SECTION 4,
LIGHT END - LIQUID RELATIONSHIPS
  • IDEAL RELATIONSHIP IN PYROLYSATES AND UNALTERED OILS

    There is a consistent relationship between SF(C3-nc5) and SF(P15-P25) in unaltered oils, as initially described under the heading "SLOPE FACTOR RELATIONSHIPS" in the Glossary. Supporting evidence is presented here.

    Figure 12 , Sections 1 and 2, illustrates the closely similar features of two pyrolysates of a petroleum asphaltene and a selected reservoir fluid. The latter is one of a small number of cases among the examined PVT analyses which are deemed unaltered. The latter principally derive from the Rainbow-Virgo-Zama field area. Figure 17 illustrates the values of SF(C3-nC5) and SF(P15-P25) in the unaltered oils, and the relationship between the two slope factors. The figure also depicts the relationship in five asphaltene pyrolysates, representing increasing levels of severity and maturity.

    Figure 17 presents the regressions linking the variables, showing that the pyrolysate data closely conforms to the PVT data. It is desired to be able to estimate the "theoretical" or "hypothetical" value of light end slope which should accompany the observed liquid slope under normal conditions of maturation and in the absence of alteration. For this purpose the asphaltene data was recast to provide the inverse regression, given in the equation below:

    SF(C3-nC5)[Hypothetical] = 2.786 * SF(P15-P25) - 1.615, r = 0.88, n = 5.

    This equation is employed to determine "E3", a measure of light end enrichment or depletion, as described in the Glossary.

    Figure 18 expands the data representing the variables of Figure 17 to a large random selection of oils and gas-condensates from western Canada.


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