Getting gas from Crude
This then will be a relatively simplistic look at the different potential hydrocarbons that might make up a crude oil, and how we can get them apart. I'll post next time on how we can break the separated flows into other products. This, then, is a short techie talk in the oil production series, earlier posts in which are given at the end of the post.
Crude oil is made up of a mixture of hydro-carbons, which are the different ways in which carbon and hydrogen can combine, starting with such simple compounds as methane (CH4) and progressing to more complex ones with greater numbers of carbon atoms. Oils from different places have different combinations of the major constituents, for example, this is from Kuwait. Because they are fluids mixed together, it is not very easy to separate out the different valuable parts (known as fractions) by a mechanical means. However if you heat up the crude oil blend, then it will vaporize.
As the combined vapors from the heated crude enter at the bottom of the tall tower (called a column) they pass up through different trays that are placed at set heights up the column. When the gas reaches a tray it passes up through it into a bubble cap, this is a cover over the hole that pushes the gas down so that it has to bubble up through the liquid that has already condensed onto that tray.
The liquids in each tray, as the vapor rises higher in the column, are kept at lower temperatures, so that the heavier oils, that condense at a higher temperature, will condense lower down the column. As the lighter vapor rises through successive trays, the temperature of the liquids drops, and lighter fractions of the oil also begin to condense out, until the very lightest are collected at the top, still as gas, and fed on to a cooler. The liquids then drain, either back down to a lower tray, or through a side-draw pipe that taps the fluid from the trays and takes it away for either further division or for storage and sale. A typical initial distillation might yield
Each year the EIA publishes its world distillation capacity which is the necessary part of getting from crude to useful product.
I will continue this next time, talking about the further stages in refining, and cracking of compounds to break them into lighter fractions, so that the next product from a refinery might at the end, look something like this (courtesy of the EIA).
This is part of an ongoing weekend series on technical aspects of oilwell (and natural gas) drilling. Previous posts can be found at::
completing the well
flow to the well
working with carbonates
spacing your well
directional drilling 1
directional drilling 2
types of offshore drilling rigs
Hydrofracing a well