Rock Eval, Total Organic Carbon of the 29 rock samples from Mali. Unfiled Report April

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Pauline Maud Davidson
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1 Rock Eval, Total Organic Carbon of the 29 rock samples from Mali Unfiled Report April

2 Dear Sir, We have analyzed your 29 rock samples from Mali. The rock samples were pyrolyzed using our Rock-Eval TM /TOC technique. This technique evaluates oil and gas shows, oil and gas generation potential, thermal maturity and identifies the organic matter type after Behar et al., 2001; Espitalie et al. 1985; Peters, 1986; Tissot and Welte, 1978, p Rock-Eval TM /TOC measures three types of products, hydrocarbons (HC), carbon dioxide (CO2) and carbon monoxide (CO) evolved during both anoxic pyrolysis and oxidative pyrolysis. Older versions of the device such as Rock-Eval 2 had only a CO2 detector and they measured only HC and CO2. It is a useful screen for recognizing sources and stained lithologies. The analysis gives five key parameters: S1, S2, S3, TOC and Tmax, which are included in the3 Table of results. 1. The S1 parameter measures free or adsorbed hydrocarbons volatilized at moderate temperatures ( o C). 2. S2 measures the hydrocarbons liberated during a ramped heating (-550 o C at 25oC/min.). 3. The S3 parameter measures organic CO2 and CO generated from the kerogen during rapid heating (-390 o C at 25 o C/min.). (Milligrams product per gram rock sample, the equivalent to kilograms per tonne, is the measure of these three parameters.) 4. Total Organic Carbon (TOC) is measured in weight per cent. 5. Tmax, the temperature corresponding to the S2 peak maximum temperature is measured in o C. Rock-Eval TM results correlate to other techniques (Espitalie et al., 1985; Tissot and Welte, 1978). Source rock potential is sensitive to lithology, TOC and S2 values (Table 1, attached). It is a common practice to rate carbonate rocks with lower TOC as comparable with richer clastic rocks. Extractable HC yields from leaner carbonate rocks are comparable to richer clastic rocks (Tissot and Welte, 1978, p. 430; Gehman, 1962).

3 The organic matter associated with carbonate rocks is often more hydrogen-rich and thermally labile than that of fine-grained clastic rocks. As a result, more TOC in carbonate rocks may be transformed into bitumen compared with average clastic source rocks of comparable maturity. Rock analysis results for 29 core samples from Mali in West Africa, submitted for analysis by Tom Jerzykiewicz, are in the attached files named: TJ xls and TJ zip The zip files contains FID pyrograms for each individual sample analyzed including, 9107 internal lab standards, in a pdf format. Rock-Eval TM /TOC parameters have significance only above the thresholds for TOC, S1 and S2 values. If TOC is less than 0.3% then all of the parameters have questionable significance and the experiment suggests no potential. Also, Oxygen Index (OI = S3/TOC), has questionable significance if TOC is less than 0.5 percent. Both Tmax and Production Index (PI = S1/(S1+S2)), have questionable significance if S1 and S2 values are less than about 0.2. Results can be affected by mineral matrix effects. These either retain generated compounds, generally lowering the S1 or S2 peaks, while increasing Tmax, or by liberating inorganic CO2 and increasing S3 and OI. These effects are important if TOC, S1 and S2 are low, an effect not significant in this study as most sources have TOC values less than 0.5 percent. OI values greater than 150 mg/g TOC suggest either low TOC or a mineral matrix CO2 contribution during pyrolysis. All of the 29 Mali rock samples are thermally over mature and no significant petroleum source rock potential should be assigned to these samples. Assuming that they were initially Type II or Type I organic matter, we can infer that to begin with, they were poor to lean samples. The bedding style of the more organic rich intervals suggest that these rocks were thin poor to lean source rocks at first, and then the pyrolyzable carbon has been completely transformed at some unspecified time. The opportunity for significant volumes of petroleum generation from these rocks is considered not likely and the risks of petroleum preservation are greatly reduced because of the age of the samples. Many of the samples are essentially displaying a baseline response, as can be seen from the pixelated nature of the curves in the zip files of the pyrograms.

