Basic Petrophysics
Introduction
 |
| Basic Petrophysics |
The petrophysicist’s job is to use all available information to analyze the physical and chemical properties of the rocks in the sub-surface, and their component minerals, with particular emphasis given to the amount and distribution of those fluid minerals that we know of as water, oil, and gas. The petrophysicist will use extensively wireline log data and data from experiments done on cores extracted from the well, and will occasionally use other sources of information such as engineering and production logs, as well as mud logging data. Initially, it is the aim of the petrophysicist to differentiate between oil, gas and water bearing formations, estimate the porosity of the formations and the approximate amount of hydrocarbons present in each formation. Ultimately, the petrophysicist also uses laboratory data to estimate how easy it will be to extract the hydrocarbons in place, and to design reservoir management strategies to optimize long term oil recovery.
How to speed up your PC & Laptops
advertisement
Conditions Allowing the Accumulation of Hydrocarbons in a Reservoir
Oil and gas reservoirs have come into being over large periods of time as the result of geological processes. The gasses and oils have been formed from organic remains, have migrated into the reservoir rock, and then have been trapped there by overlying rock formations with very low permeability. Hence, for a hydrocarbon reservoir to exist we need the following to be available at the same location:
1. A source rock containing the original organic remains.
2. Pressure and temperature conditions suitable to convert the organic remains into oil and gas.
3. A porous, permeable reservoir rock where the hydrocarbon can accumulate.
4. A migration pathway from the source rock to the reservoir rock for the hydrocarbons.
5. A suitable trap to keep the hydrocarbons in the reservoir rock until we wish to exploit it
Calculating Hydrocarbon Volumes in a Reservoir
We can define a reservoir rock as one that has a porosity and permeability that allows it to contain a significant amount of extractable hydrocarbon, AND contains hydrocarbons. A non-reservoir rock may have a porosity that is too low, a permeability that is too low, or a low or zero hydrocarbon saturation. The major control is often the basic lithology. For example, shales often contain hydrocarbon with high saturations, but have porosities and permeabilities that are much too low for the hydrocarbon to be extractable. Shales are considered to be non-reservoir rock. In contrast a high porosity, high permeability sandstone could be a reservoir rock providing that the hydrocarbon saturations are sufficiently high, i.e., above the oil water contact.
Continue reading
Download full PDF in Comment section
advertisement
Basic Petrophysics
ReplyDelete