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Introduction
Safety and the Environment
The Planning Process
Fluid Categories
Fluid Density
Crystallization Temperature
Temperature and Pressure Effects
Estimating Required Fluid Volume
Fluid Compatibility
Temperature and Pressure Effects
When a brine is put into service, the downhole temperature profile will cause the brine to expand, lowering the average density of the fluid column. Pressure has the opposite effect and causes an increase in density. Adjustments will need to be made to the fluid density to compensate for the combination of bottomhole pressure and bottomhole temperature.

For fluids with densities less than approximately 12.0 lb/gal, thermal expansion will typically be in the range of 0.26 lb/gal to 0.38 lb/gal per 100°F (lb/gal/100°F) increase in temperature. From 12.0 lb/gal to 19.0 lb/gal, the expansion ranges from 0.33 lb/gal to 0.53 lb/gal per 100°F increase. Typically, the density correction is made for the average temperature of the fluid column. Pressure effects are much smaller and range from 0.019 lb/gal per thousand psi to 0.024 lb/gal per thousand psi. Table 2 shows some representative values for thermal expansion (A) and hydrostatic compression (B) based on data reported in literature (Bridges, 2000).

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TABLE 2. Density Corrections for Temperature and Pressure

Fluid Type Selected
Densities
Temperature
Expansion
(A)
Hydrostatic
Compression
(B)
  lb/gal1 lb/gal/100ºF1 lb/gal/1000 psi1
NaCl 9.0 0.314 0.0189
NaCl 9.5 0.386 0.0188
NaBr 12.0 0.336 0.0190
CaCl2 9.5 0.285 0.0188
CaCl2 10.0 0.289 0.0187
CaCl2 10.5 0.273 0.0186
CaCl2 11.0 0.264 0.0187
CaCl2/CaBr2 12.0 0.325 0.0190
CaCl2/CaBr2 12.5 0.330 0.0193
CaCl2/CaBr2 13.5 0.343 0.0201
CaCl2/CaBr2 14.5 0.362 0.0212
CaCl2/Zn-CaBr2 15.5 0.387 0.0226
CaCl2/Zn-CaBr2 16.5 0.416 0.0244
CaCl2/Zn-CaBr2 17.5 0.453 0.0264
CaCl2/Zn-CaBr2 18.0 0.475 0.0276
CaCl2/Zn-CaBr2 18.5 0.501 0.0288
CaCl2/Zn-CaBr2 19.0 0.528 0.0301
1Values in Table 2 above are adapted from data in Bridges (2000), Completion and Workover Fluids, SPE Monograph 19.

The fluid density corrected for temperature and pressure (dc) is calculated using Equation 5 with input values from Equation 3 and Equation 4 and values for A and B from Table 2.

Temperature Correction

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EQUATION 3.

Equation 3 Graphic

Pressure Correction

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EQUATION 4.

Equation 4 Graphic

The results of Equation 3 and Equation 4 are used in Equation 5 to obtain the corrected density (dc).

Corrected Density

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EQUATION 5.

Equation 5 Graphic

The actual corrected density (dc) of the fluid mixed and delivered to location will be slightly greater than determined, based solely on TVD and BHP in Equation 2.

CBF Temperature and Pressure Profile Software (TP-Pro)

A TETRA fluids specialist is equipped to make a more accurate analysis of the temperature, pressure, and density profile for the entire fluid column. Using TETRA’s TP-Pro™ program, fluids specialists can analyze the temperature and pressure conditions along the entire length of the flow path to ensure that an accurate and reliable prediction of corrected density is made for your particular application.

TETRA’s TP-Pro program calculates the thermal expansion and pressure compressibility behavior of clear brine fluids in a wellbore. The program can be used to model onshore and offshore wells. Solid free brines are especially susceptible to thermal expansion and pressure compressibility, which can significantly alter the effective density of the brine in a downhole application. Because of this susceptibility, a TP-Pro simulation is recommended for every solid free brine application to determine the required surface density of the brine for the necessary effective density.

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TABLE 3. TP-Pro Example of Input Variables

TP-Pro Input Variables
Surface Temperature 70ºF
Mudline Temperature 39ºF
Rig Floor Elevation 82 feet
Water Depth 3,440 feet
Water Depth + Elevation 3,522 feet
Bottomhole Temperaure (BHT) 275ºF
True Vertical Depth of Zone of Interest (TVD) 17,880 feet
Bottomhole Pressure (BHP) 13,200 psi
Overbalance 250 psi
Required Effective Density 14.47 lb/gal
Selected Surface Density 14.60 lb/gal
Pressurized Crystallization Temperature (PCT) 0ºF
Fluid Composition (One, Two, or Three Salt) One Salt
Actual Overbalance 305 psi
Effective Density at 17,880 feet (TVD) 14.53 lb/gal

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TABLE 4. TP-Pro Example of Output Variables

Vertical Depth Actual Density Effective Density Temperature
Feet lb/gal lb/gal psi °F
0 14.60 14.60 0 70
41 14.60 14.60 31 70
82 14.60 14.60 62 70
Water Surface
770 14.63 14.62 585 64
1,458 14.67 14.63 1,109 58
2,146 14.70 14.65 1,635 51
2,834 14.73 14.66 2,161 45
3,522 14.76 14.68 2,689 39
Mudline
4,240 14.74 14.69 3,239 51
4,958 14.71 14.70 3,789 63
5,676 14.68 14.70 4,337 74
6,394 14.65 14.69 4,885 86
7,112 14.63 14.69 5,431 98
7,829 14.60 14.68 5,977 110
8,547 14.57 14.67 6,521 122
9,265 14.54 14.66 7,065 133
9,983 14.52 14.65 7,607 145
10,701 14.49 14.64 8,148 157
11,419 14.46 14.63 8,689 169
12,137 14.43 14.62 9,228 181
12,855 14.40 14.61 9,766 192
13,573 14.38 14.60 10,304 204
14,291 14.35 14.59 10,840 216
15,008 14.32 14.57 11,375 228
15,726 14.29 14.56 11,909 240
16,444 14.27 14.55 12,442 251
17,162 14.24 14.54 12,974 263
17,880 14.21 14.53 13,505 275

The results of a TP-Pro simulation are based on best available information and assume equilibrium and static well conditions.

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