The ability to monitor and control water content in oil and gas is key to producing high-quality petroleum products. From a business point of view, the presence of water in oil and gas reduces the percentage of hydrocarbon components, making the products less pure and valuable. With greater water content in oil and gas, more money is wasted on transport (and compression for the latter). From a technical point of view, moisture can affect the distillation properties and performance of oil and gas, alter their product specifications, and accelerate corrosion of pipelines used in transport and catalysts used in refining.
As a result, there is huge incentive for companies to analyze moisture content in their oil and gas materials accurately and precisely, and dehydrate them to remove as much water as possible.
Moisture analysis technologies for oil and gas
Water contamination in oil and gas can cause premature material degradation, increased corrosion, and accelerate wearing of machines. There are a few ways to analyze water content in oil, but each method comes with different limitations.
The fastest and cheapest way is the visual crackle test. It involves adding a few drops of oil onto a hot plate. If water is present, heating of the oil would create crackling or bubbles. However, this method is non-quantitative and does not provide the value of water contamination. The Fourier transform infrared spectroscopy (FTIR) method makes use of infrared radiation to generate spectral signals of each molecule in a material. Due to its low sensitivity, FTIR is only useful to detect for water content of more than 1,000 parts per million (ppm) while most applications require the level to be lower than 100 ppm.
While Karl Fischer titration is commonly considered the gold standard method due to its dynamic range, it can still be challenging to measure very low water content, especially in hydrophobic oil and gas mixtures. Readings from Karl Fischer titration can also be affected by reagent instability (such as iodine), accuracy of sampling handling, and humidity. This method also requires cumbersome equipment that is not portable.
A moisture analyzer is one of the more popular tools for determining water content in solid and liquid samples, as it can provide real-time data for quick assessment. Moisture analyzers also have the capability to be sensitive enough to detect moisture levels in parts per billion by volume. This instrument works by heating samples in an enclosed chamber to vaporize water content and dry the samples.
There are two main modes of heating using halogen and infrared heat lamps. A halogen heat lamp provides faster and more uniform heating, which is suitable for oil and gas applications where there is accelerated temperature. On the other hand, an infrared heat lamp provides a slower rate of heating and is less likely to damage, burn, and oxidize samples for repeated testing of the same samples. It is also less expensive than a halogen heat lamp. In cases where there is high water content, a moisture analyzer with microwave-based heating could be considered because it provides data much faster.
“A moisture analyzer is one of the more popular tools for determining water content in solid and liquid samples, as it can provide real-time data for quick assessment.”
The chamber in the moisture analyzer allows a sample to be isolated from environmental perturbations such as humidity. Different drying methods, including standard drying, fast drying, ramp drying, and step drying can also be used to understand how samples react to dehydration and even rehydration, and how the properties of the oil and gas samples may be altered.
Most moisture analyzers currently on the market can provide information on percent moisture determination, percent moisture regain determination, and weighing. Compared to methods like the visual crackle test, moisture analyzer testing is non-destructive, which is useful to minimize waste of precious samples as the same sample can be retested multiple times for precision. An additional advantage of using moisture analyzers over Karl Fischer titration is portability, which enables field testing and minimal sample processing.
Moisture analyzers are most suitable for solid and liquid samples because the water level in samples is determined by mass difference. For gas samples, a chilled mirror hygrometer is typically used to determine the dew point temperature for calculating moisture content using a reference chart. This method is considerably accurate and reproducible, but the temperature measurement must be very accurate. Hygroscopic quartz crystals are also popular for more accurate water level measurements based on minute detectable changes in vibrational frequency of the quartz crystals in the presence of water.
Challenges and emerging solutions
Although there are various methods for detecting moisture in oil and gas, there are still challenges associated with measurement. Oil and gas mixtures can contain multiple interfering substances, causing inaccuracy in measurement. Moisture analyzers are also not as suitable for use with volatile liquid samples.
Importantly, moisture content analysis needs to be high throughput and low cost for business considerations. The measurement of water is essential for raw crude oils and intermediate refinery products because water levels affect all stages of oil and gas processing, such as transport, storage, refining, formulating, safety, and performance of end products. Finally, the variable sensitivity of each technique also means that at different stages of oil and gas production, different methods may be more suitable than the others.
An emerging method for analyzing water content in oil includes near-infrared (NIR) spectroscopy using filtered light and changes in spectral signals. Frink and colleagues also proposed a rapid, automated headspace gas chromatography that detected water content with high sensitivity from 12 to 3300 ppm from 15 petroleum products.
Moisture analyzers possess advantages such as being cheap, portable, and fast. Although moisture analyzers have lower sensitivity than other tools on the market, they can be extremely useful for field testing and measuring water content in samples in a high throughput manner with minimal training. These benefits make moisture analyzers a powerful piece of equipment for the oil and gas industry.