Contamination estimation of formation samples

A non-transitory computer-readable medium storing one or more executable instructions that, when executed, cause one or more processors to:

• actuate collection or extraction of a mud filtrate sample at a subsurface location;
• instruct a formation tester tool to retrieve the mud filtrate sample at a surface;
• determine a surface density of the mud filtrate sample at the surface;
• estimate downhole density of the mud filtrate sample based, at least in part, on the surface density for a given temperature and a pressure downhole;
• determine a plurality of formation fluid densities for a period of time;
• determine a constant pumping rate, wherein the constant pumping rate is based on a pumping rate at which a plurality of pumping rates associated with a predetermined time interval are within a range of deviation of each other;
• filter the determined plurality of formation fluid densities based, at least in part, on the constant pumping rate;
• perform an analysis of the determined plurality of fluid densities associated at the constant pumping rate versus an exponential function of time to determine a best fit linear regression, wherein all of the analysis is performed at the constant pump rate, wherein the constant pump rate is predetermined from a median or an average of the plurality of pump rates;
• determine a clean fluid density based, at least in part, on a linear regression of the filtered determined plurality of formation fluid densities versus an exponential function of time corresponding to the constant pumping rate;
• estimate a contamination based, at least in part, on dividing a first calculated density by a second calculated density, wherein the first calculated density comprises subtracting the clean fluid density from a real-time formation fluid density measurement, and wherein the second calculated density comprises subtracting the clean fluid density from the estimated mud filtrate density;
• estimate a pump-out time based, at least in part, on the estimated contamination and a trend of the estimated contamination;
• compare the estimated contamination to a contamination threshold, wherein the contamination threshold is about 20%;
• and
• collect a reservoir fluid sample based, at least in part, on the comparison, wherein the reservoir fluid sample is collected when the estimated contamination is at or below the contamination threshold.

A system for contamination estimation, comprising:

• a mud filtrate sample, wherein the mud filtrate sample is collected or extracted at a subsurface location;
• a formation tester tool configured to retrieve the mud filtrate sample at a surface;
• a processor;
• a non-transitory memory coupled to the processor, the non-transitory memory comprising one or more instructions that, when executed by the processor, cause the processor to:
• determine a surface density of the mud filtrate sample at the surface;
• estimate downhole density of the mud filtrate sample based, at least in part, on the surface density for a given temperature and a pressure downhole;
• determine a plurality of formation fluid densities for a period of time;
• determine a constant pumping rate, wherein the constant pumping rate is based on a pumping rate at which a plurality of pumping rates associated with a predetermined time interval are within a range of deviation of each other;
• filter the determined plurality of formation fluid densities based, at least in part, on the constant pumping rate;
• perform an analysis of the determined plurality of fluid densities associated at the constant pumping rate versus an exponential function of time to determine a best fit linear regression, wherein all of the analysis is performed at the constant pump rate, wherein the constant pump rate is predetermined from a median or an average of the plurality of pump rates;
• determine a clean fluid density based, at least in part, on a linear regression of the filtered determined plurality of formation fluid densities versus an exponential function of time corresponding to the constant pumping rate;
• estimate a contamination based, at least in part, on dividing a first calculated density by a second calculated density, wherein the first calculated density comprises subtracting the clean fluid density from a real-time formation fluid density measurement, and wherein the second calculated density comprises subtracting the clean fluid density from the estimated mud filtrate density;
• estimate a pump-out time based, at least in part, on the estimated contamination and a trend of the estimated contamination;
• compare the estimated contamination to a contamination threshold, wherein the contamination threshold is about 20%;
• and
• collect a reservoir fluid sample based, at least in part, on the comparison, wherein the reservoir fluid sample is collected when the estimated contamination is at or below the contamination threshold.