The Reservoir Forming Main Control Factors And Distribution Law Of The Upper Cretaceous Slope Migration Type Oil Sands In Songliao Basin

Oil sands are the important unconventional resources. In recent years, with theincreasingly development of the study of unconventional oil-gas resources, a number ofpotential oil sands mines have been discovered in China, such as western slope ofSongliao Basin. The oil sands reservoir on the western slope of Songliao basin is theresearch object in this paper and the drilling, logging and geochemical methods are used todo the detailed anatomy, then study the lithology, physical property, electrical propertyand oiliness of oil sands reservoir, build oil sands logging interpretation model andlogging facies model, divide the oil sands reservoir into sandstone layer, mudstone layer,main oil layer, poor oil layer, conventional heavy oil layer and so on, even establish theeffective thickness of oil sands. These studies provide basic data for investigating theinfluencing factor and distribution law of oil sands reservoir.In order to grasp the distribution law, it is necessary to study the oil sands reservoirforming conditions, and oil sands accumulation process is established: the oil sources inwestern slope are from the source rocks of Qingshankou Formation in the centraldepression, which are highest quality hydrocarbon source rocks in shallow layer ofSongliao Basin, and the peak period of hydrocarbon generation is in the middle and latedepression period. There is the tectonic compression that comes from the tectonicinversion in the late Yanshan and early Himalayan movements for Songliao basin. Thetectonic compression probably cause the lateral migration of oil-gas in the centraldepression. The middle-shallow sand body layers that are overlaid each other orcommunicated by faults constitute the main migration channels. When oil migrate into thearea near the migration channels with good reservoir-cap configuration relation, oil sufferfrom destructive action (biodegradation, washing and oxidation action), and the viscosity increases. Then the oil sands are accumulated in the shallow layers of Songliao basin edge.The accumulation model of the Upper Cretaceous oil sands reservoir in the western slopeof Songliao Basin is the simple slope migration type.Based on the further analysis, the main reservoir controlling factors of oil sands onthe western slope are: the rich oil sources of Qingshankou Formation in the centraldepression, which are the important oil sources of oil sands reservoir; the two compressiontectonic movements provide the main impetus for oil-gas long distant and rapid migration;middle-shallow sand bodies (continuous superposition or communication by fault)constitute the long distance migration pathway, and the sand bodies and the nearbymudstone cap rocks are the regional controlling factors for oil sands enrichment;sedimentary microfacies and physical characteristics of sand bodies are local controllingfactors of oil sands enrichment. Variety of thickening effects make the oil sands oilviscosity increase and finally oil sands reservoir can be deposited in shallow region ofthe basin edge where the diagenesis is weak, physical properties are good and local coversare incomplete.The study of oil sands reservoir conditions and main control factors indicate that oilsands are mainly distributed at the edge of Songliao Basin with the characteristics of thesource in the far area controlling. There is the distribution sequence of the conventionalcrude oil, heavy oil field and oil sands from the depression center to the western slope inSongliao Basin. Oil-gas migration pathway and the areas with good reservoir-capconfiguration relationship near migration pathway are the favorable areas of oil sandsdistribution. Sedimentary facies and physical properties are the local controlling factors ofoil sands distribution. Sand bodies with better continuity and physical properties in thelower part of underwater distributary channel and the upper part of the mouth bar areadvantageous to oil-gas migration. The main reservoir space of oil sands are these bettersands bodies which formed until the top, the underside and the side edge of sand bodiesseparated by the mudstone. Finally, based on the study above, the favorable areas of oilsands are optimized in Zhenlai area and the oil content method in tradition and montecarlomethod with mathematical statistical significance are used in calculating the oil sandsresource in the favorable areas. And the resourse evaluation system is established which issuitable for this area.