Pressure management unit of the annulus of an oil well and control method for pressure regulation

Abstract

A pressure management unit (1) for the annulus of a well comprises a control unit (80), connected to a sensor (94, 95, 96) and to valves (57, 66) to compare the pressure against predetermined thresholds. If the pressure is too high, the control unit (80) commands a pressure discharge according to a predefined depressurisation function. If the pressure is too low, the control unit (80) commands a pressurisation according to a predefined pressurisation function. A control method for regulating the pressure of an annulus comprises: monitoring the pressure (P) in the annulus via a sensor (94, 95, 96), and commanding the opening of a regulating valve to depressurise the annulus according to a first predefined discharge function or commanding the opening of another regulating valve to pressurise the annulus according to a second predefined pressurisation function.

Description

"PRESSURE MANAGEMENT UNIT OF THE ANNULUS OF AN OIL WELL ANDCONTROL METHOD FOR PRESSURE REGULATION" DESCRIPTIONFIELD OF THE INVENTION

[0001] The present invention concerns a pressure management unit of the annulus of an oil well and is particularly suitable for wells in which a bottom ESP pump is installed . PRIOR ART

[0002] As is known, the tubing-casing-annulus ( TCA) is the void space between the production tubing and the smallest casing string in an oil and gas well . The TCA takes its name from the corresponding geometric concept of an annulus , which is the region between two concentric circles . This annular region is not merely a passive space , but a critical functional component in the architecture of a well . In a completed well , there can indeed be many distinct annuli . A typical well will generally have an "A" annulus , which is the void space located precisely between the production tubing and the smallest casing string . The "A" annulus is of fundamental operational importance , as it can perform a series of crucial tasks , including, for example , gas li ft and well kill .

[0003] In addition to the primary annulus , a typical wellwill also have a " R" annulus and frequently aannulus , located between the various concentric casing strings that make up the well structure . The management of sustained pressure in all these annuli is a constant and primary concern in the management of well integrity throughout their entire li fe cycle . To ensure the safety and longevity of the infrastructure , pressure must be regularly monitored, with an increase in the monitoring frequency especially necessary for older wells , which are more subj ect to wear and potential failure . It is a fundamental principle of reservoir engineering that all types of wells , without exception, must be operated within the designed operating range .

[0004] The issue of pressure management becomes particularly relevant in speci fic operational contexts . The increase of TCA pressure is indeed signi ficantly accelerated in ESP (Electrical Submersible Pump ) wells . These are wells that are produced with the aid of submersible pumps equipped with an electric motor, instrumentation capable of drastically altering the thermodynamic conditions of the well . The acceleration of the pressure increase is due to their intrinsic capacity to instantaneously produce large volumes of hot reservoir fluids , rapidly bringing them to the surface and causing signi ficant thermal expansion of the fluids in theannulus . Consequently, the discharge rate of the "A‘ annulus pressure becomes a critical factor to ensure the longevity of an ESP system .

[0005] Inadequate management of this pressure can have catastrophic consequences . Improper discharge o f the tubing-casing-annulus ( TCA) pressure can cause an explosive decompression (ED) of the various components of the ESP cable . This phenomenon can lead to a premature and sudden failure of the electrical system, compromising the entire operability of the well . The explosive decompression (ED) of the ESP cable is a well-known failure mechanism that occurs when there is a rapid los s of pressure in a gaseous medium, causing the structural failure of the cable materials .

[0006] The presence of high pressure in the annular space of a well , i f not controlled, can cause multiple undesired consequences . Such pressure can be caused by various factors , including the aforementioned thermal expansion of the trapped fluid, the failure of a mechanical barrier ( such as a packer ) , or the unintentional action of an operator . The thermal expansion of the completion fluid trapped in the tubing- casing-annulus ( TCA) , located between the upper ESP completion packer and the tubing attachment , presents by itsel f several serious risks for the integrity of thewell. These risks include, among others, tubing collapse, wellhead rupture, packer failure, casing failure, ESP cable failure, and electrical packer penetrator failure.

[0007] To understand and prevent such failures, the collection of data from multiple sources, such as failure analyses from dismantling and post-mortem inspections of ESP systems (known as Dismantle Inspection and Failure Analysis - DIFA) , data from ESP downhole sensors, and laboratory test results, represents a critical step for the accurate identification of the causes of problems generated by uncontrolled annular pressures.

[0008] Despite the criticality of this problem, current technical solutions present significant limitations. To date, automatic systems for TCA pressure control and management are, in most cases, limited to valve and sensor systems capable of transmitting real-time data to operators and sending alarms. These alarms serve to indicate parameter variations that require attention for possible corrective actions, however, often remain manual or semi-automatic. In some cases, technology has advanced to automate the opening of discharge valves installed on the hydraulic circuit of the annulus, allowing the discharge of excess pressure.

[0009] However, these solutions only address part of the problem. To date, no known technology allows for thecomplete automation of annulus pressure control . In particular, there is no automatic activation of the fluid pumping system to actively pressurise the TCA in the event of pressures below the minimum threshold required by the operator . Moreover, there is no possibility to discharge excess pressure safely and in-line , in a controlled manner, and not merely by opening a discharge valve to the atmosphere .

[0010] The purpose of the present invention is to overcome the above-mentioned drawbacks of traditional annulus pressure monitoring systems . It aims to fill this technological gap and, furthermore , to extend the possibility of thoroughly studying the phenomenon of explosive decompression (ED) of the components of the ESP cable . This study would allow the definition of operational usage limits , improve the production performance of the well and the service li fe of the ESP pump, as well as define a predictive approach to pump maintenance interventions . The obj ect is to extend the service li fe of the pump by addressing one of the most critical factors , namely the integrity of the power cable system .

