Method and apparatus for water-based mud filtrate contamination monitoring in real time downhole water sampling

A method for contamination monitoring, comprising:

• measuring a water based mud filtrate density and a water based mud filtrate resistivity at surface conditions;
• converting via a downhole apparatus the measured water based mud filtrate density and resistivity to downhole conditions;
• logging via the downhole apparatus properties of a downhole fluid to find at least a resistivity and a density of a fluid sample at the downhole conditions;
• establishing via the downhole apparatus a linear relationship between a water based mud filtrate conductivity at downhole conditions and the water based mud filtrate density at the downhole conditions;
• determining via the downhole apparatus an existence of a high quality pressure gradient at the downhole conditions;
• fitting via the downhole apparatus at least one of a density and a resistivity data for native formation water using a power function and obtaining at least one of a density and a resistivity for native formation water when no high quality pressure gradient exists;
• estimating via the downhole apparatus the density for native formation water from the pressure from the high quality gradient when the high quality pressure gradient exists;
• estimating via the downhole apparatus the resistivity for native formation water, using the linear relationship between the water based mud filtrate conductivity and the water based mud filtrate density;
• estimating via the downhole apparatus a density for water based mud filtrate using the linear relationship between the water based mud filtrate conductivity and the water based mud filtrate density;
• and
• estimating via the downhole apparatus a water based mud filtrate contamination based on the water based mud filtrate density.