RESEARCH ON STRUCTURAL FEATURE CONTROLANDNANO-SCALE EVOLUTION PROCESS OF SLAB STRATA OFLONGMAXI FORMATION IN WEIYUAN GAS FIELD CHINA

摘要

The pore characteristics of shale reservoir de- termine the shale gas content. This article uses three shale gas wells in Weiyuan area as the research ob- ject. Based on scanning electron microscopy and low-temperature liquid nitrogen adsorption experi-ments, the effect of shale lithofacies on the pore structure of the Wufeng-Longmaxi formation is stud-ied by combining semi-quantitative and quantitativeexperiments. The results show that the shale of the LMI-LM3 interval in Weiyuan area located at the bottom of the Longmaxi Formation, is composed mainly of siliceous minerals, with high organic con- tent. The LM4-LM8 interval located in the middle of the Longmaxi Formation has high content of clayminerals and carbonate minerals and low organic matter content. The shale pores in the LMI-LM3 in- terval are mainly provided by organic matter, and the shale pores in the LM4-LM5 interval are mainly pro- vided by organic matter and clay minerals. Car- bonate minerals have a certain contribution to the de- velopment of shale pores. The organic pores have relatively good homogeneity, which contributes themost to pores below 10nm. The internal pore devel-opment of carbonate minerals is highly heterogene- ous, and the pore size is mainly distributed between20 and 100 nm. The pores of clay minerals are highly heterogeneous, and the pore diameters are mainlydistributed between 60 and 200 nm, which makes a great contribution to the pores of LM4-LM5 and LM6-LM8 formations. In the process of shale sedi mentary diagenesis, fluid substances modify the sol-uble substances in the rock, providing space for the methane in the shale.