[0011] SUMMARY OF THE INVENTION

[0012] The stated obj ectives are achieved by a pressure management unit for the annulus of an oi l well and by acontrol method for regulating the pressure of an annulus in accordance with the accompanying independent claims. The dependent claims specify further advantageous aspects. In particular, the pressure management unit and the method allow overcoming the limitations of known systems, which are limited to monitoring or uncontrolled pressure discharge, whereas the invention provides a completely automated solution for the active and bidirectional management of the annulus pressure.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Fig. 1 illustrates an axonometric view of the first section (20) and the second section (40) of the pressure management unit (1) for an annulus of a well, in accordance with an embodiment of the present invention;

[0014] Fig. la illustrates an exemplary image of a failure of the ESP pump power cable due to explosive decompression probably caused by a rapid decompression of the TCA;

[0015] Fig. 2 illustrates an axonometric view of a part of the first section (20) and the second section (40) of the pressure management unit (1) and of a central control unit (80) , in accordance with an embodiment of the present invention;

[0016] Fig. 3 illustrates an axonometric view of a third section (50) and of an overpressure protection section(90) of the pressure management unit (1) for an annulus of a well, in accordance with an embodiment of the present invention;

[0017] Fig. 4 illustrates an axonometric view of the third section (50) and of a pressure discharge section (70) of the pressure management unit (1) for an annulus of a well, in accordance with an embodiment of the present invention;

[0018] Fig. 5 illustrates a general P&ID (Piping and Instrumentation Diagram) of the pressure management unit (1) for an annulus of a well, in accordance with an embodiment of the present invention;

[0019] Fig. 6 illustrates a P&ID diagram of the pressure management unit (1) configured for water-only feeding and pressurisation, in accordance with an embodiment;

[0020] Fig. 7 illustrates a P&ID diagram of the pressure management unit (1) configured for nitrogen-only feeding and pressurisation, in accordance with an embodiment;

[0021] Fig. 8 illustrates a P&ID diagram of the pressure management unit (1) configured for hybrid feeding and pressurisation using both water and nitrogen, in accordance with an embodiment;

[0022] Fig. 9 illustrates a PFD (Process Flow Diagram) of the pressure management unit (1) in a hybrid water and nitrogen configuration, in accordance with an embodiment;

[0023] Fig . 10 illustrates a flowchart of the control method for the initial liquid fluid filling procedures , for example water, in accordance with an embodiment ;

[0024] Fig . 11 illustrates a flowchart of the control method for the subsequent pressurisation procedure (both with water and nitrogen) , in accordance with an embodiment ;

[0025] Figs . 12 , 12a, 12b il lustrate a flowchart of the control method for the pressure regulation procedure , in accordance with an embodiment ;

[0026] Fig . 12c illustrates a flowchart of the control method for mass balance management , in accordance with an embodiment .DETAILED DESCRIPTION

[0027] One aspect of the present invention relates to a pressure management unit 1 for managing the pressure of an annulus of an oil well . A pressure management unit can be understood as an integrated mechatronic system, designed to monitor, control , and actively modi fy the pressure of a fluid within a defined volume . An annulus , in the context of an oil well , can be understood as the annular space existing between the production tubing and the casing string or between di f ferent concentric casing strings . An oil well can be understood as a borehole drilled into the ground for the extraction ofhydrocarbons . Thi s configuration provides a dedicated and automated system to speci fically address pressure problems in the annulus , which are critical for well integrity, especially in the presence of ESP pumps .

[0028] The pressure management unit 1 comprises one or more supply lines 27 , 42 for a pressurisation fluid . A supply line can be understood as a conduit or hydraulic / pneumatic circuit designed to transport a fluid under pressure . A pressurisation fluid can be understood as a liquid ( for example , water ) or a gas ( for example , nitrogen) used to actively increase the pressure in the target volume . This configuration provides the physical means to perform the active pressurisation of the annulus .

[0029] It is provided that said pressure management unit 1 comprises a discharge line 64 . A discharge line can be understood as a conduit designed to transport fluid from the annulus to a release point or a process line . This configuration provides the physical means to perform the active and controlled depressurisation of the annulus .

[0030] It is provided that said pressure management unit 1 comprises a pressure sensor 94 , 95 , 96 configured to measure a pressure in said annulus and to generate a pressure signal . A pressure sensor can be understood as a transducer that converts the applied pressure force intoan electrical signal . This configuration provides essential real-time feedback to the control unit , allowing the system to know the current state of the annulus .

[0031] The pressure management unit 1 comprises a first regulating valve 57 arranged on said supply line 27 , 42 and a second regulating valve 66 , 66 ' arranged on said discharge line 64 . A regulating valve can be understood as a device capable of modulating the opening of a conduit , thereby varying the flow rate of the fluid passing through it , as opposed to a simple on / of f valve . This configuration provides the physical actuators that allow the control unit to finely modulate the fluid flow into and out of the annulus .

[0032] It is provided that said pressure management unit 1 comprises a control unit 80 connected to said pressure sensor 94 , 95 , 96 and to said first regulating valve 57 and second regulating valve 66 , 66 ' . A control unit 80 , such as a Programmable Logic Controller ( PLC ) , can be understood as an industrial computer that executes a program logic to automate a process . This configuration provides the central intelligence of the system, capable of receiving inputs ( from the pressure sensor ) and performing actions (by commanding the regulating valves ) .

[0033] Control unit 80 is configured to receive thepressure signal and compare it with a first maximum pressure threshold value and a second minimum pressure threshold value . This configuration defines the safe operating range ( the "deadband" ) within which the annulus pressure is considered acceptable .

[0034] Furthermore , it is provided that i f said pressure signal exceeds said first maximum pressure threshold value , the control unit 80 is configured to send a command to said second regulating valve 66 , 66 ' to reduce the pressure in said annulus according to a first predefined depressurisation function . A predefined depressurisation function ( for example , a ramp defined in bar / min) can be understood as a controlled discharge profile over time . This technical advantage is crucial : instead of a sudden discharge , the pressure management unit 1 discharges the pressure gradually, preventing rapid pressure di f ferentials that cause explosive decompression (ED) and damage to ESP cables .

[0035] Furthermore , it is provided that i f said pressure signal falls below said second minimum pressure threshold value , the control unit 80 is configured to send a command to said f irst regulating valve 57 to increase the pressure in said annulus according to a second predefined pressurisation function . Similarly, a predefined pressurisation function prevents an excessively rapidpressure increase . This bi-directional , automatic control based on defined ramps keeps the annulus always within the safe operating window, overcoming known systems that are passive or only manage discharge .

[0036] Another aspect of the invention relates to a control method for regulating the pressure of an annulus of an oil well . The method comprises monitoring ( P ) the pressure in said annulus by means of at least one pressure sensor 94 , 95 , 96 . This configuration provides the input data for the control cycle .

[0037] It is provided that , i f said pressure P exceeds a first maximum pressure threshold maxDP, the method commands the opening of a second regulating valve 66 , 66 ' to depressurise the annulus according to a first predefined discharge function (bar / min) , for example a first predefined ramp, until reaching a first minimum pressure threshold minDP . This configuration def ines the intervention logic for overpressure , ensuring controlled discharge and not a sudden venting .

