Oilfield Production: What Happens At The Surface

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Previously, we’ve talked about the depositional environments in major basins; we’ve discussed geological and geophysical analysis of the subsurface; we’ve discussed drilling, casing, perforating and completing; and we’ve examined how to lift hydrocarbons to the surface.

But what are we actually lifting to the surface?

Previous to Edwin Drake, hydrocarbons were considered an unfortunate byproduct of drilling for water. In areas with shallow hydrocarbons, like Pennsylvania, there are many historical stories of water wells being flammable. But Drake had a whim there might be a market, and innovated a method to extract oil and exclude surrounding ground water. Within a decade Kerosene was the king of lighting, the whales were saved, and crude oil went on to become the most important component in the global economy.

What we bring to the surface when drilling for oil and gas, however, continues to be a mixture of fluids and gases, and the stabilization, separation, storage, dispensation, transportation, taxation, and in some cases disposal of those portions of the production could use some observation. Since that’s a lot of territory to cover, this post marks the beginning of a series that will cover a number of these angles.

To begin, we will look at the technology used in the oilfield to separate the hydrocarbons and make them ready for delivery into the midstream.

Oil Wells and Gas Wells – Is There a Difference?

To a certain extent, yes.

  • Due to the nature of gas vs. liquid as a phase of matter, gas wells often lift under their own pressure, and are thus outfitted with a “Christmas tree” wellhead at the surface, as opposed to the common “beam pump” associated with oil wells.
  • Gas is typically diverted into some sort of pipeline for delivery into the system, whereas liquids can be stored in localized containers and then picked up by trucks (or trains or pipelines) periodically.
  • Oil and gas wells are often taxed differently – in fact there has been something of a boom in re-classifications in the past few years.

How Do We Deal The Mix of Hydrocarbons and Water

Heater-treaters have been discussed as a crucial piece of equipment to deal with the relatively more volatile condensate production typical of today’s unconventional wells. Today I would like to look at 2 other pieces of equipment that are commonly used to separate gas and oil and water.

First, let’s look at The Separator. The Separator is a piece of equipment that is designed to separate any condensed liquid from gas, and additionally separate hydrocarbons from water. This excellent short video shows the standard process.

Removing water from the system as early as possible is always important, first because water can make equipment rust (or it can freeze and bust pipes or it can react with the hydrocarbons and create unwanted compounds), and second because you don’t want to pay to transport something if you don’t have to.

With that in mind, we turn to The Glycol Dehydrator. Water is a pretty tenacious compound – even as vapor – so we have to take additional steps to remove it before sending gas into the midstream. Glycol is a fascinating liquid that, among other properties, is hygroscopic, meaning that it attracts and absorbs water. A Glycol Dehydrator, therefore, is a device that counterflows glycol through the produced gas and gas liquids, and effectively strips water molecules along the way. The first few seconds of this video gives a pretty good idea of what that process looks like.

These are the main pieces of equipment used at or near the well for initially separating the various components of production. In a future post we will look at how operators report their production, and then move on from there.

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Eric Roach

Eric Roach is the editor of Drillinginfo's blog, which was selected as the Top Oil & Gas Industry Blog based on visibility, engagement and relevance. He also prepares a weekly newsletter of top industry news for blog subscribers, and would be grateful if you would subscribe and tell your friends. (There's a box on the upper right of the page where you can subscribe).