Editing Petroleum geology (section)

===Reservoir analysis===
The existence of a reservoir rock (typically, [[sandstone]]s and fractured [[limestone]]s) is determined through a combination of regional studies (i.e. analysis of other wells in the area), stratigraphy and sedimentology (to quantify the pattern and extent of sedimentation) and seismic interpretation.  Once a possible hydrocarbon reservoir is identified, the key physical characteristics of a reservoir that are of interest to a [[hydrocarbon exploration]]ist are its bulk rock volume, net-to-gross ratio, porosity and permeability.<ref name=":1" />

Bulk rock volume, or the gross rock volume of rock above any hydrocarbon-water contact, is determined by mapping and correlating sedimentary packages. The net-to-gross ratio, typically estimated from analogues and wireline logs, is used to calculate the proportion of the sedimentary packages that contains reservoir rocks. The bulk rock volume multiplied by the net-to-gross ratio gives the net rock volume of the reservoir. The net rock volume multiplied by porosity gives the total hydrocarbon pore volume, i.e. the volume within the sedimentary package that fluids (importantly, hydrocarbons and water) can occupy. The summation of these volumes (see [[STOIIP]] and [[Gas Initially In Place|GIIP]]) for a given exploration prospect will allow explorers and commercial analysts to determine whether a prospect is financially viable.

Traditionally, porosity and permeability were determined through the study of drilling samples, analysis of cores obtained from the [[wellbore]], examination of contiguous parts of the reservoir that outcrop at the surface (see e.g. [[#References|Guerriero et al., 2009, 2011]], in references below) and by the technique of [[formation evaluation]] using [[Wireline (cabling)|wireline]] tools passed down the well itself.  Modern advances in [[seismic]] [[data acquisition]] and processing have meant that [[seismic attribute]]s of subsurface rocks are readily available and can be used to infer physical/sedimentary properties of the rocks themselves.