TUBING, 

 25% 



.CASING 

 75% 



.CASING 

 50% 



TUBING. 

 75% 



.CASING 

 25% 



Figure 20-7. In a static-interface survey, two fluids are injected down tubing and casing 

 simultaneously; proportional rates of flow control depth of interface, as determined 

 by amounts of fluid accepted by various subsurface zones. 



through the annulus, an interface will develop between the fluids at some depth 

 in the well below which only the first fluid enters the formation. The interface is 

 detected by a conductivity cell located on the outside of the tubing and connected 

 by appropriate leads to conventional instruments at the surface. The tubing- 

 string may be moved up and down through a stuffing box in order to locate or 

 follow the interface. The injection rates of the two fluids are adjusted to a 

 constant flow rate, so that their sum is the normal injection rate of the well. 

 Separate determinations are made in which the proportional volumes of fluid 

 injected down the tubing and annulus are altered. Detecting the point at which 

 the interface stabilizes, locates the depth below which the fluid injected into 

 the tubing (10%, 20%, etc., of total injected fluid) enters the formation. 



The fluid-velocity survey method is a comparatively recent development 

 that has had extended field application. Its principle of operation is quite 

 simple. While fluid is injected into the well at a constant, controlled rate, a 

 subsurface flowmeter is lowered slowly to the bottom of the well. Fluid velocity 

 data, as measured by this tool, is transmitted to the surface through an insulated 

 electric cable and recorded on automatic instruments. As in the moving interface 

 type of survey, each change in fluid velocity (corrected for variations in hole 

 diameter) represents fluid loss into the zone being traversed. These changes 



402 



