Deepwater Offshore Technology Paper


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Paper on the developments of ROV hydrate remediation skids, and non-ROV hydrate skids. A market comparison. Authored by Fernando C. Hernandez for Wrights Well Control Services

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Deepwater Offshore Technology Paper

  1. 1. New Developments forUltra Deepwater Hydrate Remediation Technology in the Gulf of Mexico Authored By: Fernando C. Hernandez
  2. 2. Hydrate Remediation WWCSIntroductionHydrate FormationHydrates (a freezing of condensate and other liquids, mixed with hydrocarbons, solids and gases) occurswhen a combination of temperature and pressure is reached in a subsea pipeline or other asset. TheHydrate Formation Curve is illustrated in the graph below.Hydrate DiagnosisThere are different methods to indentify hydrate has formed in a subsea asset: The emergence of a pressure differential between two transducers within the same circuit, where pressure builds higher, and or lower than a sensor which is located within the same circuit. Examples of such locations are on a PLET, Pipeline, Riser, Tree, Umbilical, BOP, etc.Note: multiple hydrates can form within a single circuit Loss of continuity within the same subsea assets will reveal that there is no longer a path from which product can flow interrupted. In some cases the hydrates are mixed with asphaltyne and paraphin within the same circuit.Disassociating HydratesThe methods below are employed to remove/remediate hydrates, and are split into six categories. Usinga singular approach is practical, but greater progress is achieved when multiple methods are utilized. 2
  3. 3. Hydrate Remediation WWCS Heat Application- This method requires an operator to circulate heated fluids to the area affected by hydrate Mechanical application- Coiled tubing can be employed to drill, or used to circulate heated fluids to affected area Condensate and Gas Separation- The separation method is highly effective, as it separates fluids and gases which decreases the chances of forming hydrates in the equipment which is being utilized to displace/remove hydrates from source Utilization of pressure- Pressuring against a hydrate can allow an operator to attempt to dislodge the hydrate, but can also cause greater solidification in the plugged area in the region where the hydrate is formed De-pressurization- By choosing this method the operator can bring the pressure below the hydration formation curve which correlates with temperature Chemical Injection- Clients can equally choose to inject thermodynamic inhibitors through tubing or a chemical injection line, directly to the point of blockage. Such inhibitors include, glycol, methanol, or low dose hydrate inhibitors, injections are also used to dose the equipment which is removing the hydrateWright’s Well Control Services (WWCS)has hybridizeda majority of these methods, and has patented theWWCS Hydrate Remediation System consisting of a pump/motor assembly in a 71’ long skid with a andmodular gas separator which sits atop the skid. The WWCS Hydrate Remediation System can robustlyinject chemicals, while pressurizing or depressurizing. Note: The heat and mechanical approachesmentioned above are not used by WWCS, but are listed to provide the readerwith an in depthunderstanding of the different hydrate remediation processes.Identifying the Exact Location of Hydrates to Begin RemediationOnce a blockage is confirmed the operator will begin to form a plan of action utilizing the methods listedin the above section. During the planning process the operator can opt to pump from a host platformand perform testing to see if continuity can be achieved in a circuit. If this surface method is not fruitfulthe hydrate will need immediate remediation via subsea intervention. For efficient and successfulintervention, the hydrate(s) must be properly located. However, as a Host Platform will only register themost immediate point of blockage or where there is a sensor for monitoring pressure. The utilization and advancements in non-intrusive technology in regards to nucleonic measurement greatly aids in locating blockage. Such instrumentation is radioactive, and highly robust. This particular instrument is attached to the ROV and is utilized to scan a pipeline. In lengthy pipelines/circuits the scans conducted by this system are segmented and done in sections. However, scans of the entire asset are most effective. All scans are logged via a topside controller. The raw data received is then interpreted by electronics equipment/hardware and software. 3
