The new interpretation of the geological origin about differentiation phenomenon of resistivity in the tight sandstone reservoir

Resistivity differentiation of tight sandstone reservoirs refers to the phenomenon in which the resistivity values of some oil (gas) layers and water layers similar and the test results of reservoirs with higher resistivity are diversified. Therefore, in tight sandstone reservoirs, the geological genesis interpretation of the resistivity difference is an outstanding problem that needs to be resolved. A new interpretation method includes traditional experiments, wettability experiments and NMR experiments. High water salinity and clay mineral additional conductivity in a formation will cause changes in reservoir resistivity and certain differences in different reservoirs. The development of conductive minerals reduces the reservoir resistivity and increases differences in reservoir resistivity. The difference in pore structure and difference in wettability are the main reasons for the difference in reservoir resistivity. Based on the results of experimental research, a comparative analysis is performed on the reservoir resistivity difference between Well J8 and Well Z3. The reservoir resistivity of Well J8 is not notably different from that of the water layer. The reservoir resistivity value of Z3 is relatively large, which is a characteristic of normal gas layers. The reservoir characteristics of Well J8 are also different from those of Well Z3. In the tight sandstone reservoirs of the Shaximiao Formation of the study area, the geological genetics of the resistivity difference are obtained by comprehensive analysis. The main model of geological genetics is the difference in pore structure + difference in wettability, and the secondary model is the difference in formation water salinity + additional conductivity of clay minerals + conductive minerals.