Contamination estimation of formation samples

Abstract

Contamination estimation of a mud filtrate or reservoir sample requires a robust handle on the properties of mud filtrate at downhole conditions. Coupling acquired data with downhole measured data provides a robust estimation of contamination by encompassing the entire available data. Downhole density of the mud filtrate sample may be estimated based on a characteristic of the mud filtrate sample. A density of a formation fluid of the reservoir may be determined using a formation tester tool. The contamination of the formation fluid may be estimated based on the clean fluid density and the estimated mud filtrate density by, for example, using a material balance equation or ratio. An estimated pump-out time for the formation fluid may be determined based on the estimated contamination and a trend of the estimated contamination of the formation fluid.

What is claimed is: 
     
         1 . A method for contamination estimation, comprising:
 collecting a mud filtrate sample;   determining a surface density of the mud filtrate sample;   estimating downhole density of the mud filtrate sample based, at least in part, on the surface density;   determining a plurality of formation fluid densities for a period of time;   determining a constant pumping rate;   filtering the determined formation fluid density based, at least in part, on the constant pumping rate;   determining a clean fluid density based, at least in part, on a linear regression of the filtered determined formation fluid density versus an exponential function of time;   estimating a contamination based, at least in part, on the clean fluid density;   comparing the estimated contamination to a contamination threshold; and   collecting a reservoir fluid sample based, at least in part, on the comparison.   
     
     
         2 . The method of contamination estimation of  claim 1 , further comprising receiving one or more formation fluid density measurements from one or more sensors, wherein the determined formation fluid density is based on the one or more formation fluid density measurements. 
     
     
         3 . The method of contamination estimation of  claim 1 , further comprising positioning a formation tester tool within a wellbore, wherein the formation tester tool collects the reservoir fluid sample. 
     
     
         4 . The method of contamination estimation of  claim 1 , further comprising determining one or more mud filtrate characteristics of the mud filtrate sample, wherein the estimated downhole density of the mud filtrate sample is based, at least in part, on at least one of the one or mud filtrate characteristics. 
     
     
         5 . The method of contamination estimation of  claim 1 , wherein determining the constant pumping rate comprises determining a pumping rate at which a plurality of pumping rates associated with a predetermined interval of time are within a range of deviation. 
     
     
         6 . The method of contamination estimation of  claim 1 , wherein the clean fluid density is determined based, at least in part, on extrapolation of the linear regression for a time that approaches infinity. 
     
     
         7 . The method of contamination estimation of  claim 1 , wherein estimating the contamination comprises calculating a first calculated density, calculating a second calculated density and dividing the first calculated density by the second calculated density, wherein calculating the first calculated density comprises subtracting from a real-time formation fluid density measurement the clean fluid density, and wherein calculating the second calculated density comprises subtracting from the estimated mud filtrated density the clean fluid density. 
     
     
         8 . The method of contamination estimation of  claim 1 , wherein the intensifier comprises a plurality of intensifiers, and wherein distribution of the hydraulic fluid to each of the plurality of intensifiers is based, at least in part, on a fuel map. 
     
     
         9 . A non-transitory computer-readable medium storing one or more executable instructions that, when executed, cause one or more processors to:
 actuate collection of a mud filtrate sample;   determine a surface density of the mud filtrate sample;   estimate downhole density of the mud filtrate sample based, at least in part, on the surface density;   determine a plurality of formation fluid densities for a period of time;   determine a constant pumping rate;   filter the determined formation fluid density based, at least in part, on the constant pumping rate;   determine a clean fluid density based, at least in part, on a linear regression of the filtered determined formation fluid density versus an exponential function of time;   estimate a contamination based, at least in part, on the clean fluid density;   compare the estimated contamination to a contamination threshold; and   collect a reservoir fluid sample based, at least in part, on the comparison.   
     
     
         10 . The non-transitory computer-readable medium of  claim 9 , wherein the one or more executable instructions that, when executed, further cause the one or more processors to receive one or more formation fluid density measurements from one or more sensors, wherein the determined formation fluid density is based on the one or more formation fluid density measurements. 
     
     
         11 . The non-transitory computer-readable medium of  claim 9 , wherein the one or more executable instructions that, when executed, further cause the one or more processors to position a formation tester tool within a wellbore, wherein the formation tester tool collects the reservoir fluid sample. 
     
     
         12 . The non-transitory computer-readable medium of  claim 9 , wherein the one or more executable instructions that, when executed, further cause the one or more processors to determine one or more mud filtrate characteristics of the mud filtrate sample, wherein the estimated downhole density of the mud filtrate sample is based, at least in part, on at least one of the one or mud filtrate characteristics. 
     
     
         13 . The non-transitory computer-readable medium of  claim 9 , wherein determining the constant pumping rate comprises determining a pumping rate at which a plurality of pumping rates associated with a predetermined interval of time are within a range of deviation. 
     
     
         14 . The non-transitory computer-readable medium of  claim 9 , wherein the clean fluid density is determined based, at least in part, on extrapolation of the linear regression for a time that approaches infinity. 
     
     
         15 . The non-transitory computer-readable medium of  claim 9 , wherein estimating the contamination comprises calculating a first calculated density, calculating a second calculated density and dividing the first calculated density by the second calculated density, wherein calculating the first calculated density comprises subtracting from a real-time formation fluid density measurement the clean fluid density, and wherein calculating the second calculated density comprises subtracting from the estimated mud filtrated density the clean fluid density. 
     
     
         16 . The non-transitory computer-readable medium of  claim 9 , wherein the intensifier comprises a plurality of intensifiers, and wherein distribution of the hydraulic fluid to each of the plurality of intensifiers is based, at least in part, on a fuel map. 
     
     
         17 . A system for contamination estimation, comprising:
 a mud filtrate sample;   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;   estimate downhole density of the mud filtrate sample based, at least in part, on the surface density;   determine a plurality of formation fluid densities for a period of time;   determine a constant pumping rate;   filter the determined formation fluid density based, at least in part, on the constant pumping rate;   determine a clean fluid density based, at least in part, on a linear regression of the filtered determined formation fluid density versus an exponential function of time;   estimate a contamination based, at least in part, on the clean fluid density;   compare the estimated contamination to a contamination threshold; and   collect a reservoir fluid sample based, at least in part, on the comparison.   
     
     
         18 . The system for contamination estimation of  claim 17 , wherein the one or more instructions that, when executed by the processor, further cause the processor to receive one or more formation fluid density measurement from one or more sensors, wherein the determined formation fluid density is based on the one or more formation fluid density measurements. 
     
     
         19 . The system for contamination estimation of  claim 17 , wherein the one or more instructions that, when executed by the processor, further cause the processor to determine one or more mud filtrate characteristics of the mud filtrate sample, wherein the estimated downhole density of the mud filtrate sample is based, at least in part, on at least one of the one or mud filtrate characteristics. 
     
     
         20 . The system for contamination estimation of  claim 17 , wherein estimating the contamination comprises calculating a first calculated density, calculating a second calculated density and dividing the first calculated density by the second calculated density, wherein calculating the first calculated density comprises subtracting from a real-time formation fluid density measurement the clean fluid density, and wherein calculating the second calculated density comprises subtracting from the estimated mud filtrated density the clean fluid density.