ANOMALY PATTERN ORIGINS OF THE WIRE-ADSORBED HYDROCARBON INDICATORS-OVER THE JURASSIC GAS RESERVOIR OF WELL YINGNAN 2 IN THE TARIM BASIN

A research on the causes of the anomaly patterns of the wire-adsorbed geochemical indicators over the Jurassic gas reservoir of Well Yingnan 2 in the Yingjishu Sag of the Tarim Basin has been conducted.The knowledge was gained that the water lock effect provides the favorable trapping and accumulation conditions for this gas reservoir,and the hydrocarbon gases within the reservoir can migrate upward through different ways(such as diffusion and permeation).The Jurassic gas reservoir of Well Yingnan 2 was chosen to conduct the research of the geochemical field characteristics and the anomaly patterns of the light wire-adsorbed hydrocarbon(C_2-8) and the heavy wire-adsorbed hydrocarbon(C_15-19) indicators.It is found that both the characteristics of the geochemical field and the anomaly patterns of the 2 kinds of indicators differ obviously from each other.The analysis results indicate that the water lock effect of the tight sandstones and the microseepage and diffusion ways of the hydrocarbons are the root causes of these differences;and the diffusion rate of the light hydrocarbons within the water-locked sandstone area in the gas reservoir is less than that within the area without water lock effect in the edge of the gas reservoir,which causes the high anomaly values of the light wire-adsorbed hydrocarbons(C_2-8) in the edge of the gas reservoir and the sub-high anomaly values of these hydrocarbons in the gas reservoir area.The study also indicates that the low-content of heavy hydrocarbons in the gas reservoir and the local diffusion coefficient of the reservoir hydrocarbon gases are the geological causes of the high value anomaly of the heavy wire-adsorbed hydrocarbon indicators(C_15-19) over the top of the this gas reservoir.