in accordance with one or more embodiments of the present. As previously discussed, closure mechanism 200 controllably opens valve 600 to enable production fluids to flow toward the surface and is designed to automatically close valve 600 during emergencies and other contingencies. As more clearly shown in this detailed view, flow tube 260 and closure piston 290 are at least partially disposed within closure housing 210, where closure piston 290 is at least partially disposed within flow tube 260, at least partially disposed within hydraulic chamber 220, and at least partially extending through closure port hole 295. Hydraulic communication port 230 is in fluid communication with a control line (e.g., 145 of FIG. 1) that communicates hydraulic actuation pressure from the surface to hydraulic chamber 220. While the volume of hydraulic chamber 220 changes with movement of closure piston 290, it is sealed by radial seal 280 of shoulder 270 and radial seal 285 of flow tube 260, such that hydraulic chamber 220 is in fluid communication with hydraulic communication port 230 and the control line (e.g., 145 of FIG. 1) that communicates hydraulic actuation pressure from the surface. As such, the hydrostatic head pressure in the control line (e.g., 145 of FIG. 1) effectively bears on shoulders 270, the application of which causes closure piston290 to axially translate downward providing downward force for a mandrel (e.g., 330a) removably attached below it, and in the absence of sufficient hydraulic actuation pressure, whether intentionally or otherwise, the upward force provided by the one or more power spring mandrels (not shown) and the formation pressure in the gas- pressure-unassisted mode of operation or the upward force provided by the one or more power spring mandrels (not shown), the formation pressure, and the booster piston (now shown) in the gas-pressure-assisted mode of operation causes closure piston 290 to axially translate upward which causes flow tube 260 to axially translate upward, and thereby close or enable the closure of the closure device (not shown) disposed above flow tube 260. While closure mechanism 200 is described for the purposes of illustration, one of ordinary skill in the art, having the benefit of this disclosure, will appreciate that the type and kind of closure mechanism used may vary based on an application or design in accordance with one or more embodiments of the present invention.

[0047] Continuing, FIG. 4B shows a detailed view of modular spring module 300a of a subsurface safety valve 600 in accordance with one or more embodiments of the present. As previously discussed, modular power spring module 300a includes a power spring 350a that compresses during hydraulic actuation to store energy and facilitate opening the closure device (not shown) of closure mechanism 200, thereby enabling production fluids to flow toward the surface and, in the absence of sufficient hydraulic actuation, releases the stored energy of spring 350a to provide an upward force that facilitates, at least in part, closing or enabling the closure of the closure device (not shown) of closure mechanism 200. Modular power spring module 300a may include an upper threaded connection end 310a for removable attachment to a device disposed above it, in this example, closure mechanism 200. Likewise, modular power spring module 300a may include a lower threaded connection end 320a for removable attached to a device disposed below it, in this example an additional modular power spring module 300b but it could be pressure compensated downhole actuation mechanism 400 in single modular power spring module 300 embodiments. Protection fluid chamber 240 of modular power spring module 300a is in fluid communication with protection fluid chamber 240 of closure mechanism 200 disposed above it, and, in embodiments that include one or more additional power spring modules 300 disposed below it, with their respective protection fluid chambers 240. While modular power spring module 300a is described for the purposes of illustration, one of ordinary skill inthe art, having the benefit of this disclosure, will appreciate that the type and kind of spring mechanism may vary based on an application or design in accordance with one or more embodiments of the present invention.

[0048] Continuing, FIG. 4C shows a detailed view of pressure compensated downhole actuation mechanism 400 of subsurface safety valve 600 in accordance with one or more embodiments of the present. In the gas-pressure-assisted mode of operation depicted, the interior pressure of protection compensation chamber 415 is becoming less than the gas charge pressure in gas charge chamber 425, causing booster piston 450 to axially translate upward. While shown in axial translation, as the interior pressure declines, there comes a point where the pressure difference ensures that booster piston 450 is maximally axially translated upward, such that contact surface 465 provides upward force to contact surface 355b of the mandrel disposed above it, in this case, power spring mandrel 330a.

