OCT COMPANY, INC.

Demulsifiers, also known as Emulsion Breakers (EB), are a class of chemicals used to remove water and entrapped solids from crude oil so that it will be fit for sale to the pipeline companies and ultimately to the refineries. Removing most water from crude oil also significantly reduces corrosion tendency of the produced fluids.

 

Topics

 

OCTCO Emulsion Problem Solving Process

Theory of Emulsions

Demulsifier Bottle Testing

Applying Demulsifiers

 

OCTCO Emulsion Problem Solving Process

 

THE PROBLEM          

• Identifying Problems

  • Does an emulsion problem exist?

  • How Often is the Problem Occuring

    • Only When the Wells are Treated for Corrosion?

    • Only When the Temperature Gets too Cold?

    • Is Something Abnormal Occuring on the Lease?

    • Did the Chemical Run Out

  • What is Making the Oil Unsaleable?

    • Excess Water?

    • Excess Basic Sediment, i.e. solids and emulsions?

    • Paraffin?

• Data Collection

  • Bad Oil Frequency

  • Reason for Turndown?

  • Is the Equipment Functioning Properly?

  • Is Bad Oil Related to Corrosion Treatments?

  • Workovers Being Performed?

  • What has Changed in the System?

  • Is it Weather Related?

  • Are Tank Bottoms Being Worked?

  • Which of the two majorc Causes are involved in the problem?

    • Chemical is Not Getting to the Problem

    • Something in the System has Changed
       

THE SOLUTIONS

What are the current means for solving the problem?

• Hot Oiling?

• Batch Treat Tank and Roll?

• More Chemical?

Can the system be modified to overcome mechanical shortcomings?

• Add a Free Water Knock Out?

• Add a Gas Boot to the Gunbarrel?

• Add a Surge Tank?

• Add Draw-offs to the Vessels?

• Add Baffels to the Treating Vessels?

• Can the Bad Wells be Isolated?

What will the customer consider as an option?

Demulsifier selection

• Product formulation - Bottle Testing

 

EVALUATION

Once the program is in place, how will the performance be monitored?

• Data Collection?

• Frequency of Problem Recurrence?

• Cost Savings?

How will this Information be delivered on a routine basis?

What new steps will be taken to further optimize the system?

• Lower Dosages?

• Fewer Treatments?

• Alternative Chemicals?
   

IMPLEMENTATON

What steps will be taken To:

• Gather the Necessary Data to Define the Problem?

• Perform the Necessary Testing?

• Prepare a Presentation of the Available Options?

How will the options be delivered to the customer?

 

Theory of Emulsions

 

In order for a stable emulsion to be formed, three conditions must be met:

• Two IMMISCIBLE liquids must be present

• There must be sufficient ENERGY to mix the two

• There must be an EMULSIFYING AGENT

In an oilfield system, the two immiscible liquids are crude oil and brine. The energy that causes them to be mixed can be anything that causes fluid mixing such as perforations in the casing, pump throat, a choke in the well head or a valve. The emulsifying agents can be natural surfactants i.e. formation fines, paraffin, corrosion by-products, drilling mud or any other treating chemicals.

 

When this emulsion arrives at a vessel, it will begin some separation in the vessel into three distinct phases:

• a layer of clean top oil

• a middle layer of tight emulsion

• a bottom layer of water that has dropped out

The middel layer of emulsion consists of water droplets suspended in a continuous external phase of crude oil. The water droplets are stablizlied in crude oil by emulsifying agents.

 

Factors affecting the stability of the water and crude oil emulsion include:

• water content - generally, the more water that is produced, the easier the emulsion is to break; this is related to the concentration of the natural emulsifiers at the interface between the fluids

• temperature - the lower the temperature is, the higher the viscosity of the crude oil, this makes it more difficult for the water to settle out of the oil

• viscosity of the crude - lower gravity, higher viscosity crude form more stable emulsions because of the inherent resistance to water settling

• density differential - the greater the density difference between the oil and brine, the easier it is for the water to settle out of the oil

 

In order to break an emulsion, two things must happen to the water particles that are now dispersed in the oil: 1) the water droplets must physically contact each other; 2) once contact is made, the droplets must be able to join or coalesce meaning that the energy barrier must be broken.

