Experimental Determination of Drilling Fluid Thermal Parameters When Calculating APB

Thermal parameters of the drilling fluid affect the prediction of annular pressure buildup (APB) and play an important role in the type selection of casing. The high-temperature and high-pressure PVT tester is used to measure the volume increment of the salt water, water-base drilling fluid, and oil-base drilling fluid. According to the equation of state, the thermal expansion coefficient and compressibility coefficient of annular fluid at different temperatures and pressures are obtained. The results show that the expansion coefficient and compressibility coefficient of the salt water and oil-base fluid are directly proportional to temperature and inversely proportional to pressure; the expansion coefficient of the water-base fluid is directly proportional to temperature, but the compressibility coefficient is inversely proportional to temperature; the expansion coefficient of the water-base drilling fluid is inversely proportional to the density of the drilling fluid, while the density has little effect on the compressibility coefficient of the water-base drilling fluid; the expansion coefficient of the oil-base drilling fluid with oil-water ratio of 8:2 tends to be stable for temperatures over 50 degrees C, and the thermal expansion coefficient of the oil-base drilling fluid with oil-water ratio of 7:3 is stable for temperatures over 75 degrees C. Determination of the drilling fluid thermal parameters provides a theoretical basis for the APB prediction and the type selection of casing.