Oil and water emulsification in oil and gas gathering and transportation

Why is oil-water emulsion formed in the process of oil and gas gathering and transportation?

The formation of oil-water emulsion requires the following basic conditions:

(1) There must be oil and water medium in the system.

(2) There must be an emulsifier

(3) There must be stirring, heating and other factors to make one phase exist stably in the other phase

In oil and gas gathering and transportation, crude oil containing water and some natural emulsifiers such as cyanine, gum, naphthenic acid, fatty acids, nitrogen and sulfur organic matter, paraffin, clay, sand, etc. are the internal factors to generate crude oil emulsion. In oil and gas gathering and transportation, there are inevitably external factors such as stirring, so that crude oil has different degrees of emulsification.

According to the distribution of phase in oil-water emulsion, it can be divided into “oil-in-water” emulsion and “oil-in-water” emulsion. When the water is the internal phase and the oil is the external phase, the emulsion is the “oil-in-water” type (O/W) and the other is the “oil-in-water” type (W/O). Oil-water emulsification is gradually formed in oil and gas exploitation and oil and gas gathering and transportation.

The adverse consequences of oil-water emulsification:

Increase the difficulty of oil-water separation. Due to the existence of oil-water emulsion in crude oil, the oil-water separation problem cannot be solved by simple gravity sedimentation, heating and other methods, and additional equipment (such as electric dehydrator, etc.) must be added to increase the stage of oil-water separation to achieve satisfactory oil-water separation goals.

With the development of marginal oil fields and the application of multiphase measurement, the existence of oil-water emulsion inevitably increases the error of multiphase measurement, which affects the accuracy of the entire oil field measurement.

Compared with the viscosity of pure crude oil or aqueous phase under the same conditions, the viscosity of oil-water emulsion is tens or hundreds of times larger. In particular, the inner phase particle size is small and dense, or the water content of 50~70% of the emulsion, the viscosity value is larger, which undoubtedly increases the friction of the pipeline, and then increases the power consumption of the pipeline.

It is very difficult to completely avoid the formation of oil-water emulsion in oil and gas gathering and transportation. In addition to adopting new equipment and new technology to deal with oil-water emulsification, appropriate measures can be taken to slow down the degree of oil-water emulsification.

Optimize the overall arrangement: keep the oil, gas and water separation device and dehydration device as close to the well as possible to avoid excessive stirring of the oil, gas and water mixture during the gathering and transportation process. If there are no conditions for three-phase separation of oil, gas, and water near the wellhead, the associated gas can be separated separately and then the oil-water mixture can be transported to the destination, which will greatly reduce the oil-water emulsification

Chemical demulsifier: chemical demulsifier can effectively inhibit the emulsification of unemulsified oil and water caused by agitation, and can further demulsify the oil-water emulsion. Adding chemical demulsifier should pay attention to the following two things:

1) Comparative analysis of different chemical demulsifiers should be injected to optimize the selection of chemical demulsifiers suitable for the application of crude oil;

2) It is necessary to select the correct position of adding chemical demulsifier, and the position should be set in front of the wellhead oil nozzle or the inlet of the booster pump.

However, the formation of oil-water emulsification can not be completely avoided, and only appropriate application mitigation can be used

To slow down water emulsification, we should start from the three basic conditions of water emulsification formation, that is, oil-water separation; Emulsifiers present in oil-breaking water; In gathering and transportation, the measures that are not conducive to the stability of oil and water should be reduced, such as stirring and heating.

In the actual application, water emulsification mitigation is not the decisive factor, so it is necessary to adopt appropriate measures to slow down oil and water emulsification selectively according to the actual application situation.