[0038] It is provided that, i f said pressure P falls below a second minimum pressure threshold minPP, the method commands the opening of a first regulating valve 57 to pressurise the annulus according to a second predefined charging function (bar / min) , for example a second predefined ramp, until reaching a second maximum pressurethreshold maxPP . This configuration defines the intervention logic for underpressure , ensuring controlled pressurisation . The method thus implements the automatic and bi-directional control logic of the pressure management unit 1 .

[0039] A further aspect of the invention relates to a control method for the initial filling of an annulus of an oil well , implemented by a control unit 80 . The method comprises veri fying pressure of a protection system 90 , and proceeding with subsequent steps only i f said pressure is within a safety range ( e . g . > 0 barg) . This configuration ensures a safety check before starting any operation, ensuring that the system i s intact .

[0040] It is provided that the method comprises setting a target filling volume for a liquid fluid . This configuration defines the obj ective of the filling procedure not in terms of pressure , but in terms of volume .

[0041] It is provided that the method commands the opening of a liquid supply line to introduce said liquid fluid into the annulus . This is the active filling step .

[0042] It is provided that the method monitors an inlet flowmeter and commands the closure of said liquid supply line upon reaching said target filling volume . This configuration implements a closed-loop control based onvolume , ensuring that the annulus is filled with the correct amount of fluid before starting pressurisation .

[0043] In accordance with an embodiment , the pressure management unit 1 is configured such that the one or more supply lines 27 , 42 comprise a gas supply line 27 for a gaseous fluid and a liquid supply line 42 . Control unit 80 is configured to manage the pressurisation of the annulus by sending an opening or flow-closing command selectively to said gas supply line 27 or to said liquid supply line 42 or to a hybrid combination of said gas supply line 27 and said liquid supply line 42 . This configuration of fers high operational flexibility ( hybrid mode ) , allowing the operator to choose the most suitable pressurisation fluid ( for example , water for filling, gas for fine pressurisation) or to use them in combination .

[0044] In accordance with an embodiment , the pressure management unit 1 further comprises at least a first flowmeter, for example a first gas flowmeter 33 and / or a first liquid flowmeter 48 arranged on said one or more supply lines 27 , 42 , configured to measure an amount of fluid introduced into the annulus ; and at least a second flowmeter, for example a second gas flowmeter 68 and / or a second liquid flowmeter 69 arranged on said discharge line 64 , configured to measure an amount of fluid discharged from the annulus . The control unit 80 isfurther configured to calculate a mass balance based on said amount of fluid introduced and said amount of fluid discharged and to determine a signal indicative of a possible well leakage based on the calculated mass balance . This configuration provides a signi ficant diagnostic technical advantage : by comparing the inlet and outlet volumes , the system can detect anomalies ( a discrepancy in the mass balance ) indicating a loss in well integrity, generating an alarm .

[0045] In accordance with an embodiment , in the pressure management unit 1 , the discharge line 64 is part of a pressure discharge section 70 suitable for being connected to a closed-loop process line 78 of the well . The control unit 80 is further configured to command the opening of the second regulating valve 66 , 66 ' or of an actuated valve 73 only when the pressure in the discharge line 64 is higher than the pressure in said closed-loop process line 78 . This conf iguration of fers two advantages : first , the closed-loop discharge eliminates atmospheric emissions , improving environmental and personnel safety; second, the di f ferential pressure control prevents undesirable backflow from the process line into the management unit .

[0046] In accordance with an embodiment , the pressure management unit 1 comprises a first skid (A) installablein a safe area and a second skid (B ) installable in an ATEX area, that is , an area where there is a risk of formation of an explosive atmosphere caused by flammable gases , vapours , mists , or dusts in mixture with air . The first skid (A) comprises control unit 80 and at least one pump 41 or a gas source , and the second skid (B ) comprises at least said first 57 and second 66, 66 ' regulating valves in a third control section 50 . This modular ( skid) configuration optimises safety and costs , allowing the control and actuation components ( skid B ) to be installed near the wellhead (hazardous ATEX area ) , while keeping the main control unit and the supply sources ( skid A) in a safe area .

[0047] In accordance with an embodiment , pressure management unit 1 comprises an overpressure protection section 90 arranged between the third control section 50 and the annulus . Said protection section 90 is conf igured to hydraulically isolate the pressure management unit 1 from the annulus in case of exceeding a safety pressure threshold, preferably via valves 91 , 93 commanded by a 2- out-of-3 logic from the pressure sensor 94 , 95 , 96 . This configuration, known as a HIPPS system (High- Integrity Pressure Protection System) , provides a fundamental level of safety, protecting the unit (which has a lower pressure rating) from pos sible abnormal overpressurescoming from the well (which has a higher pressure rating) . The 2-out-of-3 logic ( two-out-of-three sensors must agree ) ensures high reliability ( SIL ) .

[0048] In accordance with an embodiment , the pressure management unit 1 is configured according to the following main components of the various sections : the first section 20 ( or gas supply section) with three nitrogen packs ; the second section 40 ( or liquid supply section) with a pump 41 ; the third control section 50 with its automatic line 55 (with first valve 57 ) and manual line 60 ; and the pressure discharge section 70 with its components . This architecture defines a speci fic implementation of the invention .

[0049] In particular, the gas supply line 27 is in a gas supply section 20 for nitrogen pres surisation comprising three supply lines 26 with three nitrogen packs upstream . The liquid supply line 42 is in a liquid supply section 40 for water pressurisation, which comprises a pump 41 suitable for pressurising the liquid supply line 42 . The pressure management unit 1 also comprises a third control section 50 for pressure control connected to the gas supply section 20 and to the liquid supply section 40 . Said third control section 50 comprises an automatic line 55 with a first automatic pressure regulating valve 57 driven by a pressure transmitter 58 and with a manualbypass line 60 . The discharge line 64 is part of a pressure discharge section 70 comprising two pressure transmitters 71 , 72 installed upstream and downstream of an actuated valve 73 . The control unit 80 is a programmable logic controller configured to regulate the pressure of the annulus by managing pressure variations through the generation of control signals to regulate the opening percentage of said automatic pressure regulating valve 57 and said second regulating valve 66 , 66 ' .