[0049] FIG. 5 shows a functional setting depth window of a subsurface safety valve (e.g., 600) equipped with a pressure compensated downhole actuation mechanism (e.g., 400) in accordance with one or more embodiments of the present invention. At the outset, formation pressure 710 varies over the life of well 105. When well 105 is new and recently completed, formation pressure 710 is typically at its maximum value. However, as the well produces and ages, formation pressure 710 continuously declines. Subsea Christmas tree 103 sits on sea floor 110 and is fluidly connected to a production flow line (not shown). A casing string 115 is disposed below subsea Christmas tree 103 as well as production tubing string 130, with the space between them defining annulus 140. One or more liners or packers 125 are disposed above the hydrocarbon bearing formation and directs production fluids from well 105 into the bottom distal end of production tubing string 130. A hydraulic pump 720 disposed on the surface fluidly communicates hydraulic actuation pressure to valve 600, which, for the purpose of this illustration is shown as a wireline-retrievable safety valve but could be a tubing- retrievable safety valve (not shown) or other downhole flow control device (not shown). As discussed above with reference to conventional SSSVs, the point was established that these conventional valves have a very narrow functional window of operation that narrows and ultimately closes as formation pressure declines. The top of this functional setting depth window is commonly 300 to 1000 feet below subsea Christmas tree 103, but consideration must be given to where corrosive or adhesive elements may be deposited in production tubing 130 that can foul subsurface safety valve 600 and renderit inoperative. As such, these considerations may require that valve 600 be set deeper. The major forces that effect the operation of pressure compensated downhole actuation mechanism 400 (as well as other downhole flow control devices) include: 1) the hydrostatic head pressure at depth in the control line 145 that fluidly communicates hydraulic actuation pressure from the surface; 2) the energy stored in the one or more power springs; and 3) the formation pressure, which, as discussed above, may vary significantly from when newly completed to having been produced and aged. While the functional window 730 may be substantially narrowed or entirely closed as formation pressures decline with the use of conventional SSSVs, the present invention provides a substantially wider functional window 730 that resists restriction and closure by providing additional boost via pressure compensated downhole actuation mechanism 400 as the formation pressure declines.

[0050] FIG. 6 shows a wireline-retrievable subsurface safety valve equipped with a pressure compensated downhole actuation mechanism in accordance with one or more embodiments of the present invention. As previously discussed, conventional tubing- retrievable SSSVs 810 were being set deeper and deeper in the well due to their use in deepwater and ultra-deepwater wells. However, conventional tubing-retrievable SSSVs 810 had difficulty operating due to the hydrostatic head pressure in the control line 145. Because conventional tubing-retrievable SSSVs 810 are run in as part of the production tubing 130 during initial completion of well 105, the failure of a conventional tubing- retrievable SSSV 810 is extremely difficult and expensive. While conventional tubing- retrievable SSSVs 810 are required in deepwater and ultra-deepwater applications, unfortunately, when they fail, the well must be re-completed in a time-consuming and expensive process that requires floating a drilling rig back onto the well site, pulling the production tubing, replacing the failed tubing-retrievable subsurface safety valve, and re-deploying the production tubing with the replaced tubing-retrievable subsurface safety valve. In addition to the substantial costs associated with the above-noted re- completion activities, profits lost for the duration of these operations are substantial. As noted in the real-world example, the frequency of failure of conventional deep-set tubing-retrievable SSSVs 810 and the substantial time and cost required to re-complete a well jeopardize the safety of operations and many operators are shying away from such deepwater and ultra-deepwater plays, where a significant amount of oil and gas reserves are known to exist.

[0051] In a failed conventional tubing-retrievable subsurface safety valve, often set at a depth less than 3,500 feet, one avenue for proceeding is to deploy a wireline-retrievable SSSV within the failed tubing-retrievable SSSV 810. A wireline-retrievable SSSV 600 equipped with a pressure compensation downhole actuation mechanism (e.g., 400) may be run into the well 105 on a lock that locates wireline-retrievable SSSV 600 within a desired location of failed conventional tubing-retrievable SSSV 810. Wireline- retrievable SSSV 600 equipped with a pressure compensation downhole actuation mechanism (e.g., 400) typically includes packing elements (not shown) that isolate the hydraulic chamber (not shown) that was previously used to control the now failed conventional tubing-retrievable SSSV 810. The process of opening up the original hydraulic actuation pathway of the failed conventional tubing-retrievable SSSV 800 for use with wireline-retrievable SSSV 600 equipped with a pressure compensated downhole actuation mechanism (e.g., 400) is referred to as communication. Once communication has been achieved, a surface-controlled pump (not shown) may pump hydraulic actuation fluid through the hydraulic chamber (not independently illustrated) of the failed conventional tubing-retrievable SSSV 810 to the hydraulic chamber (e.g., 220) of wireline-retrievable SSSV 600 equipped with a pressure compensated downhole actuation mechanism (e.g., 400) to enable hydraulic actuation of wireline-retrievable SSSV 600 equipped with a pressure compensated downhole actuation mechanism (e.g., 400) in a similar manner to that of the failed conventional tubing-retrievable SSSV 810.

