Abstract:

Based on information from casting thin sections, scanning electron microscopy (SEM), core photos and constant speed mercury pressure analysis, and with the consideration of the material source, clay mineral, pore type and diagenesis, the Chang 6₁ reservoir of Wangpanshan is divided into six different diagenetic facies. The dominant reservoir facies are kaolinite+chlorite cementation-intergranular pore, kaolinite cementation-dissolved pore+intergranular pore, and chlorite+kaolinite cementation-dissolution pore. This study shows that the microscopic pore structures and logging responses of the different diagenetic facies are various. The variation of micro-pore throat in each diagenetic phase is distinct, especially in the capillary pressure curve and throat. Correlation between the throat radius and permeability is better than that between the pore radius, porosity and permeability. Moreover, the pore throat radius of the dominating diagenetic facies is more uniform, with better connectivity and seepage ability, which keep high mercury saturation under the same pressure of the mercury intake. The logging response characteristics of the different diagenetic facies are summed up by using natural gamma ray, sonic time difference, resistivity and other logging curves. We then established the logging response identification template for each diagenetic facies, and determined the quantitative identification criteria for logging response of the different diagenetic facies. With that, we identified and divided the vertical upper diagenetic facies of the single well, which provide an important reference for the prediction of sweet spot in low permeability sandstone reservoirs.

Key words: Chang 6₁ reservoir, diagenetic facies, constant speed mercury penetration, throat, logging curve