Characteristics Of Volcanic Weathering Crust Of Carboniferous And Its Control Over Reservoirs In Kelameili Gas Field

It is the heavy weathering and denudation process that make the lithology of Carboniferous volcanic in Kelameili gas field very complex which impede the study of hydrocarbon accumulation in volcanic reservoirs and set a limit to the exploration. Therefore, this thesis carry out the deep study on the relationship between volcanic weathering crust and hydrocarbon accumulation based on the identification of weathering crust structure.A complete weathered volcanic crust can be divided into five-layer structure, which includes soil layer, hydrolysis zone, leached zone, broken-down zone and underlying bedrock, comprehensively using lithology, physical property, conventional logging, weathering index and so on. On this basis, the thesis study the characteristic of lithology, lithofacies and reservoir space through the core observation, the microscopic description, logging data and physical property analysis data. In this area, basalt, andesite, breccia, tuff and granite porphyry are mainly developed in volcanic weathering crust which is characterized by pore-fissure dual media reservoir space, especially the secondary dissolved pores and structural fractures. Combined with the large quantity analysis data, this thesis study the control of structural layer to physical properties of reservoirs. It is mesoporosity and lower permeability in hydrolysis zone; higher porosity and higher permeability in leached zone; mesoporosity and medium permeability in broken-down zone; and lower porosity and lower permeability in underlying bedrock. In addition, the thickness, physical property and vertical structure are controlled by weathering-leaching period, lithology and palaeogeomorphology respectively.Based on the study on weathering crust structural layer and the reservoir characteristics, combined with accumulation elements, the thesis build up the “self-generation and selfreservoir” accumulation model. According to the morphology and the relationship with surrounding rocks, the gas reservoir fall into stratiform and massive, such as Dixi14 area and Dixi17 area. The volcanic reservoir in Kelameili is characterized by the multiple transport system, weathering-leaching process in long period, positive tectonic background and proximal accumulation, which are also the most significant controlling factors.