Pore Characteristics Of The Longmaxi Gas Shale From Northwest GuiZhou And Controlling Factors

The reservoirs of Shale gas has a wealth of nano-pores, and the permeability is quite low. The study of the pore has an extremely important significance on exploration and production of Shale gas. In this paper, XRD, organic geochemistry experiment, scanning electron microscopy and gas adsorption are applied for exploring pore characteristics of the Longmaxi gas shale from Northwest GuiZhou and influencing factorsThe results show that the average content of brittle minerals of Well Tongye-1 and Xiye-1 is 74.30% and 62.2% respectively. And the average content of clay minerals is 25.7% and 37.8%. Both of them have similar mineralogical characteristics: brittle minerals are quartz and carbonate minerals; clay minerals are mainly chlorite and illite. The average total organic carbon(TOC) of the samples is relatively high and the Ro ranges from 1.83% ~ 2.87%, 2.23% on average, indicat-ing that the shale reservoirs are in the over-mature stage. The samples contain marine type Kerogen II2.SEM results show that nano-pore of shale contains organic-matter pores、interparticle pores and intrapraticle pores. The morphology of organic-matter pore usually is circular or oval, and most of the pore are mesopore, whose diameter range from 2 to 50 nm, however occasionally some pore have a diameter more than 50 nm. Interparticle pores generally are found between clay minerals or pyrite particles, whose diameter are more than 100 nm.and the diameter of intrapraticle pores within shallow-buried mud may be even more than1 μm. However, during buring and compaction, Interparticle pores greatly shrunk. Intrapraticle pores are found in the carbonate minerals and quartz. With respect to organic pores, intrapraticle pore are usually macrcopore and irregular, the diameter rarely less than 50 nm.The results of N2 adsorption show that the BET of the samples range from 5.514m~2/g to 23.96 m~2/g, with an average of 11.81m~2/g, the average diameters range from 3.484 nm to 4.418 nm, total pore volume range from 0.011cc/g to 0.042cc/g, the volume of micropore and mesopore account for 80% of the total volume.Based on the test data of TOC, Ro and mineral composition, the controlled factors were analyzed. TOC has a positive factor for both total pore volume and micro-mesopore, and it has a greater positive correlation with mesopore. Otherwise, carbonate minerals and quartz has a negative correlation with total volume, and most of the pore are macropore. The abundance of clay minerals has significant control on micropore, a weak positive correlation with macropore and negative correlation with mesopore.