In this blog, we discover how scientists use filtration analyses to test the quality of crude oil in midstream processing – ensuring refineries receive high quality oil that is free of contaminants.
Once extracted from wells at the reservoir, crude oil reaches the midstream stage of field processing at an onsite oilfield facility. At this stage, petroleum engineers perform crucial tests on the oil that enable them to choose safe temperatures and pressures for transport and storage, and ensure that the equipment for transport and storage remains free from corrosion.
The main function of the oilfield facility is to separate water and solids from the oil so it can be measured, sold, and finally transported to refineries by pipeline or other means of transportation. Scientists at the oilfield facility also perform tests for chemical contaminants present in the oil that can pose a risk of damaging downstream transportation and storage equipment.
Secondary processes that occur at oilfield facilities include treatment of waste water for disposal, which might involve removal of dissolved hydrocarbons and filtration techniques.
Characteristics such as solid sediment and salt content, the presence of contaminants, and vapor pressure of oil are all important to measure during field processing. In this blog, we will highlight two tests performed at this stage, and explore how scientists use membrane filtration analysis to ensure oil meets purchasing specifications set out by refineries and secure a steady and reliable supply of oil for making downstream petroleum products.
Visit our knowledge center for articles and tools to support your filtration needsMeasuring the sediment content of crude oil
Crude oil contains natural impurities including dirt and other solid particles. If the sediment content of crude oil is too high, it can corrode transportation pipes and damage equipment such as pumps and tanks at refineries, leading to problems in downstream oil processing.
Exposing equipment to sediment over long periods can also lead to expensive shut-downs, which is why refineries impose upper limits on the sediment content of the crude oil they purchase.
To protect equipment and maintain the profitability of oil wells, petroleum engineers perform filtration analysis of the sediment content of oil, so that the sediment can be effectively removed during midstream processing.
The membrane filter test
The American Society for Testing and Materials (ASTM) is an organization that issues standards for testing crude oil and petroleum products. In the ASTM 4807 standard, the organization defines a filtration procedure for measuring the sediment content of crude oil.
In this method, a crude oil sample is dissolved in hot toluene and driven under vacuum through a membrane filter suitable for use with organic solvents, such as the 0.45 µm Whatman™ nylon membrane filter, which has a pore size suited for filtration of sediment encountered in most oils.
The filter and associated residue are then washed, dried, and weighed. The change in mass of the filter provides a measure of the sediment content.
Measuring sediment with an extraction thimble
The extraction method is another simple and rapid test to measure the sediment content of crude oil, outlined in ASTM D473.
In this test, an engineer places a sample of crude oil in a glass extraction thimble, such as the Whatman™ high-purity borosilicate glass microfiber thimble. They then place the sample funnel containing the thimble into a flask of toluene, which is boiled and allowed to condense and drip into the thimble.
The toluene washes out the crude oil, leaving sediment in the thimble. Like the membrane filter test, the change in mass of the thimble provides a measure of the amount of sediment in the crude oil sample.
Maintaining supply of high-quality oil
In addition to hydrocarbons, which are useful for downstream fuel products, crude oil might also contain asphaltenes. These are high molecular weight cyclic compounds that can precipitate in oil reservoirs and around pipes, preventing the extraction of oil. Asphaltene in crude oil can also precipitate during transport and storage, leading to spoiling and the need for expensive treatment to remove the contaminants.
To assess the level of asphaltenes and determine an appropriate course of action, petroleum engineers can perform filtration analysis.
The specific test for asphaltenes is detailed in ASTM D6560, and involves mixing the crude oil sample with heptane, heating it, and then collecting the precipitated asphaltenes using membrane filters such as Whatman™ ME24 0.2 µm mixed cellulose ester membranes. Waxy substances are then removed by washing with hot heptane in an extractor, before the asphaltenes are dissolved in toluene and weighed.
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Testing extracted petroleum at oil facilities is an important quality control practice in midstream oil processing. Filtration analyses provide scientists with rapid and convenient methods of measuring the level of particulates and chemical contaminants in crude oil feedstocks. In turn, these measurements help ensure that refineries receive a high-quality raw material for the generation of downstream petroleum products.
For help with any of the techniques mentioned here, or for any other filtration related questions, contact our scientific support team.
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