Petroleum migration in the Miocene Monterey Formation, California, USA: constraints from fluid-inclusion studies

Abstract

The Miocene Monterey Formation constitutes a fracture-controlled petroleum reservoir, with intercalated calcareous and fine-grained siliceous rocks serving as both the source and reservoir for oil accumulations. Petroleum is produced from macroscopic fractures, and numerous tar and asphalt seeps at the surface attest to the present-day movement of hydrocarbons through fractures in the Monterey Formation. Many fractures are filled with carbonate (mostly calcite and dolomite), quartz, baryte and anhydrite. These same fractures often contain tar or oil filling openings, and occasionally a thin layer of oil can be seen coating growth surfaces between two generations of vein-filling minerals.Evidence for migration of fluids through these fractures in the geological past is provided by aqueous and petroleum fluid inclusions contained within vein-filling minerals. Vein-filling dolomite from Jalama Beach contains three different types of primary petroleum inclusions (based on fluorescence characteristics)--indicating that oils with significantly different API gravities flowed through the fractures. Petrographic and microthermometric analyses of oil and coexisting aqueous inclusions indicate that the fracture-filling minerals precipitated from aqueous solutions of seawater salinity at -75-100 ~ and that oil was introduced into the fracture system episodically during mineral growth. A sample from the Lion's Head area consists of early calcite and late quartz, both of which contain aqueous inclusions with seawater salinity. Inclusions in quartz homogenize at slightly higher temperatures than those in calcite. These data are consistent with calcite deposition during an early heating event, followed by quartz deposition during cooling. No petroleum inclusions were observed in the Lion's Head sample.

Late Palaeozoic hydrocarbon migration through the Clair field, West of Shetland, UK Atlantic margin

“…Studies have shown that oil inclusions of higher API gravity and maturity fluoresce in the blue end of the visible spectrum, whereas those of lower API gravity and maturity fluoresce in the red region (McLimans, 1987;Bodnar, 1990). Largely the relationship is based on observations made concerning the fluorescence properties of crude oils (Downare and Mullins, 1995;Ralston et al, 1996).…”

Analysis of organic inclusions using fluorescence microscopy and micro-FT. IR techniques

“…It can be concluded that the secondary organic inclusions are the record of secondary migration of the oil generated from Es4 . The abundance of the organic inclusions reflects the migration direction of oil or gas ( Bodnar, 1990) . The contents of organic inclusions in Es3 are much higher than those of Es4, also suggesting that the migration direction of oil and gas be from Es4 to Es3.…”

Characteristics of diagenesis, isotopic relations and reservoir properties of the Middle Miocene sandstones in the Carpathian Foredeep (Poland and Ukraine)

“…The eutectic tem per a tures sug gest the NaCl-CaCl 2 -MgCl 2 -H 2 O system, while the ice melt ing tem per a ture in di cates fluid sa lin ity of 13.52 wt.% NaCl eq. (Brown, 1982;Burruss, 1987;Bodnar, 1990;Jarmo³owicz-Szulc et al, 2011). In the east ern part of the study area, the microthermometric re sults of one-phase in clusions (Skhidne Dovhe 3, Lanivka 1) sug gest sa lini ties of 9 wt.% NaCl eq., den si ties of ~1.1 g/cm 3 trap ping con di tions <60°C and pres sures of about 375 bars (see Jarmo³owicz-Szulc et al, 2011).…”