Naill's Model of Natural Gas Exploration

Naill's model was developed in Dynamo, the software described in Appendix D in the book. A Stella version of his model is shown in Figure 4.

Figure 4. Stella version of Naill's 1973 model of the exploration and production of natural gas.

In adapting the model to Stella, I have taken the liberty of changing the units from cubic feet (CF) to trillion cubic feet (TCF). I have also changed the variable names from the short names that are customary with Dynamo to the longer names in Figure 4. Table 1 provides a comparison of the names and units assigned to the stocks and flows in the two models. Table 2 provides a similar comparison for the converters in the two models.

Dynamo Names	Old Units	Longer Names for the Stella model	New Units
UPR	CF	unproven reserves	TCF
PR	CF	proven reserves	TCF
AUR	CF/yr	average useage rate over past few years	TCF/yr
UR	CF/yr	usage rate	TCF/yr
DR	CF/yr	discovery rate	TCF/yr

Table 1. Stocks and flows in the two models.

Dynamo Names	Old Units	Longer Names for the Stella model	New Units
AURAD	yrs	averaging interval for the useage rate	yrs
MAR	dim'less	cost margin	dim'less
COE	$/CF	cost of exploration	$/kcf
DRPR	yrs	desired reserves to production ratio	yrs
DD	yrs	discovery delay	yrs
EIIE	$/yr	effective investment in exploration	B$/yr
FURR	dim'less	fraction of unproven reserves remaining	dim'less
GC	1/yr	growth constant	1/yr
UPRI	CF	initial amount of unproven reserves	TCF
URI	CF/yr	initial useage rate	TCF/yr
IIE	$/yr	investment in exploration	B$/yr
COEN	$/CF	normal cost of exploration	$/kcf
PIEE	dim'less	percent invested in exploration	dim'less
URP	CF/yr	potential useage rate	TCF/yr
P	$/CF	price	$/kcf
RPR	yrs	reserve-production ratio	yrs
SR	$/yr	sales revenue	B$/yr
STC	$/CF	smoothed total cost	$/kcf
TC	$/cf	total cost	$/kcf
TCSD	yrs	total cost smoothing delay	yrs
		cost of exploration multiplier	dim'less
DM	dim'less	demand multiplier	dim'less
		percent invest. in exploration multiplier	dim'less
PM	dim'less	price multiplier	dim'less
ROIM	dim'less	return on investment multiplier	dim'less

Table 2. Converters in the two models.