[0052] While pressure compensated downhole actuation mechanism 400 and modular power spring module 300 have been illustrated in use as part of various types of subsurface safety valves including both tubing-retrievable SSSVs and wireline- retrievable SSSVs, one of ordinary skill in the art, having the benefit of this disclosure, will appreciate they may be used individually or in combination with other downhole tools including, but not limited to, other inflow control devices and other outflow control devices.

[0053] Advantageously, in one or more embodiments of the present invention, a pressure compensated downhole actuation mechanism widens and sustains the functional window of operation of an SSSV, enabling such valves to placed deeper, perform more reliably regardless of setting depth, and continue to operate even as the well ages and formation pressures decline.

[0054] While the present invention has been described with respect to the above-noted embodiments, those skilled in the art, having the benefit of this disclosure, willrecognize that other embodiments may be devised that are within the scope of the invention as disclosed herein. Accordingly, the scope of the invention should only be limited by the appended claims.

Claims

What is claimed is:

1. A pressure compensated downhole actuation mechanism comprising: an actuator housing comprising: a pressure compensation chamber including a pressure communication port that permits an interior pressure of the pressure compensation chamber to substantially equalize with an exterior pressure, a gas charge chamber disposed below the pressure compensation chamber, and a partition separating the pressure compensation chamber from the gas charge chamber, the partition including a booster piston port hole, a sealing surface formed within the booster piston port hole, and a radial seal disposed within the sealing surface, wherein the radial seal is isolated from wellbore fluids in the pressure compensation chamber; and a booster piston comprising a catch end disposed within the gas charge chamber and a piston shaft at least partially extending through the booster piston port hole, wherein the piston shaft includes a contact surface on an upper distal end, wherein the booster piston axially translates upward when the interior pressure of the pressure compensation chamber is less than a gas charge pressure in the gas charge chamber such that the contact surface of the piston shaft provides an upward boost to a contact surface of a power spring mandrel at least partially disposed in the pressure communication chamber above the booster piston.

2. The pressure compensated downhole actuation mechanism of claim 1, wherein the booster piston axially translates downward when the interior pressure of the pressure compensation chamber exceeds the gas charge pressure in the gas charge chamber such that the contactsurface of the piston shaft does not make contact with the contact surface of the power spring mandrel at least partially disposed in the pressure communication chamber above the booster piston, even when the power spring mandrel axially translates downward.

3. The pressure compensated downhole actuation mechanism of claim 1, wherein the actuator housing further comprises a threaded connection on a top distal end for connecting to one or more modular power spring modules.

4. The pressure compensated downhole actuation mechanism of claim 1, wherein the actuator housing further comprises a lower protection fluid port for circulating protective fluids through the pressure compensation chamber as part of the protective fluid chamber.

5. The pressure compensated downhole actuation mechanism of claim 1, wherein the actuator housing further comprises a gas injection port for injecting gas into the gas charge chamber.

6. The pressure compensated downhole actuation mechanism of claim 1, wherein the gas charge chamber is pressurized with inert gas.

7. The pressure compensated downhole actuation mechanism of claim 1, wherein the gas charge chamber is pressurized with inert nitrogen.

8. The pressure compensated downhole actuation mechanism of claim 1, wherein the gas charge chamber is not pressurized and is at atmospheric pressure or a vacuum state.

