Optimization of sample cleanup during formation testing

A method for extracting formation fluid from an earth formation penetrated by a borehole having a drilling fluid, the method comprising:

• conveying a formation testing tool through the borehole, the tool comprising:
• a sample flow element configured to extract formation fluid from the formation in a sample zone;
• a sample zone seal forming a perimeter defining the sample zone;
• a contamination removal flow element configured to extract formation fluid contaminated with the drilling fluid from a contamination removal zone in the formation;
• a contamination removal zone seal forming a perimeter defining the contamination removal zone, which surrounds and excludes the sample zone;
• one or more sensors configured to measure a property of the formation fluid extracted by the sample flow element and/or the contamination flow element;
• a sample flow control device configured to control flow of extracted formation fluid from the sample flow element;
• a contamination removal flow control device configured to control flow of extracted formation fluid contaminated with the drilling fluid from the contamination removal flow element;
• and a controller comprising an input and an output and being configured to:
• (i) receive input from the one or more sensors and (ii) provide a control output to control a sample flow rate in the sample flow element by modulating or adjusting the sample flow control device and a contamination removal flow rate in the contamination flow removal element by modulating or adjusting the contamination removal flow control device according to a calculation of a change in an amount of contamination in extracted formation fluid over an interval of time;
• controlling the sample flow rate and the contamination removal flow rate according to the calculation in order to decrease an amount of time required to acquire a sample of the formation fluid having an acceptable amount of contamination using the controller;
• receiving as input to the controller an amount of contamination in the formation fluid extracted by the sample flow element as measured by a sensor;
• receiving as input to the controller a sensor measurement of a parameter related to a constraint imposed on at least one of the sample flow rate and the contamination removal flow rate;
• calculating a first derivative of the first amount of contamination over time;
• and
• controlling the sample flow rate and the contamination flow rate to maximize the first derivative of the first amount of contamination over time as a negative value within the constraint.

A non-transitory computer-readable medium comprising computer-executable instructions for extracting formation fluid from an earth formation penetrated by a borehole having a drilling fluid by implementing a method comprising:

• controlling a sample flow rate;
• controlling a contamination removal flow rate in order to decrease an amount of time required to acquire a sample of the formation fluid having an acceptable amount of contamination using a formation testing tool comprising:
• a sample flow element configured to extract formation fluid from the formation in a sample zone;
• a sample zone seal forming a perimeter defining the sample zone;
• a contamination removal flow element configured to extract formation fluid contaminated with the drilling fluid from a contamination removal zone in the formation;
• a contamination removal zone seal forming a perimeter defining the contamination removal zone, which surrounds and excludes the sample zone;
• one or more sensors configured to measure a property of the formation fluid extracted by the sample flow element and/or the contamination flow element;
• a sample flow control device configured to control flow of extracted formation fluid from the sample flow element;
• a contamination removal flow control device configured to control flow of extracted formation fluid contaminated with the drilling fluid from the contamination removal flow element;
• and a controller comprising an input and an output and being configured to:
• (i) receive input from the one or more sensors and (ii) provide a control output to control the sample flow rate in the sample flow element by modulating or adjusting the sample flow control device and the contamination removal flow rate in the contamination flow removal element by modulating or adjusting the contamination removal flow control device according to a calculation of a change in an amount of contamination in extracted formation fluid over an interval of time;
• receiving as input to the controller an amount of contamination in the formation fluid extracted by the sample flow element as measured by a sensor;
• receiving as input to the controller a sensor measurement of a parameter related to a constraint imposed on at least one of the sample flow rate and the contamination removal flow rate;
• calculating a first derivative of the first amount of contamination over time;
• and
• controlling the sample flow rate and the contamination flow rate to maximize the first derivative of the first amount of contamination over time as a negative value within the constraint.