Abstract: Evidence weight method based on Bayesian conditional probability is a common method for oil and gas resource assessment using geographical information system (GIS). After analyzing the natural gas reservoir-forming conditions of Kuqa depression in Tarim basin, this paper created seven geological evidence layers including source bed, caprock, reservoir, fault and strata pressure. By the evidence weight method integrated with overlay analysis of GIS, the weight of every layer is given and independence test of every two layers is made. At last, a posterior probability map of gas exploration potential is presented, by which the study area is classified into four grades, of which Ⅱgrade areas are defined target areas.

Key words: oil geological anomaly, geographic information system (GIS), overlay analysis, evidence weight method, Kuqa depression