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Protocol for Non-Toxic Concentrations of Drilling Fluid Additives Dr. John Ashworth Soil Science Director, ALS Environmental - Edmonton Vince Walker Director of Operations, ALS Environmental - Fort St. John Formerly

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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 Canadas crude and 80% of its natural gas in 2004/2005 fiscal year, revenues from oil and gas accounted for more than 34% of Albertas 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) PSACs Mud List - drilling fluid additive product listing for potential toxicity:

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Toxicity Thresholds To be listed, a products 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 ) 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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EC 50 (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) EC 50 (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 EC 50 (15 min) > 75%

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Determination of EC Correction factor (R t ) = ratio of light output of control at time t to initial light output of control (used to correct for time-dependent changes): R t = I t /I o Gamma (G t ) = ratio of light lost at time t to light remaining at time t (calculated for each sample dilution):G t = [(R t x I o )/I t ] - 1 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: Therefore, when log gamma = 0 (x-intercept), this is the point where light output is halved, and represents the EC 50 concentration at time t after the anti-logarithm is applied.

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Measures of Uncertainty Confidence limits (CLs) are estimated for every analysis performed, based on the deviation of light output readings obtained (derivation of R 2 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 (CLs) 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 EC 50 (15min) - 2 x (%RSD x mean/100) Modified, we get the following: lower CL = mean EC 50 (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 EC 50 (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/m 3 = (4/3) x 10 x mean EC 50 (15 min) x (1 - 2 x %RSD/100)

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%RSD and WCMUC Since its 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 revealed a skewed frequency distribution of %RSD values

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Neglecting 2 %RSDs over 100 caused by test liquid instability; the mean of 31 RSD values is 28%

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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 = x EC 50 (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 %RSDs; 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

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