Filtration of Oil and Gas Well Completion Fluids
When comparing VPL/DE with conventional FP plate systems of the same sized unit, the FP system typically only has a 50% effective flow area compared with the VPL/DE system, which has a massive 90% effective flow area available for filtration duties. This is due to the need to intimately support the filtration media within the FP system. The increased effective area in the VPL filter is due to the robust, self- supporting structure of the leaves.
When similar effective flow area systems are compared, the VPL can typically filter 25–30% more fluid before an unacceptable differential pressure builds up across the filtration system and self- cleaning is required. This makes the VPL/DE filtration system a much more viable and cost-effective technology for the filtration of completion fluids.
system. They should be small in footprint and all wetted parts should be made from 316L stainless steel. To enable easy maintenance, they should provide safe and easy access to the pressure vessel and be of a robust design to cope with the aggressive working environment.
Typical System Requirements
Each completion fluid filtration system needs to be designed to meet the needs of the actual well, its surrounding formation and the specific fluid being used. Having said this, there are some general requirements that are true of all such systems.
Completion fluids are typically specially prepared brines and are generally known as drilling fluids.
Additional benefits of VPL/DE filtration systems are:
• they have a much smaller footprint than FP systems – saving space in offshore installations;
• they have a higher efficiency than FP systems, resulting in lower NTU readings due to improved laminar flow design though the vessel;
• they are closed-loop systems with no fluid spillage; • they are quick to clean – only 10 minutes is required to reduce the differential pressure back to the norm; and
• they have semi-automatic cleaning, requiring only one operator.
These benefits combine with an integrated system design and ancillary filtration and processing equipment to provide an oil and gas producer with an efficient completion fluid filtration system.
Typical Vertical Pressure Leaf/Diatomaceous Earth and Duplex Filter Installation
A typical closed-loop completion fluid filtration system comprises all of the equipment required for brine storage, pumping and filtration. Fluid from the clean brine tank is fed into the well. After use and prior to filtration, is it sent to a dirty brine tank. Here a robust self-priming pump then transfers it to the VPL/DE filtration system, which removes the bulk of solids and contaminants. Downstream of the VPL/DE system, the fluid is passed through a duplex cartridge filter unit where final polish and cleaning of the fluid is carried out prior to returning it to the clean brine tank for reuse in the well.
Duplex Cartridge Filtration System
Downstream of the VPL/DE filtration system, the duplex cartridge filter unit carries out the final polish and cleaning of the fluid prior to the fluid being re-used in the well borehole. These duplex filter systems are designed to handle comparable flow rates and throughputs to the main VPL/DE system and work as an integral part of the complete
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Typical system requirements will include the need for overall filtration capability to remove the maximum volume of solid contaminants with a high flow/throughput. The system should offer an easy-to-operate semi-automatic cleaning system and filter cartridge replacement procedure. The safety of operators is also a major consideration so adequate safety railings and work platforms should be an integral part of the overall design.
The advantages of a closed-loop system ensure that spillages and any potential pollution of the surrounding work area and local environment are minimised.
System control required for the pre- and body coat operations, pumping and recirculation procedures, filter cartridge removal, maintenance and operation control should all be able to be carried out from one easy to manage and operate control panel. Pumps and compressors should be able to use existing services, such as being diesel-driven, powered by electricity or air-actuated.
The design of the pressure vessels needs to comply with international manufacturing standards, such as ASME VIII/DNV/TUV/PED, to ensure that the vessels are designed and constructed to the appropriate standards to handle high pressures and operational requirements. The aggressive nature of the fluids being filtered means that it is best to ensure that all wetted parts are made from 316L stainless steel, which means that equipment will have a good service life.
Small footprint designs utilising framed and skid-mounted units make transportation to the site/location and installation easier. Such designs also save on valuable space and make it simpler to integrate them into the overall scheme of the wellbore and surface fluid system.
Conclusion
Clean completion fluids and brines are required for effective completion and maximum oil and gas production. They contribute to overall productivity. Cleaning of completion fluids can be carried out with a combination of VPL filters with duplex cartridge filters used for the final polishing of the fluid.
Well designed, manufactured and installed closed-loop VPL filters perform better than any FP system of the same size. They are safe to use and environmentally friendly compared with other systems.
The operational success of VPL filters is derived from using an experienced provider of well-designed and -engineered equipment that is capable of providing technical back-up and support as well as using well trained operators. n
EXPLORATION & PRODUCTION – VOLUME 8 ISSUE 1
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