Geological characteristics and enrichment model of Ordovician oil and gas in Tazhong Uplift
Based on the data of structural analysis,fault distribution,production dynamics,and geochemistry,an analysis is conducted on the characteristics of oil and gas properties as well as productivity distribution in the Tazhong area during the Ordovician period.The factors contributing to oil and gas accumulation are examined from three perspectives:oil and gas charging,transport system,structure,and the relationship between migration and accumulation.Consequently,an accumulation model is established.The results show that:(1)The crude oil found in the Tazhong area during the Ordovician period is predominantly light crude oil with low density,viscosity,and sulfur content.Its density ranges from 0.75 to 0.85 g/m3,while the gas-oil ratio varies between 119 and 82,367 m3/m3.This region contains multi-phase oil and gas reservoirs where there is no distinct boundary between the oil and gas phases.The dryness coefficient of natural gas ranges from 0.70 to 0.98,and the carbon isotope composition of methane in natural gas shows a wide variation ranging from-35.7％o to-61.4％o.Different regions exhibit amantane index(MDI)values ranging from 0.33 to 0.64.The eight major oil and gas charging points exhibit characteristics such as low crude oil density,high gas-oil ratio,and elevated levels of methane carbon isotope and MDI.Moving along the strike-slip fault zone towards the south or away from it results in an increase in density,while the gas-oil ratio,methane carbon isotope,and MDI all decrease.Variations in gas penetration intensity across different blocks may lead to localized differences in these patterns.(2)The distribution pattern of oil and gas in the study area is primarily influenced by localized oil and gas charging.Oil and gas wells surrounding the 8 charging points typically exhibit high production rates,due to reservoir development scale,there may be occasional occurrences of low-producing wells near the charging points.The regional distribution of filling points'production capacity can be categorized into three types:"northern dominance in natural gas,southern abundance in crude oil,""central prevalence of natural gas with flanking areas rich in crude oil,"and"generally abundant natural gas with localized presence of crude oil".However,low-producing wells and those located far from the charging points are dispersed over a wide range.(3)The oil and gas enrichment mode in the study area during the Ordovician period is characterized by tension-torsional large faults controlling vertical hydrocarbon charging,unconformity and strike-slip faults governing lateral hydrocarbon migration,interlayer karst within fracture zones providing reservoir space for hydrocarbon accumulation,and local structural highs and platform areas serving as favorable directions for hydrocarbon accumulation.
light crude oilamantane indextension-torsional large faultsstrike-slip faultunconformityfracture zoneskarstificationOrdovicianTazhong UpliftTarim basin
万方数据
维普