[0050] In accordance with an embodiment , the gas supply section 20 comprises three independent supply lines 26 that merge into a single flow line of said gas supply line 27 , on which are sequentially installed a pressure reducer 28 ( to lower the high pressure of the packs ) , with adj ustable pressure between 80 bar and 90 bar, a safety valve PSV 29 , a pressure transmitter 30 connected to the control unit 80 , preferably a programmable logic controller, a s ingle-line actuated valve 31 , and a single-line control valve 32 .

[0051] In accordance with an embodiment , control unit 80 i s configured to choose to pressurise the management unit 1 either through the first section 20 or through the second section 40 , by acting on the single-line actuated valve 31 and the second actuated valve 44 , thereby enabling hybrid selection between gas or water .

[0052] In accordance with an embodiment , the liquid supply line 42 is protected in the event of overpressure by a water line safety valve PSV 46 . This configuration provides a safety protection for the liquid supply section .

[0053] In accordance with an embodiment , in the pressure management unit 1 , the third control section 50 is connected with the pressure discharge section 70 . The second regulating valve 66 , 66 ' is suitable for modulating the discharge , and upstream and downstream thereof are positioned two manual shut-of f valves 65 , 65 ' , 67 , 67 ' . This configuration detai ls the depressurisation line 64 , allowing manual isolation of the regulating valve 66 , 66 ' for maintenance .

[0054] In accordance with an embodiment , the control unit 80 monitors the pressure of the nitrogen packs and, i f the operating pressure reaches values between 110 bar and 250 bar, it sends an opening signal to a first actuated valve 23 and pres surises the single flow line of said gas supply line 27 during the first start-up, wherein three ball valves 25 are commanded into the open position and discharge valves 22 are commanded to be kept closed .

[0055] In accordance with an embodiment , when a nitrogen pack among the one or more nitrogen packs is empty, the control unit 80 sends an operational alarm signal , sendsa closure signal to the corresponding first actuated valve 23 of a corresponding line , and simultaneously an opening signal to one of the two first actuated valves 23 of the other two supply lines . This configuration describes the automatic failover logic of the nitrogen packs : when a pack is empty, control unit 80 automatically closes it , opens a backup pack, and sends an alarm for replacement , ensuring operational continuity .

[0056] In accordance with an embodiment , the third control section 50 comprises three valve assemblies of the High Integrity Pressure Protection System type , which ensure the safety of the pressure management unit 1 in the event of overpressure in the annulus of the oil well .

[0057] In accordance with an embodiment , the pressure management unit 1 comprises three pressure transmitters 94 , 95 , 96 , operating in 2o3 logic, with three valve groups 91 , 92 , 93 , which ensure the safety of the pressure management unit 1 in the event of overpressure from the annulus .

[0058] In accordance with an embodiment , the control method of the present invention comprises a subsequent pressurisation step B ) , comprising the fol lowing steps : Bl ) veri fying that the filling step up to the target filling volume is completed;B2) selecting a pressurisation fluid between a liquid fluid and a gaseous fluid;B3) commanding the opening of a supply line corresponding to liquid fluid or gaseous fluid (40 or 20) according to the selection in step B2) to introduce into the annulus said pressurisation fluid selected in step B2) , according to a predefined pressurisation function (bar / min) , until reaching an operating pressure threshold or second maximum pressure threshold (maxPP) .

[0059] This configuration describes the transition from the filling step (Step A) to the pressurisation step (Step B) , verifying the completion of the filling (Bl) , selecting the fluid (B2) , and pressurising according to a predefined function (B3) up to an operating threshold (maxPP) .

[0060] In accordance with an embodiment, in the control method, the subsequent pressurisation step B) is hybrid and comprises, in step B2) , selecting exclusively the gaseous fluid to carry out the pressurisation step. This configuration specifies a hybrid operational mode: filling with liquid (incompressible) and pressurisation with gas (compressible) .

[0061] In accordance with an embodiment, the control method comprises a monitoring procedure comprising:- on an electronic control unit 80, calculating a massbalance by comparing volumes and / or flow rates measured by at least one inlet flowmeter and at least one outlet flowmeter ;- optionally, monitoring the density of the outlet fluid;- generating an alarm signal i f said mass balance or said density di f fers from a predefined value or is outside a predefined range of values , indicating a potential leak .

[0062] This configuration thus details the logic for mass balance calculation ( comparing inlet / outlet flow rates / volumes ) and optional density monitoring, to generate a leak alarm .

[0063] It is clear that the subj ect matter of the present invention includes a pressure management unit 1 in which the control unit 80 is configured to perform the steps of the control method according to any embodiment described herein .

[0064] With more speci fic reference now to the accompanying figures , the present invention is divided into several interconnected sub-sections , mechanically via rigid or flexible tubing of suitable rating and electrically via signal cables . As illustrated in the diagrams of Figures 5 , 6 , 7 and 8 , the main sections of the pressure management unit 1 are :First Section 20 - Nitrogen feed system or nitrogen supply / pressurisation system .Second Section 40 - Water feed system or water supply / pressurisation system .Third Control Section 50 - Pressure control skid - pressure regulation and control system .Fourth Section 90 - Overpressure protection system - subsection of the third control section 50 .Pressure Discharge Section 70 - Depressurisation system or closed-loop depressurisation system .Section 80 - control unit ( Programmable Logic Controller, PLC ) and management software .

[0065] As previously described, explosive decompression ( Fig . la ) exposes the copper conductors of the ESP (Electric Submersible Pump ) power cable to the fluids of the annulus , causing an electrical short circuit .

[0066] The present invention provides a solution by acting on the management of the annulus pressure . The pressure management unit 1 allows regulating the annulus pressure , setting pressure values within ranges established by the well operator ( typically between 5 and 60 bar ) , and, by means of predefined depressurisation and pressurisation ramps , pre-calculated and loaded into the control unit 80 ( PLC ) , it enables the study of the physical parameters that cause the phenomena of explosive decompres sion .

[0067] The system power supply for pressurisation is of a hybrid type , with nitrogen ( or air ) or water . In thecontrol unit 80, it is possible to select the operational mode, that is, whether to activate the first section 20 or the second section 40 of the pressure management unit 1.

[0068] Figures 1 and 2 show axonometric views of the first section 20 and the second section 40, installed on a first skid (A) for safe area, together with the control unit 80.

[0069] Figures 3 and 4 show axonometric views of the third control section 50 (with its sub-section 90) and of the pressure discharge section 70, installed on a second skid (B) for ATEX area.

