Part 2: Making an Energy Map
Unlike WPX’s Niobrara Shale discovery in the Piceance Basin – which is made up of pelletal argillaceous mudstone – the material in our Gallup Sandstone discovery is what our scientists call “a bioturbated shaly sandstone reservoir.”
Both formations were deposited in part of the same Cretaceous Western Interior Seaway formed a long time ago, says Sophie Berglund, a geoscientist on WPX’s exploration team in Denver.
“While the Niobrara was deposited in an offshore setting, the Gallup Sandstone area was deposited closer to the shoreline, so it’s sandier and more permeable,” Berglund says.
“The higher permeability is a good thing – oil is comprised of larger molecules than gas, so in order for oil to flow from a reservoir it must be relatively permeable.”
Still, the challenge of the Gallup Sandstone discovery was to find that perfect spot since many oil pockets have already been produced through the years.
WPX studied the geology and evaluated the broad scale stratigraphic framework of the basin to understand what the conditions were when the sandstones were deposited, and ultimately to find favorable reservoir characteristics.
“We ran some specialty logs in the pilot holes to help us get an idea of what interval would best produce from a horizontal well,” says Geology Team Leader Amy Richardson.
“We looked at a lot of well data – what had been tested and what produced in vertical wells – then tried to characterize that area by thickness, porosity and saturation levels. The big thing is that we were looking at this from a horizontal standpoint now.”
WPX professionals studied core samples from the area, which are cylindrical samples of the rock used to analyze the mineral composition of the earth, thousands of feet underground.
“Our first concept was to examine the main sand bodies, which were mature fields that had been developed using vertical wellbores. We wondered if there were thin “halos” of sand surrounding the main fields that could be accessed horizontally,” Berglund says.
“But we realized that wasn’t going to produce economic quantities of oil, so we continued to evaluate other ideas.”
A gut feeling
After more research and good instincts, the exploration staff found the prize they were looking for in WPX’s lease area: an untapped regionally continuous oil reservoir.
Past operators hadn’t developed the reservoir across a large area based on historical logs and other indicators, Berglund says. “So we incorporated data from many townships to make regional maps of the Gallup.”
Mathematical calculations and petrophysics aside, sometimes it’s that instinct that makes all the difference in a project, especially when you’re looking for something that’s essentially hiding.
“We’d look at the data, compare notes with colleagues, ask for viewpoints from WPX’s experienced technical staff, and discuss the probability of finding oil there. That’s what’s great about this – with experience comes an instinct, too.”
Bob Brooks, Doug Ostby, Craig Knight and Cheryl Poteet were among those who supported the exploratory work.
It takes a multi-disciplinary team of people to discover hydrocarbons according to Steve Natali, senior vice president of exploration.
“With any one discipline missing – from microseismic and reservoir engineering to risk modeling and database management – you have very little likelihood of success,” Steve says.
WPX excels at “getting really creative with challenges,” says Bob Revella, regional vice president. “Through good technical work we’ve ended up in the right places.”
Revella says the asset team’s goal is impressive – producing an exit rate of 3,400 barrels of oil equivalent per day by the end of the year – but they’re up for the challenge.
“Our challenge is very clear, and we’re ready,” he says.
Editor’s note: Stay tuned to wpxenergy.com tomorrow for Part III of our Gallup Sandstone series.