2K7 Biocide for Coiled Tubing Applications
In formations across North America, conditions exist that promote the growth of bacteria in coiled tubing (CT) units potentially leading to microbial influenced corrosion (MIC) (Fig. 1). This can result in costly and dangerous premature CT string failures.
The bacteria that cause MIC are not only viable at the surface, but can pose a risk to asset integrity and flow assurance by causing further damage such as souring of the formation, plugging of equipment and other types of downhole failure.
To mitigate MIC, CT service companies are turning to biocides for microbial control. But not all biocides are equally effective in this specialized application. OSP 2K7 biocide products are formulated to provide the best combination of performance and chemical compatibility in a single product.
2K7 is effective in:
- High salt and high hardness
- High suspended solids
- Anionic and cationic
- Varying viscosities
- Any water/oil ratio
2K7 will not:
- Crosslink and polymerize friction reducers
- Polymerize or destabilize lubricants and inhibitors
- Sequester iron or generate insoluble sulfides
- Alter fluid viscosities or rheology profiles
- Inhibit gel sweep hydration and viscosity
2K7 Biocode Treatment Program
The first step in determining the required 2K7 biocide CT fluid treatment plan is to measure total bacteria levels using the OSP LifeCheck ATP Test Kit, which provides results in less than 10 minutes. Based on these results, OSP can recommend a course of action including initial, maintenance and pre-transport/storage treatments that will provide long-term mitigation of CT fluid bacterial loads.
The initial treatment is implemented using 2K7 Water Soluble Paks (WSP) in the open top flowback tank, which provides adequate time for the biocide to take effect before the CT fluid is pumped downhole. Maintenance treatments are either performed in the open top tank, and/or saddle tanks on the CT unit if available. In the latter case, 2K7 Bugsticks, a solid stick format that of 2K7 are utilized. 2K7 Bugsticks are also used for treatment of the CT unit prior to transport or storage to provide long-term bacterial control.
In cases where vapor recovery units are used such that the CT fluid is not open to the atmosphere, 2K7 Solution, a liquid format of the biocide, can be added directly to the closed flow loop via an injection manifold downstream from the wellhead or to the saddle tanks on the pump truck.
Approximate 2K7 Biocide Treatment Equivalent
|2K7 Biocide||Volume of Fluid||Treatment Level|
|1 Bugstick||1 m3/6.3 bbl||100 ppm|
|5 Bugsticks||5 m3/31.5 bbl||100 ppm|
|1 WSP (1 kg/2.2 lb)||10 m3/63 bbl||100 ppm|
|4 WSPs (4 kg/ 8.8 lb)||40 m3/250 bbl||100 ppm|
|1 box WSP (25 kg/55 lb)||250 m3/1,575 bbl||100 ppm|
|1 Drum Solution (220 kg/485 lb)||220 m3/1,385 bbl||100 ppm|
|1 Tote Solution (1,115 kg/2,458 lb)||1,115 m3/7,015 bbl||100 ppm|
2K7 Biocide Case Studies
In conjunction with CT service companies in the U.S. and Canada, 2K7 biocide has been shown to significantly reduce MIC in coiled tubing operations and associated string failures. Two case studies using 2K7 biocide in CT bridge plug mill-out operations are summarized below. In both cases, since the 2K7 treatment program was implemented, no additional CT string failures associated with MIC have been recorded.
- Four boxes (25 x 1 kg paks per box) of 2K7 WSP were added to the open water tank as an initial shock treatment, which reduced ATP levels from an average of ~10,000 pg/ml ATP (~107 bacteria/ml) to less than 150 pg/ml ATP.
- A second treatment of 1 box of 2K7 WSP was performed prior to the same water being reused for a second well operation as the bacterial load had rebounded to ~1,540 pg/ml ATP during transport.
- Maintenance treatments were required due to the continued addition of water to reduce solids and the CT unit was treated with 2K7 Bugsticks before storage to provide extended control.
- Field studies conducted on three separate well pads showed that 2K7 biocide effectively reduced bacterial levels in surface water from 106 to 104 with agitation of the fluid reducing the reaction time.
- Bacteria levels rebounded at surface due to the infusion of flowback water that contained additives from stimulation operations which, along with dissolved formation nutrients and increased temperatures, provided an ideal environment for bacterial regrowth.
- The ability to identify the source of bacterial population rebound in real-time using the OSP LifeCheck ATP Test Kit enabled implementation of lower, maintenance treatments of the surface water with 2K7 biocide.