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Geology 4 min read

An Interview with Ross Crain

Published on September 26, 2022

Petrophysics, teamwork, and what tools a geologist needs to be successful.

Can rocks make you money? Sure, they can, if you find the right ones. When it comes to energy and resource exploration, knowing the petrophysical properties of those rocks is the key to success. With this in mind, SeisWare developed a geology calculator to help geoscientists who want to incorporate more petrophysics into their everyday workflows. The Calculator has a library of calculations for porosity, water saturation, permeability, net pay, and more. The equations are a great starting point and can be customized right in the calculator. We didn’t make them up – the calculations are straight from Crain’s Petrophysical Handbook.

Our team at SeisWare wanted to go beyond the equations and explore the power of petrophysics, so we went right to the source: Ross Crain. SeisWare Product Owner, Amber Padilla, recently sat down with Mr. Crain, a professional engineer, world-renowned petrophysical expert, and author of Crain’s Petrophysical Handbook, to learn more about the importance of petrophysics, teamwork, and what tools a geologist needs to be successful.

Amber Padilla: Why is petrophysics an important consideration in the oil and gas industry?

Ross Crain: Everybody uses petrophysics one way or another. This includes people in the field, the drilling team, the completion engineer, geologists, geophysicists, and even management when deciding if they are going to complete a well. All of these disciplines use petrophysics to analyze logs that help them answer questions about the reservoir. For a full list of who uses logs and why, check out this video: What CEOs, Investors, New Hires, and Old Timers Need to Know About Well Logs, Petrophysics, and the Bottom Line.

AP: How does petrophysics help a company when it comes to reservoir evaluation or well placement?

RC: Petrophysics is essential in reservoir evaluation and well placement. It has to be done. You need to look at well log data analysis, core data, sample descriptions, production test information, and more, i.e., integrated petrophysics. It tells you whether you have a reservoir worth completing. If it is, what is the rock’s composition, porosity, and water saturation, and can it make money? All of these questions involve petrophysics.

Every public company (regulated by the stock exchange) is obliged to have a 3rd party come in and evaluate reservoir properties to help determine how much oil and gas they potentially have access to. This lets investors know the value of the company and whether to invest in their endeavors. Even though private companies are not required to have these evaluations, it’s still wise to know the answers to these same questions because lenders and private investors need to know before they will lend or invest.

AP: How has petrophysics changed over time?

RC: I’ve been at this for 60 years and it’s been quite dramatic, yet slow. Today’s tools are either more accurate than they used to be, or they are new. For example, there are now logs that can see through casing, like induced gamma ray spectroscopy logs. Gamma Ray Spectroscopy logs measure the elements in the formation like iron, oxygen, and carbon as opposed to directly measuring porosity or water saturation and instead invert the element yields to generate the minerals and fluids in the rock. Porosity and hydrocarbon content comes from the fluids analysis. Tools today allow you to measure up to 31 elements versus only 9 in the past! Technology like this allows you to obtain a more accurate picture of what kind of rock you are in and whether you have oil, gas, or water. My advice is – accept the new technology!

AP: Why is petrophysics important to incorporate into geology and geophysics workflows?

RC: This question goes back to the integrated petrophysics approach. Geologists, Geophysicists, and Engineers are all on the same team and need to talk to each other. Everyone on the team needs to know the reservoir they are working in. There is a concept called the Shared Earth Model, where basically the reservoir engineer, geologist, and geophysicist are all working on the same reservoir or area and should interchange knowledge so everyone understands what is happening underground. Successful companies are the ones where they work together.

AP: Where does petrophysics fit in a geologist’s workflow?

RC: Petrophysicists work with the Geologist. The Geologist asks for certain wells to be analyzed and the Petrophysicist does the work. If a Geologist is solo they need some training in the petrophysical sciences to be able to do the required analysis and answer the questions they need to be answered. Questions such as what is this reservoir’s mineralogy, porosity, water saturation, permeability, etc. The answers to these feed into other parts of your investigation. Permeability for instance helps you decide where you want to do your perforations and where to produce in the zone of interest.

AP: How are statistics used in Petrophysics?

RC: Petrophysics uses percentiles in log normalization. The reason being older logs don’t have the same answers as newer logs. You look at the median, minimum, maximum, 90th, and 10th percentiles and use that to determine how to scale the log. Having your logs as calibrated as you can is essential. However, if you over-calibrate, you can potentially lose geological variations within the reservoir, so be careful! Remember geology changes and logs reflect those changes.

There are also statistical and probabilistic models where you give ranges of possibilities for input parameters, mainly logs, and it does a probabilistic model instead of a deterministic model. Probabilistic models are hard to control. We don’t know the range of possibilities so it’s hard to tell the program what to work with.

Geostatistics is also used. This is a method that helps extrapolate or interpolate data between wells and helps with reservoir simulation.

Thank you, Mr. Crain, for your time and insights! Petrophysics is truly a powerful and evolving reservoir evaluation tool!


More information

For more petrophysical information, check out Crain’s Petrophysical Handbook.

To learn more or request information about Geology and the Geology Calculator, visit our Geology by SeisWare page.



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