Diagenesis and fluid flow in response to uplift and exhumation
Published:January 01, 2002
John Parnell, 2002. "Diagenesis and fluid flow in response to uplift and exhumation", Exhumation of the North Atlantic Margin: Timing, Mechanisms and Implications for Petroleum Exploration, A. G. Doré, J. A. Cartwright, M. S. Stoker, J. P. Turner, N. White
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Uplift of sedimentary rocks is accompanied by a wide range of physical and chemical changes that contribute to diagenesis and modify fluid flow regimes. Topography becomes a major driving force behind fluid flow patterns, and meteoric water may penetrate to several kilometres below the surface. Typical diagenetic processes include alteration and leaching of feldspars and other unstable minerals, precipitation of iron oxides and kaolin, and leaching of carbonate and sulphate cements. Reservoired oil may be degraded by near-surface waters, but reservoir rocks may become more oil-wet.
Brittle fracturing is enhanced near the surface, and fluid flow may become predominantly fracture-bound as fractures dilate. Uplift also causes tilting of fluid contacts and remigration of hydrocarbons. Exsolution and expansion of gas similarly causes remigration of oil to peripheral traps.
Although basin uplift is generally regarded as being detrimental to hydrocarbon prospectivity, especially as a result of breaching of traps, there is also an enhanced potential for hydrocarbon plays based on reserves of exsolved gas, condensate dropout, peripheral traps and fractured reservoirs.
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Exhumation of the North Atlantic Margin: Timing, Mechanisms and Implications for Petroleum Exploration
Northwest Europe has undergone repeated episodes of exhumation (the exposure of formerly buried rocks) due to such factors as post-orogenic unroofing, rift-shoulder uplift, hotspot activity, compressive tectonics, eustatic sea-level change, glaciation and isostatic readjustment. The main observational legacy of this exhumation around the North Atlantic is preserved in the comparatively young (Mesozoic and Cenozoic) geological record of this region. Despite a rapid increase in the understanding of the exhumation of this area, there are still many unknowns: the relative intensity of the various phases and their geographical variation; mechanisms of uplift; primary causes of exhumation. Tied to these problems is the larger-scale question of whether the circum-North Atlantic is unique or whether its behaviour is typical for passive margins.
There have been several attempts in recent years to bring together researchers to address these questions, but these have often focused on one particular geographical area or one particular exhumation phase. Before an integrated story can emerge, disciplines that have traditionally remained apart need to come together: geomorphology and offshore seismic interpretation; Palaeogene and Neogene studies; Scandinavian and British-Irish research schools. This volume represents a first step in this direction by providing an inter-disciplinary set of studies over a wide latitudinal range of the NW European margin.
The studies presented here are based on a variety of techniques that have been employed to address the main concerns of North Atlantic exhumation history, including timing, mechanisms and the sedimentary response of the continental margin. The 25 papers presented in this volume have been arranged in four sections to reflect the highly varied approach to this subject and the commercial implications. Part 1 is concerned with exhumation mechanisms, focusing primarily on the Iceland Plume. Parts 2 and 3 present ongoing research on the continental margin record offshore Scandinavia, Britain, Ireland and the Faroes. The papers in these two parts illustrate the communication that is now occurring between the two regional research schools and the acknowledgement of a multiphase Cenozoic denudation chronology for both areas. Part 4 contains five papers describing the significant changes to the hydrocarbon systems that occur in exhumed basins, detailing the implications for hydrocarbon-bearing basins.
Exhumation of the North Atlantic Margin: Timing, Mechanisms and Implications for Petroleum Exploration is the most up-to-date and complete volume integrating all aspects of the Mesozoic-Cenozoic exhumation of North Atlantic borderlands. Itwill be of interest to those within the oil industry, geomorphologists and other workers with an interest in NW European regional geology.