Fractal characteristics of the Longtan formation transitional shale in northwest Guizhou

Based on the low temperature Nitrogen adsorption experiments of transitional facies of Longtan Formation shale in the northwest Guizhou,the pore fractal dimension was studied by using the FHH model,and the fractal dimen- sion of D1 and D2 were obtained. The average values were 2. 718 6 and 2. 782 4,reflecting the complexity of Longtan Formation shale pore. The correlation analysis of fractal dimension and other geological parameters showed that the fractal dimension with shale surface area, TOC are positively correlated, with the average pore size, the content of quartz,quartz / clay are negatively correlated,with Ro and the content of clay minerals are related positively first and negatively later at the inflection point of Ro = 2. 5% and the content of clay minerals of 50% . The study results show that D1 can be more comprehensive response to the shale pore size,volume,and surface characteristics. Also,the struc- tural features can be integrated to characterize shale pore. The numerical value is more conducive to the accumulation of shale gas. D2 is more obvious for complex pore structure characterization,and can be used in the research of shale pore structure. The value should be in a certain range,should not be too large. In the northwest of Guizhou Longtan Formation,the transitional facies shale pore fractal dimension of D1 is greater than 2. 60,and the distribution of the fa- vorable range of D2 is 2. 50-2. 80,when D2 is higher than 2. 80,then the recoverability evaluation and the fracturing design are necessary. The significance of this research is to provide new ideas and means for the exploration and devel- opment of shale gas in Guizhou area.