  4. 4. Hydrate Remediation WWCS ROV tools can also be deployed to measure and monitor pressures providing a secondary way of pinpointing the area which is affected.The following section will cover the different tools that are utilized to combat minor hydrates/blockages.Hydrate Skids and Hydrate Tooling- The Past, Present and FutureThis section will not only describe the current skids/tooling which are on the market that are used forhydrates, but will also give a visual and written description of their capabilities, strengths anddrawbacks. This section will focus on tooling that mounts via the ROV’s porch. ROV Porch with WWCS ToolingPumpsOperators typically utilizethe pumps currently available on the market for minor hydrates, whichare ROVmountable via the porch or a skid. Pumps are ideal for applications, such as removing a hydrate from atree cap, or removing a blockage from different lines in flying leads - CFL, HFL, SFL’s. The drawback topumps is that they do not inject or pull suction at a specific rate, but instead fluctuate with each strokecausing sudden pressure spikes. Also pumps rates are in gallons per minute (GPM), and due to thefluctuation of the stroke, the pump will have an average of 2.5 GPM during operations. Pumps canreach high pressures for chemical injections, but as pressure increases, GPM output is reduced. Whatmakes pumps robust is that they can pump gas, water, and condensate, and likewise pull a vacuum.Pumpswill not be able to pull large quantities of these materials from a pipeline nor flush through it (Ifthe pipeline is measured in miles), due to its GPM capacity.A second style of pump is commonly used to flood a pipeline with methanol to treat a hydrate. Thesepumps are also ROV mountable via the porch or through a skid. Such pumps can pump at a specific rate,however they are not designed to handle condensate, gas and water mixtures. 4
  5. 5. Hydrate Remediation WWCSAs stated previously the ability to mount on to an ROV porch, directly or via attachment (non skid),allows for quick deployment. These pumps are very limited in regards to output capacity, since the inputpressure and flow are dictated by an ROV, which is in the 20 GPM range, and function at mediumpressure (This figure will vary due to the different ROV system’s on the market). One must keep in mind,that these pumps are tied in to the main hydraulic supply of a SUB, which will affect the ROV’smaneuverability in regards to its thrusters, manipulators etc.Electronic tooling/software utilized for hydrate remediation Transducersare sensors which are used in subsea applications to monitor pressure input and allow the operator to see fluctuations of pressure, which are highly indicative of hydrate breakage and also gives great insight in how the internals of the pipeline are behaving (reference locating hydrates section). Flow Metersare used to monitor injection rates via an ROV mountable pump. Certain styles of pump will register the output. This allows the user to monitor the input of chemicals to ensure the storage bladder is not damaged while the inlet part of the pump tries to pull chemicals. Flow meters are equally important when injecting chemicals/fluids, as this gives the end user a way to monitor progress and the amount of product displaced from the pipeline. Valve Packs are submersible remotecontrol systems that are hydro-electric and are composed of software, and hardware. This allows a user to give commands while transmitting and receiving data remotely. This data can then be collected, analyzed, interpreted and gathered. The end result is a system which is self contained and controlled via a topside computer. A valve pack can easily control the input flow and pressure which comes from the ROV to independently control the mounted pumps, since tooling suites are aftermarket attachments and are not developed with the ROV. The same logic can be applied to transducers if one looks at them as aftermarket products, the data received by the transducers must be registered through the valve pack.Note: utilizing an ROV porch has its drawbacks as the space is very limited due to it being populated bycomponents for the ROV, which are attached to the porch. Equally if various ROV tools are being used,the operator will not be able to deploy all tooling at once, but will have to remove and re-attach toolingduring operations, increasing down time.ROV Attachable SkidsWhen these components referencedin the ROV Porch tooling section are consolidated and used inunison, a hydrate skid is the finished product. Skids provide the ability to control and arrange multiplepumps, flow meters, and transducers in one locale, which are monitored via a mascot. A hydrate skid isan exoskeleton frame that mounts directly below an ROV. The key to mounting is a “sandwich plate”that mates the skid to the ROV, by doing so the ROV can attack various points of interest to inspect andremove hydrates. 5
  6. 6. Hydrate Remediation WWCSPumps in ROV attachable skids offer a higher and consistent output over a stand-alonepump. However,these skids do not have the ability to immediately pull a vacuum on a pipeline, andmust be first returnedto the surface for reconfiguration.Skids also cannot be deck deck-tested, leading to downtime asanalyzing the system for faults can only be done during operations.Lastly, new technologies are constantly evolving in the ROV tooling industry. The skids discussed in thissection make up the majority of the ROV skid hydrate remediation market.ROV Tooling and IntegrationTooling, whether it is electrical or hydraulic, has to be integrated with the ROV to be fully sustainableand functional. Hydraulic-To integrate a valve on a skid hydraulically, a hydraulic circuit must be composed of a pressure and return line, which is plumbed into a valve pack. This configuration distributes the hydraulic energy to the necessary components, via valves stored in the valve pack. The ROV commonly has such valve assemblies, but if not, a skid can be populated with valve packs to function as a manifold enabling the skid to perform