13B-1

The Lease Pumper’s Handbook

Chapter 13Testing, Treating, and Selling Crude Oil

Section B

METHODS USED TO TREAT BS&W

B-1. Overview of Treating Methods.

Separation is the procedure whereby amixed fluid of gas, oil, and water separatesinto these different components. Manyfactors influence the separation of water andoil, and often work at the same time withvarious degrees of success. Some of themore important factors include:

· Gravity· Time· Movement· Chemicals· Heat· Electricity.

A knowledgeable pumper understands allfactors and combinations of factors thatresult in a good pipeline oil separation witha minimum drain on time and expensivechemicals. As wells become marginal andproduction is from the final stripping of thereservoir, the oil can become much moreemulsified and difficult to treat.

B-2. Gravity.

Gravity causes the separation of crude oiland water. Water will slowly separate fromthe crude oil from the time it is produceduntil it is sold. The water can be free water,which falls out rapidly, or it can beemulsified with oil, paraffin, and otherelements and compounds, become very

difficult to separate, and require a lot oftime. This natural separation also occurs atan ever slower rate.

Gravity affects larger droplets of watermore forcefully, causing them to sink to thebottom more rapidly. Smaller droplets fallslower than larger droplets. Crude oil islighter than salt water, and gravity will causethe water to work toward the bottom. Thesmaller the droplet of water, the less thegravity pull and the harder it is to remove. Ifthe heavier water can be broken loose fromthe oil and paraffin, then gravity will causethe water to work its way down through theliquid to the bottom of the vessel. Paraffinand other compounds form a strong surfacetension around these droplets, and with lowgravity oil the tension cannot be reducedwithout assistance by the use of time,movement, chemical, heat, electricity, or acombination of procedures.

Flash and slow water gravity separationin treating crude oil. To successfully treatcrude oil and make it sellable, the pumperneeds to consider what needs to beaccomplished and the best way to proceed toachieve that goal. Two concepts to fullyunderstand are flash separation and slowseparation. If separation occurs within a fewminutes, it is referred to as flash separation.Slow separation requires hours or days.

After these fluids have separated, they areusually removed from the vessels throughdifferent lines.

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B-3. The Use of Time in Treating Oil.

It takes time to break the water out of theoil. Some produced water will separate soslowly that it would require far more timethan is available, so action is taken to beginthis process as soon as a last tank of oil issold. If a pumper waits until a tank of oil isalmost full before treatment, the ability touse time is lost.

Many decisions concerning time aregoverned by how much oil is produced andthe treating problems anticipated. If oil issold every few days from a tank battery andhas treating problems, the pumper shouldbegin treating the oil as soon as it is takenoff the sales line. More chemicals thanusual can be used because, with frequentsales, income is higher and funds areavailable.

If the wells are marginal producers,production is low, and there can be severalweeks or even months between sales. Thepumper will have a lot of time but not muchchemical available because of the lowincome. The pumper will learn how to usetime and movement and natural separationto an advantage.

B-4. Separating Crude Oil and BS&W byMovement.

Total separation is not feasible. Asemulsion falls out, it accumulates near thebottom of the tank. The emulsion must berecirculated with crude oil from the stocktank back through the separation cycle toassist the process and keep tank bottomsclean.

Movement is the cheapest of all treatingprocesses after time alone. If a smallamount of oil is regularly circulated from thestock tank through the heater/treater or washtank (gun barrel), this movement alone willtreat much of the water out of the oil.

B-5. The Effects of Chemicals in TreatingCrude Oil.

Chemicals are one of the most effectiveand common methods of treating water outof crude oil. An oil soluble surfactant canbe added to the crude oil either at thewellhead or just ahead of the separator orfirst tank battery vessel. This oil solublechemical is usually a form of soap thatreduces the surface tension in paraffin andwater droplets. This allows the water toseparate by breaking apart from thehydrocarbons.

Figure 1. A chemical reservoir tank,electric pump, and lines for chemicalinjection at the wellhead. Note that

chemical identification information hasnot yet been added.

Treating oil is just one of many reasons forusing chemicals on the lease. The pumpershould know the functions of all chemicalsand how to apply them properly.

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B-6. The Effects of Heat in TreatingCrude Oil.

Heater/treaters (Figure 2) are usedextensively to heat and treat crude oil. Heatis applied to the crude oil by both the sunand by burners in heater/treaters.

Figure 2. Chem-electric heater/treater fortreating crude oil.

When possible, flow lines are left on thesurface in order to take advantage of

summer heat. During this time, heat isturned off and the vessel becomes a largethree-stage separator.

As little heat as possible is used to treatoil. Some oil companies have set up anobjective of eliminating all use of heat andfire boxes in treating oil. This is anextremely aggressive approach that willresult in a dramatic reduction in lease gasconsumption. However, technology tocompletely eliminate heating from thetreating process is several years away.

B-7. Treating Oil by Chemical-ElectricalProcesses.

The electrical heater/treater is the mosteffective method for treating high volumesof crude oil. Because of the cost ofelectricity, this method is not practical forextremely low producing wells.

One chem-electric heater/treater will out-perform several standard verticalheater/treaters. Consequently, it is verypopular where there are large volumes totreat as well as offshore where platformspace is extremely expensive to build.

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