The advent of 3-D seismic technology in the oil patch not so many years ago marked a humongous technological advance in the industry.
Today, geoscientists are looking beyond 3-D seismic as a standalone tool.
In many instances, they are harnessing the power that comes from integrating various other data types with 3-D seismic to predict sweet spots, potential productivity of yet-to be drilled wells and more.
Southwestern Energy, for example, recently completed a successful study combining various data with their 3-D seismic data in an area of their extensive [PFItemLinkShortcode|id:1863|type:standard|anchorText:Fayetteville shale holdings|cssClass:|title:Fayetteville Model Has ‘Predictive Value’|PFItemLinkShortcode].
Steve Trammel, senior manager for industry relations at IHS, gave the EXPLORER an overview of the practice of integrating varied data with seismic – and, in his words, what it means for operators:
Let’s Get Together
“The interesting theme being pursued now is integrating seismic data with all of the other data you can get from a well and logs and so forth. Shale gas and tight oil plays unlocking unconventional resources has completely changed the oil and gas supply picture in North America and represents perhaps the most exciting development in our lifetime.
“But these plays have tremendous variability, even within the same play. Integration of data from seismic and the wellbore itself holds the key to understanding the reservoir potential.
“We’ve found a lot of gas, and that was good for the consumers and energy security, but not so good for the producers due to the lowered gas prices.
“The payoff has been those same technologies, i.e. horizontal drilling and hydraulic fracturing plus the combination of all the other geophysical work, has unlocked tight oil zones and created a true renaissance in North American oil supply.
“The same variability noted in shale gas plays is a key issue for tight oil plays. I say tight oil because it’s not just shale. Tight oil reservoirs are low permeability sands, silts, dolomitized zones often intermingled with shaly zones. It’s complex plumbing.
“With all this variability across plays, operators have had to focus on how they can use geophysical technology we have today to help us understand what the risks are with all that variability – and to illuminate the sweet spots.”
Isn’t That Sweet?
“Like any resource plays, these plays typically are over a huge geographic area, so the key is finding those sweet spots – and that key overall is the integration of geophysics with other data.
“A reservoir in reality is a three dimensional section of the earth. Common sense says you need to create multiple views of that reservoir from a variety of data to have a full understanding of the reservoir. People in general are integrating 3-D with as much borehole data that are available at the start of the workflow and throughout the whole process.
“As an example, fracturing in tight rocks is critical to production, and 3-D can be used to define structures and faulting. So some of the output they want to get is direct mapping. They look at amplitude analysis and analyze via pre-stack inversion processes to understand variation in the brittleness of the formation.
“Brittleness directly translates into ‘fracability.’
“Then you combine those geophysical attributes with borehole data and work up resistivity mapping from logs, for example, as part of the borehole data.
“You put all that together, and it can really show sweet spots and high grade where the well locations should be.
Let’s Get Small
“Another geophysical technology comes into play when they integrate in the microseismic data.
“Microseismic is done to evaluate how successful the hydraulic fracturing jobs are – fracture development, extent and direction. Also, the rock properties picture comes into focus, and you really start to see your reservoir.
“Another important piece to this is that it identifies any geohazards, such as a massive fault or overpressure.
“If you have a big fault you could lose all of your treatment – your fracturing water – to the fault and not have it crack the rock per design. You want to make sure you’re not getting into an area that has greater than anticipated faulting.”
Extremely Loud and Incredibly Close
“This big theme of integration enables advanced imaging of the reservoirs and corrects a lot of the noise of the rock overburden – overburden noise can mask some pretty subtle attributes at the reservoir level.
“Once you look at production data, logs and other wellbore data after this overburden noise from the seismic is removed, you can start to see azimuth anisotropy, travel times and amplitudes – and that becomes a much more reliable way to pick those sweet spots.
“Generally, this integration of data reveals pretty subtle structural features in the rocks, helping to determine your original-oil-in-place and estimated ultimate recovery numbers, which are critical for the plays to judge them on how well they’re going to perform.”
“The 3-D data will illuminate rock strength and stresses, closure stress and faults and natural fractures.
“Many of those formation stress factors can be derived from Poisson’s Ratio. Estimating the ratio helps you understand changes in stress gradient relative to the surrounding layers.
“Understanding what kind of stress this rock is under provides critically important help in designing hydraulic fracturing designs for the wells.
“You can combine geo-mechanical and stress properties with log data to estimate shale and carbonate content, porosity, hydrocarbon content and water saturation, natural fracture locations, trends and orientation.
“Data integration provides a more complete picture than any individual data views by themselves.”
“What I’ve read and also learned from attending various symposia is that geophysicists are focusing their attention in four major areas today:
- Predicting anisotropy from full azimuth data.
- Acquire a good prediction of rock properties.
- Predict the principal stresses on the formation.
- How to characterize the fractures in the rock.
“In the integrated workflow, you take those four primary areas and link that to petrophysics you will get from logs. You do this integration early, and tie rock properties to the seismic response so you’re getting a model of what these different rocks are going to do in different basins and geologic facies.
“Bring in completion data, engineering data coming from the well, production data and include production data from multiple wells in the area. Drill, hydraulically fracture and then run microseismic to see how the fracture designs are working.
“This work not only helps when drilling additional wells and designing their completions, it starts to create some analogs for those plays when you’re within a play that typically covers a huge geographical area.
“Those analogs also get you started evaluating other plays’ potential.
“I have a friend who says these unconventional rocks are so variable that in many cases people need to drill 20 to 30 wells at a cost of millions of dollars per well or more – that’s really expensive lab work. Mitigating that time and expense with an integrated workflow of seismic and wellbore data shortens the rock code-breaking process.”
Success in the ‘Beautiful Mess’
“As we said, in the real world, rocks are three-dimensional and have overburden stress, lateral stresses and faults, and all the complex plumbing attributes of unconventional reservoirs. You can see some of this with seismic, but some gets masked with that overburden noise.
“It’s only when you bring in other views of the rocks that you can really get a complete picture to eliminate some of the variability that poses risks causing sweet spots to be missed, slowing down your development of best practices for a specific play and ultimately affecting your economic success.
“Integration already is a reality. It’s just good to get it underscored and realize this is what people are doing today. This whole integration theme entails taking reservoir evaluation methods developed over the last 20 years or so for conventional reservoirs and bringing it all together.
“As we continue to understand the complex plumbing in unconventional reservoirs, we know Mother Nature is beautifully messy. Seismic data integration with wellbore data helps us move from uncertainty to variability to predictability.”