multiple functions. If a single pump is used, a pressure and return line will only have to be applied to that single item. Electrical- To function or communicate at depths up to 10,000’ with tooling, there is a series of conditions that must be met. First a multiplexer and a demultiplexer are set in place to turn electrical data signals within copper into light which is then ran as a fiber optic signals. It is imperative to send data this way for a variety of reasons: o The umbilical on the ROV winchhas to be long enough to reach the ROV and travel through the ROV’s tether. The tether is what allows the ROV to travel freely through an X,Y and Z axis. Note: electrical signals travelling through copper cannot go as far as one which is running fiber optically. o To communicate with electronic tooling, which in this casewould be a valve pack, a communication path must be established. Also a power source is required to energize printed circuit boards and related components which make up electronic tooling. o Lastly, connecting various electrical components has its limitations due to the electrical power that is required - again this form of energy is also borrowed from the ROV itself.Chemical InjectionsChemicals such as methanol have a dual function, the first is to be able to inject in to the affected area,and the second is the obvious treatment of hydrate removal equipment. It is not practical to inject andthen dispel methanol.The chemicals which have been injected are eventually pulled out of the affected source duringpumping when a vacuum is being applied. These chemicals will need to be stored, due to the fact thatwhen they are removed from the source the presence of hydrocarbons is highly likely, making it 6
  7. 7. Hydrate Remediation WWCSimperative to control and contain the incoming gas, condensate, or water. Chemicals upon beingremoved can be captured subsea with a secondary or bladder, or they can be brought to surface withthe utilization of coiled tubing. The incoming material can be separated, or taken in as single product.Separation is ideal as it removes gas from condensate, which takes the two volatiles mediums throughseparate circuits which greatly decreases rehydrating of the equipment used inthe removal.Chemical injections can be split into three categories, the first deals with the injection point, the secondis the location/source of the chemical (surface or subsea), and the third deals with chemical dosing. Injection Point- a proper injection port must be located and/or configured, this ensures that the hydrate will be properly targeted. Hydrate ROV panels are utilized to tie in to a PLET, FLET, pipeline, etc. Other engineered interfaces are used, which is solely dependent on affected area. Dosing- dosing is highly critical to keep the equipment which is removing the hydrate, from itself becoming hydrated. Dosing can be accomplished at multiple points but depends on configuration. It is typical to dose the parts of the equipment that see the incoming hydrate and also to dose the line that will store the product which is coming out of the affected area. Dosing has its limitations if the pipeline targeted for remediation is miles in length, which would require immense amounts of methanol injection and removal. Chemical Location- methanol can be stored in tanks on the back deck of a vessel. If this is not an option then the methanol supply will have to come from a subsea source. There are two different ways of supplyingfluid,one option would be to do so through a host platform that can supply methanol via a UTA, or a subsea asset which can output methanol. The second option would be to have a crane deploy a subsea bladder/reservoir to store methanol. While this solves the source problem in regards to methanol, new issues arise as now there is a limited fluid supply. Once the supply is depleted the bladder must be recovered and brought to surface to be refilled and returned back to the ocean floor to provide methanol – often multiple times.The Wright’s Well ControlServices Approach to HydrateRemediationThe Wright’s Hydrate Remediation System is different from the alternatives outlined above in that itdoes not depend on limited hydraulic energy from the ROV. This skid is a completely independentsystem, powered from the surface. The next sections will highlight and explain the differentcomponents of this system which has achieved results far exceeding current hydrate remediationsolutions.Hydrate SkidPrior to the hydrate skid being over-boarded via a crane on a MSV (Multi Service Vessel), mud mats areput in place on the ocean floor, these mats keep the skid above the mud line by providing extra stabilityand support. The skid is then deployed from a MSV and upon reaching the splash zone is lowered to 7
  8. 8. Hydrate Remediation WWCSoperational depth.The skid itself is composed of a motor and pump assembly, which is powered from surface from a MSVby filtered seawater via coiled tubing. The skidhas a redundant motor and pump, allowing operations tocontinue should there be any difficulties with the initial setup used. Hydrate SkidGas SeparatorThe gas separator is deployed in a modular fashion as an independent system that is designed tointerface on the top of the hydrate skid, and separates gas from the fluids via coiled tubing. The first coiltubing line sends gas freeflowing to a surface gas separator and/orflare boom. The second coil tubingreturn line receivesthe processed hydrocarbons and otherfluids to the surface for additionalprocessing and containment.Additional features of the gas separator include a methanol injection panel to prevent the formation ofadditional hydrates. Several injection points throughout the hydrate skid and separator are able toreceive methanol. Also a ball check in the stack prevents fluid from filling the gas line and the gasseparator has a built in sand trap. 8