4 The following criteria and instrumental limitations are considered in our analysis: Table 1: Standard Criteria for Rating Potential Source Rocks Total Organic Carbon (TOC) Value (Weight Per Cent), as reported in results spreadsheet wt% TOC Rating in shales: Poor ; Fair ; Good ; Very Good ; Excellent 4.00 > S2 Rating Value (mg of Hydrocarbons / g of rock) Poor Less than 2.00 Fair Good Greater than 5.00 For 23 out of the 29 Mali core samples analyzed, TOC values range from 0.02 to 0.42 wt% which indicates that most samples are organically lean. The remaining 6 samples have only a poor to fair TOC content ranging from 0.51 to 0.94 wt percent. All of the samples have very low S2 yields ranging from 0.01 to 0.07 mghc/g rock. Therefore, based on the low TOC content, which is nearly all residual carbon, and the very low S2 yields of less than 0.10 mghc/g rock, it can be concluded that none of the samples have any remaining source rock potential. The rocks are all clearly thermally over mature, and the S2 yields are too low to obtain meaningful or reliable Tmax values. However, based on the low S2 yields and character of the FID pyrograms, the samples are post mature. The most interesting rock samples are: F-1 26, F-1 27 and F These exhibit some of the characteristics of samples having shale gas potential, although rocks are not properly shales in the typical shale gas reservoir sense. These samples have high PI values ranging from 0.41 to 0.68 and they have low Tmax values ranging from O C. This suggests that these samples may be stained by introduced petroleum.

5 Whether the staining is from migration or contamination cannot be certain, but it is suggested to check the drilling fluids to see if they were oil-based and may have been the source of potential contamination. Further evidence supporting this suggestion are the FID pyrograms for these three samples which exhibit relatively large S1 peaks that do not return entirely to their baseline but they have rather pronounced low-temperature shoulders which dominate the S2 peaks, resulting in low Tmax values. In fact, with the exceptions of the samples F-2 31, F-2 32 and F-2 33, all of the other samples evaluated in this study, have anomalously low Tmax values. That is, the Tmax values are coming from a petroleum that has been either migrated into the rock, or introduced as a contaminant. We tend towards the contamination hypothesis. Another sample with an interesting FID pyrogram is the F-1 3 sample, which has an anomalously low Tmax value of 341 O C. The pyrogram for this F-1 3 sample exhibits a relatively large S1 peak and a distinctly bimodal S2 peak, with the lowtemperature portion of the peak dominant. Anomalously low Tmax values (<400 O C), often indicate the presence of what are most likely contaminants that are not volatilized during the S1 heating stage of the experiment. The residual bitumen that forms the low-temperature portion of the S2 peak, must be occupying a matrix pore space. Many of the samples show a sharp decline of the S2 peak at about 455 o C, which is the limit for Type II OM pyrolytic carbon. Therefore we assume the original Organic Matter was probably Type II and that the original TOC content is probably twice the residual carbon content. The highest TOC, RC values are 0.94 and 0.93 from sample Therefore all of the samples probably had original TOC's of not more than 2.0%, and most of the samples would have had a much lower original TOC, which when combined with their thin bedding/lamination form, they suggest a fair to poor initial source rock potential. Regarding further work, we suggest that you try to collect samples of the gas. The origin and alteration of natural gases is well illustrated using a combination of gas wetness ratio and the stable carbon isotopic values or methane and carbon dioxide. The TOC results are disappointing, but we hope that the lack of source rock potential, now and in the past is clearly understood. Don't hesitate to ask if you have any additional questions. Sincerely, K.Ross Stewart and Kirk Osadetz

6 References: Behar, F., Beaumont, v., and Penteado, H. L. De B., 2001 Rock-Eval 6 Technology: performances and Developments. Oil and gas Science and Technology -- Revue de l'institut Francais du Petrole, v. 56, p Espitalie, J., Deroo, G. and Marquis, F Rock Eval Pyrolysis and Its Applications. Preprint; Institut Francais du Petrole, Geologie No , 72 p. English translation of, La pyrolyse Rock-Eval et ses applications, Premiere, Deuxieme et Troisieme Parties, in Revue de l'institut Francais du Petrole, v. 40, p and ; v. 41, p Gehman, H. M. Jr., Organic matter in limestones; Geochimica et Cosmochimica Acta, v. 26, p Peters, K. E., Guidelines for evaluating petroleum source rock using programmed pyrolysis. American Association of Petroleum Geologists, Bulletin, v. 70/3, p Stasiuk, L D and Fowler, M G Thermal maturity evaluation (vitrinite and vitrinite reflectance equivalent) of Middle Devonian, Upper Devonian, and Mississippian strata in the Western Canada Sedimentary Basin; Geological Survey of Canada, Open File 4341 Tissot, B. P., Pelet, R., and Ungerer, P., Thermal history of sedimentary basins, maturation indices, and kinetics of oil and gas generation. American Association of Petroleum Geologists, Bulletin, v. 71/12, p Tissot, B. P., and Welte, D. H., Petroleum formation and occurrence; Springer-Verlag, Berlin, 538 p.

