Large scale hot water migration systems around salt diapirs in the Danish central trough and their impact on diagenesis of chalk reservoirs

Journal Article · Sun Jan 01 04:00:00 EST 1989 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(89)90274-3· OSTI ID:7270499

Jensenius, J ^[1]; Munksgaard, N C ^[2]

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1. Institute of Petrology, Copenhagen (Denmark)
2. Maersk Oil and Gas A/S, Copenhagen (Denmark)

Fracture filling calcite from the piercement fields of East Rosa, Skjold, Rolf, North Arne, Nils and Vagn and the dome field Dan have been studied by fluorescence and cathodoluminescence microscopy, fluid inclusion microthermometry and carbon and oxygen isotopes. The carbon and oxygen isotope compositions of the reservoir matrix chalk have also been measured. The temperature estimates obtained from fluid inclusion data suggest that the fracture filling calcite of the piercement fields precipitated during hot water flushing of the reservoirs. The flushing system only existed around the salt diapirs and was probably related to expulsion of overpressured fluid from the surrounding sediments. The thermal anomaly and the faults associated with the diapirs probably were important factors in focusing the ascending water. Lower {delta}{sup 18}O values with shallower depth of burial suggest that the porosity of chalk in the shallower fields was more severely reduced by calcite cementation during the flushing event than in the deeper fields. In the case of North Arne, Nils, Vagn and Dan, {delta}{sup 13}C values of the fracture filling calcites are similar to those of normal chalk (0.5 to 3.5 {per thousand}). However, calcites from Rolf, Skjold and East Rosa are depleted by {minus}1.8, {minus}6.2 and {minus}16.7 {per thousand}, respectively. Only in East Rosa is the matrix chalk itself depleted in {sup 13}C. The low {delta}{sup 13}C values are interpreted as the result of biodegradation. Sulfate originating from the underlying diapirs was flushed into the reservoir and used by bacteria to degrade present hydrocarbons. This process produced {sup 13}c depleted bicarbonate which was incorporated into the fracture-filling calcites.

• OSTI ID: 7270499
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Journal Name: Geochimica et Cosmochimica Acta; (USA) Vol. 53:1; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

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