The Structural Characteristics And Pools Of Petrileum Accumulation Of Raoyang Sag In Jizhong Depression

Making use of theories and methods about extensional structure, basing on the guide of the theories such as structural geometry, petroleum geology, sequence stratigraphy, sedimentology, etc., combinating of data of stratum, seism, well-logging, core and so on, the paper studies the characteristics of structural-sedimentary evolution in Raoyang depression, structural styles and its forming mechanism. The influence of structure to sedimentary systems as well as the generation, migration and accumulation of petroleum are discussed.Raoyang depression went through three stages of structural evolution in Cenozoic:fault-down thrown basin, faulted-sag basin and sag-faulted basin. Two sets of fault system were developed. Northern-east is primary orientation, Northern-west is secondary. The structural styles of entire area are controlled by the two sets of fault system in Raoyang depression. There are many types of structural styles in Raoyang depression. According to the forming mechanism, the dominating structural styles can be divided into following types:basement-involved fault uplift-buried hill, extensional structure in sediment cover, extensional-shortening superimposed structure and extensional-strike-slip superimposed structure, etc. On account of structural evolution stage, the sedimentary systems are various in different part of Raoyang depression, such as coastal underwater fan, river facies, braided river delta, fan delta-turbidite fan, coastal sand barrier and shoal of lake and carbonate rock(mainly organic limestones) etc.There is an obvious difference between the internal structures of Raoyang depression. The development of sedimentary systems are controlled by the stage of structural evolution. Different sedimentary systems are occurred in different position of the depression. The favorable reservoir and cap rocks are related with the stratum and the space position of the sedimentary system. It is recognized that the accommodation zone controls the position in which water system enters into lake basin in Raoyang depression, and along the flow channel, the fan bodies and delta are developed.The hydrocarbon reservoirs having been discovered in Raoyang were divided into six kinds, including geomorphic buried hill reservoir, fault block-geomorphic buried hill reservoir, structural reservoir, stratigraphic reservoir .lithologic reservoir and structure -stratigraphic-lithologic reservoir combinatim. In three sets of stratum(Pre-rift Period , Rifting Period and Post-rift Poriod), developed different hydrocarbon reservoirs, such as "new-generating and old-accumulating" , " self-generating and self-accumulating " , "dowm-generating and up-accumulating" .The hydrocarbon accumulations are superimposed as though "three-floors building" . Based on the controlling of above mentioned structural and sedimentary factors, different distributing modes of reservoir are occurred in different tectonic zones of Raoyang depression.