The dynamic Flory-Huggins-Zuo equation of state

Wang, Kang; Zuo, Julian Y.; Chen, Yi; Mullins, Oliver C.

doi:10.1016/j.energy.2015.08.063

Cited by 12 publications

(14 citation statements)

References 76 publications

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“…According to our recent theoretical research on dynamic FHZ EOS, [29] it is found that asphaltene expulsion is strongly dependent on methane and asphaltenes concentration. The reservoir fluid is described simply as a single fluid phase including only three components: methane (as a typical gas component in light hydrocarbons), maltenes, and asphaltenes.…”

Section: Density Inversion Formation When Gas Charge Into a Black Oilmentioning

confidence: 95%

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Dynamics of Tar Mat Formation Due to Asphaltenes Accumulation Under Gas Charge in Reservoirs

et al. 2015

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Tar mats in reservoirs can cause severe issues in oil production such as preventing aquifer pressure support and water sweep. Therefore, it's important to understand the fluid geodynamics that occur in geologic time that give rise to heavy oil gradients and to tar mats. A common event in reservoirs especially in deepwater is a late gas charge into an oil-filled reservoir. In this case, the gas can quickly migrate to the top of the reservoir through fault planes without mixing (except locally) with the existing reservoir fluid. This newly charge gas can then diffuse down into the oil column thereby significantly altering solution gas and dissolved asphaltene content and their gradients. In particular, an increase in solution gas causes a reduction of asphaltene solubility. This process can result in significant variations in asphaltene concentration throughout the column. Moreover, a density inversion can be created due to the combined effects of methane diffusion and diffusion and expulsion of asphaltenes. This results in convective flow of asphaltene-rich fluids which can yield large asphaltene concentrations and tar mats at the base of the oil column. In addition, rapid gas charge can overwhelm the ability of asphaltenes to migrate thereby leading to upstructure tar deposition. Both scenarios can be associated with Flow Assurance concerns over part or all of the field. In this paper, we discuss case studies that exhibit such potentially problematic fluid columns. Simulated cases are also modeled to provide guidance for understanding the fluid geodynamics. The ability to model density inversion and asphaltenes gravity currents is seen to help significantly in understanding of reservoir fluids dynamics.

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Section: Density Inversion Formation When Gas Charge Into a Black Oilmentioning

confidence: 95%

“…[29] In this case, the fluid in the oil column initially is homogeneous only containing maltenes and asphaltenes. C is the mole concentration.…”

Section: Density Inversion Formation When Gas Charge Into a Black Oilmentioning

confidence: 99%

Dynamics of Tar Mat Formation Due to Asphaltenes Accumulation Under Gas Charge in Reservoirs

et al. 2015

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“…The so-called “dynamic” FHZ EoS with two pseudo-components can be used to determine the time required for equilibrium asphaltene distributions in oil reservoirs without influxes and outfluxes under different initial conditions . Equilibrium fluid distributions are shown to be independent of initial conditions and always converge to the Gibbs sedimentation criterion characterized by the FHZ EoS.…”

Section: Modeling For Reservoir Fluid Geodynamicsmentioning

confidence: 99%

“…The second enabler for RFG has been the development of the industry’s first equation of state for asphaltene gradientsthe Flory–Huggins–Zuo Equation of State (FHZ EoS) − and its reliance on the Yen–Mullins model of asphaltenes. , The FHZ EoS can model the gradient of asphaltene content of crude oil within a reservoir if the fluid has achieved thermodynamic equilibrium. Equilibrium indicates the fluid chemical composition is no longer changing with time, which generally occurs long after reservoir charging is complete; reservoir charging refers to the entry of new fluids into the reservoir.…”

Section: Introductionmentioning

confidence: 99%

Reservoir Fluid Geodynamics: The Chemistry and Physics of Oilfield Reservoir Fluids after Trap Filling

