Hello Faith,
I hope you don't mind, when I join the discussion, I have just some remarks to add. You are claiming that
Faith writes:
age is not really a functional factor in the practical seeking of oil. Physical considerations such as depth, position, composition and hardness of rock etc. are the useful factors, and the conventional labels of the various strata such as "Paleocene" and "Cretaceous" and "Mississippian" are no doubt also of use for identifying the conditions favorable or unfavorable to the location of oil or anything else. Age is really quite incidental to the process in all the descriptions so far given
I think we can agree that a correct understanding of a structure like the Mississippi Interior Salt Basin helps to decide where to drill for oil. But how do we get this information about depth, position, composition and hardness of rock? We have only sparse direct observations, for example by drill holes, which give exact but punctual information and by aeromagnetic or seismic data, which are useful for the big picture, but don’t provide much detail.
That means, to build a stratigraphic map we have to interpret the data, better said, to connect the dots. This connection will be more accurate when it is based on a adequate model of basin formation. The description of basin scale stratigraphy is helpful, it is needed for predicting changes in depositional setting, lithology, and texture when logs or core are not available [1], but it is not sufficient, a regional scale model of burial and thermal history is necessary for the prediction of trends in hydrocarbon accumulation, as we can see from the following quotes [1]:
Burial-history modeling is crucial in crucial in determining the generation, migration, and preservation of hydrocarbons in the basin. Since it is dependent upon a sound regional model for the basin's tectonic and depositional history, the magnitude of depositional and erosive events are critical to interpreting the
burial and thermal history
Thermal history modeling, which builds on burial history modeling, is crucial to deter-
mining whether a basin has hydrocarbons in commercial quantities and whether they are oil, natural gas, or both. Information critical to thermal analysis includes determining present-day heat flow and paleoheat flow and thermal conductivity, as well as the amount and type of kerogen and timing of heating events.
The mentioned models for basin formation, burial history and thermal history are based on physical processes which require almost always time spans in the order of millions of years . That should be evident after a short look at the plots of BasinMod [2], the program for basin modeling which was used by the authors of the quoted article.
But that’s probably not enough to convince you, therefore lets have a look at one of the models. (The following argument is a paraphrase from [3], page 179, Thermal and subsidence History of Sedimentary Basins)
The basic idea here is to explain one type of sedimentary basin as result of cooling. Assumed is an area which at one point in history was hot, for example due to volcanic activity or seafloor spreading. At this time no sediment covered our region , the top layer had a temperature T(1) and the density rho(m). When the surface cools down, for example because the volcanic activity stops, the contraction of the rocks causes subsidence and in consequence the development of a basin. Under the assumption that there is sufficient supply, the basin will be filled by sediments (if not a deep ocean basin will develop). In both case is the depth of the resulting basin proportional to the square root of time.
The depth can be calculated by
y = ((2*rho(m)*alpha(m)*( T(1)-T(0)) /(rho(m)-rho(s))) * ((k(m)*t)/pi)^0.5
With
rho(m) - density of mantle
rho(s) - density of sediment
alpha(m) - volumetric coefficient of thermal expansion (mantle)
T(1)-T(0) - temperature difference between base and surface
k(m) - thermal diffusivity of mantle
t - time since cooling started
With a slight modification we can use the same expression to calculate the depth of each layer of sediment, instead of the time since cooling started, we use the time since sedimentation started.
An example of a basin which was created by cooling is the Los Angeles basin. Volcanic rocks from drill holes have ages between 10 and 15 million years. At about 10 million year BP volcanic activity ceased and the basin started to develop.
When we apply the model to the south west block of the basin, which is the site of several major oil fields and therefore geologically well known, we get reasonable good agreement between the measured and the predicted depths of Pleistocene and Miocene layers. (At an age of 10 million years, the model predicts about 2.9 km)
When we assume an age of the earth of 10.000 years, the model would predict a maximum of 94 m for the depth of the LA basin and for all other basins as well. Because in real life most of the basins are deeper than 100 m, the model is not compatible with the assumption of a young earth .
Your conclusion is probably, that for this reason the model has to be wrong. In this case I would ask two questions:
When the world is only 10000 years old, nearly all the models from standard geology - at least all which have something to do with heat, kinetic energy, friction and so on - would not only be wrong but useless.
Why does the oil industry ignore this?
Why don't we see a successful tool for oil exploration based on young earth assumptions?
- Bernd
References
[1]
Whoops! Page Not Found | Petroleum Technology Transfer Council
[2]
PRA | Platte River Associates – Serving the Global Oil and Gas Industry for over 25 years!
[3] Turcotte, Schubert (2001)
Geodynamics
Cambridge University Press
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