Geology/cross sections intrepretation
Hello ! i like to do geological cross section making but i have some questions about :
has the axial surface have any importance by means of drilling?
in an area with too much faults and folding , what care has to be taken for drilling? how to choose a most favorable area for drilling?
what type of maps is used in todays petroleum world ?
If by axial surface you mean the strike plane, yes it does. The axial surface will depict the true vertical depths to the horizon surfaces on the cross section.
Any cross section drawn at arbitrary angles to any structure will be subject to changing geometry when it comes to the true vertical depth to the surfaces of the structure.
Because of this relationship, a well drilled on the basis of a cross section, might intersect a horizon lower than what is optimal for recovering any fluids in the target area of a reservoir.
A highly faulted reservoir may be divided into a number of "Packets" or compartments, which contain fluids that ARE NOT in communication with each other and which do not have gas-oil- water contacts that are at the same level.
So if you were to drill at a location chosen on a cross section that crosses a plunging structure, the well might intersect the targeted compartment, but hit below the oil water contact. It would only have a water show, when in fact the compartment contains oil and gas in the up dip direction. By drilling on the cross section you ended up drilling too far down dip.
So one must always consider the structural dip, sand thickness, and faulting.
The key is to make as many cross sections in as many directions as you can across the structure from well to well to get a good sense of the structure.
You can do this by creating net sand maps and gross sand maps of the structure. These show the total sand permiablity and porosity that may be available in a trap to trap hydrocarbons.
The best trap in the world is useless if there is not any porous, permiable reservoir interval in it.
Net to gross isopach maps are used for volumetric calculations, depth maps for structure mapping and fault maps, made from mapping faulting intervals on the cross sections and then transferred to map view over the reservoir. These are then overlaid with the net to gross maps to determine how much useable interval is found in each compartment of the reservoir.