{"id":3606,"date":"2026-10-29T18:04:49","date_gmt":"2026-10-29T10:04:49","guid":{"rendered":"http:\/\/www.cellphonechina.com\/blog\/?p=3606"},"modified":"2026-10-29T18:04:49","modified_gmt":"2026-10-29T10:04:49","slug":"how-is-residual-oil-saturation-measured-4c29-16d43a","status":"publish","type":"post","link":"http:\/\/www.cellphonechina.com\/blog\/2026\/10\/29\/how-is-residual-oil-saturation-measured-4c29-16d43a\/","title":{"rendered":"How is residual oil saturation measured?"},"content":{"rendered":"

If you\u2019ve ever spent time around oil and gas operations, you\u2019ve probably heard the term \u201cresidual oil saturation\u201d (ROS) thrown around a lot. At its core, ROS is the amount of oil left trapped in a reservoir rock after we\u2019ve done what we can to pull out the easy stuff\u2014primary recovery, water flooding, maybe even some gas injection. It\u2019s that stubborn oil that\u2019s stuck in tiny pore spaces, clinging to grain surfaces, and it makes up a huge part of a reservoir\u2019s total potential. But here\u2019s the thing: if you don\u2019t measure ROS correctly, you\u2019re flying blind when it comes to planning enhanced oil recovery (EOR) projects, calculating how much oil you can actually get out, or even deciding if a reservoir is worth developing. Residual Oil Saturation<\/a><\/p>\n

<\/p>\n

As someone who\u2019s been deep in the ROS game for over a decade now (I started out in a lab running core tests, and now I\u2019m on the supply side helping operations teams get the right tools to measure ROS reliably), I\u2019ve seen my fair share of mistakes. Early on, I watched a team waste $2 million on an EOR project because they used a quick, flimsy ROS test that gave them numbers way too high\u2014turns out the residual oil was actually way lower, so their injection plan was overkill. That\u2019s why I want to break down how ROS is actually measured, what works, what doesn\u2019t, and why the supplier side matters so much here. Let\u2019s cut the jargon where we can, but keep it real\u2014no textbook fluff, just the stuff that matters to folks in the field or lab.<\/p>\n

First off, let\u2019s get one thing straight: ROS isn\u2019t a single number. It changes depending on the reservoir rock, the type of oil, the fluids we inject, even the temperature and pressure downhole. That\u2019s why measuring it isn\u2019t a \u201cone-and-done\u201d test. You\u2019ve got to match the method to the specific reservoir you\u2019re working with.<\/p>\n

Let\u2019s start with the most common method out there: core analysis. If you\u2019ve ever drilled a well, you know you pull out these long cylinders of rock called cores, right? Those cores are like a time capsule of the reservoir. To measure ROS, you take a small plug of that core (an inch or two long, an inch wide) and put it in a core flood setup. That setup is basically a pressure vessel that mimics downhole conditions\u2014we crank up the pressure, heat it to the reservoir temp, and then we flood the core with water (or whatever fluid the operation uses to push oil) until no more oil comes out. Then we measure how much oil is left in the plug.<\/p>\n

Wait, how do we measure that residual oil, exactly? Two main ways here: retort method and Dean-Stark extraction. Let\u2019s keep it simple. The retort method is where you heat the core plug super hot (like 600 degrees F or so) in a closed chamber. The oil and water in the rock vaporize, and we collect those vapors, cool them down, and measure the volume of oil that condenses. It\u2019s fast\u2014takes a few hours\u2014and that\u2019s why a lot of teams use it for quick checks. But here\u2019s the catch: if the rock has any heavy oil or bitumen, some of that might not vaporize, so you get an undercount. Also, if there\u2019s any clay in the rock, it can hold onto water that gets counted as oil sometimes.<\/p>\n

Then there\u2019s Dean-Stark, which is more reliable but takes longer. You crush up the core plug, mix it with a solvent like toluene, and heat it. The solvent dissolves the oil, and you separate the oil from the solvent (and water) in that Dean-Stark apparatus. This is way better for heavy oils, because you\u2019re actually pulling the oil out with solvent instead of just vaporizing it. The downside? It takes a day or two, and you have to crush the core\u2014once it\u2019s crushed, you can\u2019t test the same plug for other things like permeability later. That\u2019s a big deal if your core samples are limited (most teams only get a few good cores from a well).<\/p>\n

Now, if core analysis is like digging up a piece of the reservoir and testing it in a lab, there\u2019s another method that\u2019s 100% downhole, and that\u2019s well logging. Well logs are the tools you lower into the wellbore to measure properties of the rock around the hole. For ROS, the big ones are nuclear logs\u2014specifically, spectral gamma-gamma logs and nuclear magnetic resonance (NMR) logs. Let\u2019s break that down.<\/p>\n

