Structural Evolution and Hydrocarbon Accumulation of Luxi Depression

Hongliang Li, Qian Hua Xiao, and Angui Lei

Located in the eastern Inner Mongolia Autonomous Region, China, Luxi Depression covers an area of 760 km² and is one of the more than 250 small rifts of Northeast Rift System, the basement of which is Hercynian fold belt. The Depression has undergone two Late Jurassic events: rifting and depression. The rifting sedimentation (the main period) may be divided into four stages: in the initial tensional faulting stage (Yixian Age) are accumulated a set of mantle-sourced volcanic rocks; in the fast subsiding stage (Jiufotang Age) the sedimentary system is distributed in belts under the control of boundary faults; in the steep area alluvial fans and near-shore sublacustrine fans are developed; in the gentle area braided deltas are developed; in the central deep area ark mudstones and sublacustrine gravity flows are developed. Meanwhile the rollover structures began to form on the down-thrown walls of the faults and the drape structures are formed on the convex side of the volcanic rocks. The stable subsiding stage (Shahai Age) is mainly a shallow-semi-deep lacustrine system; the rollover structures are generally finished (Fuxin Age). Most of the fill of the re-rising shrinking stage are near-shallow-lake and marsh facies sedimentation. There are five kinds of oil reservoirs distributed around the oil-generating depressions: rollover anticline, structure-lithology reservoir, updip pinch out, lenticular sandstone, and impermeable sandstone seals. Such reservoir formation models are relatively representative in rift system and can be a model for oil an gas exploration in similar depressions.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California