three valuations are made; or, all three segments are combined to get a com- 

 posite of acre-feet of sand. To composite these figures, multiply 48 X 40 to get 

 1920 acre feet, 68 X 36 to get 2448 acre feet, and 44 X 32 to get 1408 — or an 

 aggregate of 5776 acre feet of producing sand under the 160 acres (the product 

 of A, acreage, and the T, thickness, of the formula) . It is already known that 

 oil fields in this trend can be expected to produce 400 barrels per acre-foot. An 

 experienced valuator in the trend thus could estimate around 2,310,400 barrels 

 (5776 X 400) of ultimate recovery. 



It is found that when the eight wells on the lease were drilled, no cores 

 were obtained. It is learned that core laboratories ran cores from a well on an 

 adjoining lease; average porosities of 21, 23, and 24 percent were obtained from 

 three cores. The Gulf Company has run porosities, which average 23 percent 

 on most of its wells. Permeabilities averaged 550 millidarcys. It is concluded 

 that 22 percent is about the average porosity for the lease being valued, and 

 that permeabilities are satisfactory. This conclusion appears to be in line with 

 known porosities in nearby fields producing from the same formation and on 

 strike. 



The next factor in the formula is / (interstitial or connate water). In an 

 older field, the amount of connate water will probably involve an estimate — as 

 in the early days there were no connate-water determinations. In fact, many 

 then thought connate water did not exist. If no connate-water determinations 

 are available, estimates can be made based on known determinations in similar 

 formations in on-strike fields. Connate water ranges from 10 to 50 percent of 

 the pore space; and, in estimating, around 20 percent in good porous reservoirs 

 and 30 percent in mediocre reservoirs are fairly safe averages. 



In this field, the development has been more recent — all of the wells have 

 electric logs. Cores from one nearby well were analyzed by the resto red-state 

 method in the Texas Company's laboratory; some companies do systematic core 

 determinations on all of their own wells and sometimes on adjacent wells. Three 

 pieces of cores were analyzed on this well and showed connate-water content of 

 35, 32, and 36 percent. Comparison with the electric log indicates that the higher 

 values came from the normal parts of the sand and that the 32 percent was from 

 the most porous part of the sand. 



It is learned that the Shell Company has made connate-water determinations 

 in their own laboratory on all the cores taken from their wells on this structure. 

 The valuator has a geologist friend at Shell, and while he cannot see their core- 

 analysis reports, he is able to "swab" the information that they are using 33 

 percent for connate water. Putting all of this information together, he concludes 

 that 34 percent is probably a safe factor for the interstitial water. 



Fortunately, a nearby well logged the producing sand below the water 

 contact, so that the resistivity of this sand saturated with water (R factor) 



801 



