Abstract: Lithology of Carboniferous volcanic inner buried-hill reservoirs in the Ke-Bai fractured zone is complicated and various, so it is hard to recognize the lithology comprehensively by conventional logging data and interpretation process. On the basis of classification and naming of the rocks, hierarchical decomposition strategy was used to solve the problem of lithology identification. The main connotation of the strategy is "component identification in first, structural division later". By establishing logging parameters of M[(Δt_f-Δt)/(ρ_b-ρ_f)], N[(φ_Nf-φ_N)/(ρ_b-ρ_f)]and R_t/R_xo, the crossplots of N-GR, N-M and GR-R_t/R_xo were compiled. New parameters M and N are more useful to identify lithology, R_t/R_xo is sensitive to rock texture and structure by eliminating the effect of oil and water in pores, while, GR responses the levels of radioactive substances. By using the crossplots created and the method of FMI, which is visually effective in texture and structure recognition, lithology of the Carboniferous volcanic inner buried-hill reservoirs was identified. Crossplot of N-GR is useful to distinguish sedimentary rocks and volcanic rocks;N-M crossplot is effective to recognize basic volcanic rocks and intermediate volcanic rocks;Crossplot of R_t/R_xo-GR is helpful to identify lava rocks, pyroclastic rocks and subvolcanic rocks in terms of their specific textures. The identification results were tested by petrographical identification of eighteen wells and the accuracy rate was eighty-nine percent. This study establishes a new means and technique process for lithology identification in Carboniferous volcanic inner buried-hill reservoirs of the Ke-Bai fractured zone. It is also useful for comprehensive lithology identification, volcanic rocks exploration and seismic calibration of the research area.

Key words: low permeability reservoir, natural fracture, fractal dimension, productivity forecast, specific production index per-meter