Spectral gamma-gamma works by shooting gamma rays into the formation. The rock, oil, and water in the formation all absorb gamma rays differently. Oil has hydrogen, but wait\u2014water has hydrogen too, right? So we have to adjust for that, but the key is that the amount of gamma rays that bounce back tells us how much hydrogen is there, and then we can subtract the water hydrogen to get oil hydrogen, which translates to ROS. It\u2019s great because it\u2019s continuous\u2014you get ROS measurements all along the well, not just at the core plug spots. The problem? It\u2019s less accurate than core tests, especially in messy formations with lots of different rock types or heavy oil.<\/p>\n

NMR logs are newer, and they\u2019re game-changing for a lot of operations. NMR measures the way hydrogen atoms spin. Water and oil hydrogen spin at different rates\u2014water spins fast, oil spins slow. So the NMR tool can tell the difference between hydrogen in water and hydrogen in oil, and calculate how much oil is left. It\u2019s non-invasive, gives you a profile of the entire well, and works way better for heavy oils than gamma-gamma. The downside? It\u2019s expensive, and you have to know the right parameters for your specific reservoir (like the oil\u2019s viscosity) to get the numbers right. I\u2019ve worked with a team that switched from gamma-gamma to NMR for a sandstone reservoir and cut their ROS measurement error by 15%\u2014that\u2019s thousands of barrels of oil they can now recover, all because of a better log.<\/p>\n

Then there are newer methods that are popping up as EOR gets more advanced, like tracer tests. You inject a small amount of a tracer (a chemical that doesn\u2019t mix with oil, or one that binds to oil) into the reservoir, and then you track how much comes back. The amount of tracer left in the reservoir tells you how much oil is around, so you can calculate ROS. It\u2019s super useful for whole-field scale measurements, not just single well or core plug. But tracers have their own issues\u2014they can stick to rock, or mix with other fluids, so you have to pick the right tracer for your reservoir. A lot of teams love tracers because they can measure ROS after they\u2019ve been injecting EOR fluids for months, which core tests can\u2019t do (you don\u2019t want to crush up a whole reservoir just to check ROS).<\/p>\n

Now, here\u2019s the part that a lot of people don\u2019t talk about: the supplier\u2019s role in all this. I know, I know, this is a blog about ROS measurement, not a sales pitch. But let\u2019s be real\u2014if you\u2019re out there buying supplies to run these tests, whether it\u2019s core flood equipment, Dean-Stark kits, NMR logging tools, or tracers, the quality of what you get directly impacts your ROS numbers.<\/p>\n

For example, if you buy a cheap Dean-Stark kit that\u2019s not calibrated right, you\u2019ll get wrong volume measurements, and your ROS will be off. Or if you buy a tracer that\u2019s too sticky, it\u2019ll give you false high ROS numbers because half the tracer is stuck in the rock, so you think less oil is there than there actually is. I\u2019ve seen teams go with the cheapest core flood pumps they could find, and those pumps can\u2019t maintain the consistent pressure needed for accurate ROS measurements\u2014pressure fluctuations make oil move in and out of the rock, so you end up with a messed-up residual count.<\/p>\n

That\u2019s why when I work with ops teams, I don\u2019t just sell them gear\u2014 I walk them through which method makes sense for their reservoir. If they\u2019re working with a tight sandstone with light oil, I tell them core flood with Dean-Stark is the way to go, and here\u2019s what calibration checks they need to do every time. If they\u2019re doing a whole-field EOR project, I\u2019ll help them pick tracers that work with their reservoir rock type and fluid, so their ROS numbers are reliable. I\u2019ve even set up quick training sessions for field teams on how to run simple ROS checks on site, not just rely on lab results that take a week to come back.<\/p>\n

Let me share a recent example to make this real. Last year, a mid-sized operator in the Permian reached out to me. They were planning a polymer flooding EOR project, and their previous ROS measurements from a local lab said 28%\u2014which would mean the EOR project could recover an extra 12 million barrels. But they were skeptical, because their own quick well log readings were pointing to 22% ROS. They didn\u2019t want to waste $1.5 million on a project that would only get 5 million barrels, so they asked for our help.<\/p>\n

We worked with them to run a hybrid test: we used their existing core plugs, but brought in our calibrated Dean-Stark equipment (way better than the cheap stuff the local lab was using) and ran parallel tests. Turns out, the local lab had undercounted heavy components in their oil, so their ROS was actually 21%\u2014close to their log numbers. We also ran a quick NMR log to confirm along the wellbore, and that matched the core test. So they adjusted their EOR plan, optimized the polymer injection rate, and ended up recovering 10.8 million barrels\u2014almost exactly what the corrected ROS numbers predicted. They would have overspent and underdelivered if they\u2019d stuck with the wrong ROS measurement from a cheap supplier.<\/p>\n

