Formation Process And Distribution Of Laumontite Cements In Yanchang Formation (upper Triassic) Of Ordos Basin

Although laumontite cements in Yanchang formation of Upper Triassic of Ordos Basin occupied the lots of porosity, its dissolution provides more secondary porosity, it is major stored space of oil-gas. Therefore, the formation process and distribution of laumontite cements are very important for exploring reservoirs.Using core observation, the microscope, fluid inclusions analysis, SEM and energy spectrum, clay mineral X-diffraction and electron microprobe et., studied the petrologic characters of Yanchang Formation sandstone. Based on the geological setting and research findings about laumontite in the early, studied the diagenesis of sandstone in the Yanchang formations and established the mode of the diagenesis. More knowledge of the precipitation mechanism of the laumonite cements was gotten.The main conclusions are as follows:1. Laumontite plane distribution in the basin, northeast to southwest direction from the source with increasing distance in the trend of declining, when source completely from the West or south-west of the basin were missing laumontite. Vertically on top of chang7 - chang6 - chang4 +5 - chang3 - chang2 content of has the gradual downward trend. For the purposes of chang6, from the bottom to the top content of laumontite has trend of decreased. However, occasional exceptions.2. A large number of laumontite porosity solution in chang6 should be more source rocks in the role of hydrocarbon come from chang7 formed by decarboxylation of organic acids into the overlying strata. In accordance with laumontite dissolution to determine the distribution of the porosity into the overlying strata channel should be mainly fracture.3. The research show that formation of laumontite of the yanchang formation is relation of sediments formed by volcanic activity and volcanic tuff rock come from the Yinshan fold belt. Laumontite were in the course of diagenetic hydration and albite plagioclase the results of the combined effect of petrochemicals. The formation of laumontite divided into two: First of all, in the early diagenesis period, montmorillonite of tuffaceous mudstone and volcanic clastic components gradually with increasing temperature dehydration and eventually the formation of water-bearing little and more stable laumontite and albite. Second, enter the period of diagenesis, source come from the north-eastern basin of the reservoir sandstone in a large number of plagioclase by albite plagioclase petrochemical form laumontite.