Water-rock interaction during meteoric flushing of a limestone: Implications for porosity development in karstified petroleum reservoirs
- BP Research Centre, Middlesex (United Kingdom)
- Univ. of Birmingham (United Kingdom). School of Earth Sciences
- Univ. of Cambridge (United Kingdom). Dept. of Earth Sciences
- BP Exploration, Middlesex (United Kingdom)
The Lincolnshire Limestone, comprising a succession of Jurassic wackestones, packstones, and oolitic grainstones, forms an important carbonate aquifer in eastern England. Meteoric waters enter at outcrop and penetrate between confining strata at least 25 km down-dip. This water dissolves and interacts with the limestone, and even water samples collected at or near outcrop are calcite-saturated. Net limestone dissolution is thus a process that is most dominant in the near-surface environment. Water samples taken at increasing distances from outcrop have increasing Sr and Mg contents, and [delta][sup 13]C values of dissolved bicarbonate increase from [minus]15[per thousand] to [minus]8[per thousand] (PDB), while [sup 87]Sr/[sup 86]Sr falls from 0.7082 to 0.7077. Isotopically light bulk-rock carbon near joint surfaces suggests that reprecipitation of calcite in the form of cement could be concentrated preferentially in and near joints. The Lincolnshire Limestone may be used as an analogue for karstified petroleum reservoirs, specifically those which have been buried and lost their unstable carbonate minerals (aragonite, high-Mg calcite) prior to uplift and karstification. The present water chemical data suggest that, in such reservoirs, influx of meteoric water at an unconformity creates porosity and enhances permeability through limestone dissolution, but this may be concentrated close (tens of meters) to the unconformity. Such factors should be taken into account when exploring for, and appraising, karstified petroleum reservoirs.
- OSTI ID:
- 7112740
- Journal Information:
- Journal of Sedimentary Research - Section A; (United States), Vol. A64:2
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
02 PETROLEUM
AQUIFERS
ROCK-FLUID INTERACTIONS
PETROLEUM DEPOSITS
RESERVOIR ROCK
POROSITY
UNITED KINGDOM
CALCITE
CAVES
DISSOLUTION
GEOLOGIC FORMATIONS
GEOLOGIC MODELS
PRECIPITATION
CARBONATE MINERALS
CAVITIES
DEVELOPED COUNTRIES
EUROPE
GEOLOGIC DEPOSITS
MINERAL RESOURCES
MINERALS
RESOURCES
SEPARATION PROCESSES
WESTERN EUROPE
580000* - Geosciences
020200 - Petroleum- Reserves
Geology
& Exploration