Abstract:

For the hard formation of high matrix resistivity the difference between formation resistivity and tight surrounding rock resistivity are caused by reservoir fractures and fluid property in the pore space when the factors such as mudstone, pore and other conductive minerals are eliminated. Based on volcanic lithology identification, the resistivity of gas-bearing reservoir and tight surrounding layer with the same lithology  were used to determine the formation true resistivity formula of gas-bearing intervals that eliminate the factors of reservoir factures and fluid property in the pore space by use of numerical inversion method. Then the differenceratio value of structural resistivity was defined as the ratio difference of formation true resistivity and deep investigation laterolog resistivity to deep investigation laterolog resistivity, and this parameter mainly reflect the influence of the reduced rate of resistivity due to reservoir fractures and fluid property in the pore space.This method can identify fluid property of volcanic fractured formation, and form the identification plate of oil layer, gas layer and water layer for volcanic reservoir. Combined with other well logging curves, reservoir performance data and gas surveying information, it can effectively evaluate and identify the natural gas layers of volcanic fractured formation.This method has been applied to volcanic natural gas layer identification in the Junggar basin research area and has got good application effect, the interpretation conclusions and oil testing results are basically consistent.

Key words: volcanic rocks, creviced formation, the difference-ratio value of structural resistivity, plate of identify gas zone, natural gas layer