Overview of Kinetics Technology

Sirius Exploration Geochemistry can determine source-rock kinetics in several ways. Our most-common and preferred method is to use a single pyrolysis run made on an extracted rock sample using our Source Rock Analyzer (SRA) at a heating rate of 30°C per minute. We then specify the A factor and from the pyrolysis data and A we derive the activation-energy distribution from the pyrolysis data using the proprietary ORFA software, which was developed jointly with StratoChem Services. For A we use ORFA’s default value, which is 2×1014 s-1 (Waples, in press, 2000; Waples et al., 2002, 2010). Numerous tests by StratoChem have shown that Ea distributions derived from a single pyrolysis run are essentially identical to those derived from the standard three pyrolysis runs (Waples, in press). In addition, the one-run kinetics are much quicker and less expensive to generate. For further information, visit StratoChem’s ORFA page.

Left: Pyrolysis data from laboratory analysis (yellow), showing excellent quality of fit by cyan values predicted by the activation-energy distribution (right) selected by StratoChem’s ORFA software. Not shown here is the A factor, which was specified as 2×10^14 s^-1.

Left: Plot showing excellent fit between measured laboratory pyrolysis curve (yellow) and pyrolysis yield predicted from using the kinetic parameters derived by our ORFA software (cyan). Right: Activation-energy distribution derived by ORFA that was used in calculating the cyan pyrolysis curve. Not shown here is the A factor, which was specified as 2×1014 s-1.

An alternative method is to determine the Ea distribution from archived Rock-Eval or SRA data. This technique can often work very well for data obtained on the Rock-Eval 6 or the SRA, but is unlikely to be successful using data acquired on the Rock-Eval 2. The other main disadvantage is that archived data were almost certainly acquired on unextracted samples. If those samples were contaminated or stained by migrated oil, or if large amounts of generation have occurred, it is difficult or impossible to obtain reliable kinetics. The main advantages of the archived data approach are that (1) new samples are not required, (2) it is less expensive than analyzing new samples, and (3) in favorable situations, this approach allows one to acquire very large data bases.

A third method is to convert published or previously acquired kinetics data that have an A factor that is suspect, wrong, or simply inconvenient to a new A factor, such as our favored one, 2×1014 s-1. This conversion involves a simple algebraic operation that requires neither rock samples nor new laboratory analyses. We offer this service. This step is always advisable when working with published kinetics data or data generated by other laboratories, and is essential if the original A factor differs significantly from our favored value, since some A factors are scientifically unreasonable (Waples, in press). Use of kinetics with incorrect A factors (and correspondingly wrong Ea distributions) can cause serious errors in estimating maturity levels in maturity modeling (Stainforth, 2009; Waples, in press).

Published and converted activation-energy distributions and their corresponding A factors. Left: published data for the Mae Sot kerogen (Type I, onshore Thailand [Tegelaar and Noble, 1994]). Right: Converted Ea distribution when A is set to 2×10^14 s^-1.

Published and converted activation-energy distributions and their corresponding A factors. Left: Published data for the Mae Sot kerogen (Type I, onshore Thailand [Tegelaar and Noble, 1994]). Right: Converted Ea distribution when A is set to 2×1014s-1.

The importance of using kinetics with a reasonable A factor is clear when we compare the results of modeling at geological temperatures. The example below shows the relationship between Transformation Ratio and Ro for both the original and adjusted Mae Sot kinetics. Exploration conclusions using the two sets of kinetics might be very different.

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Finally, ORFA can separate the standard kinetics, which do not distinguish oil generation from gas generation, into separate kinetics for oil and gas. The resulting kinetics will give a more accurate picture of the timing of generation of each phase. This transformation can be applied to any existing Ea distribution. It is an estimate rather than an exact measurement, but it is based on trends of existing data in which such kinetics have been directly measured. Other kinetics software does not offer this option.

Left: Kinetics for the Green River Shale, which generates about 10% gas. Right: Kinetics for the Abu Roash “D”, which is a Type III kerogen that generates a higher percentage of gas. Cyan histograms show total hydrocarbon kinetics, while the other two displays divide those kinetics into oil (green) and gas (red) kinetics, displayed in two different formats.

Top: Kinetics for the Green River Shale, which generates about 10% gas. Bottom: Kinetics for the Abu Roash “D”, which is a Type III kerogen that generates a higher proportion of gas. Cyan histograms show total hydrocarbon kinetics, while the other two displays divide those kinetics into oil (green) and gas (red) kinetics, displayed in two different formats. All this output was derived using our proprietary ORFA software.