Characteristics and Evolution of Fluid-Rock System Near the Top Surface of Deep Overpressure
, Central Junggar Basin, Northwest China
Zhi Yang
China University of Geosciences, Department of Petroleum Geology and Engineering,
Faculty of Earth Resources, Wuhan, Hubei Province, P.R.China
[email protected]
This study is to make clear characteristics and evolution of fluid-rock system near top overpressure
surface in central Junggar Basin and to better understand the processes of episodic
hydrocarbon
migration, fluid-rock interaction, secondary porosity formation and
hydrocarbon
accumulation controlled by overpressured system.
Junggar Basin is a late-Palaeozoic, Mesozoic and Cenozoic superimposed foreland basin, with present-day geothermal gradient 22/km. The thickness of sedimentary rock sequence in central basin is about 15,000m and consists of Carboniferous to Quaternary rocks that overlie a pre-Carboniferous metamorphic basement. Overpressured system exists large-scale and the vertical distribution
of pore pressure is comprised of an upper hydrostatic pressured system and a deeper overpressured system in study area. The observed surplus pressures range from about 10 to 60 MPa in depth interval of about 4400-7000m. Overpressured system is one of the most important factors in controlling
hydrocarbon
distribution
.
Assistant with numerical modeling, look for evidences from analysis on relative data near top overpressure
surface, such as
hydrocarbon
-bearing fluid inclusions, carbon-oxygen isotope of calcite cement in sandstones, organic geochemistry characteristics, diagenesis characteristics especially the plagioclase dissolution and carbonate cementation and dissolution, crude oil property, formation water geochemistry, pressure-temperature field and so on.
Deep overpressure
is typical and important geological phenomena in study area.
Overpressure
is probably
hydrocarbon
-originated and post-diagenesis-stage
overpressure
. Studying on characteristics and evolution of fluid-rock system near top
overpressure
surface, will help to understand the processes of geofluids activity related to overpressured system and to give some useful instructions for oil-gas exploration actions.
AAPG Search and Discovery Article #90094 © 2009 AAPG Foundation Grants in Aid