Formation Mechanism Of Ordovician Fracture-cavity Carbonate Condensate Gas Reservoirs In The Eastern Part Of Lungu

Tarim Basin is abundant in oil and gas resources, it is one of the important bases for oil and gas production in China. the condensate gas reservoir is widely distributed inside the basin, the type of condensate gas reservoir is complex and changeable, the mechanism of oil-gas origin is very complex, intensifying the study on the mechanism of origin of condensate oil and gas, building the model of reservoir forming of condensate oil-gas field are undoubtedly of a great significance to the exploration of oil and gas inside the basin. This paper took the condensate gas reservoir of Ordovician fracture-cavern type carbonate in the eastern area of Lungu oil field as an analytical object to specifically discuss the mechanism of origin of condensate gas reservoir in the work area in terms of the basic features of condensate gas reservoir, the features of fractural reservoir and their origin, the origin of condensate oil and gas and the model of reservoir forming of condensate oil-gas based on a lot of on-site and assay test data, believing that:1. According to the saturability feature, the condensate gas reservoir of Ordovician fracture-cavern type carbonate consisted of two types, saturated condensate gas reservoir and unsaturated condensate gas reservoir, the fluid property presented a feature of "dried gas and heavy oil", the pilot production presented a feature of fracture-cavern type oil-gas reservoir with a high initial potential and short production time and a fast production decline.2. Ordovician carbonate reservoir can be divided into four types as cavern-type, hole-type, crack-hole-type and crack-type, different type of reservoir corresponded to different seismic response feature, the reservoir development was mainly controlled by buried hill karst and interlayer karst.3. The mechanism of origin of condensate oil and gas in the Ordovician carbonate reservoir was caused by the phase change of crude oil in the reservoir, which was mainly formed due to the east-to-west invasion to the early oil reservoir by the highly-matured natural gas or crude oil cracking gas.4. By the analysis on the pitch of reservoir and fluid inclusion, Ordovician oil-gas Reservoir had three primary oil-gas charging periods:charging of heavy quality oil and gas in early Hercynian period, charging of medium-quality oil and gas in indo-china period, charging of light-quality oil and gas or dried gas in Yanshanian to Himalayan period.5. The oil and gas accumulation in the eastern part of Lungu oil field had experienced multiple stages, oil accumulation prevailed in the early stage, later on, due to the crust uplift, gas accumulation prevailed, a re-accumulation happened in the new entrapment along the fault zone during the late stage.