There are usually 2-3 of this type question running at all times. The fact of the matter is that dead trees in general, and oak in my experience, whether standing, laying on the ground, laying across other dead wood so it is not on the ground, or cut to log length and stored in a lean-to under cover will maintain a significant amount of moisture content for years, and years. There are so many factors that would need to be considered:
How much moisture it starts with - often up to 40%
How much sunlight, wind, humidity exist in the environment where it lays
How dry you personally want it before you consider it ready - usually around 20%, but hey folks are different
The bottom line, it really isn't going to season till it is cut to firewood length and split. I doubt you could ever get a guaranteed answer to a question like this over the internet. Your own experience will serve you much better. Second best, invest in a Moisture Meter, they cost less than $10. Then check the wood you cut, and check it every three months till it is where you want it to burn. That will give you a good sense of how rapidly, or slowly the moisture content of a particular type of wood, when split and stacked will season. And, you will know for future reference, and you can chime in with authority on questions like this.
I cut standing dead Red Oak all winter long, and have for about 10 years. I don't really need to consult my MM any longer. Tree after tree, year after year, global warming or not, my dead red oak barely begins to dry till it is cut, split, and stacked where it will have plenty of sun, wind, and time. And, then it seasons at a rate that is entirely predictable. And, with dead Red Oak, on this hilltop, split at the size I make, and stacked in the open in single ranks will take 10 months minimum, 12 months is better to be ready for clean burning.
