Publication Date:
2022-05-25
Description:
Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Organic Geochemistry 41 (2010): 812-821, doi:10.1016/j.orggeochem.2010.05.003.
Description:
Hydraulic connectivity of petroleum reservoirs represents one of the biggest uncertainties for
both oil production and petroleum system studies. Here, a geochemical analysis involving bulk and
detailed measures of crude oil composition is shown to constrain connectivity more tightly than is
possible with conventional methods. Three crude oils collected from different depths in a single well
exhibit large gradients in viscosity, density, and asphaltene content. Crude oil samples are collected
with a wireline sampling tool providing samples from well‐defined locations and relatively free of
contamination by drilling fluids; the known provenance of these samples minimizes uncertainties in the
subsequent analysis. The detailed chemical composition of almost the entire crude oil is determined by
use of comprehensive two‐dimensional gas chromatography (GC×GC) to interrogate the nonpolar
fraction and negative ion electrospray ionization Fourier transform ion cyclotron resonance mass
spectrometry (ESI FT‐ICR MS) to interrogate the polar fraction. The simultaneous presence of 25‐
norhopanes and mildly altered normal and isoprenoid alkanes is detected, suggesting that the reservoir
has experienced multiple charges and contains a mixture of oils biodegraded to different extents. The
gradient in asphaltene concentration is explained by an equilibrium model considering only gravitational
segregation of asphaltene nanoaggregates; this grading can be responsible for the observed variation in
viscosity. Combining these analyses yields a consistent picture of a connected reservoir in which the
observed viscosity variation originates from gravitational segregation of asphaltene nanoaggregates in a
crude oil with high asphaltene concentration resulting from multiple charges, including one charge that
suffered severe biodegradation. Observation of these gradients having appropriate magnitudes
suggests good reservoir connectivity with greater confidence than is possible with traditional techniques
alone.
Description:
The mass spectrometry work was
supported by the NSF Division of Materials Research through DMR‐06‐54118, and the State of Florida.
Keywords:
Compositional grading
;
Reservoir connectivity
;
Comprehensive two‐dimensional gas chromatography
;
GC×GC
;
Fourier transform mass spectrometry
;
Ion cyclotron resonance
;
FTMS
;
FT‐ICR
;
Electrospray ionization
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
Format:
application/pdf
