The Main Factor Controlling Petroleum Migration Along Unconformity in the Junggar Basin

Key words: 
• unconformity /
• vertical structure /
• petroleum migration /
• Junggar Basin

Abstract: Many oil and gas pools have been found above or below the unconformity in the Junggar Basin, indicating that the unconformity is a good conduit for petroleum migration. Based on the petroleumbearing fluid activities in unconformity zones, we suggested that vertical structure of unconformity is the most key factor controlling the petroleum migration. Two layers of unconformity were divided, i.e. bottom conglomerate (upper layer) and weathered crust (lower layer). In addition, if some mudstone were developed on the top of weathered crust, the unconformity was threelayer structured. The weathered crust could be further divided into weathered fractured crust based on volcanic rocks, and weathered solution crust based on detrital rocks. Then, we defined three types of unconformity according to lithostratigraphic features of the bottom conglomerate and the weathered crust. They include overlapbase type, sandstoneconglomerate type, and sandstonemudstone type, among which the first one is the most favorable for petroleum migration, the second intermediate, and the last could generally not be considered as a conduit.