9. A modular power spring module comprising: a power spring housing comprising:an upper threaded connection end comprising an upper power spring mandrel port hole, a protection fluid chamber, and a lower threaded connection end comprising a lower power spring mandrel port hole; a power spring mandrel comprising a stop collar disposed within the protection fluid chamber, an upper mandrel shaft portion above the stop collar that at least partially extends through the upper power spring mandrel port hole, and a lower mandrel shaft portion below the stop collar that at least partially extends through the lower power spring mandrel port hole; and a power spring disposed around the lower mandrel shaft portion below the stop collar within the protection fluid chamber.

10. The modular power spring module of claim 9, wherein the upper threaded connection end removably attaches to an additional power spring module disposed above the power spring module.

11. The modular power spring module of claim 9, wherein the upper threaded connection end removably attaches to a closure mechanism disposed above the power spring module.

12. The modular power spring module of claim 9, wherein the lower threaded connection end removably attaches to an additional power spring module disposed below the power spring module.

13. The modular power spring module of claim 9, wherein the lower threaded connection end removably attaches to a pressure compensated downhole actuation mechanism disposed below the power spring module.

14. A subsurface safety valve comprising: a closure mechanism having a closure device; at least one modular power spring module disposed below the closure mechanism; and a pressure compensated downhole actuation mechanism disposed below the at least one modular power spring module, wherein application of hydraulic actuation pressure compresses a power spring of the at least one modular power spring module causing the closure device to open enabling fluids to flow through the valve toward the surface and the absence of sufficient hydraulic actuation pressure causes the closure device to close under normal formation or tubing pressure, wherein the pressure compensated downhole actuation mechanism provides an upward boost to the power spring of the at least one modular power spring module when the formation or tubing pressure is less than a gas charge pressure in a gas charge chamber of the actuation mechanism.

15. The subsurface safety valve of claim 14, wherein the closure device comprises a flapper, a ball, or poppet.

16. The subsurface safety valve of claim 14, wherein the modular power spring module comprises: a power spring housing comprising:an upper threaded connection end comprising an upper power spring mandrel port hole, a protection fluid chamber, and a lower threaded connection end comprising a lower power spring mandrel port hole; a power spring mandrel comprising a stop collar disposed within the protection fluid chamber, an upper mandrel shaft portion above the stop collar that at least partially extends through the upper power spring mandrel port hole, and a lower mandrel shaft portion below the stop collar that at least partially extends through the lower power spring mandrel port hole; and a power spring disposed around the lower mandrel shaft portion below the stop collar within the protection fluid chamber.

17. The subsurface safety valve of claim 14, wherein the least one modular power spring module comprises a plurality of modular power spring modules arranged in series, wherein the number of modular power spring modules deployed is based in part on the opposing force required to overcome an anticipated hydrostatic head pressure in a control line from a surface to the valve at its anticipated setting depth.

18. The subsurface safety valve of claim 14, wherein the pressure compensated downhole actuation mechanism comprises: an actuator housing comprising: a pressure compensation chamber including a pressure communication port that permits an interior pressure of the pressure compensation chamber to substantially equalize with an exterior pressure, a gas charge chamber disposed below the pressure compensation chamber; anda partition separating the pressure compensation chamber from the gas charge chamber, the partition including a booster piston port hole, a sealing surface formed within the booster piston port hole, and a radial seal disposed within the sealing surface, wherein the radial seal is isolated from wellbore fluids in the pressure compensation chamber, and a booster piston comprising a catch end disposed within the gas charge chamber and a piston shaft at least partially extending through the booster piston port hole, wherein the piston shaft has a contact surface on an upper distal end, and wherein the booster piston axially translates upward when the pressure in the pressure compensation chamber is less than a gas charge pressure in the gas charge chamber such that the contact surface of the piston shaft provides an upward boost to a contact surface of a power spring mandrel at least partially disposed in the pressure communication chamber above the booster piston.

19. The subsurface safety valve of claim 18, wherein the booster piston axially translates downward when the interior pressure of the pressure compensation chamber exceeds the pressure in the gas charge chamber such that the contact surface of the piston shaft does not make contact with the contact surface of the power spring mandrel at least partially disposed in the pressure communication chamber above the booster piston, even when the power spring mandrel axially translates downward.

20. The subsurface safety valve of claim 18, wherein the actuator housing further comprises a lower protection fluid port for circulating protective fluids through the pressure compensation chamber as part of the protective fluid chamber.

