A Study On Reservoir Characteristics And Mechanism Of Hydrocarbon Accumulation In Halahatang Oilfield Of Tarim Basin,in Xinjiang,China

Tarim basin is the largest oil and gas basin in China,and it is rich in hydrocarbon resources in Ordovician reservoirs of the northern uplift.Halahatang oilfield is located in the central of northern uplift and the west wing of the large NE-trending anticlines in Lunnan-Halahatang area,it is the oil enrichment zone which is recently discovered.The yijianfang formation and yingshan formation carbonate reservoirs of Ordovician are the major exploration target layers.It belongs to the ultra deep oilfield in the depth of 6500-8000m.It brought many difficulties for the oil and gas exploration because of the characteristics of the strong heterogeneity of fractured-vuggy reservoir,the complex relationship between oil and water distribution,the various reservoir types,the varied fluid,and the inconformity of the oil-water interface and so on.It is analysis of the origin and sources of the hydrocarbon study and analysis of the test sample and the drilling data in this area,discussed the hydrocarbon filling accumulation processes.According to the data of inclusions and the analysis of experiment,the homogenization temperature of fluid inclusions in Ordovician reservoir are mainly distributed in 85-105? with the single peak characteristic.Analysis with the thermal history and burial history,it is shows that the accumulation time is at the end of the Permian,that is the late Hercynian.The Ordovician carbonate reservoirs of Halahatang oilfield was formed in the early-middle Caledonian,and the strata rised,the fault system developed,the karst reservoirs has been further development in the late Caledonian tectonic movement.The oil and gas from Manjar depression filled into north along the faults and unconformities,entered the favorable reservoirs,formed huge oil and gas reservoirs in the late Hercynian.Since the Triassic sedimentary,the reservoirs were in continuous buried depth,and conserved with the late Hercynian characteristics.The formation and distribution of the reservoirs in Halahatang oilfield are mainly controlled by the faults,structure,reservoir and caprock.The early-middle Caledonian faults not only controlled the formation of karst reservoirs,but also are the main channel of the hydrocarbon migration.The nose uplift in Halahatang area is the enrichment zone of the high-yield wells distribution.The high positions are for hydrocarbons,and the low site for water.The hydrocarbons are complexity and controlled by the late Hercynian caprock.The late Hercynian caprock in the north buried hill had an serious erosion,resulting in hydrocarbons seriously suffered biodegradation.There is no erosion for the late Hercynian cover in the south,and the reservoirs preserved well.The density of oil,wax content,sulfur content and asphaltene and other physical properties of oil gradually increasing from south to north,with the thinning of the late Hercynian cover,and the dry coefficient and the gas-oil ratio are on the contrary.So the study on the reservoir characteristics of Halahatang oilfield and the main control factors can guide the oil exploration and development work effectively.