ter. Baseline testing used a solution of KCl (2%) a breaker, a
friction reducer, and a non-emulsifier.
The cell stack was slowly ramped up to a closure stress of
2,000 psi and then heated to 112. 8° C. The stack was left at
temperature and pressure for 12 hr before baseline readings
were taken.
About 200-250 ml of treatment fluid then flowed through
each of the proppant packs at temperature and pressure. Re-gain-conductivity measurements were taken after flushing
the packs with about 200-250 ml of 2% KCl brine.
Permeability was reduced less in source water with a biocide ( 11.3% of baseline) than in untreated source water with
bacteria ( 32.2% of baseline). Permeability was not affected in
KCl-only solutions.
References
1. Struchtemeyer, C.G., Morrison, M.D., Elshahed, M.S.,
“A critical assessment of the efficacy of biocides used during
the hydraulic fracturing process in shale natural gas wells,”
International Biodeterioration & Biodegradation, Vol. 71, , July
2012, pp. 15-21.
2. Dawson, J.C., Cramer, D.D., Le, H.V., “Reduced
Polymer Based Fracturing Fluid: Is Less Really More?” SPE
Annual Technical Conference and Exhibition, Houston, Sept.
26-29, 2004.
3. Dawson, J., Wood, M., “A New Approach to Biocide Application Provides Improved Efficiency in Fracturing Fluids,”
SPE/EAGE European Unconventional Resources Conference
and Exposition, Vienna, Mar. 20-22, 2012.
4. Ezeuko, C.C., Sen, A., Gates, I.D., “Modelling biofilm-induced formation damage and biocide treatment in subsurface geosystems,” Microbial Biotechnology Vol. 6, No. 1,
January 2013, pp. 53–66.
5. Fink, J., “Oil Field Chemicals,” Gulf Professional Publishing, 2003, Houston, pp. 233-275.
6. Williams, D.A., Newlove , J.C., Horton, R.L., “
Hydraulic Fracturing with Chlorine Dioxide clean up,” US Patent
4,964,466, 1990.
7. “Field Monitoring of Bacterial Growth in Oil and Gas
Systems,” National Association of Corrosion Engineers
(NACE) International, NACE Standard TM0194-2004, 2004.
crowning time. A rheometer measures stability of the gel ( 25
ml) held at at 80° C. and 200 psi for 2 hr. For a slick-water
test, tap water (200 ml) is placed in a Waring blender and
mixed at 300 rpm. The biocide and an anionic or cationic
friction reducer (0.4 ml) are then blended for 5 min. A viscometer collects viscosity data at room temperature to 60°
C. for 30 min.
We maintained control group (biocide-free) gel integrity
at 350-500 cp. With 10 ppm free chlorine dioxide, the gel
was also maintained between 350-500 cp at 80° C. As the
concentration of chlorine dioxide increased, however, viscosity decreased. The gel broke quickly in chlorine dioxide
concentrations of more than 100 ppm (Fig 2a). An unbroken
gel containing a compatible biocide is viscous with good lipping behavior. An incompatible biocide or a biocide at too
high a dosage causes low viscosity and poor lipping behavior
or rapid breaking of the gel.
Testing of selected concentrations of the other biocides
determined their effects on gel integrity. Viscosity was
maintained between 350-500 cp at 80° C., using up to 200
ppm hypochlorous acid biocide and 100 ppm 2,2-dibromo-
3-nitrilopropionamide and hydantoin derivative biocides.
Hydantonin demonstrated the largest decrease in viscosity
compared with the control group (Fig. 2b).
Fig. 3a-b shows the biocides’ effect on selected anionic
and cationic slick water. Viscosity decreased more than 30%
when chlorine dioxide at 10 ppm was added to anionic slick
water. A more than 50% viscosity decrease occurred when
chlorine dioxide was added to cationic slick water. These results suggest that chlorine dioxide biocides will reduce the
performance of some slick-water systems (Fig. 3a).
The other biocides studed had no significant effect on anionic slick water. Viscosity of cationic slick water, however,
increased in the hypochlorous acid biocide. The hydantoin derivatives and 2,2-dibromo-3-nitrilopropionamide biocides decreased viscosity and therefore may affect the performance of some cationic friction reducers (Fig. 3b).
Untreated water’s effect
A proppant and Barea sandstone cores were put into three
conductivity cells to determine the effects of untreated wa-
BIOCIDE TESTING, BACTERIA-BROTH BOTTLES
2,2-Dibromo- 3
Chlorine Hypochlorous acid Hydantoin derivative nitrilopropionamide
Dioxide biocide biocide biocide
Control 10 100 200 100 200 100 400
–––––––––––––––––––––––––––––––––––––––––– ppm –––––––––––––––––––––––––––––––––––––––––––––––––
APB anaerobic 104 — 104 104 104 1,000 104 103
Thioglycolate
anaerobic 105 — 105 104 105 105 105 103
API SRB
anaerobic 105 — 104 103 103 101 104 103
Phenol Red
aerobic 105 — 105 105 105 104 105 103
API aerobic 105 — 105 104 104 10 105 102
