“…Aiming at the special downhole environment in oil and gas while drilling, the limitation of borehole space to measurement system size, as well as the effect of downhole pressure, temperature, multiphased fluids containing oil and gas bubbles and solid particles plus the variations of downhole fluid domain on measurement, instrument measurement accuracy, and response characteristics, needs comprehensive consideration. In the literature, the researchers proposed different methods and solutions such as acoustics [2][3][4], pressure difference [5,6], and electromagnetics [7,8] for the downhole annular flow measurement while drilling. These methods have achieved some successes but have some problems.…”