Fluid charging history in Ledong 10 area, Yinggehai Basin, revealed by CO2 inclusion characteristics

Abstract

The Cenozoic strata of Yinggehai Basin is rich in natural gas, and exploration breakthroughs have been achieved in the middle and deep strata of the basin in recent years. The discovery of gas fields in the Ledong 10 area had attracted concerning for the migration and accumulation of natural gas in lithologic reservoirs in the middle and deep strata of nondiapir structures. The natural gas reservoir in the Miocene Huangliu Formation in the Ledong 10 block appeared to have a high content of CO2. The characteristics and periods of CO2 migration to natural gas reservoirs were discussed by the approaches including Laser Raman spectroscopy and combined with inclusion petrographic observation. Five types of fluid inclusions were classified, including brine inclusions, CO2 inclusions, gas-phase CH4 inclusions, gas-mixed inclusions and gas-mixed brine inclusions. According to the homogenization temperature and density of CO2 inclusions measured by Laser Raman and microthermometry analysis, and combined with the estimation of the capture conditions of CO2 inclusions, sedimentary characteristics, burial history as well as isotopic composition of CO2, two-stage filling mode for CO2 gas reservoirs was then concluded. The first stage was high-density inorganic-origin CO2 charged between 1.4-0.9 Ma; the second stage was medium-density inorganic CO2 charged between 0.7-0.4 Ma.

Keywords

• co2 inclusion
• laser raman analysis
• filling period
• cenozoic
• ledong 10 area
• yinggehai basin