• Ionic Barrier - where droplets repel each other because of like electrical charges

• Mechanical Barrier - where the emulsifying agent forms an elastic membrane

• Solids Barrier - where solids at the interface exhibit both water wet and oil wet characteristics

 

Mechanisms for destabilizing emulsions include: 

• Gravity - given enough time, emulsions will resolve according to Stokes Law which say that the rate of settling by the water is directly proportional to the size of the water droplets. As they coalesce and grow, they will settle.

• Heat - heat helps to resolve emulsions by reducing the viscosity of the crude oil so that the water can move through it more easily; it can act to dissolve paraffin particles that also act to stabilize the emulsion.

• Electrostatic - alternating electric fields can be used to rupture the films that are created by the emulsifying agents around the water droplets, causing them to coalesce and settle more rapidly.

• Chemical Demulsifiers - act to deactivate the emulsifying agents; the surface active nature of the chemicals allows them to move to the interface where they can act upon the emulsifiers.

 

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Demulsifier Bottle Testing

 

The three basic requirements for breaking a water-in-oil emulsion are:

• Addition of a chemical capable of reducing the thickness of the oil film surrounding the water droplets and thus making possible their coalescence on contact.

• Enough agitation to get the chemical to the oil-water interface.

• Enough quiet settling period to allow water droplets to settle and coalesce further into a separate water phase.

One of the steps is chemical and two are mechanical. In bottle testing the problem is usually not to select the most effective chemical to be used under ideal conditions, but rather, to find the one which works best with the existing conditions of agitation and settling in the system. The challenge is to
duplicate these conditions in the bottle test.

 

In running bottle tests we would like to duplicate the plant conditions as closely as possible. The single most important variable is the magnitude and duration of agitation. In the field this usually depends upon the line sizes, flow rates, fluid temperature, chemical injection point and the design and location of phase separators.

The degree of agitation or turbulence of a fluid is indicates by a dimensionless constant called the Reynold’s Number (RN). The RN of a system is dependent upon the pipe diameter, flow velocity, fluid density and fluid viscosity. A RN above a value of 2500 indicates turbulent flow conditions. At values below 2500 the flow is laminar. In turbulent flow the fluid forms eddies against the pipe wall. This promotes rapid mixing, but also causes frictional loses and drag on flow. In laminar flow there is no turbulence and mixing takes place at a much slower rate. 

 

Many factors in the field make it difficult to duplicate the correct amount of agitation in the bottle test. Among these are the large volumes of free and emulsified water produced with most crude oils, the constrictions and sharp bends in flow and the turbulence occurring in gas separators and flow through
heaters. The presence of free water with the emulsion greatly reduces the apparent fluid viscosity and also increases turbulence and water-droplet contact.

 

All of these effects are helpful to field treating, assuming that chemical addition is made as far upstream as is practical. For these reasons, field use concentrations are generally less than the concentrations required to treat in the bottle.

 

These considerations lead to some general rules on bottle test conditions.

1. Use plenty of agitation as near to plant conditions as possible. When in doubt, use more agitation rather than less.

2. Use mechanical shakers if possible. They are faster and more uniform than hand shaking.

3. Use less chemical rather than more. Stress the chemicals and separate results as much as possible by reducing dosage for good performance differentiation.

 

Applying Demulsifiers

 

A chemical demulsification process consists of the following 5 steps. 

1. Introduction and mixing of the demulsifier in the oil phase of the emulsion

2. Demulsifier enters the water - oil interface

3. The energy barrier at the interface is disrupted

4. The water droplets collide and coalesce

5. The enlarged water droplets settle and sweep

HOW and WHERE the demulsifier is added to the system are as important as what is added. Even if the right demulsifier is added at the right concentration, it will not work effectively if it is not mixed properly in the system. The addition of demulsifier must be positioned so that the bulk of the water does not fall out before it can sweep out the very small droplets.

 

Special care should be taken when optimizing the dosage rate for a particular system. Generally, the system will operate within a band of operational performance levels. This variability in operation will stress the demulsifier’s ability to work satisfactorily in the system at a constant injection rate. If the dosage rate is optimized into this danger level, then performance will become variable and highly dependent upon system operational conditions. It is generally best to operate at dosage levels above this danger range to maintain a smooth operational system. The amount of chemical necessary to stay out of the danger range is generally about 30-50% higher than the minimum level required to operate the system under the very best of conditions.