Combining biomarker and bulk compositional gradient analysis to assess reservoir connectivity

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.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.The mass spectrometry work was supported by the NSF Division of Materials Research through DMR‐06‐54118, and the State of Florida

Mathematical modeling of the mechanisms of bubble transport in single capillaries

A generalized lubrication approach for channels of arbitrary cross section was developed. This was applied to the steady state motion ofsemi-infinite and finite isolated bubbles in circular capillaries and bubbles present in bubble trains. A matching technique based on a composite equation which is valid in both the thin film and cap regions was found to extend the range of bubble speeds by an order of magnitude in which the lubrication approximation agreed with two dimensional solutions of the Stokes equation. While film thickness decreased with quality for bubble trains, pressure drop was not a function of quality for a mobile gas-liquid interface. In addition, this general approach was applied to semi-infinite bubbles in square capillaries. Snap-offof axisymmetric gas threads at a single-mode constriction in circular and square channels was modeled with the generalized lubrication equation. The approach was a weakly nonlinear one which utilized an asymptotic expansion in the constriction strength. The initial successive excitation of the higher harmonics was studied with a short-time approximation. The eventual dominance of a small band of wavenumbers was deduced from a large-time approximation. Simple leading order approximations ofthe snap-off time were derived and found to be upper bounds for experimental data. The effect ofsurfactant transport on the front of a semi-infinite bubble was modeled with the inclusion of the transport equations for both the interface and bulk liquid. Two models were developed in which the two-dimensional transport problem could be reduced to a one-dimensional set oflubrication equations. In the first, equilibrium was established instantaneously between the interface and the bulk liquid. Finite resistance to mass transfer was included in the second model. Both models predicted a maximum increase of a factor of 2.5 over the pure system results for film thickness and pressure drop across the front interface. For large bubble speed, the models approach the pure system model. However, at moderate and low bubble speed, the predicted film thickness is qualitatively similar to measured film thicknesses for pure system. This indicates that adsorbed impurities could be the cause ofthe discrepancy between measured film thickness and the pure system theory.Chemical and Biomolecular Engineering, Department o