[0070] With reference to the P&ID diagrams of Figures 5, 7 and 8, the first section 20 (Nitrogen feed system) is described in detail. The nitrogen supply is preferably provided by three nitrogen packs (Pack 1 N2, Pack 2 N2, Pack 3 N2) , external to the unit 1. Each nitrogen pack has, downstream, an independent supply line 26. Each line 26 comprises a pressure transmitter 21, a ball valve for discharge 22, a first actuated valve 23, a calibrated orifice 24, and a ball valve 25. The three supply lines 26 are then connected to each other into the gas supply line 27 and to a pressure reducer 28 (adjustable between 80 and 90 bar) . Control unit 80 monitors the pressure of the packs via the pressure transmitter 21. If thepressure is sufficient (e.g. between 110 and 250 bar) , the first actuated valve 23 is opened. When a pack is empty, the control unit 80 closes the corresponding valve 23, opens the valve 23 of a backup pack, and sends an alarm (as described in claim 12) . Downstream of the pressure reducer 28, the gas supply line 27 will have a lower rating and will be monitored by the pressure transmitter 30 and protected by the safety valve PSV 29. The first section 20 is isolated by a single-line control valve 32 and a single-line actuated valve 31 (as described in claim 8) .

[0071] With reference to the P&ID diagrams of Figures 5, 6 and 8, the second section 40 (Water feed system) is described in detail. The liquid supply (e.g. water) is entrusted to a pump 41 that pressurises the liquid supply line 42 (e.g. between 80 and 90 bar) . The switching on and off of pump 41 are regulated by the second pressure transmitter 43. The water line safety valve PSV 46 protects the line. A control valve 45 and a second actuated valve 44 allow the second section 40 to be isolated. Control unit 80 chooses which section to activate (hybrid mode) by commanding valves 31 and 44. In the diagram of Fig. 6 (water only) , section 20 is not present. In the diagram of Fig. 7 (nitrogen only) , the second section 40 is not present.

[0072] With reference to the P&ID diagrams of Figures 5, 6,7 and 8, the third control section 50 (Pressure control skid) is described. This section is connected to the supply lines 27 and 42. It comprises a ball shut-off valve 51 and discharge valves 52 and 53. A third pressure transmitter 54 monitors the pressure upstream of the regulation system. The regulation system comprises an automatic line 55 (with ball valve 56, the first pressure regulating valve 57 driven by the pressure transmitter 58, and a second ball valve 59) and a manual or bypass line 60 (with needle valve 61) . The depressurisation is managed by the discharge line 64, composed of manual shut-off valves 65, 65' , the second regulating valve 66, 66' (also driven by the pressure transmitter 58) , and a manual shut-off valve 67, 67 ’ . The control unit 80, depending on the selected supply, manages the pressurisation ramps by varying the opening percentage (%) of the first regulating valve 57.

[0073] With reference to the same figures, the fourth section 90 (overpressure protection system) is described. This section connects pressure management unit 1 to the well annulus. It consists of two actuated block valves 91 and 93 in series, an actuated bleed-off valve 92, and three pressure transmitters 94, 95, 96 (or pressure sensors) . In the event of abnormal pressures from theannulus, the transmitters 94, 95, 96 with 2-out-of-3 logic activate control unit 80, which closes valves 91 and 93 and opens valve 92 to safely vent, isolating the pressure management unit 1.

[0074] With reference to the same figures, the pressure discharge section 70 (Depressurisation system) is described. This section receives the fluid from discharge line 64. It consists of a pressure transmitter 71, an actuated valve 73, a calibrated orifice 75, a second control valve 74, a pressure transmitter 72, and a ball valve 76. Control unit 80 monitors the pressure of the discharge line (via 71) and of the closed-loop process line 78 (via 72) . When the pressure difference is sufficient (e.g. > 15 bar) , the control unit 80 opens the actuated valve 73 for controlled discharge (also ensured by the orifice 75) into process line 78.

[0075] Figure 9 illustrates a PFD (Process Flow Diagram) of the hybrid configuration (water and nitrogen) , showing the main process flow and the key components described for Fig. 8, but with a simplified level of detail, omitting fine control instrumentation and manual isolation valves, to highlight the fluid path. Note the three N2 packs (N2 pack 1, N2 pack 2, N2 pack 3) , the gas supply line 27 (N2) , and the liquid supply line 42(Water) converging towards the HIPPS system (i.e.,section 90) and then towards the annulus. Also visible is the discharge line 64 (discharge) starting from the pressure control system. On these lines, flowmeters are indicated, corresponding to flowmeters 33, 48 and 68, 69.

[0076] Figure 10 illustrates a flowchart of the control method implemented by the control unit 80 for the initial filling of an annulus of an oil well. The process begins with the filling procedure ("START FILLING PROCEDURE") . Note that, as shown in the subsequent Figure 11, related to the pressurisation step, even when filling is not complete ("FILLING PROCEDURE IS DONE? NO") , the control method starts the filling procedure.

[0077] Preferably, the method provides for checking the HIPPS system pressure (Al: "Check HIPPS pressure > 0 barg") . If the pressure is safe (YES) , a maximum volume is set (A2 : "set max water in volume") , the water feed system is started (A3: "start water feed system", "open water feed o / c valve", "open water in pressure control valve", "open HIPPS system") . The system monitors the volume achievement (A4 : "design volume reached (water in flow transmitter value) ?") . If the volume is reached (YES) , the filling procedure ends ("END") .

[0078] If the filling is complete (YES to the question "FILLING PROCEDURE IS DONE?") , the subsequent pressurisation procedure begins ("START PRESSURIZATIONPROCEDURE") , in accordance with what was described in the previous paragraphs and shown in Figure 11. The method selects the fluid (B2: "chose water or nitrogen feed system") . If nitrogen is selected ("nitrogen feed") , the nitrogen system is started (B3: "start nitrogen feed system") , the N2 pack pressure is checked ("Check N2 pack pressure") , the valves are opened ("open N2 pack 1 o / c valve", "open N2 feed o / c valve") and pressurisation occurs with a controlled ramp ("open N2 in pressure control valve with ratio bar / min") until reaching the second maximum pressure threshold (maxPP) (B3: "set maxPP is reached") . If water is selected ("water feed") , the water system is started (B3: "start pump system", "open water feed o / c valve") and pressurisation occurs ("open water in pressure control valve") until reaching the second maximum pressure threshold (maxPP) (B3: "set maxPP is reached" ) .

