Currently, a controversy exists as to whether oil charge in reservoirs has an inhibiting effect on quartz cementation. The Brae Formation sandstone reservoirs in the Miller and Kingfisher oilfields display in some areas anomalously high porosity (25-30%) preserved to depths in excess of 4km (~120°C). The high porosity in these sandstones is directly linked to low quartz cement volumes (<5%). In the Miller Field, the crestal areas of the reservoir have porosities of up to 25% and a quartz cement content of <5%. Towards the oil-water contact (OWC), and in the aquifer of this same reservoir, porosity decreases and quartz cement content increases to 14% and 15% respectively. In the Kingfisher Field, two reservoirs separated by a mudstone layer are present. The lower reservoir, which connects with the reservoir in the adjacent Miller Field, displays porosities ~14% and quartz cement contents of ~10%. The upper reservoir is of overall high porosity (25-30%) and exhibits low quartz cement contents (<5%). Combined results from fluid inclusion and basin modelling studies in the Brae Formation reservoirs show that the duration of quartz cement precipitation is linked to hydrocarbon emplacement. In the Miller Field. quartz cementation in the high porosity (up to 25%) parts of the reservoir continued until the sandstones were buried to 95-105°C. This temperature corresponds to the burial depth (3km) and time (40Ma) at which oil entered the reservoir. Results for the Kingfisher Field indicate a similar oil emplacement time in the upper reservoir with 25-30% porosity and <5% quartz cement content, but a more recent (l5Ma) oil-fill for the lower reservoir with ~14% porosity and ~10% quartz cement content. Kinetic modelling of the quartz cementation process reveals that quartz cementation rates in the oil-filled parts of reservoirs examined (10<sup>-22</sup> moles/cm<sup>2</sup>.s) are at least two orders of magnitude smaller than in the aquifers (10<sup>-19</sup> moles/cm<sup>2</sup>.s).
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:657302 |
| Date | January 2001 |
| Creators | Marchand, Ann |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/12567 |
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