It’s the end of a decade, and the advances in downhole geology during the past 10 years look more like whole areas of advancement:
- Geosteering, real-time formation and reservoir assessment, improvements in logging while drilling (LWD) and measuring while drilling (MWD), the development of azimuthal tools and other resources.
- Fracture assessment and analysis, fracturability evaluation, fracture systems modeling, microseismic.
- Advanced borehole imaging, new electrical imaging technology, video logging, imaging through mud and fluids.
- Seismic in downhole geology, virtual source seismic, downhole passive seismic, seismic while drilling.
- Developments in neutron tools and spectroscopy, low-field NMR, new ways of detecting and evaluating porosity and permeability levels.
And you could throw in advances in petrophysics, the growing importance of geochemical analysis downhole, plus developments in computing power and software.
It's been an interesting decade.
Not the least because of unconventionals, pushing forward advances in drilling and fracturing. The industry has gone from marveling at the ability to geosteer a short lateral wellbore to not thinking twice about today's 5,000- or 10,000-foot steered laterals.
AAPG member Jason Pitcher is global well placement solutions champion for the Sperry Drilling product service line of Halliburton in Houston.
“Ten years ago, if you had asked me what was the limit for staying in a formation and not going out of it, I would have said about 20 to 25 feet,” he said.
Today, “we’ll put a 10,000-foot (lateral) well in a 15-foot-thick or less section,” he noted.
Improvements in downhole tools helped make that possible – and Pitcher said improved density imaging tools developed first.
“We’ve been able to map the density changes in a 3-D picture around the wellbore, which conventional tools just weren’t able to do,” he said.
Two types of azimuthal tools also provide important information, Pitcher noted. One is the azimuthal resistivity tool.
“The other kind of tools is the azimuthal deep imaging tools,” he continued. “Before the advent of those tools, if I was drilling along in a reservoir and came to changing resistivity, I couldn’t have told you if I was at the top of the formation or the bottom.”
These new and advanced tools were developed to address specific needs and are less about replacing the traditional triple-combo than capturing additional information.
“In the past 10 years there has been an accelerating focus on LWD tools that are less about replacing wireline data,” Pitcher observed.
“The industry has been very focused on tools that add value for the clients by giving them better placement,” he said. “We’re seeing things now that 10 years ago we had no idea would come along.”
In downhole geology assessment, “we’re finding new ways to use old tools,” Pitcher said. An example is use of a sonic tool to place wells for effective hydraulic fracture stimulation.
“Looking forward,” Pitcher predicted, “an area that’s going to get a great deal more attention is seismic while drilling.
“I can look to the side very effectively,” he added. “What I can’t see very well is ahead of the bit. Ahead-of-the-bit technology is really about seismic.”
While shale gas and ultra-deepwater were the dominant exploration stories in the U.S. during the past 10 years, downhole geology saw advances in many areas with few major breakthroughs.
AAPG member Laird Thompson is an adjunct professor at Utah State University and a researcher in Auburn, Calif. He spent 30 years in research at Mobil earlier in his career.
“I don’t really see anybody these days doing a huge job of pushing the envelope, like was done from the mid-1970s through the 1980s,” Thompson said.
“There’s incremental movement and there’s radical movement, and I think it’s been incremental movement,” he noted.
Those incremental moves forward have improved not only the quality of borehole imaging but also the industry’s capabilities in obtaining downhole images.
“The most recent advances in borehole imaging in the past 10 years probably have been in getting better images for mud-filled holes, because oil-based muds are always a problem for the imaging tools,” Thompon said.
In his view, the lack of direct investment of time and money in fundamental research has hurt the industry’s ability to develop breakthrough tools.
“It used to be that all the majors had their own research labs. There’s almost nobody left in the oil patch that’s doing these things. For the service companies, their driver isn’t science. It’s economics,” he observed.
Thompson also believes the industry under-utilizes borehole imaging data, even when companies go out of their way to get downhole imaging.
“I think that image logs are the most under-used data sets in the industry,” Thompson observed.
Operators let service companies acquire and interpret the borehole image data, but the results are not mined for additional information or data efficiency, he noted.
“They get the quick answer,” he said, “and put $100,000 worth of image data on the shelf.”
Let’s Get Small
A future area for downhole development is microseismic, Thompson said. It’s not technically a downhole application, but microseismic does capture information about what goes on downhole.
Most downhole tools start at the wellbore and just beyond, with an expansion of measurements into the larger formation.
“Microseismic comes at it from the other end, using a surface array or a combination surface-downhole array, where you’re going from the large rock picture down to the small,” Thompson said.
The difference in measurement and detection scale among the various types of downhole tools makes combining the results a tricky challenge, he noted.
“With all logging tools you have to be aware of the volume of rock you’re investigating, so you can do this consistently,” he said.
There’s also a difference in the relative coarseness or fineness of information detail captured by downhole tools.
“To rectify those things and combine them coherently, that’s an area that could stand further investigation,” Thompson stated.
Today, many researchers and downhole specialists see the fully integrated combination of seismic data, logging data and other downhole information as the next big challenge in downhole geology.
Thompson said the goal is “a fully holistic, integrated, 3-D model” of the subsurface.
“One of the things we were working on at Mobil was in terms of trying to integrate the different kinds of logging information on the same scale,” Thompson recalled.
“I won’t say it’s the Holy Grail,” he said, “but it’s an extremely useful exercise.”