7 APPENDIX

8 TOC F1 Minimum value 0.03 Maximum value 0.94 Average value 0.32 If the value is: % of the values are equal to or lower 41% of the values are higher 40.0% TOC F1 35.0% 30.0% 25.0% 20.0% 15.0% 10.0% 5.0% 0.0% Data values 17 Error values 0 Bin Size 0.18 Number of bins 7 Cumulative Cumulative Frequencies: Frequencies: Frequencies: <= % <= % => % >0.03 to % <= % => % >0.21 to % <= % => % >0.39 to % <= % => % >0.58 to % <= % => % >0.76 to % <= % => % > %

9 TOC F2 Minimum value 0.02 Maximum value 0.67 Average value 0.23 If the value is: % of the values are equal to or lower 33% of the values are higher 35.0% TOC F2 30.0% 25.0% 20.0% 15.0% 10.0% 5.0% 0.0% Data values 12 Error values 0 Bin Size 0.13 Number of bins 7 Cumulative Cumulative Frequencies: Frequencies: Frequencies: <= % <= % => % >0.02 to % <= % => % >0.15 to % <= % => % >0.28 to % <= % => % >0.41 to % <= % => % >0.54 to % <= % => % > %

10 Samp l e Dep th S1 S2 S3 TO C Tmax HI OI (m) (mg m/ g m) (mg m/ g m) (mg m/ g m) (w t%) (Cel ci u s) F % 41% F % 35% F % 104% F % 46% F % 45% F % 48% F % 32% F % 22% F % 63% F % 164% F % 155% F % 189% F % 150% F % 343% F % 186% F % 700% F % 12% Samp l e Dep th S1 S2 S3 TO C Tmax (m) (mg m/ g m) (mg m/ g m) (mg m/ g m) (w t%) (Cel ci u s) F % 45% F % 70% F % 21% F % 25% F % 16% F % 114% F % 35% F % 200% F % 500% F % 500% F % 100% F % 62%

11 Tom Jerzykiewicz Mali West Africa Proterozoic Samples Depth Sample Qty S1 S2 PI S3 Tmax Tpeak S3CO PC(%) TOC RC% HI OICO OI MINC% F F F F F F F F F F F F F F F F F F F F F F F F F F F F F

12 Depth Sample Qty Tmax S1 S2 S3 PI S2/S3 PC(%) TOC(%) HI OI F F F F F F F F F F F F F F F F F F F F F F F F F F F F F

13 : S1=0.01 S2=0.04 Tmax=395 Tp S2=434.0 PI=0.24 HI=5 Sample =F-1 2 Qty =70.4 TOC= C:\VINCI\TJ110419\TJ002.R00 : FID pyrolysis graphic

14 : S1=0.02 S2=0.07 Tmax=341 Tp S2=380.0 PI=0.19 HI=9 Sample =F-1 3 Qty =70.2 TOC= C:\VINCI\TJ110419\TJ003.R00 : FID pyrolysis graphic

15 : S1=0.01 S2=0.04 Tmax=365 Tp S2=404.0 PI=0.13 HI=17 Sample =F-1 5 Qty =70.2 TOC= C:\VINCI\TJ110419\TJ004.R00 : FID pyrolysis graphic

16 : S1=0 S2=0.03 Tmax=390 Tp S2=429.0 PI=0.11 HI=9 Sample =F-1 7 Qty =70.2 TOC= C:\VINCI\TJ110419\TJ005.R00 : FID pyrolysis graphic

17 : S1=0 S2=0.03 Tmax=387 Tp S2=426.0 PI=0.14 HI=10 Sample =F-1 8 Qty =70.5 TOC= C:\VINCI\TJ110419\TJ006.R00 : FID pyrolysis graphic

18 : S1=0 S2=0.04 Tmax=385 Tp S2=424.0 PI=0.12 HI=12 Sample =F-1 9 Qty =70.3 TOC= C:\VINCI\TJ110419\TJ007.R00 : FID pyrolysis graphic

19 : S1=0.01 S2=0.03 Tmax=343 Tp S2=382.0 PI=0.25 HI=8 Sample =F-1 10 Qty =70.7 TOC= C:\VINCI\TJ110419\TJ008.R00 : FID pyrolysis graphic

