Autor: fbenelli

Complex phase behaviours related to gas injection in reservoir fluids

Posted on by fbenelli

La recuperación mejorada de petróleo (EOR, por sus siglas en inglés) incluye técnicas como la inyección de gases (como gas natural, nitrógeno o dióxido de carbono) en el yacimiento para aumentar la presión y desplazar el petróleo hacia los pozos de producción. Para que este proceso sea eficaz, es crucial que el gas inyectado y el petróleo alcancen un estado homogéneo. En particular, la Presión Mínima de Miscibilidad por Primer Contacto (FC-MMP) proporciona una estimación inicial confiable y segura de la presión necesaria para la EOR.

Este estudio presenta un algoritmo eficiente para calcular diagramas completos de presión (P) frente al porcentaje de gas inyectado a una temperatura fija (x), usando ecuaciones cúbicas de estado tradicionales. El algoritmo permite analizar diagramas Px en casos complejos, como regiones de tres fases, y estudiar el comportamiento cualitativo y cuantitativo de estos. Se evalúan diferentes fluidos de yacimientos, con y sin asfaltenos, y se analizan los efectos de inyectar gases como dióxido de carbono, nitrógeno y mezclas de gas natural sintético. También se examina el impacto de los parámetros de interacción en el equilibrio de fases y la FC-MMP, considerando la precipitación de asfaltenos en yacimientos convencionales y no convencionales. Finalmente, se comparan la FC-MMP y la MMP de contacto múltiple (MC-MMP).

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Predicting Oil Recovery from Liquid-Rich Shale Coupling Thermodynamics and Molecular Diffusion from Understanding to Practice

Posted on by fbenelli

Dr. Maria A. Barrufet – TEXAS A&M UNIVERSITY

Recent developments in technology have transformed unconventional low-permeability shales to reliable energy sources. Unconventional resources are more abundant than conventional ones in terms of hydrocarbon capacity; however, to increase the extremely low hydrocarbon recoveries from liquid-rich shale remains a global challenge to the energy sector community including academics, industry, and governmental organizations.

Based or published pore size distributions for shale formations, pores smaller than 40 nm hold up 40 to 50% of the hydrocarbons. The same reservoir models used for conventional reservoirs cannot explain the fundamental mechanisms taking place when producing unconventional resources in terms of fluid flow and thermodynamic properties. Diffusion, which is negligible in conventional reservoirs with pore sizes 4 to 5 orders of magnitude larger than the fluid molecules, becomes the dominant flow mechanism in tight shale formations. Rock-fluid interactions including capillary pressure become more significant and fluids are said to be confined.

Mass transfer, whether induced (i.e., gas-assisted) or from depletion, in liquid-rich shales requires a solid understanding of the thermodynamic and transport behavior of fluids in confined media. The flow behavior in confinement can significantly impact the recoveries, whether production takes place under depletion or using some assisted recovery scheme.

History matching can always be achieved, often at the expense of using wrong or heavily correlated parameters that lead to non-unique and/or unreliable forecasting. Our goal is to use physics based models that can be readily applied and integrated into the mathematical mainframe of commercial simulators.

There have been several experimental and numeric efforts to investigate various gas injection/cycling scenarios to improve the oil recovery of shale. With this presentation I provide a brief overview of current approaches to describe confinement along with their advantages, limitations, uncertainties, and the reasoning that led us (my group) to choose a particular approach.

We incorporated confinement in our thermodynamic model and validated the observed phenomena of bubble point pressure depression, and higher gas-oil-ratios for condensate systems. We have also proposed a model dominated by diffusion flow to model oil production from a modified huff-and-puff gas-assisted recovery and validated this approach from lab experiments within our group.

I will walk you through our research stages, modeling simplifications, experimental results, disappointments, accomplishments, current standing and future goals.