Abstract:

The Well Yuncan-1 is the first stratigraphic well in Yunlong depression,Chuxiong Basin.A severe lost circulation happened during the drilling of the well.Comprehensive analysis of the conditions and adjacent environment of the accident reveals that it may be caused by non-sealed extensive fluid motion and exchange in the study area and genetically related to the relatively large topographic relief in a short distance caused by strong and inhomogeneous reformation during the later stage of the basin formation.This indicates that modification of fluid flow is one of the most important effects during the later stage of basin formation and topographic relief is one of the basic conditions for modifications of fluid flow.Both of them contributed to the formation of fluid modification basins.Therefore,this article suggests that both topographic relief and modification of fluid flow are indispensable to analysis and evaluation of petroliferous basins.As to basins or areas featuring in large topographic relief,large amount of atmospheric precipitation,well-developed drainage system,deep fluvial incision(e.g.,basins in western and southern China),the influence of fluid modification on accumulation and dissipation,reservoiring,adjustment and distribution oil and gas shall be strengthened during oil and gas evaluation and exploration deployment.

Key words: fluid modification, topographic relief, late reformation, lost circulation, Yuncan-1 well, Chuxiong Basin