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Technical Paper: Investigation of Formation Connectivity Using Asphaltene Gradient Log Predictions Coupled with Downhole Fluid Analysis

Society: SPE
Paper Number: 124264
Presentation Date: 2009
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Abstract

Downhole fluid analysis (DFA) is an essential tool for determining compositional gradients in real time at reservoir conditions. However, DFA analysis of flow connectivity in the reservoir can be complex, especially when the reservoir fluid compositional gradients are small with depth. In this case, the analyses of bulk fluid properties may not be sufficiently sensitive. However, DFA of asphaltene gradients provides an excellent method to delineate the complexity of black oil columns. Moreover, DFA measurements are very sensitive to and often linear in the asphaltene content.

Authors present a methodology to estimate downhole fluid coloration variations with depths using an equation-of-state (EOS) approach coupled with the DFA tools. The tools are used to determine downhole fluid compositions of CO2, C1, C2, C3–C5, C6+, and the coloration associated with asphaltene contents. Delumping and characterization procedures are applied to obtain detailed compositions including asphaltenes and the parameters of the EOS model. Fluid profile and coloration logs are computed by “tuning” the molar mass of asphaltene nanoaggregates against the DFA coloration logs.

The methodology has been successful in investigating reservoir connectivity for offshore and laboratory centrifugation cases. Results demonstrate it is useful for reducing uncertainties related to reservoir compartmentalization and for optimizing DFA during logging. In addition, treating part of the Cn+ (e.g., C36+) fraction as an asphaltene component (monomer) in the traditional cubic EOS approach is contradicted by the recent observations that asphaltenes are nanoaggregates in crude oils.

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