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Subsea Products Subsea Produced Water Treatment Tank
Subsea ProductsSubsea ProducedWater Treatment Tank
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Technology Qualification Program 3
Subsea Produced Water Treatment Tank System 4
Benefits and Operational Data 5
Contents
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Technology Qualification ProgramIncreasing oil and gas exploration and production, development of more challenging environments, and increasing the amount of tie-ins of additional wells all require a more effective offshore produced water management system. Finding the best treatment solution for produced water technology is increasingly important, as there is a clear need to develop a more efficient and suitable system to achieve increased water cleanliness.
Our subsea Produced Water Treatment Tank (PWTT) system is designed to smoothen out variations in the outlet water quality (from upstream separator) and deliver water quality of dispersed Oil-in-Water of 15 ppm or lower, something that’s not currently achieved in the market, with the treated water able to be directly discharged to sea (or re-injected into the reservoir). The system is designed with high residence time for settling of solid particles and flotation of oil droplets by mainly gravimetric separation and robust baffle plates to maximize the regularity of operation.
Our technology represents the next generation of subsea produced water treatment, providing a flexible, competitive, and environmental friendly solution. The PWTT is the ideal solution for:• Tie-ins of additional wells• Deep water process• Enabling long tie-backs
As part of the “Subsea Factory”, the PWTT can be integrated with our Seabox™ and Subsea Storage Unit (SSU) as an alternative to the use of floating production storage and offloading vessels. Our aim is to take the production process to the seabed, providing the optimum solution for reliable treatment of produced water as you develop new fields, extend asset life and maximize economic recovery.
A Technology Qualification Program (TQP) has been established and initiated to deliver a safe, profitable, economical and flexible product for the market, designed and built to suit field requirements.
The primary objective of the PWTT is to develop a system that achieves the required water quality of dispersed Oil-in-Water at 15 ppm or lower. The scope of the ongoing Joint Industry Project (JIP) Phase 2 and Phase 3 is to design, build, and test a large scale system in order to qualify the technology. We have completed Phase 1 and Phase 2, and we are currently starting Phase 3: Separation Performance Test. When Phase 3 is completed, the PWTT would have reached a technology readiness level (TRL) that allows operators to engage FEED studies, allowing for further adaption of the system to suit specific fields, lowering high development risks and therefore conduct a pilot verification of the system.
PWTT Technology Qualified Q4 2022The scope of work for the JIP is divided into four main phases:
• Phase 1: Feasibility study of a JIP system.• Phase 2: Establish TQP and perform engineering work on priority technology elements. • Phase 2A: Computational Fluid Dynamics (CFD) simulations with focus on flow pattern optimization and center pipe design. • Phase 2B: Mature technical solution with focus on separation performance, sand management and pressure safety system. Design of Test Unit for Phase 3.• Phase 3: Design and perform a large scale separation performance test of the produced water treatment tank. • Phase 3A: Baseline testing in realistic and specific operating conditions (pressure, temperature, residence time, oil concentrations, oil droplet sizes, inlet devices, chemicals, temperatures and gas. • Phase 3B: Extended testing by varying the different operating parameters.
PHASE 1
DEFINE TQP & FEASIBILITY
STUDIES START: Q1 2015FINISH: Q3 2017 TE
CHN
OLO
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QU
ALIF
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PHASE 2
PRIORITY TECHNOLOGY
ELEMENTS START: Q2 2018FINISH: Q4 2019
PHASE 3
SEPARATION PERFORMANCE
DEMONSTRATION START: Q1 2020FINISH: Q2 2021
PHASE 4
PWTT PILOT VERIFICATION
START: Q2 2021FINISH: Q4 2022
Technology Readiness Level March 2020.
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Produced Water Treatment Tank SystemThe PWTT system is designed with a high residence time for settling of solid particles and flotation of oil droplets by gravimetric separation to maximize the regularity of operation, and consists of 2 identical horizontal units, including: • Sand management system• Power and control system• Fluid transfer system• Frame and foundation structure
The system can be placed at any water depth and location depending on Operator needs during the development and expansion of the field.
The PWTT is gravity based, and the produced water flows in and out at a steady flow rate with high residence time, with the robust baffle plates maximizing the regularity of operation. Consequently, the technology can meet stringent water requirements, as well as provide an environmentally friendly and robust handling of produced water.
Pressure fluctuations generated by varying flow resistance in the reservoir are considered part of steady state operation and do not represent an anomaly. Therefore as a part of the protection strategy, there is a substantial gas buffer volume inside the system. This gas phase absorbs fast pressure fluctuations and maintains a near constant overpressure at 2.0 bar relative to ambient, irrespective of back pressure fluctuations due to the reservoir, as well as ensuring enough activation time for protective devices.
A comprehensive set of CFD analysis have already been conducted for the horizontal design with a view to identify the optimal flow pattern and the corresponding mechanical arrangements, and show tremendous results in line with expectations and requirements.
The system is designed with oil and gas reject lines, while the sand present in the produced water falls down to the bottom of the tank to then be exported to the sand accumulator by way of a sand management system.
The PWTT also has active pressure release and buoyancy protection mechanisms to prevent the system from pressure loads in excess of those deliberately designed for, and from buoyancy with a water level too low inside the tank.
Robust sand managementThe sand management system is divided into an upstream sand management system (e.g. sand accumulator) and an inside system within the PWTT. The sand accumulator is included to minimize solids accumulating in the PWTT. Four important features are achieved In our sand management philosophy:
1. Sand management system is connected to the main sand accumulator.2. Larger sand particles (100 micron) are separated from the liquid prior to entering the PWTT. This reduces sand management operations for the PWTT System.3. Located at the bottom of the PWTT tank with no moving parts.4. Moving sand from 3-phase separator to the accumulator is well proven technology.
Pressure and buoyancy protection safety measures incorporated in the tank.
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Product Benefits
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Parameter Unit Min. Value Max. ValueDesign life year 10 25Design depth m 100 3,000Site/Installation depth m 100 3,000Ambient seawater temperature °C 3 25Process operational temperature °C 15 100Temperature control, temperature drop inside PWTT °C 0 20Operating pressure (above ambient hydrostatic pressure) bar 1.0 3.0Design pressure (low-pressure system) bar 2.0 10.0Design pressure (high-pressure system) bar
Oil quality API API 30 API 45Step-out distance m 50 UnlimitedProcess inlet condition, dispersed oil content (OiW) ppmv 100 20,000Process outlet condition, oil content ppmv 0 30Process inlet condition, solid content ppmv TBD TBDSolids production kg/day 0 100
FLEXIBILITY
• Adjustable in size and overall capacity• Any water depth and location• Re-deployment possibilities
FIELD DEVELOPMENT BENEFITS
• Environmentally friendly and robust• Deep water fields with long tie-backs to shore• Hydrate prevention:
OPEX
• Reduced offshore manning• Reduced chemical consumption and supply logistics
HSE BENEFITS
• No liquid chemicals use or handling
PWTT SYSTEM | TOPSIDE SOLUTION
CAPEX
• Reduced investments on infrastructure and topside
PRODUCTIONBENEFITS
• Subsea water removal• Re-injection or discharged to sea of produced water
According to production pressure requirement
Operational Data
- by removing the water, you remove the hydrates- maximized flow assurance- avoids expensive insulation and heated pipelines
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National Oilwell Varco has produced this brochure for general information only, and it is not intended for design purposes. Although every effort has been made to maintain the accuracy and reliability of its contents, National Oilwell Varco in no way assumes responsibility for liability for any loss, damage or injury resulting from the use of information and data herein. All applications for the material described are at the user’s risk and are the user’s responsibility.
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