20 : S1=0.01 S2=0.03 Tmax=363 Tp S2=402.0 PI=0.22 HI=6 Sample =F-1 11 Qty =70.7 TOC= C:\VINCI\TJ110419\TJ009.R00 : FID pyrolysis graphic

21 : S1=0.01 S2=0.05 Tmax=316 Tp S2=355.0 PI=0.21 HI=21 Sample =F-1 14 Qty =70.7 TOC= C:\VINCI\TJ110419\TJ011.R00 : FID pyrolysis graphic

22 : S1=0.01 S2=0.02 Tmax=347 Tp S2=386.0 PI=0.27 HI=18 Sample =F-1 15 Qty =70.9 TOC= C:\VINCI\TJ110419\TJ012.R00 : FID pyrolysis graphic

23 : S1=0.01 S2=0.03 Tmax=321 Tp S2=360.0 PI=0.31 HI=27 Sample =F-1 23 Qty =70.3 TOC= C:\VINCI\TJ110419\TJ013.R00 : FID pyrolysis graphic

24 : S1=0.01 S2=0.04 Tmax=389 Tp S2=428.0 PI=0.2 HI=44 Sample =F-1 24 Qty =70.9 TOC= C:\VINCI\TJ110419\TJ014.R00 : FID pyrolysis graphic

25 : S1=0.01 S2=0.03 Tmax=384 Tp S2=423.0 PI=0.19 HI=30 Sample =F-1 25 Qty =70.7 TOC= C:\VINCI\TJ110419\TJ015.R00 : FID pyrolysis graphic

26 : S1=0.13 S2=0.06 Tmax=291 Tp S2=330.0 PI=0.68 HI=86 Sample =F-1 26 Qty =70.6 TOC= C:\VINCI\TJ110419\TJ016.R00 : FID pyrolysis graphic

27 : S1=0.06 S2=0.04 Tmax=313 Tp S2=352.0 PI=0.59 HI=57 Sample =F-1 27 Qty =70.4 TOC= C:\VINCI\TJ110419\TJ017.R00 : FID pyrolysis graphic

28 : S1=0.01 S2=0.03 Tmax=356 Tp S2=395.0 PI=0.3 HI=100 Sample =F-1 29 Qty =70.6 TOC= C:\VINCI\TJ110419\TJ019.R00 : FID pyrolysis graphic

29 : S1=0.04 S2=0.05 Tmax=324 Tp S2=363.0 PI=0.41 HI=5 Sample =F-1 31 Qty =70.8 TOC= C:\VINCI\TJ110419\TJ020.R00 : FID pyrolysis graphic

30 : S1=0 S2=0.01 Tmax=355 Tp S2=394.0 PI=0.2 HI=2 Sample =F-2 18 Qty =70.7 TOC= C:\VINCI\TJ110419\TJ022.R00 : FID pyrolysis graphic

31 : S1=0 S2=0.01 Tmax=403 Tp S2=442.0 PI=0.21 HI=5 Sample =F-2 19 Qty =70.7 TOC= C:\VINCI\TJ110419\TJ023.R00 : FID pyrolysis graphic

32 : S1=0.01 S2=0.04 Tmax=345 Tp S2=384.0 PI=0.23 HI=6 Sample =F-2 20 Qty =70.9 TOC= C:\VINCI\TJ110419\TJ024.R00 : FID pyrolysis graphic

33 : S1=0.01 S2=0.01 Tmax=346 Tp S2=385.0 PI=0.28 HI=2 Sample =F-2 21 Qty =70.6 TOC= C:\VINCI\TJ110419\TJ025.R00 : FID pyrolysis graphic

34 : S1=0 S2=0.02 Tmax=363 Tp S2=402.0 PI=0.23 HI=5 Sample =F-2 22 Qty =70.6 TOC= C:\VINCI\TJ110419\TJ026.R00 : FID pyrolysis graphic

35 : S1=0.01 S2=0.02 Tmax=316 Tp S2=355.0 PI=0.2 HI=29 Sample =F-2 24 Qty =70.9 TOC= C:\VINCI\TJ110419\TJ027.R00 : FID pyrolysis graphic

36 : S1=0.01 S2=0.02 Tmax=337 Tp S2=376.0 PI=0.26 HI=10 Sample =F-2 25 Qty =70.7 TOC= C:\VINCI\TJ110419\TJ028.R00 : FID pyrolysis graphic

