Protocol for Non-Toxic Concentrations of Drilling Fluid Additives by HC121005173243


									    Protocol for Non-Toxic
   Concentrations of Drilling
        Fluid Additives
Dr. John Ashworth                            Vince Walker
Soil Science Director, ALS              Director of Operations, ALS
Environmental - Edmonton                Environmental - Fort St. John
• Introduction and Significance
• Background
• Method Description (Microtox®
  Acute Toxicity Analysis)
• Determination of Threshold Values
• Conclusion and Acknowledgements
  Introduction and Significance
• Averaging 300 wells drilled/week in
  western Canada
• Alberta produces 70% of Canada’s crude
  and 80% of its natural gas
• in 2004/2005 fiscal year, revenues from oil
  and gas accounted for more than 34% of
  Alberta’s total revenues (ie. $10 billion)
• WCSB...
        Drilling and Disposal
• Total of 19,365 (including dry and service)
  wells drilled in Alberta in 2004
• Alberta Energy and Utilities Board (EUB)
  permits on-site disposal of generated
  drilling waste provided criteria are met
  (Guide 50; EUB 1996)
• Disposal methods require quantification of
  toxicity of waste using Microtox® bioassay
• Petroleum Services Association of Canada
  (PSAC) was developed in 1981 to represent
  upstream oil and gas industry sectors (in
  response to National Energy Program)
• PSAC’s Mud List - drilling fluid additive
  product listing for potential toxicity:
        Toxicity Thresholds
• To be listed, a product’s toxic rate of
  application/addition must be known
• PSAC asked the Western Canada Microtox
  Users Committee (WCMUC) to establish
  toxic rates for new additives
• Resource group formed in 1987, consisting
  of various members dedicated to the
  standardization of Microtox® testing
• To maintain performance standards, an
  inter-laboratory quality control Round
  Robin program is run twice a year
• At present, the group consists of 17
  members with 13 laboratories participating
  in Round Robin studies
Microtox® Acute Toxicity
    Photoluminescent Bacteria
• Uses a strain of Vibrio fisheri (NRRL B-
  11177) as a test organism
• bacteria emit light as a metabolic by-
• Bacteria are reconstituted from a freeze-
  dried state, and initial light outputs are
  measured from homogenized suspensions
• Maintained at 15°C, suspensions are
  exposed to serially-diluted (2-fold)
  concentrations of osmotically-adjusted test
• Light output readings are taken at specified
  time intervals (usually 5 and 15 minutes)
              EC50(15 min)
• EC - effective concentration of a test sample
  that reduces light emission by a specific
  amount under defined conditions of time
  and temperature (also called Inhibitory
  Concentration, or IC)
• EC50(15 min) = effective concentration of a
  test sample that reduces light emission by
  50% at 15 minutes at 15°C
• NOTE: EUB defines non-toxic substances
  as those with EC50(15 min) > 75%
            Determination of EC
             Final Sample Concentrations (%)
                     Control 10.2 20.4 40.9 81.8
Raw Light      Io      94    94    90   94   91
 Output        I5     107    100   88   76   50
Readings       I15    114    76    47   25   10

• Correction factor (Rt) = ratio of light output of
  control at time t to initial light output of control
  (used to correct for time-dependent changes):
      Rt = It/Io
• Gamma (Gt) = ratio of light lost at time t to light
  remaining at time t (calculated for each sample
  dilution): Gt = [(Rt x Io)/It] - 1
                       Determination of EC
• The log of Gamma values are plotted against the log of
  concentrations for each respective time t:
                                        Log Gamma vs. Log Conc.

                                    y = 1.439x - 1.7586
                       0.8              R2 = 0.9998

           log gamma

                              0.0       0.5          1.0              1.5   2.0   2.5


                                                           log conc

• Therefore, when log gamma = 0 (x-intercept), this is the
  point where light output is halved, and represents the EC50
  concentration at time t after the anti-logarithm is applied.
      Measures of Uncertainty
• Confidence limits (CL’s) are estimated for
  every analysis performed, based on the
  deviation of light output readings obtained
  (derivation of R2 values)
• IMPORTANT - this is only a partial
  measure of within-lab uncertainty, and
  DOES NOT represent inter-lab uncertainty
  (critical in determining safe rates of additive
Determination of Threshold Rates
• Can be made from absolute EC values, but
  allowances need to be made for uncertainty
  in test results
• Confidence limits (CL’s) are normally set at
  2 standard deviations (sd) from the mean
• To be conservative, we would use the lower
  confidence limit (ie. replicates displaying
  higher toxicities) to derive threshold rates
      Lower Confidence Limit
• Since % relative standard deviation
  (%RSD) = 100 x (sd/mean), we arrive at the
  following equation:
     lower CL = mean EC50(15min) - 2 x (%RSD x
• Modified, we get the following:
      lower CL = mean EC50(15 min) x (1 - 2 x %RSD/100)
Volume and Threshold Conversion
• This lower CL is expressed as a percentage
  of the original sample concentration
  (1/100); to convert to L/m3 (1/1000), we
  apply a factor of 10
• as well, since the EUB EC50(15 min) “pass”
  threshold is set at 75% of the original
  concentration of sample, a factor of 4/3 is
  applied to the lower CL to meet this
     Equation for a Non-Toxic
         Threshold Rate

L/m3 = (4/3) x 10 x mean EC50(15 min) x (1 - 2 x %RSD/100)
         %RSD and WCMUC
• Since it’s not feasible to subject all drilling
  fluid additives to WCMUC round robin
  studies, how can we derive an appropriate
  %RSD for every additive to obtain a
  probable non-toxic rate of application?
• The examination of WCMUC Round Robin
  data from 2000-2005 revealed a skewed
  frequency distribution of %RSD values
                                    Frequency of % RSD



           % frequency


                                0     20   40       60   80   100
                                                % RSD

• Neglecting 2 %RSD’s over 100 caused by test liquid
  instability; the mean of 31 RSD values is 28%
       New Threshold Equation
• Inserting a %RSD of 28 into the equation
  for determining a non-toxic threshold rate,
  we derive the following:

           L/m3 = 5.867 x EC50(15 min) ,
               Or simply:

           L/m3 = 6 x EC50(15 min)
• Of course, depending on the stability of
  additives and consistency in results which
  they yield, % RSD will vary; it is
  recommended that this conservative
  threshold equation is used in cases where
  the additive is only tested at one laboratory
• Likewise, coloured samples display wider
  scatter of data, and thus higher %RSD’s; in
  these cases, using a factor smaller than 6 is
• Dave Horton of Brine-Add Fluids
  (representing PSAC) for providing various
  drilling fluid additives
• Dave Wong of Epcor Canada for
  distributing test liquids and for collation and
  statistical analysis of WCMUC Round
  Robin data

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