2 / 2021-03-29 22:55:46

Sedimentation - dissolution mechanism and petroleum significance of laumontite: A case study on the Jurassic Shaximiao Formation in Central Sichuan Basin, China

laumontite,sedimentation mechanism,hydrocarbon accumulation,Shaximiao Formation,Central Sichuan Basin

The mineralogical characteristics, sedimentation and dissolution mechanism of laumontite in clastic rocks in the Shaximiao Formation in Central Sichuan Basin were investigated,by using combined methods including thin section identification, SEM analysis，inclusion homogenization temperature measurement，isotope content of carbon and oxygen,and X-ray diffraction． Results show that the laumontite cement of the Shaximiao Formation in the study area mainly exists in the form of pore filling, and the heterogeneity is extremely strong. The formation of laumontite is mainly controlled by volcanic rock debris and sedimentary facies belts.The closer to the provenance area, the content of pyroclastic debris increases, and the content of laumontite becomes higher; underwater distributary channel sand bodies are conducive to the precipitation of laumontite. During the middle diagenetic stage, the underlying source rock formation expelled a large amount of acid and generated hydrocarbons. Organic acids entered the reservoir and dissolved the laumontite to secondary porosity.The precipitation and dissolution of laumontite are a complex diagenetic effect that can be summarized into a two-stage diagenesis processes. In the early stage, the normal diagenesis formed laumontite cements. In the late stage,

deep fluid upwellings that contain acidic hydrocarbon-bearing fluids dissolved and altered the reservoirs. The massively developed secondary dissolution pores of laumontite are one of the main types of storage space for commercial oil accumulation in the study area.