We investigated the development of a new criterion to quantify and rank marine shale reservoirs of the Lower Silurian Longmaxi Formation and to identify the most prospective area in the southern Sichuan Basin by examining the correlation of various parameters and forming a regionally consistent set. These reliable parameters in our model included geologic factors (rock properties), engineering factors (rock brittleness, in situ stress, and pressure gradient), and topographic factors (pipeline availability and land accessibility). In addition to the common parameters (thickness, depth, porosity, and gas in place), our system used some critical factors associated with complex tectonic evolution and gas preservation in detail, such as in situ stress, pressure gradient, and topographic conditions. An integrated data set was used for designing the well trajectory, creating large volume-induced fractures networks, and increasing the initial production of shale gas. Our integrated approach was used to classify into three ranking levels of Silurian Longmaxi marine shale reservoirs in the Changning area in the southern Sichuan Basin. The integrated approach incorporated a prediction model of pressure gradient and the distribution of in situ stress. The initial production from horizontal wells resulted in a positive assessment as high-performing affordable wells, and served as validation of the methodology used to rank prospective areas.