Simulating petroleum composition

Evolving petroleum composition during maturation is needed as input for PVT models, and this can be provided by low temperature pyrolysis conducted under closed system conditions.

There are numerous systems available, but all of them generate predominantly polar products, and there is no single correct way of simulating petroleum generation. The method we use, microscale sealed vessel (MSSV) pyrolysis, utilizing milligram quantities of kerogen or asphaltene, is an inexpensive batch technique for reproducibly (+/-3%; Quantum MSSV-2 Thermal Analyzer ) quantifying C1+ volatile pyrolysis products in a single analytical step using gas chromatography (Horsfield et al., 1989).

The utility of MSSV pyrolysis has been demonstrated by comparison with field data.

MSSV Pyrolysis Calibration

Compositional mass balances:

For Tithonian source rocks of the Sonda de Campeche and Duvernay Formation of the Western Canada Basin, MSSV pyrolysis compound classes and individual compounds matched those from a compositional mass balance of residual kerogens (Horsfield et al., 2001; Santamaria & Horsfield, 2004).

Gas-oil ratio calibration:

In the Sonda de Campeche, field GORs increase from 45 Sm3/Sm3 in the NE to 550 Sm3/Sm3 in the SW. Migration is essentially vertical along faults, and petroleum compositions directly reflect the maturity of the underlying Tithonian source rock (Santamaria et al., 1998). Thus, the relationship between GOR and Transformation Ratio is known. Predicted GOR from MSSV pyrolysis (C1-C5/C6+) matches that of the petroleum accumulations (Santamaria & Horsfield, 2004).

Black to light oil GOR distributions in the North Sea Viking Graben closely matched the predictions of MSSV pyrolysis experiments performed on the Draupne Formation source rock (di Primio & Skeie, 2004). Of special interest in this case was the observed very good match of laboratory predictions and observed GORs in high-pressure high-temperature reservoirs.