Controls on porosity of Jurassic sandstones of northwest Europe

Conference · Fri Jan 01 00:00:00 EST 1988

OSTI ID:6503863

Harris, N B

The porosities of Jurasic sandstones of the North Sea can be predicted from (1) their thermal maturity and (2) the formation pressure gradient of the reservoir. Thermal maturity measures the time-integrated thermal history; it is expressed in terms of vitrinite reflectance (R/sub o/). Formation pressure is expressed in terms of pressure gradient (psi/foot). At a fixed R/sub o/, porosities are significantly higher if the sandstone is overpressured (pressure gradient greater than or equal to0.50 psi/foot); however, increasing the degree of overpressure appears to have little effect on porosity. At a fixed pressure gradient, porosity decreases with increased thermal maturity. This approach rationalizes much of the observed variation in porosity vs. depth trends of Jurasic sandstones in different parts of northwest Europe. Average sandstone porosities at a given depth typically vary by a factor of three. The approach appears to work because there are only two significant mechanisms of porosity loss that affect the Jurassic sandstones: compaction and formation of silica cements. Compaction requires both increased matrix stress and time. Matrix stress, in turn, depends on burial depth and formation pressure. The variables, burial depth and time, are essentially incorporated into vitrinite reflectance, whereas formation pressure is identified as a separate variable. Formation of significant amounts of silica cements involves dissolution of quartz grains along stylotie planes and reprecipitation of the silica as cement. The authors' work in this area suggests that the process of dissolving quartz grains along stylolites depends on time and temperature, variables that directly enter into the calculation of vitrinite reflectance.

• OSTI ID: 6503863
• Report Number(s): CONF-880301-
• Resource Relation: Conference: Annual meeting of the American Association of Petroleum Geologists, Houston, TX, USA, 20 Mar 1988
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
03 NATURAL GAS
NATURAL GAS DEPOSITS
GEOPHYSICS
PETROLEUM DEPOSITS
RESERVOIR ROCK
POROSITY
SANDSTONES
EXPLORATION
GEOCHEMISTRY
JURASSIC PERIOD
MACERALS
MATURATION
MINERALIZATION
NORTH SEA
PETROLEUM GEOLOGY
PRESSURE EFFECTS
SILICA
TEMPERATURE EFFECTS
WESTERN EUROPE
ATLANTIC OCEAN
CHALCOGENIDES
CHEMISTRY
EUROPE
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGY
MESOZOIC ERA
MINERAL RESOURCES
MINERALS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
RESOURCES
ROCKS
SEAS
SEDIMENTARY ROCKS
SILICON COMPOUNDS
SILICON OXIDES
SURFACE WATERS
020200* - Petroleum- Reserves
Geology
& Exploration
030200 - Natural Gas- Reserves
Geology
& Exploration