Subsurface Sand Remobilization and Injection
CONTAINS OPEN ACCESS
Sand injectites form during shallow-crustal deformation. Short periods of elevated pore-fluid pressure, which developed regionally, triggered formation of hydrofracture networks into which sand was sometimes injected. Sand injection complexes preserve a record of this process and sandstone intrusions are significant reservoirs in many petroleum systems. Most known subsurface sand injection complexes are from offshore NW Europe and associated with Paleogene strata. Outcrop occurrence is global. Sand injection into unconventional host rocks, including granitoid and metamorphic basement and coal seams, raises awareness of the breadth of geological environments in which sand injection may occur. Discordance between sandstone intrusions and sedimentary hosts occurs on a scale from millimetres to kilometres and is a fundamental diagnostic of intrusions. Microscale textural characterization provides new opportunities to establish possible additional criteria for differentiating intrusions from depositional sandstone. The significance of sand injection complexes in shallow crustal evolution is exemplified by the wide range of lithological hosts and diverse tectonostratigraphic settings documented in this volume. Potential for original research still remains.
Characteristics of a wing-like sandstone intrusion, Volund Field
Published:June 24, 2021
Nicholas Satur, Andrew Hurst, Asgeir Bang, Ivar Skjærpe, Sarah Alexandra Muehlboeck, 2021. "Characteristics of a wing-like sandstone intrusion, Volund Field", Subsurface Sand Remobilization and Injection, S. Silcock, M. Huuse, M. Bowman, A. Hurst, S. Cobain
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Reservoirs in the Volund Field are all sandstone intrusions with wings on three sides forming the main reservoir volumes. The southern wing was the target of exploration and appraisal wells, which led to the field development. Identification of three smaller intrusions proves the southern wing to be a composite intrusion, similar to outcrop analogues. Identification from core and borehole logs shows that it comprises sandstone-, mudstone- and mudstone-rich intervals, including mudstone clast breccia. Mudstone clast breccia constitutes a significant missed pay candidate. Breccia is porous and has a sand-supported matrix, which gives it excellent reservoir quality. This may be missed pay using analysis of borehole logs. Well data, largely borehole logs, show consistently uniform sandstone porosity distribution within the intrusions, independent of depth. Significantly, at about 100 m from the depth at which the wing emanates from sills, porosity has a broader spread of values. The spread of values is attributable to mudstone clast breccia and thin-bedded sandstone and mudstone. Porosity derived from borehole logs does not differentiate breccia from siltstone, but inference is possible using calibration of logs with core.