'jft310' pid='59076' datel Wrote:PET how does gas migrate .?.Would you guess it migrated before the faulting ?.That faulting now blocking connectivity ?.If it migrated after faulting then there is some type connectivity my non geologic mind concludes. You do not think Ant and Ant S connect so the double faulting must have occurred after the migration?? Thanks for the geology lesson in advance .
JFT- You have to think long term. Millions of years. That is long term. All of these limestones and reefs were formed over the same time period and were all one connected body of limestone and reef is a shallow sea. The reefs formed on top of the limestone in the most shallow water. Over millions of years the limestone and reefs were buried under a few thousand feet of sediments. The moving of the earth’s crust caused faults and fractures separating the limestone and reefs into different segments i.e. Elk/Antelope/Antelope South/Raptor/Whitetail/Mule Deer etc. All at different depths and the blocks were all pushed around with some forming traps with faults and anticlines. The gas migrated from deeper zones that were deposited millions of years before the limestone. All of these rocks are what we call sedimentary rock which means they were formed in water. So at one time all of the porosity in these rocks were filled with water. So we had all of these traps formed and they were full of water. As the gas formed in the lower sediments it started to rise because gas is lighter than water. The gas migrates through any kind of permeable path it can find. That may be faults, fractures, permeable sandstones or limestones. Over millions of years it probably even migrated through the shales which we consider to be impermeable in real time. As the gas migrates toward the surface it enters some of these traps formed by faults and anticlines. The traps are sealed by impermeable barriers so the gas accumulates in the top of the trap and displaces the water out leaving gas at the top and at some point below a gas/water contact.
If a very thick limestone zone has a fault through it with small movement that leaves the limestone in both blocks in contact it is “possible” that there could be pressure communication. I think that is the case between Elk and Antelope but even there GLJ says the blocks are not in communication because they have different gas/water contacts, pressure and I think slightly different gas composition. Most of these prospects are separated by several faults and the depths are different by hundreds to thousands of meters. The SPA says the hydrocarbons must be in contact. That is not possible where the different blocks are separated by hundreds to thousands of meters and they all have different pressures and gas/water contacts and different gas composition.
There may be some connectivity between the blocks over millions of years for gas migration but we have to deal with days and years and over that kind of time frame there is no connectivity.