Invasion Analysis of Oil-Based Drilling Fluid Based on NMR Experiment

Abstract

In order to clarify the intrusion characteristics of deep and ultra-deep oil-based drilling fluids in the southern margin of Junggar basin and its influence on nuclear magnetic resonance (NMR) logging, NMR experiments are conducted to analyze the influencing factors such as lithology, physical properties, drilling fluid intrusion time, drilling fluid composition, drilling fluid oil-water ratio, fluid properties and temperature. The experimental results show that the invasion modes of oil-based drilling fluid are displacement and imbibition. The NMR T2 spectra of the filtrate and the base fluid are both 400ms, indicating that the filtrate of the oil base drilling fluid invading the formation is its base fluid. The NMR T2 spectral characteristics are not affected by the oil-water ratio of oil-based drilling fluid, but are controlled by the viscosity. NMR peak morphology is influenced by fluid properties and permeability, but not by lithology and porosity. Oil-based drilling fluid does not affect the total NMR porosity, but causes changes in the mobile porosity, resulting in the illusion of increasing the mobile porosity. The degree of change is mainly controlled by permeability and invasion time. The experimental results lay a foundation for understanding the invasion characteristics of oil-based drilling fluid and nuclear magnetic resonance porosity correction.

Keywords

• oil-based drilling fluid
• nuclear magnetic resonance logging
• rock physics experiment
• intrusion characteristics
• southern margin of junggar basin