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Abstract

Laboratory data are presented on the changes in the densities of 11-18 lb/gal oil and water base drilling fluids in the temperature and pressure ranges of 70 deg. -400 deg. F and 0-14,000 psig. Results indicate that the change in density of a given type of drilling fluid appear to be independent of the initial density of the fluid, and as oil base drilling fluids are subjected to high temperatures and pressures, they become more dense than water base drilling fluids. The test apparatus and calibration are also described.

Introduction

Liquids expand when heat is applied and are compressed by pressure. Therefore, the density of the fluid decreases with increasing temperature, but increases with increasing pressure. As a drilling fluid is pumped downhole, its density is changed by these temperature and pressure effects.

A survey of the literature showed experimental data on the effect of temperature and pressure on the density of an asphaltic oil base mud and calculated data on density changes with temperature and pressure of fresh water, salt water, and oil base pressure of fresh water, salt water, and oil base muds. This investigation was begun to develop experimental data on the effect of temperature and pressure on the density of oil base and water base pressure on the density of oil base and water base drilling fluids.

EXPERIMENTAL

The equipment for this investigation consisted of an autoclave with a volume of 210 cm3. The autoclave was heated by an aluminum block heater and the temperature was controlled and measured within 5 deg. F. Pressure was controlled by use of a 47 cm screw press, rated at 20,000 psig working pressure. Pressure was controlled within 100 psi. One volume unit of the press contained 0.058 cm. A line with a volume of 3 cm connected the screw press to the autoclave. A schematic drawing of the apparatus is shown in Figure 1.

The autoclave, connection line, and screw press were filled with the test fluid at 70 deg. F. press were filled with the test fluid at 70 deg. F. The screw press was adjusted to a volume of 47 cm and the entire system was shut in. The total system volume was 260 cm . Pressure was varied in 2000 psi increments by adjusting the screw press. once the 70 deg. F data were collected, the press. once the 70 deg. F data were collected, the autoclave was heated to a given temperature and pressure was again adjusted with the screw press. pressure was again adjusted with the screw press. Temperature, pressure, and screw press volumes were tabulated. The apparatus was first calibrated for temperature effect with distilled water at 70 deg. -300 deg. F and 0 psig pressure. Since the screw press was not heated, the response was not linear. Correlation of the volume of water transferred versus water densities gave the following equation:

(1)

Distilled water-was then tested in the 70 deg. -400 deg. F temperature and 2,000-14,000 psig pressure range. The water densities were then calculated by use of equation (1). Comparison of the calculated densities with published data 2 showed the calculated data to diverge positively from published densities. This was not unexpected since pressure will distort the apparatus. A correction factor for pressure was then calculated and is shown in equation (2).

(2)

Combining equations (1) and (2) gives:

(3)

This method of calibration forced a fit of the observed data to known values of water.