Research of Mud Intrusion Characteristics in Low Permeability Reservoir and Time-lapse Resistivity Log Evaluation

The East China sea is rich in low-permeability oil and gas resources. However, low permeability reservoir is extremely sensitive, so protecting low-permeability reservoirs is the prerequisite for the development of low-permeability reservoirs. Two kinds of drilling fluid system are used respectively, which are reverse osmosis water-base mud and shortening oil-base mud. To study the intrusion characteristics of these two kinds of mud system, a low-permeability core intrusion experiment is carried out, which includes three kinds of core: （0.1～1）×10⁻³ µm²,（1～5）×10⁻³ µm² and（5～10）×10⁻³ µm². The result shows that both water-base mud and oil-base mud intrude into cores, making different degree of low-resistivity intrusion or high-resistivity intrusion characteristics. The mud intrusion depth, fluid properties and movable water condition can be analyzed effectively by using different mud intrusion characteristics combined with time-shift resistivity logging, which offers useful technical support for wellbore protection for low-permeability reservoirs and oil and gas perforating interval selection.