Main Controlling Factors and Identification Method of Low-Resistivity Reservoirs in Deep and Ultra-Deep Layers of the Hetao Basin

The deep and ultra-deep areas of the Xinglong Structural Belt in the Hetao Basin still develop medium-porosity and medium-permeability high-quality reservoirs, which greatly expands the space for oil and gas exploration and has become an important reserve growth area and productivity replacement area in Huabei Oilfield in recent years. Influenced by special geological characteristics such as saline lake, low geothermal gradient, late deep burial and weak diagenesis, the resistivity of oil layer in Hetao area varies greatly (0.9Ω · m-20Ω · m), and the absolute value of resistivity is low. It is different from the conventional low resistivity oil layer with the ratio of oil layer resistivity to typical water layer resistivity less than 2. This paper analyzes the main controlling factors of ultra-deep low-resistivity reservoirs in Hetao Basin from four aspects: high-salinity formation water, influence of rock particle size, complex pore structure, clay minerals and shale content. Based on these analyses, four oil and water layer identification methods were established in the Xinglong Structural Belt of Hetao Basin, including porosity and resistivity crossplot method, oil index method, array induction intrusion factor fluid identification method, and fluid identification method based on nuclear magnetic resonance.