It wasn’t until the mid-to-late 1990s that geologists and geophysicists began to move beyond laboring only on their respective turf.
As 3-D seismic gained prominence in the industry, the two professions realized they needed each other, and the ensuing synergy soon became routine.
Geophysical data quickly became invaluable to the geologist as a means to create 3-D geological models to visualize aspects of the subsurface over sizeable areas, in both working basins and frontier areas.
Today, model building expertise has been refined significantly. Among innumerable applications, it’s now becoming a must-have for horizontal wells, which often are more complex than previously thought. And, in the century to come, ongoing advances in the underlying technology will make it even more indispensable, faster and far less expensive.
Given the borderline-wild leasing activity currently occurring in the Permian Basin, where certain land prices zoomed upward toward $40,000 per acre at one time recently, it’s timely to take a look at the role that models can play in the Permian drilling action.
The basin overall harbors a plethora of shale zones that ordinarily demand horizontal wellbores in order to give up their usually voluminous hydrocarbon volumes in the most efficient and cost-effective manner.
It’s not unusual to drill a lateral and to perforate every 100 to 200 feet or so, with the idea being that the reservoir is the reservoir. But that’s a pricey undertaking, which increasingly is being considered not only unnecessary, but even a bit foolhardy.
In the Permian, the rocks range from conventional sandstones all the way to mudrocks and everything in between, often with many low permeability, tight interbedded zones.
Smart, or Caveman?
The experts at longtime industry player Fasken Oil and Ranch Ltd. in Midland, Texas have honed considerable expertise in this region.
“What I’ve seen in these tighter, low permeability rocks is advances in petrophysical analysis, so over the next decade I see us coming up with very robust techniques for petrophysical evaluation,” said senior geologist Stonnie Pollock at Fasken.
“The reason this has to take place is we’re dealing with nanodarcy and microdarcy permeability rocks and dealing with rocks rich in TOC (total organic content),” Pollock noted. “But a lot of that organic richness is immovable oil, or bitumen.
“Some of the advances we’ll see is how to better understand how much of those hydrocarbons are movable versus immovable,” he added. “We’re already seeing some of that as some of our more experienced petrophysicists and geochemists are beginning to unlock that.”
Pollock also mentioned that there will likely be increasing technology in the realm of geochemical acquisition tools and more advanced software and computer modeling, and he emphasized that nanotechnology will be a big part of the industry for modeling and measurement in the future.
This will meet some far-ranging needs.
“With horizontals, there needs to be much more advanced mineralogical and petrophysical modeling to determine where to drill the laterals and where to initiate your completions because you have to frac all this type rock,” noted Fasken geophysicist Ron Bianco.
For so long, the lateral drilling rationale was that the well is in the same pay zone for thousands of feet, so completions theoretically could occur in the rock over the entire length of the lateral. Pollock noted, however, that geologists and geophysicists can see changes occur in the lateral direction in the target interval.
The practice of perforating at predetermined, equally spaced intervals all along the lateral may soon be over, according to Glenn Winters, chief geophysicist at Fasken.
“In the future, people are going to want to measure and model the best quality even in the lateral direction, and we’ll see advances in this and more selective fracturing,” Winters said. “You can call it smart versus caveman completions,” he added.
“Already, people are looking at their seismic, looking at where they have digital logs and saying they’re going to place these perfs only in zones they think are the best,” Winters said. “That’s where the modeling and integration are going to come in.”
Although there are tools to measure rock properties through the horizontal wellbore, they are pricey and can significantly raise the mechanical risk. This mechanical impact explains why there’s little logging acquisition in horizontal wellbores. The Fasken team predicts there will be advances in that realm.
“Our logging will get better, and we’ll be able to integrate that with our engineering production and our seismic data,” Winters said. “Right now, we’re at the beginning of trying to use seismic data to forecast where we think we’ll see better reservoir rocks.
“In the future, I see us using the production we have and reintegrating that in the forecasting with the logging tools we have in order to come up with a better and finer model – ‘finer’ meaning better lateral and vertical resolution,” he commented.
Better Data Management
Pollock added that better logging information used in combination with the right technology can yield a gamma ray model showing clay or shale content. With continuous logging, they could use the information to change the model as it’s created. Winters joined in, emphasizing that modeling software is advancing dramatically, which is going to help considerably.
“The reason the future is so exciting is because for the first time in our industry, it seems like companies and individuals have the ability to purchase fairly inexpensive computer capacity that’s finally met the technology we’ve been pushing,” Bianco said. “Now you can buy computers with capacity to run huge neural network modeling looking at all kinds of reservoir attributes, and do it overnight or in a day instead of the three to four months it used to take.
“I can change my model and completely revamp all the reservoir qualities overnight or in a few hours,” he said. “Now we all will be able to do modeling in-house and put our own spin on it.
“Modeling is the way of the future, and neural networking technology gets better every day,” he noted. “I think that statistical analysis is going to solve most of the problems we have in any of the basins where we have a high amount of data.”
The Human Factor
Still, caution is the buzzword.
Pollock noted that a model is nothing but a theory without proof of hard evidence, indicating that uncertainty lurks wherever.
Maintaining geological meaning during modeling is key and is the most formidable challenge in the process, according to Bianco.
The service companies clearly are skilled with applying the data, but Winters emphasized that things can be misunderstood unless the geoscientist(s) is doing the work.
“You must be careful with the model as anyone with good computer software can model anything,” he said. “You must have a good geologic analog and understand the geometry and the reservoir attributes of those intervals, or the model is meaningless.”
He mentioned for example that someone could interpret a carbonate debris flow extending for several miles, while another person might limit it to a half mile.
“We can do things so quickly now, and as long as there’s good geological and geophysical understanding, I think we’ll see huge improvements in earth models,” Winters added.