Complex Resistivity Of Shale Core Laboratory Testing And Analysis

Geological studies have shown that organic-rich shales in southern China has good prospects for exploration and production. Due to the unique storage conditions makes it difficult to use conventional geophysical methods to predict dessert area. Complex resistivity(CR) method, based on the induced polarization effect, can reflect the rocks and minerals dispersion information and has used to detect hydrocarbons more in recent years. Different oil saturated rock complex resistivity amplitude?phase spectrum produce obvious abnormalities with oil saturation increased in conventional reservoirs.In recent years based on a set of mechanisms of complex resistivity method to detect hydrocarbon reservoirs target and applied research is gradually transferred to shale gas exploration. However, due to shale reservoir cores get difficult, combined with complex structural components, obviously anisotropic and microporous structure penetration, So that the basis research work based on complex resistivity of reservoir shale core features rarely carried out. The experimental work is still weak. It is one of the reasons that use complex resistivity method to predict organic-rich shale "sweet zone" is controversial. Therefore, in order to expand the complex resistivity method in shale gas exploration, complex resistivity of reservoir shale core features and its influencing factors were analyzed in this paper.This paper summarizes the work of previous studies, introduced the Cole-Cole model that describe the characteristics of the rock induced polarization, and the model amplitude spectrum and phase spectrum characteristic curves of variation with the complex resistivity model parameters. We use two forms of Cole-Cole model product and the relative dispersion rate to describe the spectral characteristics and polarization characteristics of shale cores. Then based on the induced polarization characteristics of rocks, proposed a induced polarization response semi-quantitative formula of shale core. Summed up the temperature, pressure and saturated liquid salinity affecting shale complex resistivity characteristics of external factors, and clay minerals(brittle mineral), TOC, pyrite and other components are internal. And described the complex resistivity reservoir core spectrum characterized by experimental measurements; experimental analyzed the three major external factors affecting shale complex resistivity characteristics; saturated liquid salinity(salinity), temperature, pressure, etc. Finally, by focusing on the analysis of shale core zero frequency resistivity and polarizability, Combining rock characteristics, porosity and permeability structure and the causes, create a link between shale core resistivity and polarization and Porosity, permeability, clay minerals(brittle mineral), TOC and pyrite; The experimental results were all reasonable explained. We found that increased porosity, permeability, TOC and pyrite have helped to reduce the resistivity of the core, enhanced polarization characteristics; And low clay mineral content and high mineral content helps low brittleness resistance and the formation of high polarization characteristics. Experimental results show that high TOC of shale specimens containing more pyrite microparticles, broadband complex resistivity measured parameters exhibit low resistance at low frequencies, high polarization anomalies. The results provide an effective physical basis of using the electromagnetic sounding exploration the organicrich shale reservoirs, and can be the mechanism of shale reservoirs electrically anomalies, also has an important meaning on exploration of shale reservoirs.