Determining fluid composition from fluid properties

A method of determining the composition of a downhole fluid, having a first component and a second component, comprising:

• measuring a density of the downhole fluid;
• and
• determining a normalized fluid contamination using the measured density;
• and
• plotting the measured density versus the normalized fluid contamination;
• wherein the normalized fluid contamination is calculated using the response of density to fluid contamination, wherein the response is expressible as ⅆ ρ mix ⅆ f = ( ρ 1 - ρ 2 ) ,
• wherein ρ1 is the density of a first component of the downhole fluid, ρ2 is the density of a second component of the downhole fluid and, ⅆ ρ mix ⅆ f
• is the incremental change of the density of the downhole fluid, ρmix, to the change in fluid contamination, f.

A method for determining a composition of a fluid comprising:

• pumping fluid through a downhole measurement module;
• measuring the density of the fluid in the downhole measurement module;
• transmitting the measured density data to a control system at the surface;
• and
• determining a normalized fluid contamination using the measured density and the response of the measured density to fluid contamination;
• wherein the normalized fluid contamination is calculated using the response of density to fluid contamination, wherein the response is expressible as ⅆ ρ mix ⅆ f = ( ρ 1 - ρ 2 ) ,
• wherein ρ1 is the density of a first component of the fluid, ρ2 is the density of a second component of the fluid and, ⅆ ρ mix ⅆ f
• is the incremental change of the density of the fluid, ρmix, to the change in fluid contamination, f.