DENSITY: A CORE PARAMETER AT KEY POINTS
For companies in the oil industry, improving productivity and product quality and increasing profi ts are always on the agenda. Measuring the density of crude oil and petroleum products throughout the oil recovery process, distillation, and processing contributes to achieving these goals.
Upstream research and crude oil analysis
Increasing the yield of crude oil from the reservoir is the number one priority. Knowing the properties of the crude oil in the ground is the solid basis for making major decisions on how to enhance the output.
A density measurement on live crude oil at reservoir conditions – up to 200 °C and 1400 bar – simulates in the laboratory the crude’s behavior in the reservoir and delivers the information needed to make the choice of solvent for the extraction process. Knowledge of the crude oil properties and use of the right solvent leads to increased output and the ability to predict the potential output quantity of the drill hole reservoir based on hard facts instead of rudimentary assessments. Insights based on density results lead to the right choice of solvent and make it possible to increase the yield of crude oil to 80 % or even 90 %.
To evaluate the behavior of the crude oil in the reservoir the same reservoir conditions are simulated in the density meter and the bubble point is determined. To do this a small sample of crude oil (no more than a few milliliters) is fi lled into the measuring cell and the pressure in the density meter is slowly decreased until a large density change is detected at a certain pressure level. This is the bubble point.
It is not possible to use just any density meter for this measurement. It has to be a device which is capable of measuring at pressures slightly higher than below ground to keep the live crude oil in one phase. The temperature required for these measurements is also exceptional. Recommended for this type of measurement is DMA HPM from Anton Paar, a robust density meter which is thermostatted using a climatic chamber or an oven.
API characterisation
After exploration and before distillation, the characterisation of crude oil by its API grade is needed to defi ne the optimum blending mixture as well as the refi nery operating parameters and therefore the yield of production. The fastest way to ensure that crude oil complies with specifi cations according to regulations is to use a digital density meter such as DMA 4500 M, a rugged and
die-hard workhorse which gives 5-digit density results according to ASTM D5002.
Accurate density measurement proves that the crude oil is clean, dry, and without sedimentation. A large advantage to using a digital instrument is that it removes the need for tempering the sample, doing manual corrections, and noting down the results. Results are typically available within minutes. As the amount of sample needed per measurement is small, this saves on the volume of solvent needed for cleaning. Implementing fi lling checks and having precise temperature control eliminates the errors which typically arise from manual measurement with conventional methods. A digital density meter is also able to measure at one specifi c temperature between 0 °C and 100 °C or automatically perform a temperature scan within a short time.
Trading crude oil
When buying or selling crude it is important to make sure that the indication of quantity is correct. Density measurement is a reliable way to calculate the weight of crude oil from the given volume. From a known volume, DMA M density meters measure the density and apply a software-automated calculation to deliver the weight of the quantity to be traded. The measurement is performed at either 15 °C or 60 °F and the correct invoice is then just a few seconds away. DMA 4500 M covers all products, from light to heavy crude. For even higher accuracy, DMA 5000 M provides 6-digit results which leads to more accurate calculations and therefore to more profi t. Dual control of the measurement is provided by a real-time camera monitoring the measuring cell plus an algorithm detecting fi lling errors automatically. This information is part of the fi nal result that is stored on the instrument (ready for export or printing later on).
Fig. 1: Density meter: DMA 1001
At the refi nery
There is a need for density measurement whenever crude oil or the subsequent products are moved between processing steps in the refi nery. In these cases the measurement may be needed at tanks or from containers and requires a portable or at least very lightweight density meter. To protect employees the device must be Ex-certifi ed, as is the case with the portable density meter DMA 35 Ex Petrol. This lightweight device is intrinsically safe, specially designed for work on-site at tank farms and refi neries, and is ASTM D7777 compliant. Measurement requires only one hand and is possible when wearing gloves. Its light weight makes it ideal for measuring hard-to-reach samples from tanks or similar containers. An RFID functionality means sample points can be scanned and the appropriate measurement settings implemented automatically.
As an alternative to measurements on-the-go with a portable device, it often makes sense to equip a small lab space for quick
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