Protocol for Non-Toxic Concentrations of Drilling Fluid Additives Dr. John Ashworth Soil Science...
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Transcript of Protocol for Non-Toxic Concentrations of Drilling Fluid Additives Dr. John Ashworth Soil Science...
![Page 1: Protocol for Non-Toxic Concentrations of Drilling Fluid Additives Dr. John Ashworth Soil Science Director, ALS Environmental - Edmonton Vince Walker Director.](https://reader035.fdocuments.net/reader035/viewer/2022062417/5518c552550346881f8b57d1/html5/thumbnails/1.jpg)
Protocol for Non-Toxic Concentrations of Drilling
Fluid Additives
Dr. John AshworthSoil Science Director, ALS Environmental - Edmonton
Vince WalkerDirector of Operations, ALS Environmental - Fort St. John
Formerly
![Page 2: Protocol for Non-Toxic Concentrations of Drilling Fluid Additives Dr. John Ashworth Soil Science Director, ALS Environmental - Edmonton Vince Walker Director.](https://reader035.fdocuments.net/reader035/viewer/2022062417/5518c552550346881f8b57d1/html5/thumbnails/2.jpg)
Overview
• Introduction and Significance
• Background
• Method Description (Microtox® Acute Toxicity Analysis)
• Determination of Threshold Values
• Conclusion and Acknowledgements
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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...
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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
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Background
• 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:
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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
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WCMUC• 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
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Microtox® Acute Toxicity Assessment
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Photoluminescent Bacteria
• Uses a strain of Vibrio fisheri (NRRL B-11177) as a test organism
• bacteria emit light as a metabolic by-product:
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Procedure• 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 sample
• Light output readings are taken at specified time intervals (usually 5 and 15 minutes)
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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%
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Determination of EC
• 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
Control 10.2 20.4 40.9 81.8
Io 94 94 90 94 91
I5 107 100 88 76 50
I15 114 76 47 25 10
Final Sample Concentrations (%)
Raw Light Output
Readings
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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
R2 = 0.9998
-1.2
-0.8
-0.4
0.0
0.4
0.8
1.2
0.0 0.5 1.0 1.5 2.0 2.5
log conc
log
gam
ma
• 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.
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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 use)
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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
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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 mean/100)
• Modified, we get the following: lower CL = mean EC50(15 min) x (1 - 2 x %RSD/100)
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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 criterion
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Equation for a Non-Toxic Threshold Rate
L/m3 = (4/3) x 10 x mean EC50(15 min) x (1 - 2 x %RSD/100)
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%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
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• Neglecting 2 %RSD’s over 100 caused by test liquid instability; the mean of 31 RSD values is 28%
Frequency of % RSD
0.0
10.0
20.0
30.0
40.0
0 20 40 60 80 100
% RSD
% f
req
uen
cy
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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)
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Conclusion• 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 advisable
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Acknowledgements
• 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