A PCA model transforms a matrix of measured values into sets of projection sub-spaces delineated by principal components (each a linear combination of all P variables), which display variance-maximised interrelationships between samples and variables, respectively. The PCA-defined rock types help to:
- Reduce the lithological heterogeneity of the reservoir-section classes
- Provide the highest possible rock-type resolution at prospective intervals
- Reduce the rock-type resolution at non-prospective intervals
Services
- Geochemical characterisation of relevant sections by high-resolution scanning of cores, cuttings and outcrop samples using handheld XRF apparatus
- Rock typing by means of principal component analysis (PCA) on geochemical and/or wireline-log data such as flex log or lithoscanner log
- Calculation and prediction of log responses including prediction of dynamic rock modulus
Processes at the oil/water contact and water type characteristic in reservoirs
General description of the topic
Microbial-mediated carbonate cementation is a result of degradation of organic carbon and the subsequent production of bicarbonate. The process provides an additional source of carbonate cement that may form localised around sites of high microbial activity such as the oil/water contact in a hydrocarbon reservoir or even at the gas/water contact. The source of microbial-mediated cement has a characteristic isotope signature with respect to δ13C, which makes it possible to identify this source of cement. In combination with δ13C, the oxygen isotope signature (δ18O) of the carbonate cement may provide a relative timing of the cementation process with respect to the thermal history (reservoir temperature) or hydrodynamic events. The presence of a cemented oil/water and/or gas/water contact may have huge impact on the reservoir performance since the cementation may create baffling zones and may lead to compartmentalisation of the reservoir. Therefore, knowledge of the microbial processes that are likely to have occurred in a reservoir is of importance when production is planned and when history matching is made in a reservoir simulation.
Relevant competences
GEUS has since 2009 worked on characterising the microbial-mediated carbonate cement in sandstone reservoirs in the North Sea and along the Norwegian continental shelf. The principal senior staff involved from GEUS’ side has been Niels Schovsbo that holds a PhD degree in geochemistry and have more than 10 years of experience in using geochemistry in reservoir characterisation. Relevant competences comprise:
- Regional understanding of microbial isotope signature in the Danish part of the North Sea
- Best practice of sampling of isotopically heterogenic carbonates
- Isotope database of microbial end-member characteristics from the reservoirs in the Danish North Sea