Borehole influx detector and method

DETAILED DESCRIPTION With this and other objects in view, the present invention contemplates a borehole influx detector incorporated in a housing arranged for coupling a drill string.
The detector measures parameters of the density of the borehole fluid which are compared with the nominal or average density of the drilling fluid to determine if formation fluids have flowed into the drilling fluid system.
In one embodiment of the invention, a radiation source and detector are mounted in a recess on the outer wall of a subassembly housing, so that a portion of the stream of drilling fluids passes through the transmission path of the source and detector.
The detector count is determinative of the borehole fluid density.
When discrete measurements of borehole fluid density are compared to nominal or average values of the fluid density, changes are indicative of formation fluid influx.
Another embodiment of the invention uses a highly collimated radiation source and detector which substantially counts only radiation passing through borehole fluids in the annulus between the housing and borehole wall.
In still another embodiment of the invention, radiation source and detector assemblies are mounted on the inner and outer walls of the subassembly housing so that a comparison of drilling fluid densities may be made between fluids before they exit the bit and after they have mingled with formation fluids to give an even more distinct comparison between fluid densities at these points in the drilling fluid system.
Another aspect of the invention involves the mounting of the radiation source and detector in a collimated in line configuration to provide a direct transmission path of radiation through the mud stream.
Yet another aspect of the invention involves the use of a relatively low strength radiation source for measuring drilling fluid density.