The Oil Beneath the Oil
At its peak in 1972, the Texas oil industry produced about 3,000,000 barrels per day
There’s oil, deep in West Texas’ Permian Basin — and plenty of it. After nearly 90 years of production, most of the basin’s oil remains in the ground.
“Traditionally, you get between 20 and 40 percent of the oil in a reservoir, depending on the type of rock that surrounds it,” says Chip Groat, a professor of Geological Sciences at the University of Texas at Austin.
University of Texas at Austin
Much of the basin’s remaining oil, however, lies in residual oil zones (ROZs). These pools of oil lie beneath primary production zones, often separated from them by rock or brine reservoirs.
But Texans are reaching for that untouched crude. With a U.S. Department of Energy grant of nearly $1.2 million, scientists and students from the University of Texas of the Permian Basin (UTPB) are leading research into the use of enhanced oil recovery, or EOR, in residual oil zones. The most recent grant is the third UTPB has received for its oil recovery research.
The state’s signature type of crude oil, known as West Texas Intermediate (WTI), remains the major benchmark of crude oil in the Americas.
“In the Permian Basin, we have primary oil production everywhere from 2,000 feet down to 15,000 feet,” says Bob Trentham, director of UTPB’s Center for Energy and Economic Diversification. “What we don’t know is how deep we can recover oil, because there isn’t much data on residual oil zones.”
Texas Oil Facts
Texas has more than
Texas has more than
of the nation’s
petroleum refining capacity,
at more than
barrels of oil per day
The Lone Star State
Barrels of oil each month,
of all U.S. production
Source: U.S. Energy Information Administration
The Texas oil and natural gas industry employs an estimated 243,000 people.
Flooding the Zone
EOR includes various techniques that can wring more oil out of a mature production area. The most common type of EOR used in the Permian Basin is CO2 injection, a proven technology dating back almost 40 years.
As oil is produced, the pressure within the reservoir drops, making it more difficult for the remaining oil to flow toward the well. CO2 injection floods the reservoir with the gas to repressurize it, encouraging further oil production. (See sidebar for more on oil recovery techniques.)
To better understand how EOR techniques could recover oil in a residual zone, researchers first have to understand how it got there.
“That’s where we are right now with ROZs,” Trentham says. “We need to understand them better and that’s what this grant will help us do.”
UTPB researchers, along with corporate partners Legado Resources and Melzer Consulting, will focus on developing ROZ data on a specific oilfield to build a better understanding of how to pull oil from it.
“We know the ROZ is there,” Trentham says. “With data donated by our corporate partners, we can develop a picture of what the ROZ looks like, its characteristics, how it might flood better — all the things we need to know before we go blindly ahead and try to pull oil from it. CO2 flooding has doubled the potential size of the recovery prize in the residual zones.”
Old Oilfields, Like New
Reaching ROZs could greatly increase our estimates of oil reserves. Traditionally, when oil is discovered and the field is studied, producers estimate both the amount of oil “in place” and the recoverable amount, says UT-Austin’s Groat.
“When a field is analyzed, you say we have ‘X’ million barrels in place,” Groat says. “Reserves are the part that can be recovered using standard techniques. The rest of that oil in place is not considered part of the reserve because you can’t get it out. If new techniques allow us to get to it, then it becomes part of the proven reserves. And it wouldn’t be a new oil find. It’d just be old oil recovered more efficiently.”
Adding to those reserves — and potentially lessening U.S. dependence on foreign oil — are among Trentham’s goals. And the latest grant will help make it happen.
“We believe that we are the model for the rest of the country as far as how this should be done,” he says. “There’s huge potential for the Permian Basin as well as basins nationwide.” FN
Keep it Pumping
Pumping crude oil from the ground is done in three ways:
- Primary — When an oil field is first tapped, gravity or the reservoir’s natural pressure pushes oil to the well. Pumps and other implements can help bring oil to the surface. Typically, primary recovery can pull 10 to 20 percent of the oil from a field.
- Secondary — Over time, the original pressure in a primary zone subsides and production slows. Typically, water or gas is then injected into the oil field to drive oil to the well. In the case of water, however, the more that is pumped into a field, the more comes up with the oil, which leads to less recovered oil. Secondary production can claim an additional 10 to 30 percent of a field’s available oil.
- Tertiary — This type of recovery can include using CO2, chemical or thermal injection to recover oil. It has been used in primary oil zones for years, but is now being explored as an option in developing residual oil zones. It is costly, however, and CO2 in Texas is a “highly sought after commodity, not a waste product,” says UTPB’s Bob Trentham. Tertiary recovery can ultimately pull 30 to 60 percent of the original oil from a field.
UTPB provides a variety of residual oil zone materials, including symposium discussion presentations and notes, Permian Basin maps and more.