New insights into reservoir filling and mixing processes

Stainforth, J. G.

doi:10.1144/gsl.sp.2004.237.01.08

Cited by 40 publications

(29 citation statements)

References 28 publications

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“…Oil compositional gradients and resulting vertical and lateral oil viscosity variations (discussed below) are common on both reservoir thickness (tens of meters) and field scales (kilometers) and are a defining characteristic of heavy oilfields. Such gradients in a minority of heavy oilfields can certainly be produced by restricted vertical mixing and by density stratification of an evolving oil charge, as originally suggested by Khavari-Khorasani et al ( 1998 ) and more recently by Stainford ( 2004 ). Importantly it is in-reservoir oil biodegradation that substantially produces the systematic compositional gradients seen in heavy oilfields (Larter et al, 2003 ).…”

Section: An Introduction To Heavy Oil Systemsmentioning

confidence: 80%

Life in the slow lane; biogeochemistry of biodegraded petroleum containing reservoirs and implications for energy recovery and carbon management

2014

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Our understanding of the processes underlying the formation of heavy oil has been transformed in the last decade. The process was once thought to be driven by oxygen delivered to deep petroleum reservoirs by meteoric water. This paradigm has been replaced by a view that the process is anaerobic and frequently associated with methanogenic hydrocarbon degradation. The thermal history of a reservoir exerts a fundamental control on the occurrence of biodegraded petroleum, and microbial activity is focused at the base of the oil column in the oil water transition zone, that represents a hotspot in the petroleum reservoir biome. Here we present a synthesis of new and existing microbiological, geochemical, and biogeochemical data that expands our view of the processes that regulate deep life in petroleum reservoir ecosystems and highlights interactions of a range of biotic and abiotic factors that determine whether petroleum is likely to be biodegraded in situ, with important consequences for oil exploration and production. Specifically we propose that the salinity of reservoir formation waters exerts a key control on the occurrence of biodegraded heavy oil reservoirs and introduce the concept of palaeopickling. We also evaluate the interaction between temperature and salinity to explain the occurrence of non-degraded oil in reservoirs where the temperature has not reached the 80–90°C required for palaeopasteurization. In addition we evaluate several hypotheses that might explain the occurrence of organisms conventionally considered to be aerobic, in nominally anoxic petroleum reservoir habitats. Finally we discuss the role of microbial processes for energy recovery as we make the transition from fossil fuel reliance, and how these fit within the broader socioeconomic landscape of energy futures.

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Section: An Introduction To Heavy Oil Systemsmentioning

confidence: 80%

Life in the slow lane; biogeochemistry of biodegraded petroleum containing reservoirs and implications for energy recovery and carbon management

2014

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“…2 This has been referred to as the Stainforth charge mechanism. 2 Frequently in reservoirs, there are high conductivity pathways or charge plains that enable fluids to enter reservoirs without mixing with the oil already in the reservoir.…”

Section: Stainforth Charge Mechanism and Thermal Maturity Indicatorsmentioning

confidence: 99%

A Geological Model for the Origin of Fluid Compositional Gradients in a Large Saudi Arabian Oilfield: An Investigation by Two-Dimensional Gas Chromatography (GC × GC) and Asphaltene Chemistry

et al. 2015

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The heavy oil rim of a large Saudi Arabian oilfield has been shown to be in vertical and lateral equilibrium, matching predictions of the gravity term from the Flory-Huggins-Zuo equation of state for asphaltenes in the form of 5.2 nm clusters of the Yen-Mullins model. The large (10x) vertical gradient of asphaltene concentration over a very large perimeter (>> 10 km) of the oilfield provided a stringent test of this equation of state fit. Two-dimensional gas chromatography (GC×GC) and stable isotope analysis δD and δ 13 C were used to determine consistency of the liquid phase components with equilibration and the effects of biodegradation or thermal maturity on the observed asphaltene gradient. These analyses confirm homogeneity of equilibrated liquid phase components of similar chemical character and equilibrated asphaltene isotopes. Biodegradation is minimal and there is no maturity variation among the samples. Thus, the large asphaltene gradient did not result from these secondary processes and is not remnant from how the reservoir charged with crude oil. The results are consistent with original findings that the oil column is equilibrated. Thermodynamic equilibration over such large distances (>10 km) requires convective currents and provides constraints on fluid dynamic processes in reservoirs. A simple 1-D three-component single-phase model is introduced to account for asphaltene accumulation by way of convective currents established from a diffusive gas front at the top of the oil column.

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“…A subsequent charge of a lighter hydrocarbon could have occured; in a normal burial sequence, the kerogen generates lighter hydrocarbon with longer times and greater temperature. The lighter hydrocarbon often goes to the top of the reservoir without good mixing (Stainforth 2004). This lighter hydrocarbon (could even be gas) can diffuse into the oil column and causing instability of the asphaltene .…”

Section: Figurementioning

confidence: 99%

Black Oil, Heavy Oil and Tar in One Oil Column Understood by Simple Asphaltene Nanoscience

et al. 2012

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A Jurrasic oilfield in Saudi Arabia is characterized by black oil in the crest and with mobile heavy oil underneath and all underlain by a tar mat at the oil-water contact. The viscosities in the black oil section of the column are fairly similar and are quite manageable from a production standpoint. In contrast, the mobile heavy oil section of the column contains a large continuous increase in asphaltene content with increasing depth extending to the tar mat. The tar shows very high asphaltene content but not monotonically increasing with depth. Because viscosity depends exponentially on asphaltene content in these oils, the observed viscosity varies from several to ~ 1000 centipoise in the mobile heavy oil and increases to far greater viscosities in the tar mat. Both the excessive viscosity of the heavy oil and the existence of the tar mat represent major, distinct challenges in oil production. Conventional PVT modeling of this oil column grossly fails to account for these observations. Indeed, the very large height in this oil column represents a stringent challenge for any corresponding fluid model. A simple new formalism to characterize the asphaltene nanoscience in crude oils, the Yen-Mullins model, has enabled the industry's first predictive equation of state (EoS) for asphaltene gradients, the Flory-Huggins-Zuo (FHZ) EoS. For low GOR oils such as those in this field, the FHZ EoS reduces to the simple gravity term. Robust application of the FHZ EoS employing the Yen-Mullins model accounts for the major property variations in the oil column and by extension the tar mat as well. Moreover, as these crude oils are largely equilibrated throughout the field, reservoir connectivity is indicated in this field. This novel asphaltene science is dramatically improving understanding of important constraints on oil production in oil reservoirs.

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New insights into reservoir filling and mixing processes

Cited by 40 publications

References 28 publications

Life in the slow lane; biogeochemistry of biodegraded petroleum containing reservoirs and implications for energy recovery and carbon management

Life in the slow lane; biogeochemistry of biodegraded petroleum containing reservoirs and implications for energy recovery and carbon management

A Geological Model for the Origin of Fluid Compositional Gradients in a Large Saudi Arabian Oilfield: An Investigation by Two-Dimensional Gas Chromatography (GC × GC) and Asphaltene Chemistry

Black Oil, Heavy Oil and Tar in One Oil Column Understood by Simple Asphaltene Nanoscience

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