Abstract

Brine viscosities are an important property in sand control and coil tubing operations. Viscosities are used to calculate sand settling rates for gravel packing and frictional pressure losses. Due to limited brine viscosity data, viscosites were determined for conventional completion fluids using an Oswald viscometer. Then three dimension equations were determined as a function of density and temperature for calcium chloride, calcium bromide, calcium chloride and calcium bromide, calcium bromide and zinc bromide, three salt mixture of calcium chloride, calcium bromide and zinc bromide, and sodium bromide solutions. All equations had an average deviation from the measured values of less than 10%.

Introduction

Viscosities for water and low density brines are readily available even at elevated pressures.1–2 However, very little work has been done on brines above 10.0 ppg. One source provided brine viscosities in chart form at densities up to 16.5 ppg and at temperatures ranging from 40 to 500°F.3 However, interpolating within these brine densities are difficult but were the best the industry had available. Since these viscosities were established using an Ostwald-Cannon-Fenske viscometer, measuring these brine viscosities above 250°F is impossible due to boiling of these brines. Obviously, the brine viscosities were extrapolated from the measured data above the boiling point. Since no experimental data was provided, the accuracy of these brine viscosities is questionable. Also brine viscosities above 16.5 ppg are needed.

The purpose of this work is to provide brine viscosities in equation form and to report the accuracy of these equations from the experimental data.

Experimental

The various densities of the calcium chloride brines were achieved by mixing 11.6 ppg calcium chloride with water until the desired density was reached. The densities of the calcium chloride, calcium bromide brines were achieved by combining 11.6 ppg calcium chloride with 15.1 ppg calcium bromide, calcium chloride (two salt blend) until the chosen density was attained. The densities of the calcium chloride, calcium bromide and zinc bromide brines were made by adding 15.1 ppg calcium chloride, calcium bromide to 19.2 ppg calcium bromide, zinc bromide (three salt blend) until the desired densities were achieved. The densities of the sodium bromide fluids were reached by diluting 12.5 ppg sodium bromide with water. The specific gravity of the fluid was then measured. The brines were then cooled to around 35°F. The viscosities for the calcium chloride brines were measured using a Cannon Instrument Company Viscosity Tube model number 50 Y 991. All of the other viscosities were measured using a Cannon Instrument Company Viscosity Tube model number 150 433 I. The different fluids were placed in the tube, and the amount of time for the fluid to go from the top line on the tube to the bottom line of the tube was measured using a standard stopwatch. This was done three times, and an average was taken of the three times in seconds. After the 35°F run was completed, the brine was heated in the viscosity tube using a Fisher Scientific Isotemp 2150 heater and a 4000 mL beaker of water. The same procedure regarding the viscosity tube and the stopwatch was repeated. The brines were heated to 198°F in increments of 20oF. The brines were allowed to heat for fifteen minutes to confirm that the temperature of the brine was the same as the temperature of the water in the beaker.

Equation 1 was used to calculate the viscosities at temperature.

  • Equation 1

where B is the coefficient of the viscometer, ? is the brine's density, g/cc at temperature, and t is the time in seconds. A thermal expansion factor of 0.000250/°F was used for only the two salt standard blends, and the fluids that contain zinc bromide. Other expansion factors were calculated from reference four. Viscometer coefficients of 0.004175 mm2/s2 (cSt/s) at 40°C and 0.004155 mm2/s2 (cSt/s) at 100°C were provided by the manufacturer for Viscometer No. 50. Whereas, 0.03251 mm2/s2 (cSt/s) at 40°C and 0.03234 mm2/s2 (cSt/s) at 100°C were provided for Viscometer No. 150. Linear interpolation and extrapolation were performed to determine the coefficients at different temperatures.

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