Canadian Technical Report of Hydrography and Ocean Sciences No. 45. C.D.W. Conrad, P.M. Strain, and E.M. Levy

Transcription

1 A Method for the Quantitative Determination of Oil from Oil-based Drilling Fluids in Well Cuttings and Seawater and its Application to Toxicity Testing of Cuttings from the Alma Well C.D.W. Conrad, P.M. Strain, and E.M. Levy Atlantic Oceanographic Laboratory Ocean Science and Surveys, Atlantic Department of Fisheries and Oceans Bedford Institute of Oceanography P.O. Box 1006 Dartmouth, Nova Scotia B2Y 4A2 October 1984 Canadian Technical Report of Hydrography and Ocean Sciences No. 45

2 Canadian Technical Report of Hydrography and Ocean Sciences These reports contain scientific and technical information of a type that represents a contribution to existing knowledge but which is not normally found in the primary literature. The subject matter is generally related to programs and interests of the Ocean Science and Surveys (OSS) sector of the Department of Fisheries and Oceans. Technical Reports may be cited as full publications. The correct citation appears above the abstract of each report. Each report will be abstracted in Aquatic Sciences and Fisheries Abstracts. Reports are also listed in the Department's annual index to scientific and technical publications. Technical Reports are produced regionally but are numbered and indexed nationally. Requests for individual reports will be fulfilled by the issuing establishment listed on the front cover and title page. Out of stock reports will be supplied for a fee by commercial agents. Regional and headquarters establishments of Ocean Science and Surveys ceased publication of their various report series as of December A complete listing of these publications and the last number issued under each title are published in the Canadian Journal of Fisheries and Aquatic Sciences, Volume 38: Index to Publications The current series began with Report Number 1 in January Rapport technique canadien sur l'hydrographie et les sciences oceaniques Ces rapports contiennent des renseignements scientifiques et techniques qui constituent une contribution aux connaissances actuelles mais que l'on ne trouve pas normalement dans les revues scientifiques. Le sujet est generalement rattache aux programmes et interets du service des Sciences et Leves oceaniques (SLO) du ministere des Peches et des Oceans. Les rapports techniques peuvent etre consideres comme des publications a part entiere. Le titre exact figure au-dessus du résumé du chaque rapport. Les résumés des rapports seront publies dans la revue Résumés des sciences aquatiques et halieutiques et les titres figureront dans l'index annuel des publications scientifiques et techniques du Ministere. Les rapports techniques sont produits a ('echelon regional mais sont numerotes et places dans l'index a l' echelon national. Les demandes de rapports seront satisfaites par l' etablissement auteur dont le nom figure sur la couverture et la page de titre. Les rapports epuises seront fournis contre retribution par des agents commerciaux. Les etablissements des Sciences et Leves oceaniques dans les regions eta ['administration centrale ont cesse de publier leurs diverses series de rapports depuis decembre Vous trouverez dans l'index des publications du volume 38 du Journal canadien des sciences halieutiques et aquatiques, la liste de ces publications ainsi que le dernier numero pare dans chaque categorie. La nouvelle serie a commence avec la publication du Rapport n 1 en janvier 1982.

3 Canadian Technical Report of Hydrography and Ocean Sciences No. 45 October 1984 ~ METHOD FOR THE QUANTITATIVE DETERMINATION OF OIL FROM OIL-BASED DRILLING FLUIDS IN WELL CUTTINGS AND SEAWATER AND ITS APPLICATION TO TOXICITY TESTING OF CUTTINGS FROM THE ALMA WELL...:... by C.D.W. Conrad, P.M. Strain, and E.M. Levy Atlantic Oceanographic Laboratory Ocean Science and Surveys, Atlantic Department Of Fisheries and Oceans Bedford Institute of Oceanography - P.O. Box 1006 Dartmouth, Nova Scotia B2Y 4A2

4 of Supply and Services Canada 1984 Cat. No. Fs 97-18/45E ISSN Correct citation for this publication: Conrad, C.D.W., P.M. Strain, and E.M. Levy A method for the quantitative determination of oil from oil-based drilling fluids in well cuttings and seawater and its application to toxicity testing of cuttings from the Alma well. Can. Tech. Rep. Hydrogr. Ocean Sci. No. 45. iii+ 12 pp.

