Kerogen volatiles

The randomness of the extrapolated values of about 25%, regardless of temperature, makes it safe to assume that no portion of that 25% is carbon dioxide. Of the other volatile components, 25% of the 28% in the original feed may constitute the low temperature kerogen, leaving 3%. This value is supported by the results of runs in which the shale was at temperatures high enough to achieve full low temperature weight loss (900°-1000°F), but inadequate to go any further. In these runs, the final OVC was 3.3-3.4%. 

Studies of bitumens have been far more extensive than studies of kerogen due to the relative ease with which extractable and volatile hydrocarbons can be analyzed (e.g.. Summons and Walter, 1990). The carbon skeletons found prominently include algal steroids, bacterial hopanoids, and archaeal polyisoprenoids. 

A variety of pyrolytic techniques were applied for the analysis of kerogens [19]. One of these techniques is the sealed vessel pyrolysis where the sample is heated for relatively long periods of time In a sealed vessel and the pyrolytic products analyzed off-line by conventional analytical techniques (GC, GC/MS, FTIR, etc.) [36]. Another technique is bulk flow pyrolysis in which the whole sample is pyrolysed at constant or in gradient temperature in a gas flow with on-line monitoring of the evolving volatiles [37]. This technique is closer to a thermal method of analysis than pyrolysis. 

Fig. 4.15 A van Krevelen plot showing the evolutionary trends of the main kerogen types (shaded bands after Behar Vandenbroucke 1987) and most coals (between solid lines after Killops etal. 1998). With increasing maturity kerogens follow a path towards the origin, as shown for the low/high-H coals boundary.The main hydrocarbon-generation zones are shown, with their approximate rank boundaries (as vitrinite reflectance values, %Ro), together with the effect of loss of various volatiles from different kerogen compositions (CH2 = oil). Points represent the composition of kerogens in Fig.4.14.

Barth T., Borgund A.E., Hopland A.L., Graue A. (1988) Volatile organic acids produced during kerogen maturation—amounts, composition and role in migration of oil. Org. Geochem. 13, 461—5. 

Particle Size, mm Total Volatile- Hydrocarbon Yield, % of Kerogen Light Hydrocarbon Yield, % of Total Volatile Hydrocarbon Light Hydrocarbon Yield, % of Kerogen... 

Ra = R3 -h (10Rc)/0.9. The RC (residual carbon) term represents heavy bitumens or recycled kerogens not directly volatilized by pyrolysis, but that could be oxidized to CO2 or CO in the separate oxidation step (Lafargue et al. 1997). Flowever, the Kuparuk formation often contains cements, siderite among others, which decompose to CO2 or CO at temperatures reached in the oxidation step of Rock-Eval 6 analysis. Unacceptable variability in RC was observed in pyrolysis of Kuparuk samples, possibly because of decomposition of carbonate minerals. Therefore, a Y coefficient was adopted to correlate Rock-Eval 6 pyrolysis results to petroleum density, where F=(R1+R2)/ (R1 +R2 + R3). 

Most of the information on S S values of the reduced sulfur in sediments derives from both acid volatile sulfide (FeS) and pyrite (Fe 2). In a few cases, both sulfate and other sulfur species were isotopically compared. Due to analytical difficulties, organic sulfur and elemental sulfur isotope (S S) ratios were studied only in cases where the secondary enrichment led to OM rich in sulfur. This secondary enrichment forms type II-S kerogens. 

Kawamura K., Tannenbaum E., Huizinga B. and Kaplan I. R. (1986) Volatile organic acids generated from kerogen during laboratory heating. Geochem. J. 20, 51-59. 

Therefore we attempted to simulate advanced pyrolysis using a multi-step model (MSM). This model was developed using TGA- and DSC-derived kinetic coefficients, determined for chemically and thermally treated oil shale samples by modelling particular reaction steps. The MSM is based on the reaction scheme shown in Fig. 4-116 which displays a series of parallel and consecutive first order reactions. K and B denote the kerogen and bitumen originally present in the oil shale B, B, and to /Jj are non-volatilized intermediates and products (solids and liquids) to are volatilized products (gases and vapors) and/j to/jg are the stoichiometric coefficients that fulfil the condition ... 

Petroleum is originally formed from insoluble organic matter called kerogen by pyrolysis under elevated temperatures up to 150 °C. Different factors contributed to the migration of fluids that are composed of alkanes and aromatics (Table 7.1). Cracking of long alkane chains into volatile components, such as methane, leads to pressure buildup in the reservoir. High reservoir temperatures (200 °C) also enhance the pressure accumulation under certain circumstances [1]. 

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