et al. 2017

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Oilfield reservoirs exhibit a wide array of complexities that have great impact on the efficiency of oil production. Major challenges include delineating overall reservoir architecture and the distributions of the contained fluids. Reservoir crude oils consist of dissolved gases, liquids, and dissolved solids (the asphaltenes); the corresponding compositional variations and phase transitions within reservoirs greatly impact production strategies and economic value. Standard workflows for understanding reservoir (rock) architecture are subsumed in the discipline “geodynamics”, which incorporates the initial rock depositional setting and subsequent alterations through geologic time to yield the present-day reservoir. However, reservoir fluids are not generally treated in such a systematic manner. Petroleum system modeling provides the timing, type, and volume of hydrocarbon fluids that charge into reservoirs. However, there is little treatment regarding how these fluids change after filling the reservoir. A significant limitation had been the lack of thermodynamic treatment of asphaltenes in reservoir crude oils. Consequently, projecting reservoir fluid properties away from the wellbore has been problematic. “Reservoir fluid geodynamics” (RFG) is the newly formalized discipline that incorporates changes in the distributions of reservoir fluids and phase transitions over geologic time. A key enabling advance is the recently developed ability to treat asphaltene gradients in oilfield reservoirs using the Flory–Huggins–Zuo equation of state (FHZ EoS) with its reliance on the Yen–Mullins model of asphaltenes. In addition, in situ downhole fluid analysis in oil wells provides accurate vertical and lateral fluid gradients in reservoirs in a cost-effective manner. Thermodynamic equilibrium can now be recognized; equilibrated fluids imply connected reservoirs, meaning a single flow unit. Disequilibrium fluid gradients imply ongoing or recent fluid processes in geologic time. The analysis of 35 oilfields (with more than 100 oil reservoirs) has allowed the identification of various reservoir fluid geodynamic processes. Some processes, such as biodegradation, have long been studied; nevertheless, even in these cases, inclusion of the thermodynamic modeling yields accurate predictions of distributions of key fluid attributes. Many other RFG processes are elucidated herein and are shown to impact major reservoir concerns for production. The resulting fundamental understanding of the physics and chemistry of these RFG processes enables measurements made at the wellbore to be used as a basis for accurate prediction of fluid properties throughout the reservoir.

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“…Recently, the Flory-Huggins-Zuo (FHZ) EoS was developed, which models gradients in asphaltene concentration based on the sizes of asphaltene molecules and aggregates described in the Yen-Mullins model, which synthesizes many of the results presented here. − Figure shows how the FHZ EoS can match gradients in a variety of fluid types, if the appropriate asphaltene particle size is used. The broad applicability of the equation has enabled its use in a variety of reservoirs, including those that are out of thermodynamic equilibrium, undergoing active gas entry, or undergoing biodegradation. − …”

Section: Application: Formation Evaluation In Conventional Reservoirsmentioning

confidence: 99%

Toward Molecule-Specific Geochemistry of Heavy Ends: Application to the Upstream Oil Industry

Pomerantz

2016

Ind. Eng. Chem. Res.

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Detailed molecular analysis of the composition of petroleum is typically performed on only the light (volatile) fraction, using analyses involving gas chromatography (GC). Heavier (nonvolatile) components such as kerogen, bitumen, and asphaltenes, which are relevant to conventional reservoirs and particularly to unconventional gas shale and tight oil formations, are not amenable to analysis by GC and instead are typically studied by more phenomenological techniques. This report describes a suite of analytical techniques that can provide sufficient average molecular information on the heavy ends (defined as the nonvolatile fraction) to be useful for a variety of industrial applications, expanding the discipline of molecule-specific geochemistry into the non-GC amenable fractions of petroleum materials. Heavy ends are composed of the elements C, H, N, S, and O, and the bonding environments of each can be measured by various solid state spectroscopies: nuclear magnetic resonance (NMR) and infrared (IR) spectroscopies for C, H, and O; X-ray absorption near-edge structure (XANES) spectroscopy for S and N. Additionally, advances in mass spectrometry, including techniques such as laser desorption laser ionization mass spectrometry (L 2 MS), can be used to measure the molecular weight and dominant molecular architecture of asphaltenes. Moreover, higher-order structures can be measured: samples of kerogen with representative pore geometry can be prepared, and those pore systems are analyzed with techniques such as X-ray diffraction and neutron scattering. Colloidal structures of asphaltenes can be measured with a variety of techniques, which reveal a hierarchical aggregation structure. These analyses provide sufficient structural data to enable structure−property and structure− function relationships to be determined, which can be applied to the characterization of conventional and unconventional resources. In gas shale and tight oil formations, which contain abundant inorganic minerals as well as kerogen, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) is used for simultaneous analysis of mineralogy, kerogen content, and maturity, typically performed at the wellsite. In conventional reservoirs, spatial variations in the asphaltene concentration measured by downhole fluid analysis logging tools are being interpreted with a recently developed equation of state to address upstream issues such as reservoir connectivity, tar mat formation, and fault block migration. As more heavy end analyses are developed, further scientific knowledge and industrial applications of heavy end geochemistry are anticipated.

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The dynamic Flory-Huggins-Zuo equation of state

Cited by 12 publications

References 76 publications

Dynamics of Tar Mat Formation Due to Asphaltenes Accumulation Under Gas Charge in Reservoirs

Dynamics of Tar Mat Formation Due to Asphaltenes Accumulation Under Gas Charge in Reservoirs

Reservoir Fluid Geodynamics: The Chemistry and Physics of Oilfield Reservoir Fluids after Trap Filling

Toward Molecule-Specific Geochemistry of Heavy Ends: Application to the Upstream Oil Industry

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