Flow Assurance with Grampian Consulting
Flow Assurance is a risk management approach for sustained hydrocarbon production from the reservoir to the processing facility. Interruption to production is often immensely expensive and can be caused by several issues such as solids deposition, flow transients, corrosion or erosion. Our goal is to identify potential roadblocks to economic recovery early in the project life cycle such that operational strategies can designed to optimize recovery and enhance production over the life of field.
Our approach to Flow Assurance related problems includes :
Our approach to Flow Assurance related problems includes :
- Interfacing with a variety of disciplines, from reservoir engineering to operations;
- Review of fluid sampling reports, laboratory analyses and solids prediction;
- Multiphase thermal hydraulic modeling: Simulations are performed for fluid behavior (PVT), normal operation (steady state) and transient conditions (start up, turndown, shutdown, cooldown, depressurization, pigging etc.); and
- Implementation of Flow Assurance strategies: Design philosophies, operating procedures and strategies are formulated to operate the system economically and manage all the flow assurance risks.
Flow Assurance Interfaces
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Reservoir
The interface with the reservoir team is vital in understanding the physical properties of the production fluid and the intended depletion plan. The reservoir conditions and fluid properties along with the production profile are fundamental to determine the thermohydraulic behavior of the production system and develop operating philosophies. It is therefore critical to interface with the reservoir group immediately from the project onset. Completions Flow Assurance has a direct impact on subsurface completions from both a hydraulic and thermal perspective. The production tubing sizing will influence the capacity of the system and impact the wellhead flowing tempertures, while the SCSSV is normally set at a depth below which hydrates cannot be formed. The chemical injection philsophy will dictate the number of required downhole injection points. Enhanced recovery mechanisms such as gas lift or downhole ESPs must be identified during early project phases to be included in the completions design. |
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SURF
The interface between Flow Assurance and the SURF (Subsea, Umbilical, Riser and Flowlines) group is important during Field Development Planning to support indentification and selection of the architecture options. Once the preliminary thermohydraulic studies are complete, and early operating strategies have been identified, design pressures and temperatures along with product densities will be used by the SURF group to generate their design requirements to support development of cost and schedule estimates. The subsea equipment will be designed to support the operating philosophy, which includes components that facilitate solids management, chemical injection and isolation.
Process
Flow Assurance interfaces with Process early in the project phase to provide arrival conditions for the various development options. Export conditions and compositions are also required to size the export lines. In subsequent project phases, data surrounding peak liquid and gas rates, surge volumes, compression/pumping requirements, artifical lift, chemical injection and the pressures and temperatures associated with transient operations will all be identified with Flow Assurance support. This information will be used to modify the operating philosophies of an existing host, or to create operating strategies for a new development.
Operations
Interacting with the Operations group is of utmost importance for Flow Assurance to develop operating philosophies, guidelines, and procedures that address the every day operation of the system, especially for transient scenarios. Flow Assurance provides recommendations regarding how the system should be operated to prevent flowline blockages, minimize surge volumes and maximize production. Procedures covering cooldown times, chemical injection, restart, shutdown, depressurization and pigging are included in the operating guidelines.
Chemical Vendors
Flow Assurance interfaces with chemical vendors to determine the optimal chemicals and dosages required to mitigate formation and deposition of solids such as hydrates, wax, asphaltenes, corrosion and scale. A monitoring program should also be developed to ensure that the chemical type and volumes remain effective as the field matures and formation water rates increase.
The interface between Flow Assurance and the SURF (Subsea, Umbilical, Riser and Flowlines) group is important during Field Development Planning to support indentification and selection of the architecture options. Once the preliminary thermohydraulic studies are complete, and early operating strategies have been identified, design pressures and temperatures along with product densities will be used by the SURF group to generate their design requirements to support development of cost and schedule estimates. The subsea equipment will be designed to support the operating philosophy, which includes components that facilitate solids management, chemical injection and isolation.
Process
Flow Assurance interfaces with Process early in the project phase to provide arrival conditions for the various development options. Export conditions and compositions are also required to size the export lines. In subsequent project phases, data surrounding peak liquid and gas rates, surge volumes, compression/pumping requirements, artifical lift, chemical injection and the pressures and temperatures associated with transient operations will all be identified with Flow Assurance support. This information will be used to modify the operating philosophies of an existing host, or to create operating strategies for a new development.
Operations
Interacting with the Operations group is of utmost importance for Flow Assurance to develop operating philosophies, guidelines, and procedures that address the every day operation of the system, especially for transient scenarios. Flow Assurance provides recommendations regarding how the system should be operated to prevent flowline blockages, minimize surge volumes and maximize production. Procedures covering cooldown times, chemical injection, restart, shutdown, depressurization and pigging are included in the operating guidelines.
Chemical Vendors
Flow Assurance interfaces with chemical vendors to determine the optimal chemicals and dosages required to mitigate formation and deposition of solids such as hydrates, wax, asphaltenes, corrosion and scale. A monitoring program should also be developed to ensure that the chemical type and volumes remain effective as the field matures and formation water rates increase.