[0079] Figures 12, 12a and 12b illustrate a flowchart of the control method for pressure regulation. Figures 12, 12a and 12b are a single diagram split across three drawing sheets for clarity reasons, therefore, Figure 12 continues in Figure 12a, which in turn continues in Figure 12b. In particular, Figure 12a concerns the method diagram when the liquid supply line (water) is selected, while Figure 12b concerns the method diagram when the gassupply line (nitrogen) is selected.

[0080] The flowchart of Figure 12 begins with the "START REGULATION PROCEDURE," which represents the initiation of the control logic of the control method for pressure regulation in the annulus. The first step is a verification check ("starting pressurization procedure?") to ensure that the initial pressurisation step (described in Figure 11) has been completed. If this step is not completed ("NO") , the system refers to the filling procedure ("start filling procedure") , described for example in Figure 10. If instead the initial pressurisation is completed ("YES") , the control unit 80 enters its standard operating mode for the pressure control method in the annulus. At this point, the system is ready for hybrid management, and the operator or the control unit 80 selects the pressurisation fluid ("chose water or nitrogen feed system") , directing the logic towards the water control branch or towards the nitrogen control branch.

[0081] Next, the critical parameters for the control cycle are set: "setting TCA working pressure control value for water and nitrogen" (defining the operating thresholds such as minPP, maxPP, minDP, maxDP) , "setting TCA max allowable pressure HIPPS shut down value" (setting the absolute safety threshold for section 90) , and "settingdifferential pressure of o / c discharge valve" (setting the minimum pressure differential DpDV for opening the discharge valve 73 to line 78) . Finally, the system performs the step "register volume of each flow meter as starting point," which initialises the mass balance procedure by acquiring the initial values of the flowmeters as the "zero point" for future calculations.

[0082] Simultaneously with the initiation of this regulation logic, the control unit 80 starts the parallel and continuous process of "MASS BALANCE" detailed in Figure 12c, which outlines the monitoring procedure including the mass balance calculation, as previously described in this document.

[0083] This monitoring procedure is a calculation and verification process that is executed in parallel, for example at the end of an operating cycle (such as a pressurisation procedure or a defined time interval) . The diagram starts with "START PRESSURIZATION PROCEDURE" (to be understood as "at the end of the procedure") . The first logical step is "register volume of each flow meter as end point." At this stage, control unit 80 reads and stores the values of all the involved flowmeters (both inlet, i.e. the first liquid flowmeter 48 and / or the first gas flowmeter 33; and outlet, i.e. the second gas flowmeter 68 and / or the second liquid flowmeter 69) . Thevalues are acquired and stored as final verification values. The next step is "calculate total flow in - flow out." Here, the control unit 80 performs an arithmetic calculation: it subtracts the initial volumes (recorded in the step "register volume... as starting point" of Fig. 12) from the final verification volumes, obtaining a net balance. If the integrity of the well is maintained, this net value should be zero (or within a minimal tolerance) . If this calculated "mass balance" differs from a predefined value, the control unit 80 generates a "signal indicative of a possible well leakage," corresponding to the alarm "ALARM LEAKAGE." This procedure transforms the pressure management unit from a simple control system into an advanced diagnostic tool for well integrity.

[0084] Figure 12a details the logical control cycle activated when the fluid selected in Fig. 12 is "water," i.e. liquid. The process, which begins with "start water feed system, " is a continuous loop of monitoring and action that implements the control method. The core of the diagram is a multi-stage decision scheme that evaluates the pressure P of the annulus, or "TCA pressure." The control method checks whether pressure P is within the deadband (between minPP and maxDP) . If it is within, none of the subsequent control branches isactivated and the cycle restarts for new monitoring. If, however, pressure P is not within the deadband (between minPP and maxDP) , the system checks the pressurisation branch (minPP) , verifying if pressure P has dropped below the charging threshold ("min PP > TCA pressure") , if "YES," it starts the pump 41 ("start pump system") , opens the feed valve 44 ("open water feed 0 / C Valve") , opens the HIPPS system ("open HIPPS system") , and commands the modulated opening of the first regulating valve 57 ("open water in pressure control Valve with ratio bar / min") , performing the predefined charging ramp. This cycle continues until the maximum charging threshold, or second maximum pressure threshold is reached ("set maxPP is reached") .

[0085] If pressure P has not dropped below the charging threshold ("min PP > TCA pressure") , then the control method checks whether the pressure is above the maximum discharge threshold ("max DP < TCA pressure") . If "YES," it activates the depressurisation branch (maxDP) : it opens the HIPPS system ("open HIPPS system") and commands the modulated opening of the second regulating valve 66 ("open water out pressure control Valve with ratio bar / min") , performing the predefined discharge ramp. It then executes a safety check on the density ("flow density = water density?") : if "NO," an alarm istriggered ("alarm sampling required") and the system is closed ("close HIPPS") ; if "YES," it checks the pressure variation for closed-loop discharge ("dpdP > set point") and, if sufficient, opens the discharge valve 73 ("open o / c discharge Valve") . The cycle continues until the minimum discharge threshold or first minimum pressure threshold is reached ("set minDP is reached") .

[0086] If pressure P is not above the maximum discharge threshold ("max DP < TCA pressure") , then the control method verifies whether pressure P has exceeded the absolute safety threshold ("max allowable TCA pressure < TCA pressure") . If "YES," the system executes a "close HIPPS," closing valves 91 and 93 and safely terminating the procedure ("END") .

[0087] In summary, the system monitors pressure (P) . If P > maxDP (maximum depressurisation threshold or first maximum pressure threshold) , controlled discharge is started (until P = minDP, "set minDP is reached") . If P < minPP (minimum pressurisation threshold or second minimum pressure threshold) , controlled charging is started until P = maxPP ("set maxPP is reached") . In parallel, the system performs mass balance monitoring ("MASS BALANCE") .

[0088] Figure 12b illustrates the logical control cycle for nitrogen regulation ("start nitrogen feed system") . This logic is identical to that of the liquid controldescribed previously with reference to Figure 12a, but includes an additional preliminary check on the supply source . As a first step, the system checks the pressure of the N2 pack ("Check N2 pack pressure" ) . I f the pressure is insuf ficient ("NO" ) , the control unit 80 commands the replacement ("Replace N2 unloaded pack" ) , as already described previously, and repeats the check . Once the pack pressure is confirmed ("YES" ) , the system enters the same monitoring cycle as in Fig . 12a, with the exception that this time the components ( sensors and valves ) of the gas (nitrogen) circuit are used . Therefore , for the sake of brevity, the methodological steps will not be repeated, but a skilled person in the art is able to understand the scheme of Figure 12b and deduce in the same manner the methodological steps for the control method for the gas (nitrogen) line based on the analogous description of Figure 12a .