  9. 9. Hydrate Remediation WWCS Gas SeparatorHydrate Remediation System ChokeAt surface the choke developed by Wright’s methodically designates the separated condensate and gasto the appropriate circuitry. At this point the gas and condensate returns are thoroughly measured, theamount of each particular medium is closely analyzed as it is a direct manifestation of what is internallytrapped inside the affected source.The choke also acts as a safety barrier that allows the personnel on the back deck, to shut in and keepgas and condensate returns contained. Equally, the choke can isolate both items at liberty, if the gaspressure needs to be analyzed then the choke is closed and the pressure is monitored at surface, whileallowing condensate returns to flow freely. The choke can also be adjusted to restrict the amount of gaswhich will be returning on surface, while allowing the condensate to remain unrestricted, by doing thisthe operator can further affect the hydrate remediation process.Emergency Quick DisconnectsIn the event of a MSV drive off and/or loss of power; the release of hydrocarbons; or salt water floodingthe pipeline asset and hydrates reforming, subsea accumulators engage Emergency Quick Disconnects(EQD) from the vessel. There are three methods for send the signal to initiate deployment of the EQDs: Acoustically- Allows a signal to be sent via ROVNAV on the ROV or from the bridge. The signal travels in a sound wave from the vessel surface which then activates a solenoid that releases the stored hydraulic energy 9
  10. 10. Hydrate Remediation WWCS ROV Manipulators - The gas separator is equipped with an ROV panel that includes an ROV friendly valve that can be moved to allow the stored energy to actuate the contingency circuit Wire Ropes -Provides a final line of defense to engage the emergency circuit via a steel wire rope that is tightly connected to the coiled tubing on the separator. In the event of a drive off, the coiled tubing will begin to experience tension. The wire ropedwill also absorb the tension and will offset to move an ROV friendly valveactuating the accumulators, and separating the vessel from the subsea equipment.Once actuated the EQDs initiate the follow sequence: Ongoing hydrate operations on the pipeline/subsea asset are shut off by isolating barriers All four hot stabs eject at tie in points, thus overcoming differential pressure caused by a vacuum effect in the pipeline vs. hydrostatic pressure Subsea IntegrationPressure MonitoringMultiple gages on the skid and separator have been strategically placed to measure and interpret thebehavior of the internals of a pipeline, this is very advantageous as it allows constant monitoring and foradjustments to be made instantaneously by WWCS service personnel. Both the skid and separator have 10
  11. 11. Hydrate Remediation WWCSa total of three mounted analog gages. The separator has an extra dedicated receptacle which is usedto digitally monitor pressure via three transducers. These devices are all designed to monitorcombination of pressures, which is necessary due to the skid’s ability to pull a vacuum within a pipeline.When this is accomplished the pipeline or the internal hydrate sources will have a pressure differentialdue to the hydrostatic pressure. When this differential occurs, the internals of a pipeline will ultimatelyfall below sub ambient, which requires monitoring in absolute pressure. The WWCS hydrateremediation system can operate under these parameters.Analog and Digital Advantage- By using both medias, the operator is equipped to keep a diligent view ofall segments of the equipment, likewise what a transducer provides is the utilization of data loggingequipment. Such data is relayed back to the ROV control room from where the data is not onlylogged/monitored but also gives a real time and historical log that is charted. The charting of data iswhat ultimately indicates what kind of process is being made for removing the hydrate. Pressure can bemonitored hydrostatically, while changes in differential pressure are analyzed and then compared to thepipeline, which is the primary focus with ambient pressures to determine effectiveness of operations.The Hybrid Valve Pack/ROV ToolingThe hybrid valve pack is a ROV tooling suite designed, built and tested by WWCS.The pack includes ROVdeployable bladders with a secondary pumping system to charge the accumulators subsea and toactuate the different functions during operations. From the software, to the hardware and mechanicalcomponents, this system is unique as it does not require a skid and can be mounted and prepared forservice immediately upon arriving on deck. The valve pack can monitor and record the pressuresreferenced in the prior section, as well as monitor the GPM being injected. Hybrid Valve Pack 11