(1) Fluid Inclusion Technologies Inc, Tulsa, OK
(2) Geologica, Norway
(3) University of Newcastle, United Kingdom
Abstract: The geochemical role in assessing the impact of hydrocarbon emplacement on quartz overgrowth development
The effects of hydrocarbon emplacement on porosity preservation are contentious and the timing of emplacement is critical and poorly constrained. Classical timing constraints are derived from basin modelling and mineral age dating (e.g. K/Ar of illites in oil and water legs). Newer constraints, which we will apply here, incorporate evidence from fluid inclusions, hydrothermal experiments and exemplar modelling.
Using a case study from a northern North Sea field, which contains two producing units of similar depth but with very different producing fluids, we will attempt to constrain the fluid emplacement history and characteristics and the history of quartz overgrowth diagenesis. The case study field produces from the Brent and Statfjord formations in the depth ranges 3000-3500m where reservoir pressures are 450-500 bars. The Brent contains an undersaturated oil API 37-42 at 112°C, and the Statfjord a gas condensate API 46-48 at 120°C. Both reservoirs contain abundant hydrocarbon and aqueous fluid inclusions. Fluid inclusions from the North Sea reservoirs and from hydrothermal growth experiments have been studied in order to estimate their PVT evolution. Their PVT conditions have been constrained and contrasted using classical fluid inclusion techniques (petrography and microthermometry) along with newer innovations (confocal laser scanning microscopy and crush-leach chemical analysis).
This new information was then incorporated into an exemplar model in an effort to produce a consistent history of hydrocarbon and aqueous fluid evolution and emplacement over geological time (leading to the present day situation).
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana