Method to measure and predict downhole rheological properties

Abstract

Systems and methods of the disclosed embodiments include taking a first sample of a drilling fluid at a first time, measuring, with a rheometer, a first viscosity dial reading of the first sample, taking a second sample of a drilling fluid at a second time, measuring, with the rheometer, a second viscosity dial reading of the second sample, weighting the first dial reading and the second dial reading based on an elapsed time since the first time and an elapsed time since the second time, and calculating a shear stress vs. shear rate function of the drilling fluid for a plurality of temperatures and a plurality of pressures based on the weighted first viscosity dial reading and the weighted second viscosity dial reading.

What is claimed is: 
     
         1 . A method of drilling a borehole, comprising:
 measuring, with a rheometer, a first viscosity dial reading of a first sample of a drilling fluid taken at a first time;   measuring, with the rheometer, a second viscosity dial reading of a second sample of a drilling fluid taken at a second time;   weighting the first dial reading and the second dial reading based on elapsed time since the first time and the second time;   calculating a shear stress vs. shear rate function of the drilling fluid for a plurality of expected borehole temperatures and a plurality of expected borehole pressures based on the weighted first viscosity dial reading and the weighted second viscosity dial reading; and   calculating an equivalent circulating density (ECD) at a location within the borehole based on the shear stress vs. shear rate function of the drilling fluid.   
     
     
         2 . The method of  claim 1 , wherein the first viscosity dial reading is measured at a first temperature, and the second viscosity dial reading is measured at a second temperature that is different than the first temperature. 
     
     
         3 . The method of  claim 1 , wherein the first viscosity dial reading is measured at a first temperature, the second viscosity dial reading is measured at a second temperature, and the first temperature and the second temperature are randomly selected from a range of possible temperatures, a list of possible temperatures, or a combination thereof. 
     
     
         4 . The method of  claim 3 , comprising updating the range of possible temperatures, the list of possible temperatures, or both depending on changes to the borehole. 
     
     
         5 . The method of  claim 1 , wherein the first viscosity dial reading is measured at a first pressure, and the second viscosity dial reading is measured at a second pressure that is different than the first pressure. 
     
     
         6 . The method of  claim 1 , wherein the first viscosity dial reading is measured at a first pressure, the second viscosity dial reading is measured at a second pressure, and the first pressure and the second pressure are randomly selected from a range of possible pressures, a list of possible pressures, or a combination thereof. 
     
     
         7 . The method of  claim 3 , comprising updating the range of possible pressures, the list of possible pressures, or both depending on changes to the borehole. 
     
     
         8 . The method of  claim 1 , wherein the first viscosity dial reading comprises measuring a shear stress at a plurality of shear rates. 
     
     
         9 . The method of  claim 1 , wherein the second time is weighted more than the first time. 
     
     
         10 . The method of  claim 1 , comprising:
 taking a third sample of a drilling fluid at a third time;   measuring, with the rheometer, a third viscosity dial reading of the third sample;   weighting the third dial reading on an elapsed time since the third time; and   updating the shear stress vs. shear rate function of the drilling fluid for the plurality of temperatures and the plurality of pressures based on the weighted third viscosity dial reading.   
     
     
         11 . The method of  claim 10 , wherein weighting the first dial reading, the second dial reading, and the third dial reading comprises weighting according to a linear, parabolic, or exponential weighting function. 
     
     
         12 . The method of  claim 1 , comprising adjusting a drilling function based on the ECD, pore pressure within a production formation, and fracture gradient while maximizing the rate of penetration. 
     
     
         13 . The method of  claim 12 , wherein the drilling function comprises a pressure of the drilling fluid provided by a mud pump, a density of the drilling fluid, a rotation speed of a drill string, or any combination thereof. 
     
     
         14 . A system for drilling a borehole using a drilling fluid, comprising:
 a rheometer configured to collect samples of the drilling fluid and measure a viscosity dial reading for each sample; and   a well modeling system comprising a processor configured to run instructions stored on a computer memory to:
 store the viscosity dial readings of the samples; 
 weight the viscosity dial readings based on an elapsed time since the samples were collected; and 
 calculate an equivalent circulating density (ECD) of the drilling fluid for a plurality of temperatures and a plurality of pressures based on the weighted viscosity dial readings. 
   
     
     
         15 . The system of  claim 14 , wherein the rheometer is configured to measure a first viscosity dial reading of a first sample at a first temperature, and to measure a second viscosity dial reading of a second sample at a second temperature that is different than the first temperature. 
     
     
         16 . The system of  claim 14 , wherein the rheometer is configured to measure a first viscosity dial reading of a first sample at a first pressure, and to measure a second viscosity dial reading of a second sample at a second pressure that is different than the first pressure. 
     
     
         17 . The system of  claim 14 , wherein the rheometer is configured to measure the viscosity dial readings at a plurality of shear rates. 
     
     
         18 . The system of  claim 14 , wherein the weighted viscosity dial readings comprise only the viscosity dial readings for the eight latest collected samples. 
     
     
         19 . The system of  claim 14 , comprising a mud pump configured to adjust the pressure in the well based on the calculated ECD. 
     
     
         20 . The system of  claim 14 , comprising a drill string configured to rotate while drilling the well, wherein the well modeling system is configured to change a speed of rotation of the drill string based on the calculated ECD to maximize the rate of penetration of the borehole.