1140 EXPLORATION GEOPHYSICS 



ence to a common depth-datum plane. Such isobars give important information regard- 

 ing areas where major drainage has occurred, and thus allow the assignment of 

 individual well production rates and the performance of development work to be done 

 on a better engineering basis. This type of work is of considerable importance in 

 connection with various regulatory measures and with the unit control trend of recent 

 legislation. In those instances where individual well-fluid densities are fairly uniform, 

 it is possible to attain the same objective by using shut-in fluid-level (static) data 

 directly, without their prior conversion in terms of equivalent pressures. Likewise, 

 valuable production information can often be obtained from maps showing lines of 

 equal pumping-equilibrium fluid levels. 



Gas Lift Operations. — An interesting application of fluid-level measurements in 

 Texas concerns existing or projected gas-lift installations. f If a well is being con- 

 verted from pumping or flowing to gas lift, it is convenient to be able to obtain the 

 fluid level in the annular space in advance of the pulling job. Also, the draw-down 

 at various producing rates will give valuable information regarding the size and loca- 

 tion of the valves to be installed. If a flow-valve installation is made, its operation 

 can be checked quickly and conveniently by fluid-level observations. If it is suspected 

 that a valve is sticking, a close check of the fluid-level variation when the well 

 begins to unload will show which valve is kicking off. Also, the correctness of 

 valve spacings and their effective performance can be studied. 



In wells where the conventional type insert valves are used, it is impossible 

 to run a bottom-hole pressure bomb because the valves obstruct the tubing. In all 

 gas-lift installations using flow-valves the wave reflection measurements have the 

 additional advantage that the fluid level can be watched continually and the input 

 pressure properly regulated without the possibility of changed flow conditions as a 

 result of running the pressure bomb in the flow string. 



Primary Pressure Control and Secondary Recovery Projects. — Periodic studies 

 of formation pressures are the basis of any conservation program designed to secure 

 optimum oil recovery. As a result of such studies it is often found desirable to aug- 

 ment the reservoir's native energy artificially by fluid injection. Such a program may 

 be instigated when a pool has nearly reached its economic limit by conventional pro- 

 duction procedures (secondary recovery) or during the early life of the field (primary 

 pressure control). For the latter case, the decline of subsurface pressures will be 

 materially lessened and consequently the flowing life prolonged. Thus depth pressures 

 will probably be obtained most conveniently by means of bottom-hole pressure gauges, 

 although fluid-level measurements could also be used. Once the pumping stage is 

 reached, bottom-hole pressure information may be obtained most economically by means 

 of the sonic procedures. 



It is also necessary to check the gas-input wells periodically for fluid, to see that 

 no condensate has accumulated in their bottoms. In a multi-zone field, gas may be 

 injected into two or more pays from the same well. In this case the wave reflection 

 instrument proves itself invaluable as a rapid and accurate means of measuring the 

 depths to fluid or to bottom. 



Cementing Operations. — The "squeeze" cementing technique has become a 

 standard practice in completing and reconditioning wells whenever an undesirable 

 water stratum is to be shut off. Such a procedure depends for its success upon the 

 effectiveness of a protecting packer set above the stratum to be sealed off. Should 

 any cement slurry which is forced down the tubing string under pressure escape 

 around the packer, there is danger of contamination to the oil zone above. Also, 

 this "leak" effectively lowers the pressure differential which would normally be 

 applied to the face of the watered formation. 



Such leaks during a cementing process can be detected by measuring progres- 



t Geo. Webber, "Fluid Level Indicator Useful in East Texas," The Oil and Gas Journal, 

 Dec. 19, 1938, pp. 44-50. 