[0089] Innovatively, the pressure management unit according to the present invention overcomes the drawbacks of the known art .

[0090] In particular, the management unit is configured to continuously compare the measured pressure with predefined thresholds , and i f the pressure falls below a minimum value , the control unit commands the first valve to pressurise the annulus . Thi s pressurisation occursaccording to a pressurisation function, in order to avoid pressure shocks and, consequently, damage .

[0091] Advantageously, the automatic, bi-directional control based on predefined ramps allows the annulus pressure to be maintained within a safe operating range , preventing the rapid depressurisation cycles that cause explosive decompression (ED) of ESP pump cables .

[0092] Moreover, the unit of fers signi f icant advantages in terms of flexibility and safety . It may include hybrid supply lines , for both gas and liquid, selectable by the control unit .

[0093] Advantageously, the discharge section is preferably configured for closed-loop discharge into a wel l process line , eliminating venting into the atmosphere .

[0094] Furthermore , the unit can also be configured to perform a mass balance , using inlet flowmeters to detect potential well leakages .

[0095] Additionally, thanks to the presence of an overpressure protection section, the safety isolation of the unit is ensured in case of well anomal ies .List of References1 , pressure management unit20 , First Section / gas supply section21 , pressure transmitter (N2 packs )22 , ball valve for discharge (N2 packs ), first actuated valve (N2 packs) , calibrated orifice (N2 packs) , ball valve (N2 packs) , supply lines (independent N2) , gas supply line , pressure reducer , PSV safety valve (N2 line) , pressure transmitter (downstream of N2 reducer), single-line actuated valve (N2) , single-line control valve (N2) , first gas flowmeter (N2 line) , Second Section / liquid supply system , pump , liquid supply line , second pressure transmitter (water pump) , second actuated valve (water line) , control valve (water line) , water line PSV safety valve , first liquid flowmeter (water line) , Third Control Section , shut-off ball valve (inlet skid 50) , discharge ball valve (inlet skid 50) , discharge ball valve (inlet skid 50) , third pressure transmitter (upstream of regulation), automatic line (skid 50)56, management ball valve (line 55)57, first regulating valve / automatic pressure control valve (PCV)58, pressure transmitter (downstream of regulation system)59, second management ball valve (line 55)60, manual or bypass line61, needle valve64, discharge line / depressurisation line65, 65' , manual shut-off valve (line 64)66, 66' , second regulating valve / automatic pressure control valve (PCV) for depressurisation67, 67 ’ , manual shut-off valve (line 64)70, Pressure discharge section / Depressurisation system71, pressure transmitter (of upstream discharge section)72, pressure transmitter (of downstream discharge section)73, actuated valve (section 70)74, second control valve (section 70)75, calibrated orifice (section 70)76, ball valve (of discharge section)68, second gas flowmeter69, second liquid flowmeter78, closed-loop process line / discharge line80, PLC / control unit90, Fourth Section / overpressure protection section(HIPPS)91, actuated block valve (HIPPS)92, actuated bleed-off valve (HIPPS) 93, actuated block valve (HIPPS)94, pressure sensor / pressure transmitter (HIPPS)95, pressure sensor / pressure transmitter (HIPPS)96, pressure sensor / pressure transmitter (HIPPS)SYMBOLS A, first skid (safe area)B, second skid (ATEX area)P, pressure (in the method) maxDP, first maximum pressure threshold minDP, first minimum pressure threshold maxPP, second maximum pressure threshold minPP, second minimum pressure threshold

Claims

CLAIMS1. A pressure management unit (1) for managing a pressure of an annulus of an oil well, comprising:- one or more supply lines (27, 42) of a pressurisation fluid;- a discharge line (64) ;- a pressure sensor (94, 95, 96) configured to measure a pressure in said annulus and to generate a pressure signal ;- a first regulating valve (57) arranged on said supply line (27, 42) and a second regulating valve (66, 66' ) arranged on said discharge line (64) ;- a control unit (80) connected to said pressure sensor (94, 95, 96) and to said first regulating valve (57) and second regulating valve (66, 66' ) ; characterised in that said control unit (80) is configured to receive said pressure signal and to compare it with a first maximum pressure threshold value and a second minimum pressure threshold value, and wherein, if said pressure signal exceeds said first maximum pressure threshold value, the control unit (80) is configured to send a command to said second regulating valve (66, 66' ) to reduce the pressure in said annulus according to a first predefined depressurisation function;and wherein, if said pressure signal falls below said second minimum pressure threshold value, the control unit (80) is configured to send a command to said first regulating valve (57) to increase the pressure in said annulus according to a second predefined pressurisation function .

2. The pressure management unit (1) according to claim 1, wherein the one or more supply lines (27, 42) comprise a gas supply line (27) for a gaseous fluid and a liquid supply line (42) , and wherein said control unit (80) is configured to manage the pressurisation of the annulus by sending an opening or closure command selectively to said gas supply line (2) or to said liquid supply line (42) or to a hybrid combination of said gas supply line (27) and said liquid supply line (42) .

3. The pressure management unit (1) according to any of the preceding claims, further comprising:• at least one first flowmeter arranged on said one or more supply lines (27, 42) , configured to measure an amount of fluid introduced into the annulus;• at least one second flowmeter arranged on said discharge line (64) , configured to measure an amount of fluid discharged from the annulus; wherein said control unit (80) is further configured tocalculate a mass balance based on said amount of fluid introduced and said amount of fluid discharged and to determine a signal indicative of a possible well leakage based on the calculated mass balance.

4. The pressure management unit (1) according to any of the preceding claims, wherein said discharge line (64) is part of a pressure discharge section (70) suitable for being connected to a closed-loop process line (78) of the well, and wherein the control unit (80) is further configured to command the opening of said second regulating valve (66, 66' ) or of an actuated valve (73) only when the pressure in the discharge line (64) is higher than the pressure in said closed-loop process line (78) .

5. The pressure management unit (1) according to any of the preceding claims, comprising a first skid (A) installable in a safe area and a second skid (B) installable in an ATEX area, wherein said first skid (A) comprises said control unit (80) and at least one pump (41) or a gas source, and wherein said second skid (B) comprises at least said first regulating valve (57) and second regulating valve (66, 66' ) in a control section (50) .

