Sedimentary characteristics of nearshore subaqueous fan of Neogene Ciying Formation in Luliang basin.Yunnan

The Pliocene Ciying Formation in Luliang basin mainly consists of a fan-delta depositional system of nonmarine faulted lacustrine basin,in which a nearshore subaqueous fan was deposited in the second and third member of Ciying For- mation in the step-faulted zone of the eastern basin.On the basis of the lithelogy association,the sedimentary sequcnce and the characteristics of seismic and well logging responses. the nearshore subaqueaus fan can be subdivided into three subfacies:the fan root.the fan medium and the fan end. Drilling data show that five micro-facies such as the braided stream,the space between braided streams,the leading edge of fan medium subfacies,the mud and sheet stone and the fan-end subfacies can be identified in the fan medium and the fan end subfacies,of which the braided stream of fan me- dium subfacie is the main reservoir.By combining with the analysis on pool formation,it is considered that the near- shore subaqueous fan is of setting to form the structure-li- thologic reservoir and the lithologic reservoir.The distribu- tion of reservoir obviously controls the enrichment of gas pool,and the favorite area for hydrocarbon exploration should be along the main water channel and the fan-mid- dling front sand where the fan bodies were formed.