Fluid Sampling, Laboratory Analysis and Solids Prediction
The solids anticipated during production for any field are dependent on the chemistry of the produced fluids. During the exploration and appraisal phase of a project, samples are retrieved using downhole tools. The sample collection tool is used in the open hole after the well is drilled and prior to casing the well.
Laboratory analyses are performed on the hydrocarbon samples and the scope and type of these analyses will depend on the anticipated problems. Fluid PVT (Pressure, Volume, Temperature) analysis typically includes reservoir composition, single or multi-stage flash, flashed gas and oil compositions, GOR, gas and oil gravity, viscosity under reservoir conditions, bubble points, etc. Fluid PVT characterization is performed using software tools, which form the basis of all the Flow Assurance modeling work.
Fluid PVT analyses from the laboratory typically include information about the following:
Laboratory analyses are performed on the hydrocarbon samples and the scope and type of these analyses will depend on the anticipated problems. Fluid PVT (Pressure, Volume, Temperature) analysis typically includes reservoir composition, single or multi-stage flash, flashed gas and oil compositions, GOR, gas and oil gravity, viscosity under reservoir conditions, bubble points, etc. Fluid PVT characterization is performed using software tools, which form the basis of all the Flow Assurance modeling work.
Fluid PVT analyses from the laboratory typically include information about the following:
- Differential Liberation, Constant Composition Expansion and/or Constant Volume Depletion tests;
- Wax Appearance Temperature, viscosity and pour point;
- Asphaltene Onset Pressure, if an asphaltene issue is identified;
- Hydrate curve based on the production fluid and produced water composition; and
- Produced water composition is used to evaluate scaling potential in various production scenarios.
Multiphase Thermal Hydraulic Modeling
The basic data required to setup the production thermal hydraulic simulations are reservoir conditions, productivity index, fluid composition, the geometries associated with the tubing, jumpers, flowlines and risers as well as the host arrival pressure. Additional details inlcuding bathymetry can provide better approximations for liquid hold-up. Steady state analysis is performed to represent systems during normal operation. These cases quickly estimate the system capacities, flowing pressure, temperature and velocity profiles for different production configurations and scenarios as well as abandonement pressures. These results are typically used to narrow down the design options and allow decisions to be made surrounding line size, insulation configuration and high level operating philosophy.
Dynamic simulations are performed to determine the system behavior during transient operations such as restart, turndown, shutdown, depressurization and pigging. Key outcomes from the transient analysis include cooldown time, warm-up time, liquid surge volumes, the extent of low temperature excursions, and trends and durations associated with operations such as depressurization and pigging. Additional cases can be run to simulate wax deposition, or determine the propensity of the system to form hydrates.
Dynamic simulations are performed to determine the system behavior during transient operations such as restart, turndown, shutdown, depressurization and pigging. Key outcomes from the transient analysis include cooldown time, warm-up time, liquid surge volumes, the extent of low temperature excursions, and trends and durations associated with operations such as depressurization and pigging. Additional cases can be run to simulate wax deposition, or determine the propensity of the system to form hydrates.
System Design and Operating Philosophies
Flow assurance risks and mitigation strategies should be carefully considered for system design during early stages of the project. Some of the techniques to be considered to mitigate flow assurance risks are thermal management, chemical management and the use of mechanical tools. A determination should be made regarding the field architecutre when considering single vs. dual flowlines, and loops vs. daisy chains, as well as the requirement for pressure maintenence of the reservoir and the requirement for artificial lift. If such considerations are made early in the design phase, operators will have a much easier time managing flow assurance risks.
The operating procedures contain steps for the operators to manage flow assurance risks during all modes of operations and can contain useful figures showing flow instability envelopes, deveations from normal pressure drops and the required chemical inhibitor rates as a funtion of flow rate and shake-outs. The operating procedures also include information such as no-touch time, flowline depressurization, pigging, dead oil displacement after shut down etc.
Flow assurance remediation strategy is for situations where solid deposits/blockages do occur. The remediation strategy depends on the type of blockage, here are a few examples:
The operating procedures contain steps for the operators to manage flow assurance risks during all modes of operations and can contain useful figures showing flow instability envelopes, deveations from normal pressure drops and the required chemical inhibitor rates as a funtion of flow rate and shake-outs. The operating procedures also include information such as no-touch time, flowline depressurization, pigging, dead oil displacement after shut down etc.
Flow assurance remediation strategy is for situations where solid deposits/blockages do occur. The remediation strategy depends on the type of blockage, here are a few examples:
- The flowline can be depressurized to dissociate hydrates;
- Wax deposition could be handled by raising the temperature of the flowline if possible, this is achieved through either local external heating or hot oiling;
- Chemicals can be injected to dissolve or loosen the deposits; and
- Pigging the flowline, or by mechanical intervention and scrapping.