5 iii ABSTRAcr Conrad, C.D.W., P.M. Strain, and E.M. Levy A method for the quantitative determination of oil from oil-based drilling fluids in well cuttings and seawater and its application to toxicity testing of cuttings from the Alma well. Can. Tech. Rep. Hydrogr. Ocean Sci. No. 45. iii + 12 pp. This report describes a simple, rapid method for the determination of drilling fluid base oils in oiled cuttings and seawater samples. The method is based on infra-red spectroscopy so that it can be used with low aromatic, high volatility oils, but it is equally applicable to mineral or diesel base oils. Results from applying the method to cuttings from Shell Oil's Alma F-67 well on the Scotian Shelf and to seawater samples from toxicity tests on those cuttings are given. RESUME Conrad, C.D.W., P.M. Strain, and E.M. Levy A method for the quantitative determination of oil from oil-based drilling fluids in well cuttings and seawater and its application to toxicity testing of cuttings from the Alma well. Can. Tech. Rep. Hydrogr. Ocean Sci. No. 45. iii + 12 pp. Le present rapport decrit une methode simple et rapide pour doser les huiles de base du fluide de forage dans des debris de forage contenant du petrole et des echantillons d'eau de mer. La methode repose sur la spectroscopie infrarouge, de sorte qu'elle a'applique aux huiles tres volatiles pauvres en aromatiques et aussi aux huiles de base minerales et diesel. On presente les resultats d'une application de la methode a des debris de forage provenant du puits Alma F-67 de Shell Oil sur le plateau Scotian et a des echantillons d'eau de mer provenant d'essais de toxicite menes sur ces debris.

6 Introduction Although oil-based drilling fluids can result in substantial reductions in drilling times and costs when compared with water-based fluids, they have not been used as routine drilling fluids in Canada because of the environmental threat posed by the high aromatic content of the base oils. Recently, however, base oils which are claimed to be nontoxic have been developed, and if shown to be environmentally safe their use could lead to substantial savings in drilling a well. Since considerable quantities of the base oil and other drilling mud components are lost to the marine environment during disposal of well cuttings, the first step in evaluating oil-based drilling fluids is to assess the potential environmental impact of the materials discharged. Shell applied for approval to use oil-based fluids in routine drilling operations in the deeper sections of the Alma F-67 exploratory well on the Scotian Shelf and was given permission on condition that they provide oiled cuttings to Environment Canada and the Department of Fisheries and Oceans for toxicity testing. These tests were conducted at the Bedford Institute of Oceanography in the winter and spring of 1984 using winter flounder (Pseudopleronectes americana) and soft-shelled clams (Mya arenaria) and the results are reported elsewhere (Addison et al., 1984). This report describes work performed by the Chemical Oceanography Division of the Atlantic Oceanographic Laboratory to develop simple methods to quantify the oil in cuttings from the well and in water samples from the toxicity tests. In addition, the data resulting from the application of these methods to samples from the EPS tests on Alma cuttings are presented. Base Oil Analysis A qualitative analysis of the composition of the Conoco base oil used at the Alma well by gas chromatography/mass spectrometry showed that its principal components are branched aliphatic and alicyclic compounds, most with between 8 and 15 carbon atoms. Straight chain aliphatics are minor components, and aromatics are present only in barely detectable amounts. Indeed, the upper limit for the aromatic concentration as reported by Shell (< 1 % v/v) in their presentation to the Environmental Coordinating Committee of the Canada - Nova Scotia Offshore Oil and Gas Board is considerably higher than that of the sample analyzed. As a result, 1

7 further identification and quantitation of the aromatic fraction of the oil were not considered necessary. Analytical Development Since saturated hydrocarbons are the major components of the base oil used in the drilling fluid at the Alma well, measurement of the infrared (IR) absorption at 2930 cm-1 (i.e. the stretching frequency of the C-H bond) seemed to be the most suitable technique for determining oil levels in the cuttings. Although fluorescence spectrometry is often used in environmental oil monitoring, the low aromatic content of the base oil renders it unsuitable for this application. Gravimetry, which is often used for determining oil levels in heavily contaminated materials, is also inappropriate because of the high concentration of volatiles in the base oil. Water Samples - l liter water samples from the flounder test tanks were placed in a 4 l separatory funnel and extracted with a 30 ml aliquot of cc1 4 followed by a 20 ml aliquot. The t1.vo extracts were combined prior to concentration measurement. oc1 4 was a suitable solvent because it meets the IR requirement for a C-H free material. (Additional extractions yielded no further extractable material). In some cases a water/cc1 4 emulsion formed and it was necessary for the extracts to sit for several days to allow the phases to separate. Even centrifuging failed to completely separate some of these emulsions, although it was always possible to isolate enough of the cc1 4 phase for the analysis. Because of the relatively low concentrations in these samples, a long pathlength (5 em) quartz sample cell from a UV/visible spectrophotometer was used. Although quartz is not normally considered suitable for IR use, it transmits far enough into the IR to allow measurement of the C-H stretch at 2930 cm-1 provided that the absorbance due to the cell is considered. Since the use of water-sensitive NaCl or other salt crystal optics is avoided, absolute dryness is not required and sample preparation and analysis are greatly simplified. Quantitation was performed by scanning the spectrum with a Beckman Acculab 6 IR spectrometer from 4000 cm-1 to 2400 cm-1 and measuring the % transmission at 2930 cm-1. Fig. la shows the spectrum for pure cc1 4 in the quartz sample cell; Fig. lb 2