Now, let\u2019s get to the mistakes I see all the time that mess up ROS measurements. First, trying to use one method for everything. A lot of teams default to retort because it\u2019s fast, but if your reservoir has heavy oil, that retort number is garbage. Second, not mimicking actual reservoir conditions during the test. If you run a core flood at atmospheric pressure and room temp instead of 3,000 psi and 180 degrees F, your oil will behave differently\u2014you might get way less residual oil than you actually do downhole. Third, not calibrating your equipment. I can\u2019t tell you how many times I\u2019ve seen a team run a Dean-Stark test without calibrating the collection tube, or a core pump that\u2019s off by 100 psi. Small errors there turn into big ROS mistakes.<\/p>\n

So, what does this mean for you, whether you\u2019re an ops manager, a lab tech, or someone just getting into the oil and gas space? If you need to measure ROS, don\u2019t just grab the cheapest test or the quickest method. Ask questions: does this test mimic my reservoir\u2019s pressure and temperature? Does it account for my oil\u2019s viscosity? Am I using calibrated, reliable equipment? And when you\u2019re sourcing supplies for these tests, work with a team that actually understands ROS measurement\u2014not just someone selling gear off a catalog.<\/p>\n

<\/p>\n

If you\u2019re working on a project right now and your ROS numbers feel off, or you\u2019re just starting out and need to get your first accurate ROS measurement, reach out. We\u2019ve worked with everything from small independent operators to major oil companies, and we help pick the right method, supply the calibrated equipment, and even train your team to make sure you get numbers you can trust. No jargon, no hidden fees, just straight talk about getting your ROS right so you can make better decisions for your projects.<\/p>\n

Tools For Geothermal Wells<\/a> At the end of the day, residual oil is the biggest untapped resource in most oil reservoirs. But you can\u2019t get it out if you don\u2019t know how much is there, and you can\u2019t know how much is there if you measure it wrong. That\u2019s why ROS measurement isn\u2019t just a technical step\u2014it\u2019s the foundation of every successful EOR project, every well plan, every dollar you spend. Make sure you get that foundation right.<\/p>\n

References<\/h3>\n
    \n
  1. Ahmed, T. "Reservoir Engineering Handbook." Gulf Professional Publishing, 2019.<\/li>\n
  2. Coates, G.R., et al. "NMR Logging in the Petroleum Industry." Society of Petroleum Engineers, 1999.<\/li>\n
  3. Standnes, D.C., et al. "Methods for Measuring Residual Oil Saturation in Core Samples: A Review." Journal of Petroleum Science and Engineering, vol. 112, 2013, pp. 101-115.<\/li>\n
  4. Piggott, T.M., et al. "Tracer Methods for Residual Oil Saturation Quantification in Carbonate Reservoirs." Society of Petroleum Engineers Reservoir Evaluation & Engineering, vol. 20, no. 3, 2017, pp. 567-578.<\/li>\n<\/ol>\n
    \n

    Xi’an Sitan Instruments Co., Ltd.<\/a>
    Xi’an Sitan Instruments Co., Ltd. is one of the most professional residual oil saturation manufacturers and suppliers in China for 27 years, mainly engaged in providing high quality products. Be free to buy discount residual oil saturation at low price here and get quotation from our factory.
    Address: No.22, Keji 5th Road, High-tech Zone, Xi’an City, Shanxi, China
    E-mail: sales@sitan.com.cn
    WebSite:     https:\/\/www.sitanpetro.com\/<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

    If you\u2019ve ever spent time around oil and gas operations, you\u2019ve probably heard the term \u201cresidual … How is residual oil saturation measured?<\/span>Read more<\/a><\/p>\n","protected":false},"author":27,"featured_media":3606,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[3569],"class_list":["post-3606","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-industry","tag-residual-oil-saturation-444b-17094e"],"_links":{"self":[{"href":"http:\/\/www.cellphonechina.com\/blog\/wp-json\/wp\/v2\/posts\/3606","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.cellphonechina.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.cellphonechina.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.cellphonechina.com\/blog\/wp-json\/wp\/v2\/users\/27"}],"replies":[{"embeddable":true,"href":"http:\/\/www.cellphonechina.com\/blog\/wp-json\/wp\/v2\/comments?post=3606"}],"version-history":[{"count":0,"href":"http:\/\/www.cellphonechina.com\/blog\/wp-json\/wp\/v2\/posts\/3606\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"http:\/\/www.cellphonechina.com\/blog\/wp-json\/wp\/v2\/posts\/3606"}],"wp:attachment":[{"href":"http:\/\/www.cellphonechina.com\/blog\/wp-json\/wp\/v2\/media?parent=3606"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.cellphonechina.com\/blog\/wp-json\/wp\/v2\/categories?post=3606"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.cellphonechina.com\/blog\/wp-json\/wp\/v2\/tags?post=3606"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}