Abstract:

 In view of existing difficulties in deciding the shale gas favourable region, three important steps are proposed which should be considered especially in vertical，and the characteristic value of  corresponding parameters are put forward. (1)Make the exploration threshold depth clearly and definitely. According to basic model, gas generation threshold of typeⅠ，typeⅡ1，typeⅡ2 and type Ⅲ  organic matters Ro are ordinally 1.2%、0.9%、0.7% and 0.5%.(2)Determine the threshold gas content in different depth. According to the statistical analysis of gas producing shale formation parameters in America, the gas content threshold in 1000 m, 2000 m and 3000 m depth are ordinalty 0.5 m3/t, 1.0 m3/t and 1.5 m3/t. (3)Determine the approved shale. According to the research on Longmaxi shale of Lower Silurian in southeast Chongqing, if we want 1.0 m3/t gas content, the TOC of shale in the depth of 500 m, 1000 m and 2000 m must be ordinally more than 1.4%, 1.1% and 0.9%.

Key words:  shale gas, favorable zone selection, gas content, threshold limit