Current oil prices are forcing oil companies and even more oilfield service companies to cut their spend on filtration of fluids. Many studies have shown the importance of clean completion or wellbore clean up fluids to maximize oil or gas production.
Dirty completion or workover fluids will cause formation damage which will reduce the production of an oil or gas well.
The cost of filtration depends on the effluent requirements, influent quality and many other variables.
Roughly the cost for completion fluids / well bore clean up filtration can be split in:
Equipment (rental charges, transport, maintenance)
Consumables (cartridge, DE, chemicals)
Manpower (required operators)
In general there are two types of filtration units.
1.) Dual Vessel Cartridge Filter Unit (or known as Duplex, Dual pod, Twin pod filter ) is relative cheap and easy to operate. This unit is used for small batches and polishing filtration of large batches.
Depending on the influent and effluent. Small batches can be done in one stage down to the required fluid quality of in two stage filtration with pre-filtration (50 -10 micron) and polishing filtration (10-2 micron) in one unit.
2.) DE- Filter unit as pre-filter. This can be a filter press or (VPL) vertical pressure leaf unit.
The filter press or Vertical Pressure Leaf will filter large batches and high dirt loads done to 5 micron nominal, before it is polished with the dual cartridge filter unit (1-5 micron).
Selection of Filter Press or Vertical pressure Leaf (VPL) depends on the end users preference and the type of fluid. In general heavy brines are filtered with filter presses and light brines can be filter with VPL unit. Filter press needs to be manual cleaned and VPL is semi automatic.
The DE filter is using a diatomaceous earth (DE) as filter aid.
A filter press with DE mixing skid is approximately 4x the price of a Twin Vessel cartridge filter. Same for a VPL unit. Only the average filtration area of a VPL is 600-800 sq.ft. and filter press 1200 sq.ft.
The larger the surface area the more dirt particles can be hold in the filter before it needs to be cleaned.
The cost of consumables for per removed kg of dirt in a DE-filter is about 1/15 compare to the removed kg of dirt using pleated filter cartridge in a cartridge filter unit. DE is 1/8 of the price compare to nominal rated wound or spun bonded cartridge.
Selection the right consumable
To meet the required fluids quality, a pleated absolute cartridge is 95% the only viable solution.
1. Small batch and relative clean fluid - Cartridge filter unit with just absolute pleated cartridges
2. Small batch and relative dirt fluid - Cartridge Filter unit with two stage filtration. First wound and second stage absolute pleated.
3. Large batch with relative clean fluids and coarse filtration required - Cartridge filter unit with only nominal rated cartridges wound or spun bonded.
4. Large batch - DE-filtration followed by absolute pleated.
Note: After a DE filter unit a cartridge filter unit with absolute pleated elements is mandatory because DE particle may pass the De filter and can plug the formation during completion.
- Cartridge filter units can be operated by one operator. This operation is relative simple
- DE- filters Filter Press or Vertical Pressure Leaf need to be operated by two operators and require more training to operate safe and efficient.
Filtration in oilfield operations can be done in several ways. Have the lowest OPEX use a DE-filter minimize the spend on absolute pleated cartridges. To keep the CAPEX low, a Twin Vessel cartridge filter unit can filter the fluid to the required quality but will result in a high spend on consumables.