A first property, derivable from mass, of a drilling fluid is measured at a point upstream of a cuttings removal device. A second property (also derivable from mass) is measured at a point downstream of the cuttings removal device. A difference between the properties is determined over a period of time to obtain an estimate of the rate of cuttings removal. This allows the property of the drilling fluid before and after cuttings removal to be compared to give an indication of the rate of cuttings removal, which is indicative of the borehole cleaning.

A ray transceiving system of an underwater flowmeter includes a flowmeter body. A fluid metering channel, a transmitting window, and a probing window are arranged on the flowmeter body. The transmitting window and the probing window are respectively in communication with the fluid metering channel, and each of the transmitting window and the probing window is provided with a titanium alloy isolation seat and a beryllium pad. Titanium alloy is used to seal the fluid metering channel, the titanium alloy and the beryllium pad are combined to bear pressure, and the beryllium pad is used to reduce absorption of gamma rays. A deduction metering method of the underwater flowmeter partially deducts the gamma count rate distortion caused by the Compton scattering effect, and calculates the content of each phase in a three-phase mixed flow to improve the metering accuracy of the three-phase content of oil, gas, and water.