6. The pressure management unit (1) according to claim 5, comprising a section of overpressure protection (90)arranged between the control section (50) and the annulus, said protection section (90) being configured to hydraulically isolate the pressure management unit (1) from the annulus in case a safety pressure threshold is exceeded, preferably via valves (91, 93) commanded in2-out-of-3 logic by the pressure sensor (94, 95, 96) .

7. The unit (1) according to claims 1, 2, 3 and 4, wherein said gas supply line (27) is in a gas supply section (20) for nitrogen pressurisation comprising three supply lines (26) with upstream three nitrogen packs, and wherein said liquid supply line (42) is in a liquid supply section (40) for water pressurisation, which comprises a pump (41) suitable for pressurising the liquid supply line (42) ; and wherein the pressure management unit (1) also comprises a third control section (50) for pressure control connected to the gas supply section (20) and to the liquid supply section (40) , said control section (50) comprising an automatic line (55) with an automatic pressure regulating valve (57) driven by a pressure transmitter (58) and with a manual bypass line (60) ; and wherein the discharge line (64) is part of a pressure discharge section (70) which comprises two pressure transmitters (71, 72) installed upstream and downstream of an actuated valve (73) ;and wherein the control unit (80) is a programmable logic controller configured to regulate the pressure of the annulus by managing pressure variations through generating control signals to regulate the opening percentage of said automatic pressure regulating valve (57) and said second regulating valve (66, 66' ) .

8. The pressure management unit (1) according to claim?, wherein said three independent supply lines (26) merge into a single flow line of said gas supply line (27) , on which are installed in sequence a pressure reducer (28) , pressure adjustable with values between 80 bar and 90 bar, a safety valve PSV (29) , a pressure transmitter (30) connected to the control unit (80) , preferably a programmable logic controller, a single-line actuated valve (31) and a single-line control valve (32) ; and wherein the control unit (80) is configured to choose to pressurise the management unit (1) either through the first section (20) or through the second section (40) , by acting on the single-line actuated valve (31) and on the second actuated valve (44) .

9. The pressure management unit (1) according to claim 8, wherein the liquid supply line (42) is protected in case of overpressure by a water-line safety valve PSV (46) .

10. The pressure management unit (1) according to claim 8 or 9, wherein the third control section (50) , downstreamboth the automatic line (55) and the manual bypass line(60) , is connected with the pressure discharge section (70) , and wherein the second regulating valve (66, 66' ) is suitable for modulating the pressure discharge, and upstream and downstream of the second regulating valve (66, 66' ) two manual shut-off valves (65, 65' , 67, 67 ’ ) are positioned.

11. The pressure management unit (1) according to any of claims 7 to 10, wherein the control unit (80) monitors the pressure of the nitrogen packs and, if the operating pressure reaches values between 110 bar and 250 bar, it outputs a signal for the opening of a first actuated valve (23) and pressurises the single flow line of said gas supply line (27) during the first start-up, and wherein three ball valves (25) are commanded into the open position and discharge valves (22) are commanded to stay closed.

12. The pressure management unit (1) according to claim 11, wherein, when a nitrogen pack of one or more nitrogen packs is empty, the control unit (80) sends an operational alarm signal, it sends a closure signal to the corresponding first actuated valve (23) of a corresponding line and simultaneously a signal for the opening of one of the twofirst actuated valves (23) of the other two supply lines.

13. The pressure management unit (1) according to any of claims 7 to 12, wherein the third control section (50) comprises three valve assemblies of the High Integrity Pressure Protection System type, with which the safety of the unit (1) is ensured in case of overpressure of the annulus of the oil well.

14. The pressure management unit (1) according to any of the previous claims , comprising three pressure transmitters (94) , (95) , (96) , working in 2o3 logic, with three valve groups, (91) , (92) , (93) , with which the safety of the unit (1) is ensured in case of overpressures from the annulus.

15. A control method for regulating the pressure of an annulus of an oil well, the method comprising: a) monitoring the pressure (P) in said annulus by means of at least one pressure sensor (94, 95, 96) ; b) if said pressure (P) exceeds a first maximum pressure threshold (maxDP) , commanding the opening of a second regulating valve (66, 66' ) to depressurise the annulus according to a first predefined discharge function (bar / min) , for example a first predefined ramp, until reaching a first minimum pressure threshold (minDP) ; c) if said pressure (P) falls below a second minimumpressure threshold (minPP) , commanding the opening of a first regulating valve (57) to pressurise the annulus according to a second predefined charging function (bar / min) , for example a second predefined ramp, until reaching a second maximum pressure threshold (maxPP) .

16. A control method for the initial filling of an annulus of an oil well, implemented by a control unit (80) , the method comprising:Al) verifying the pressure of a protection system (90) , and proceeding with subsequent steps only if said pressure is within a safety range (e.g. > Obarg) ;A2 ) setting a target filling volume for a liquid fluid;A3) commanding the opening of a liquid supply line (40) to introduce said liquid fluid into the annulus;A4 ) monitoring an inlet flowmeter and commanding the closure of said liquid supply line upon reaching said target filling volume.

17. The control method according to claim 16, comprising a subsequent pressurisation step B) , said step comprising :Bl) verifying that step A4 ) of filling to the target filling volume is completed;B2) selecting a pressurisation fluid between a liquid fluid and a gaseous fluid;B3) commanding the opening of a supply line correspondingto liquid fluid or to gaseous fluid (40 or 20) as a function of the selection in step B2) to introduce into the annulus said pressurisation fluid selected in step B2) , according to a predefined pressurisation function (bar / min) , until reaching an operational pressure threshold (maxPP) .

18. The control method according to claim 17, wherein the subsequent pressurisation step B) is hybrid and comprises, in step B2) , selecting exclusively the gaseous fluid to execute the pressurisation step.

19. The control method according to any of claims 15 to 18, comprising a monitoring procedure, said monitoring procedure comprising:- on an electronic control unit (80) , calculating a mass balance by comparing volumes and / or flowrates measured by at least one inlet flowmeter and at least one outlet flowmeter;- optionally, monitoring the density of the outlet fluid;- generating an alarm signal if said mass balance or said density differs from a predefined value or is outside a range of predefined values, indicating a potential leakage .

20. The pressure management unit (1) according to any of claims 1 to 14, wherein said control unit (80) is configured to perform steps b) and c) according to thecontrol method according to claim 15 or the steps of the control method according to any of claims 16 to 19 .

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