Seeing Through Crude Oil for Efficient Oil Separations using Short-Wave Infrared (SWIR) Cameras

Topics Covered

Introduction
Separation of Oil and Water
Electro-coalescence and its Optimization
SWIR Cameras for Crude Oil Analysis
Conclusion

Introduction

The produce from an oil reservoir will always be a mixture of gas, water, oil and sand, regardless of if the reservoir is in Brazil, Saudi Arabia or on the Norwegian continental shelf. Steam is used to reduce the viscosity of heavy oils and tar sands during the recovery processes.

As a result, the mixture consists of oil and water, requiring additional processing before selling it to the customer. This oil is either used in gas power plants, as natural gas in houses or as oil for producing diesel or petrol.

Separation of the components of crude oil is based on the density difference of the water, oil, gas and sand constituents.  Sand can be separated as a precipitate during sedimentation. Separation of gas is easy due to the large density difference.

Whereas, the separation of oil and water is time consuming as there is only a marginal difference in their density. The challenge lies in the efficient separation of oil and water.

Separation of Oil and Water

Separation of water from oil is based upon gravitational sedimentation, which requires big settling tanks and is time intensive. Deploying such large settling tanks can be tedious on offshore platforms.

A number of methods for promoting droplet growth have been developed to speed up the entire separation process. Of these methods, the merging (electro-coalescence) of droplets via electrostatically induced attraction methods is highly efficient.

Electro-coalescence and its Optimization

Large drops of water are formed by smaller water droplets coming together. The attraction between smaller water droplets is created by applying an electric field to the oil-water mixtures. The formation of larger drops enables faster oil-water separation because larger drops tend to settle faster than smaller ones. This process is called electro-coalescence.

Although the success of this technique has been established, there is a lack of clear understanding about the events that occur during coalescence of two drops. The optimization of this process in terms of size, frequency of the electric field and the degree of turbulence is difficult for two reasons;

One is the considerable variation in crude oil quality and the second reason is that it is difficult to visualize water droplets that are present in dark crude oil using high-speed cameras. The main problem is crude oil itself, because even studies in transparent crude oil do not yield satisfactory results.

SWIR Cameras for Crude Oil Analysis

Crude oil can be analyzed by using a high speed Short-Wave Infrared (SWIR) Cameras that are sensitive in the 900-1700 nm range. Cheetah-640-CL is a high-speed SWIR camera that is capable of seeing through crude oil to examine the events that occur when water droplets collide and coalesce, even in dark heavy oil.

Most of the SWIR photons are absorbed by water, making them appear like dark drops on a lighter background (the oil).

The time span between the collision of two drops and coalescence is less than 40 ms. Therefore, these events can be effectively captured only by a high-speed camera. Armed with such clear, high-speed SWIR images of colliding and coalescing water droplets in oil, scientists are now able to draw comparisons between test results of various qualities of heavy crude oil subjected to varying temperatures, using mathematical model calculations of equivalent effects.

Conclusion

It has been shown that electro-coalescence studies for the separation of water from heavy crude oil can be effectively performed using a high speed SWIR camera such as the Cheetah-640-CL. With 640x512 resolution and over 1000 fps, the Cheetah-640-CL enables a thorough analysis of water droplet coalescence taking place at high speed in visually non-transparent crude oil.

This information has been sourced, reviewed and adapted from materials provided by Xenics.

For more information on this source, please visit Xenics.

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