8 the spectrum for a sample extract. As shown in Fig. la,.the % transmissions for the cell containing the solvent are equal at 2930 and 3230 cm- 1 Fig. lb shows a marked decrease in transmission at 2930 cm- 1 due to the oil, but the transmission at 3230 cm-1 is virtually unchanged from that of the solvent. Therefore, after converting transmission to absorbance, the absorbance due to oil at 2930 cm-1 can be obtained by subtracting the absorbance at 3230 cm-1 from the total absorbance at 2930 cm- 1 - no need to analyze separate solvent/cell blanks during routine sample there is analysis. This corrected absorbance was converted to oil concentration using an absorbance regression line which was obtained by analyzing a series of Conoco base oil standards of known concentrations (Fig. 2). This overall procedure yields a detection limit of approximately 0.03 mg oil/liter water. Cuttings Samples - Because the two batches of cuttings received from Shell were very dense, agglutinated mixtures, it was necessary to check that the oil extraction technique used yielded complete recovery. Accordingly three different methods for the extraction of oil from cuttings samples were evaluated. Soxhlet extraction gave consistently lower oil concentrations than the other two techniques because of incomplete wetting of the sample by the solvent; samples still smelled strongly of oil after a six hour extraction. The other two procedures consistently yielded complete oil recovery. Extraction of g cuttings samples in 200 ml oc1 4 for 90 seconds in a high speed (20,500 rpm) commercial blender was the more convenient technique, although 30 minute extractions of g samples in 100 ml cc1 4 using a sonic dismembrator gave the same results. All the cuttings data in this repor~ were obtained with one of these two extraction procedures. Before final quantitation, it was necessary to dilute the extracts so that their absorbances fell within the linear absorbance range of the calibration standards. Ten IR analyses of one 400 ml sample yielded a mean oil concentration of 8.99 % wet weight with a single sample standard deviation of 0.25 wt %. In this report oil concentrations on cuttings are given in percent wet weight to allow the direct application of the results to the toxicity tests. This is also the most appropriate unit for calculating fluxes of oil discharged from the rig. The only disadvantage is that the 3

9 results are not directly comparable to those reported by rig operators using the retort method to monitor the levels of oil in cuttings and direct comparison between the two methods is possible only when the water contents are known. The retort method measures the total amount of condensible liquids collected when a cuttings sample is subjected to a high temperature (approx. 900 C) distillation. Many errors are possible under such severe conditions - e.g. destructive distillation of some oil components may lead to underestimation of oil levels. The IR method described here, with its gentler conditions and more specific detection technique, is less prone to such systematic errors. f Results and Discussion Oil concentrations measured in water samples taken from the flounder test tanks at the start and finish of the 96 hour tests are listed in Table I. The cuttings used in these tests originated from two zones of the Alma well. The first batch of cuttings contained very coarse, gravelsize material mixed with the fines from the drilling mud. These cuttings were used in all tests labelled Series 1 and in the Tank 6 flounder tests of Series 2. In the second batch of cuttings, the formation materials were so fine-grained that the mixture appeared similar to a well-sorted silty sediment. This batch of cuttings was used in the Series 2 clam toxicity tests and the Series 2 Tank 10 flounder tests. Oil concentrations in the water from the flounder test tanks increased through the period of the tests using the coarse cuttings, but such an increase was not noted in the one test using the fine cuttings. At completion of the three tests using the first batch of cuttings, water in the tanks was hazy and the surface covered by what appeared to be an aged oil/water emulsion. Both the water and its surface in the Series 2 Tank 10 test were remarkably clear at the end of the test. Oil was apparently released from the first batch of cuttings to a greater extent than from the second batch. The oil may have been more strongly adsorbed on the second batch of cuttings because of the greater surface area available on the fine-grained formation materials. The concentrations of oil measured in the cuttings from the flounder test tanks are given in Table II; the cuttings concentrations for the clam tests are given in Table III. Table IV reports the concentration of oil on cuttings from some t 4

