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Thursday, January 10, 2008

Hybrid Rationale

Khebab posted on TOD a detailed and what I consider a significant modeling study on Saudi Arabia oil reserves. It complements an earlier pair of presentations concerning his Hybrid Shock Model (HSM).

I like the HSM for a few largely pragmatic reasons. For one, it couples the empirical Logistic model to the rate driven Shock Model. Khebab's mathematical connection to the Shock Model provides two-way insight on how to bridge the gap between the models. For my own edification, it revealed the critical link from the shock model's perturbed extraction rate to an equivalent Logistic extraction rate. And I would think that for others used to looking only at the Logistic model, it provides the path to injecting some intuitive first principles from the land of empiricism. I hope this spurs other depletion analysts to migrate away from a pure Logistic model.

Secondly the HSM allows one to inject an arguably more robust predictive capability to the base shock model. Khebab has rightly stated that the original shock model does not extrapolate extraction rate beyond the currently available discovery and production data, whereas the HSM at least suggests a Logistic-like growth beyond the current point in time. This causes a natural rounding in the HSM while the base shock model can start dropping off quickly if the extraction rate is extrapolated as a constant. With a good discovery model like Dispersive Discovery, I notice that the natural rounding returns, so I will not give up on a unified discovery/shock model just yet. Who knows, at some point we may get to a completely unified model that incorporates discovery, extraction (including quasi-Logistic dependence), and then the "enigmatic" reserve growth.


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