37 : S1=0 S2=0.01 Tmax=341 Tp S2=380.0 PI=0.2 HI=25 Sample =F-2 27 Qty =71.0 TOC= C:\VINCI\TJ110419\TJ029.R00 : FID pyrolysis graphic

38 : S1=0 S2=0.02 Tmax=317 Tp S2=356.0 PI=0.16 HI=100 Sample =F-2 30 Qty =70.4 TOC= C:\VINCI\TJ110419\TJ030.R00 : FID pyrolysis graphic

39 : S1=0.01 S2=0.03 Tmax=435 Tp S2=474.0 PI=0.17 HI=150 Sample =F-2 31 Qty =70.4 TOC= C:\VINCI\TJ110419\TJ031.R00 : FID pyrolysis graphic

40 : S1=0.01 S2=0.02 Tmax=510 Tp S2=549.0 PI=0.21 HI=20 Sample =F-2 32 Qty =70.8 TOC= C:\VINCI\TJ110419\TJ032.R00 : FID pyrolysis graphic

41 : S1=0.01 S2=0.02 Tmax=435 Tp S2=474.0 PI=0.26 HI=15 Sample =F-2 33 Qty =70.8 TOC= C:\VINCI\TJ110419\TJ033.R00 : FID pyrolysis graphic

42 : S1=0.66 S2=12.05 Tmax=443 Tp S2=482.0 PI=0.05 HI=240 Sample =9107 Qty =70.3 TOC= C:\VINCI\TJ110419\TJ034.R00 : FID pyrolysis graphic

43 Dr. Tomasz L. Jerzykiewicz and Ross Stewart at the Alberta Geological Survey Rock-Eval TM Laboratory

44 Some graphical derivations by Chapman Petroleum:

50 Rock-Eval Parameters Direct measurements S1 : the already generated oil in the rock. These are the free hydrocarbons (oil and gas) already present in the sample, and they are distilled out of the sample at initial heating of the sample to a temperature of 350 C. Free hydrocarbons increase with depth. These values may be anomalously high from migration and contamination by drilling fluids and mud. S1 = 1.0 mg HC/g dry rock -- Minimum value for good source rocks. S2 : the amount of hydrocarbons generated through thermal cracking of nonvolatile organic matter (kerogen) when the sample temperature is increased to 550 C. S2 is an indication of the quantity of hydrocarbons that the rock may potentially produce should burial and maturation continue. This parameter normally decreases with burial depths >1 km. S2 >= 5.0 mg HC/dry rock -- Minimum value for good source rocks. S3 : The trapped CO 2 released during pyrolysis up to a temperature of 390 C. This value is proportional to the oxygen present in the kerogen. Carbonate rocks may increase S3 values. T max : The temperature at maximum release of hydrocarbons occurs during Rock-Eval pyrolysis. This occurs at the top of the S2 peak. T max is a maturation parameter that is kerogendependent.

51 Derived measurements HI : Hydrogen index [HI = (S2/TOC) x 100]. The ratio of S2 hydrogen (in mg HC/g dry rock) to total organic carbon (TOC), in grams. The hydrogen index is a measure of the hydrogen richness of the source rock, and when the kerogen type is known it can be used to estimate the thermal maturity of the rock. When plotted against the oxygen index (OI), the HI can be used to provide a crude assesment of the petroleum generative potential in a source rock (Peters and Moldowan, 1993). OI : Oygen index [OI = (S3/TOC) x 100]. The ratio of S3 (mg CO2/g dry rock) to TOC (in grams). This parameter measures the oxygen richness of a source rock and can be used in conjunction with the hydrogen index to estimate the quality and thermal maturity of source rocks. This index is unreliable in rocks with high carbonate content. High OI values (>50 mg/g) are characteristic of immature hydrocarbons. PI : Production index [PI = S 1 /[S 1 + S 2 ]. The production index is the ratio of already generated hydrocarbon to potential hydrocarbons. Low ratios indicate either immaturity or extreme postmature organic matter. High ratios indicate the mature stage or contamination by migrated hydrocarbons or drilling additives. The PI increases steadily with depth and associated hydrocarbon generation.

Rock-Eval and lithogeochemistry of Early to Middle Jurassic black clastic rocks within the Intermontane Basins of British Columbia.

Open File 2011-3 Rock-Eval and lithogeochemistry of Early to Middle Jurassic black clastic rocks within the Intermontane Basins of British Columbia. Filippo Ferri 1, Janet Riddell 1, Carol Evenchick 2