How does subsurface geology help oil and gas exploration?…
How does subsurface geology help oil and gas exploration?
Discovering a worthwhile and exploitable hydrocarbon reservoir involves many disciplines and techniques. Subsurface is a term used to cover all the disciplines involved in understanding what lies below the ground surface or the seabed – primarily geology, geophysics and reservoir engineering.
In the oil and gas reserves, geophysics uses seismic data to estimate the size (volume) of the hydrocarbon trap. Geology mainly utilises well and outcrop data to estimate the volume and recoverability of hydrocarbon in the trap, i.e. the thickness of the reservoir, its porosity, permeability, hydrocarbon saturation, etc. This gives a static description of the hydrocarbons in place. In addition, for an undrilled prospect, the geologist will estimate the chance of success/probability of finding hydrocarbons in the trap the geophysicist has recognised. This is done by mapping the various play elements (source, reservoir and seal) and seeing if they are likely to be present and effective at the prospect location. This is calibrated by a statistical analysis of the results from wells that have tested this play. Reservoir engineering takes the static description and models the flow of hydrocarbons into wells to give a recoverable hydrocarbon volume, i.e. a dynamic description of the reservoir.