12 RULES FOR WELL TESTING
Well testing is a powerful tool that can be used to help answer questions about your well and your reservoir. However, as with anything, there is a right way and a wrong way to go about it. The right way includes collecting good quality data and setting yourself up for an accurate and meaningful analysis.
With that in mind, here are 12 rules for well testing that will help lead you to the best possible analysis:
Bottomhole Gauges Will Always Lead To A Better Analysis
Bottomhole pressure gauges are expensive and can definitely add cost to your well test. However, the additional accuracy provided by the data generally outweighs the added cost. Without bottomhole gauges you are forced to estimate your bottomhole pressure, which means estimating hydrostatic and friction pressures. These are not easily calculated and attempting to do so leaves you open to inaccuracies.
Ask Yourself, “Does This Make Sense?”
Computers are really good at giving you an answer, even if that answer is nonsense. Whenever you analyze data, you should ask yourself if the conclusion makes sense. If the result of your analysis seems surprising, go back and check your inputs, and then check your analysis process. You might find that an error along the way that led to unusual results.
Measured Data Is Better Than Calculated Data
Measuring something directly is almost always more accurate than calculating it. Any inaccuracy in your inputs or assumptions will result in an inaccurate calculation. By measuring a parameter directly, you can remove this potential error and be confident in your data. This is especially true to bottomhole data (see Rule #1 above).
The Longer The Test, The More Information
Longer well tests give you more information about your reservoir. This is particularly true in buildup or falloff tests in which a longer test leads to a greater radius of investigation. A greater radius of investigation will result in a more of the reservoir being included in the permeability calculations and will increase your chances of seeing a boundary.
Reservoir Effects Do Not Happen Suddenly
If you see a sudden change in your data, then it is not a reservoir-related effect. Wellbore-related effects can happen suddenly, but reservoir-related effects are predictable and result in a smooth curve. If it happens suddenly, it’s not related to the reservoir.
Use the PPD to Identify Wellbore-Related Effects
The Primary Pressure Derivative (PPD) is a great tool used to help differentiate between reservoir and wellbore-related effects. In a nutshell, the PPD should always be decreasing for reservoir-related effects. If you see PPD increasing, then you know that whatever phenomenon you are seeing is not a result of the reservoir and is probably a result of something happening in the wellbore.
Use Pressure Gradient Surveys To Identify Fluid
Pressure gradient surveys are a very accurate method for determining fluid level and fluid density in a well. If you are already running bottomhole gauges in and out of a well, then adding a gradient survey is a great way to add valuable information without adding cost and time. Knowing if you have fluid in the hole is critical to an accurate well test analysis.
Take Detailed Field Notes
Things happen in the field that impact the data. Often these things are unexpected and not a part of the procedure. Therefore, it is really important for field personnel to take good, detailed notes during the test. This will help anyone analyzing the data to make sense of what they are seeing. Without good notes, people are forced to dream up ideas of what they think happened with the data. When this happens, assumptions are made, and we all know what happens when we assume!
Don’t Ignore Temperature
Bottomhole gauges will yield both pressure and temperature data. While pressure is more important, be careful not to overlook the temperature data, especially if there are some very unusual trends. Temperature has secrets to reveal as well, and it can be particularly helpful when the well test data has you scratching your head.
Start Simple
You’ve heard it said, “Keep it simple, stupid.” This is certainly true of well test analysis. If you’re first conclusion is that you have a heterogeneous, anisotropic, dual-porosity, naturally-fractured reservoir with partial penetration and turbulent flow, then perhaps you are overcomplicating things. Start with a simple model (radial flow) and add complexity as the data leads you.
Quality Costs Money
A good-quality well test requires good-quality data and good-quality engineering. Good quality costs money, and in most cases, it is worth the cost. Cutting corners will save you money in the short-term, but the lack of information, or worse, the wrong conclusions, can cost you far more money in the long run.
Garbage In, Garbage Out
The accuracy of your input parameters will directly affect the accuracy of your analysis. If you put garbage into a model, you will get garbage out. Do what you can to make sure that your have accurate inputs when it comes to porosity, thickness, and saturation.
Having insight into your reservoir is an important part of petroleum engineering. By knowing, rather than guessing, you can make more informed decisions. At FyreRok, it is our mission to help you design, execute, and analyze your well test, so that you can get the answers that you need. Contact us today and let’s begin discussing your next well testing project.
Want to read more? Click here for more Well Insights.
You can also subscribe to receive Well Insights updates directly to your inbox.