Abstract: On the Stability of Crude Oil in Deep Hot Reservoirs

R. Di Primio, B. Horsfield, H. J. Schenk

The stability of crude oil in deep hot reservoirs has been analysed using laboratory heating experiments and field studies in a three phase research project.

In the first phase a low maturity oil from the North Sea was progressively degraded into gaseous compounds and carbonaceous residues in order to determine kinetic parameters for gas generation. The extrapolation from laboratory to geological heating rates confirmed the observed preservation of liquid hydrocarbons in a North Sea well at a present day temperature of around 165°C.

Confirmation of the determined crude oil stability was subsequently sought in the analysis of three further North Sea oils by the same method. In this second phase of the study some significant differences between oil stabilities were encountered. The observed lower stability of one of the analysed oils was tentatively attributed to the presence of oxygen-rich asphaltenes, which may be active in promoting the degradation of the oil's major components.

In the final stage of this study a comparison of the gas generating potential of produced oil and residual reservoir bitumen indicate that while differences in the gas generating potential exist on a molecular level, the total amount of gas generated as well as the gross composition remain relatively constant. The analysis of produced oil stability can therefore be assumed to be representative for the entire reservoir fluid content. Additionally, and most crucially, the calibration of laboratory-derived oil to gas cracking kinetics to a natural reservoir system is currently being performed using the deep Tuscaloosa gas trend as a case history.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France