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Produced Oil: Simulating the path from formation to surface

January 31, 2023

In our last blog in this series (High Viscosity Friction Reducers (HVFR)), I focused on testing high viscosity friction reducers (HVRFs). 

The next fluid that I would like to cover in this oil and gas viscosity blog series is production (or crude) oil. Now that we have addressed some of the rheological testing methods that can be used to get fluids downhole, it is important for us to cover the next step in the process which is production and flow of the oil that we are trying to recover with the hydraulic fracturing process. Why is it important to know the viscosity of production oil? Viscosity is a fluid’s internal resistance to flow, and since the oil will be flowed through piping from the reservoir to surface and through piping at refineries; it is imperative to have a high level of understanding of how the flid will flow. The flow of the oil can be altered by changes in pressure and temperature and by addition of chemicals. Each of these methods comes with a relatively high financial burden so understanding how each component can alter the viscosity of the crude oil, and in turn the level of difficulty in pumping it, the more economic you can make your production processes.

The reservoir fluids from an oil and/or gas well tend to be multi-phase systems. They are comprised of natural gas, water and oil among other things. It is extremely difficult to determine the exact makeup of the reservoir fluid because in order to do this, you must bring a sample to surface and make sure that it maintains the exact temperature and pressure which it was at downhole. There are ways to do this by collecting samples with wireline tools and then using a PVT cell to maintain the downhole conditions until flowing the sample through a rheometer, but I do not want to focus on these fluids and this type of testing due to the fact that there are means to determine a relatively accurate breakdown of these fluids through LWD (logging while drilling) tools. This method is much more comprehensive and cost-effective than relying on surface testing of multiple fluid samples collected throughout the well’s payzones. Also, while it is important to understand phase changes of the production fluid as it travels up the production casing, I believe RheoSense is best suited to help characterize “dead oil” (crude oil with no more gas content) and assist with the pumping of this commodity.

Crude oil can range from light to heavy with viscosity that ranges from ~1 cP (Kutubu crude oil) to ~12,000 cP (Boscan crude oil). As mentioned earlier, understanding the viscosity and pumpability of the fluid is necessary to determine how much pressure is required to produce or bring the oil from the reservoir up to the surface. While there are other calculations and correlations needed, you must know the viscosity of the oil to be able to determine how much artificial lift pressure must be applied to assist the backpressure of the reservoir in order to bring the oil to surface. In the same sense, you must know the viscosity of the oil to understand how much pressure is required to transport across the miles of pipelines on surface and through the processes at refineries.

So where can RheoSense assist in this process?

For years, the viscosity of oil has been tested with capillary viscometers. This method is very simple, but it is extremely limited in what information it can provide and what parameters can be tested. If you want to know how a fluid changes under variable pressure conditions (or shear rates), you will not be able to do this with a capillary tube system. While you can alter temperature and see how viscosity is affected with the capillary tube system, this is a tedious process being highly time-consuming and difficult to clean. There are also rheological testing methods for oil that involve rotating systems. But these usually provide indexed values and not true (or dynamic) viscosity. They also do not simulate actual flow and are destructive processes so they do not simulate real-world conditions for the flow of the oil.

RheoSense technology employs a flow-through design measuring pressure drop across a rectangular-slit, microfluidic flow channel. You are able to control the flow rate of the fluid as well as the temperature of the fluid for accurate and repeatable measurements at a wide range of testing conditions. With our viscometers, you are able to test fluids at up to 105 degrees Celsius and ~300 psi without the addition of any difficult pressure cells or PVT systems to set up. You can simply use our viscometers right out of the box to test your crude oil samples and obtain a full characterization of the oil where it is defined over a wide range of shear rates (pressures) and temperatures. Our instruments are compatible with most all types of fluids so you can also add various thinning chemicals to your oil to test exactly how they will affect viscosity (and flow of the oil) without worrying about damage to the device.

Contact Us today to speak with a technical representative in your area to get started characterizing your crude oil today!

Written by: Tyler Etheredge, RheoSense Technical Sales Representative

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