10 preliminary tests by EPS to determine the mobility of the oil adsorbed on cuttings. Time series of concentrations of oil in cuttings were measured for two types of static release tests in which cuttings were covered with seawater. There was no accumulation of oil on the surface of the water as had been observed in similar tests with some drilling muds. The cuttings data in Tables II-IV all show more scatter than was observed in repeated analyses of a single 400 ml cuttings sample. Each batch of cuttings was shipped in a number of 20 1 pails. Composite samples of cuttings from the different pails were prepared for use in the toxicity tests with the aim of determining the toxicity testing of 'average' cuttings. The nature of the cuttings made it impossible to completely mix the subsamples from the different pails at the start of the toxicity tests. Differences in oil concentration between pails were apparent even on visual observation. The changes observed in oil concentrations during the course of the toxicity and mobility tests probably reflect the resulting heterogeneity in the test containers rather than changes with time or analytical imprecision. Table V compares oil concentrations for four cuttings samples analyzed by both the IR method described here and the retort method. In all cases, the IR technique yields a higher concentration. The difference between the results for the two methods is actually somewhat greater than it appears in the Table, since conversion of the IR results to % dry weight would increase the absolute numbers. It is possible that sample heterogeneity is partially responsible for these differences (the subsamples for the two types of analyses were taken from the same 20 1 pail) - a more thorough study is required to determine if the apparent differences between these methods are real and, if so, what the causes are. Concluding Remarks An unorthodox use of silica cells made possible the development of a simple infrared procedure for quantifying drilling mud base oils in water and in drill cuttings. This procedure is more specific and subject to fewer artifacts than the conventional retort method frequently used by rig operators to monitor oil levels in cuttings. The IR procedure has been applied successfully in support of tests performed to evaluate the toxicity of 'non-toxic' oil based drilling fluids used on a trial basis at Shell 5

11 Oil's Alma F-67 well on the Scotian Shelf. Reference Addison, R.F.; Doe, K.; Edwards, A.; and Vaughan, D Effects of oil based drilling mud cuttings on winter flounder (Pseudopleuronectes americanus) Absence of acute toxicity or mixed function oxidase induction. Canadian Technical Report of Fisheries and Aquatic Sciences #

12 TABLE I. Water Extracts (Flounder tests) Sample Date Collected ~oil/liter water A. Series 1 Tank 6 84/3/ Tank 6 84/3/ Tank 10 84/3/ Tank 10 84/3/ Tank 10 84/3/ Tank 11 84/3/ Tank 11 84/3/12 (duplicate) 3.41 Tank 11 84/3/ Tank 11 84/3/ B. Series 2 Tank 5 84/5/ll 1.52 Tank 5 84/6/ Tank 6 84/5/ll 3.53 Tank 6 84/6/ Tank 10 84/5/ Tank 10 84/6/ Test substrate: Series 1 Series 2 Tank 6 : clean silica sand Tank 5 clean silica sand Tank 10: 100 % cuttings Tank % cuttings, batch 1 Tank 11: 100 % washed cuttings Tank 10: 100 % cuttings, batch 2 7

13 TABLE II. Cuttings samples (Flounder tests) Sample Date Collected.! oil (wet wt) A. Series 1 Tank 6 84/3/ Tank 6 84/3/ Tank 10 84/3/ Tank 10 84/3/ Tank 10 84/3/ Tank 10 84/3/ Tank 11 84/3/ Tank 11 84/3/ Tank 11 84/3/ B. Series 2 Tank 5 84/5/ Tank 5 84/6/ Tank 6 84/5/ Tank 6 84/6/ Tank 10 84/5/ Tank 10 84/6/

14 TABLE III. Cuttings samples (Clam tests) Sample Date Collected A. Series 1 Control 100 % cuttings washed cuttings 84/3/8 84/3/8 84/3/8 o.oo B. Series 2 Control (Tank 53) 84/5/14 Control 84/6/4 100 % cuttings (Tank 56) 84/5/ % cuttings 84/6/

15 TABLE IV. Mobility experiment cuttings samples Sample Date Collected.! oil (wet wt) Cylinder method 84/3/ II 84/3/ II 84/3/ II 84/4/ Flat tray method 84/3/ II 84/3/ II 84/4/ TABLE V. Comparison of IR and retort methods IR Analysis % oil (wet weight) Retort analysis % oil (dry weight)

16 A z 0 u; (f) 20 ~ 0 (f) z <t a:: I- I- z t:5 100 a:: w a em-' Fig 1. (A) IR spectrum of cc1 4 in 5 em nuartz cell. (B) IR spectrum of Conoco base oil in CC1 4, 5 em quartz cell. 11

17 SLOPE = INTERCEPT CORRELATION =.9999 c N = 5 0 R R E c T E D 0.75 A B s R B A N c 0.25 E CONCENTRATION CUG/ML CCL4) FIG. 2. BASE OIL CALIBRATION 12