System for detecting blow out and lost circulation in a borehole

Abstract

A drilling mud flow rate detector, including a sub adapted for being positioned in the drill string, having a sonic signal generator located near the center of the sub in both the incoming mud flow path and the return mud flow path. A set of sonic signal receivers is located at both ends of the sub in both the mud input flow path and the mud return flow path and corresponding sets of sonic signal transmitters are located near the center of the sub. The distance between the transmitting transducers at the center of the sub and the receiving transducers located at each end of the sub are equal so that under a condition of no mud flow, the sonic signals arrive at each end of the sub simultaneously. During mud flow, 'doppler effect' will produce phase shifts in the sonic signals which are proportional to the direction and the rate of mud flow. Signals received by the receiving transducers are processed to produce an input mud flow rate signal and an output mud flow rate signal which are then compared. The occurrence of a change in the ratio of mud input flow to mud output flow above a preselected value will trigger an alarm indicative of the commencement of either a rapid influx of fluids from the formation into the mud stream, known as a 'blow-out', or a rapid outflow of mud into the formation, known as 'lost circulation'.