21. The subsurface safety valve of claim 18, wherein the actuator housing further comprises a gas injection port for injecting gas into the gas charge chamber.

22. The subsurface safety valve of claim 18, wherein the gas charge chamber is pressurized with inert gas.

23. The subsurface safety valve of claim 18, wherein the gas charge chamber is pressurized with inert nitrogen.

24. The subsurface safety valve of claim 18, wherein the gas charge chamber is not pressurized and is at atmospheric pressure or a vacuum state.

25. The subsurface safety valve of claim 14, wherein the closure mechanism further comprises a upper protection fluid port for circulating protective fluids.

26. The subsurface safety valve of claim 14, wherein a lower threaded connection end of the closure mechanism is removably attached to an upper threaded connection end of the at least one modular power spring module.

27. The subsurface safety valve of claim 14, wherein a lower threaded connection end of the at least one modular power spring module is removably attached to an upper threaded connection end of the pressure compensated downhole actuation mechanism.

28. A pressure compensated downhole actuation mechanism comprising: an actuator housing comprising: a pressure compensation chamber having a pressure communication port configured to allow pressure equalization between the pressure compensation chamber and an exterior environment, a gas charge chamber disposed below the pressure compensation chamber, and a partition separating the pressure compensation chamber from the gas charge chamber, the partition comprising, a booster piston port, a sealing surface formed within the booster piston port, and a radial seal disposed in the sealing surface, wherein the radial seal is isolated from wellbore fluids; and a booster piston comprising a catch end disposed in the gas charge chamber and a piston shaft extending at least partially through the booster piston port, the piston shaft having a contact surface at an upper distal end, characterized in that the booster piston is configured to translate axially upward in response to a differential pressure condition in which the pressure within the pressure compensation chamber is less than a gas charge pressure in the gas charge chamber, thereby causing the contact surface of the piston shaft to apply an upward force to a contact surface of a power spring mandrel that is at least partially disposed in the pressure compensation chamber above the booster piston.

29. The pressure-compensated downhole actuation mechanism of claim 28, characterized in that the booster piston is further configured to translate axially downward when the pressure within the pressure compensation chamber exceeds the gas charge pressure in the gas charge chamber, such that the contact surface of the piston shaft remains out of contact with thecontact surface of the power spring mandrel, even when the power spring mandrel translates axially downward.

30. The pressure-compensated downhole actuation mechanism of claim 28 or 29, characterized in that the actuator housing comprises a threaded connection at a top distal end for attachment to one or more modular power spring modules.

31. The pressure-compensated downhole actuation mechanism of any one of claims 28 to 30, characterized in that the actuator housing comprises a lower protection fluid port configured to circulate protective fluids through the pressure compensation chamber as part of a protective fluid chamber.

32. The pressure-compensated downhole actuation mechanism of any one of claims 28 to 31, characterized in that the actuator housing comprises a gas injection port configured to inject gas into the gas charge chamber.

33. The pressure-compensated downhole actuation mechanism of any one of claims 28 to 32, characterized in that the gas charge chamber is pressurized with an inert gas.

34. The pressure-compensated downhole actuation mechanism of claim 33, characterized in that the inert gas comprises nitrogen.

35. The pressure-compensated downhole actuation mechanism of any one of claims 28 to 32, characterized in that the gas charge chamber is not pressurized and is at atmospheric pressure or in a vacuum state.

6. A method of actuating a downhole tool using a pressure-compensated actuation mechanism, the method comprising: providing an actuator housing having a pressure compensation chamber and a gas charge chamber separated by a partition, the pressure compensation chamber being in fluid communication with an exterior environment via a pressure communication port to substantially equalize internal and external pressures; positioning a booster piston within the gas charge chamber, the booster piston including a piston shaft extending through a booster piston port in the partition and having a contact surface at an upper distal end; isolating a radial seal disposed within the booster piston port from wellbore fluids; maintaining a gas charge pressure within the gas charge chamber; and translating the booster piston axially upward in response to the pressure within the pressure compensation chamber decreasing below the gas charge pressure, such that the contact surface of the piston shaft engages and applies an upward force to a power spring mandrel at least partially disposed within the pressure compensation chamber.

Images