As pioneering shale gas plays and tight oil formations mature and decline in production, operators are trying to find emerging formations and resources to replace them, enabling continued growth in US production. While the industry will continue identifying new domestic unconventional shale and tight sand resources, an expert said that the methods of discovery may differ from traditional approaches.
At the 2017 SPE/AAPG/SEG Unconventional Resources Technology Conference (URTeC), Vello Kuuskraa discussed the alternative pathways companies may take to discover unconventional resources while maximizing existing plays in the near future. Kuuskraa is president of Advanced Resources International.
Kuuskraa’s presentation focused on three such pathways. He defined the first, “Looking in Your Own Backyard,” as the search for additional productive horizons in existing basins, either above or below already developed target formations. An example of such a strategy is the Meramec formation, located approximately 1,000 ft above the Cana-Woodford Shale in the northern portion of the Anadarko Basin.
In 2008, a small group of operators began exploring the formation, completing 22 horizontal wells over a 4-year period while also drilling deeper for the Woodford Shale. The Meramec has now emerged as an attractive shale play for operators. The play has doubled in size, from approximately 1,300 mi2 to more than 3,000 mi2, with hydrocarbon windows ranging from deep dry gas in the western part of the play to shallower volatile oil in the east. Kuuskraa said that the economics of the area have benefited from the infrastructure already in place from previous operator activity, as well as the geological knowledge gained from assessing the uphole portion of logs drilled for in the Woodford.
“This is a very recent phenomenon,” Kuuskraa said of the Meramec. “Here in 2013, it was viewed as an area with some gas, some condensate, and some oil in a limited type of area. In a matter of 3 to 4 years, this area has become much more complex. It’s beginning to really push the envelope of the oil window, a lower maturity oil window that is recoverable.”
The second pathway, “Turning from Vertical to Horizontal,” involves a change in well design for plays that have already been heavily drilled. Kuuskraa said that verticals have been the well design of choice for decades when developing tight gas sands, particularly in East Texas, West Texas, northern Louisiana, and the Rocky Mountains. The logic behind this strategy was that, given the extensive thickness and layered nature of formations in these regions, only a vertical well would be able to contact enough net pay to make the well economically viable. In recent years, some operators have pursued progressively closer well spacings to promote additional gas recovery in the midst of steadily declining well productivities and reserves.
One such play, the Spraberry tight oil formation in the Midland Basin portion of the greater Permian Basin, saw a drop in the rate of production decline after operators installed horizontal wells in the western core area of the play.
In the prolonged oil price downturn, Kuuskraa said the third pathway, pushing the technology envelope, is critical to maintaining economically viable unconventional development. This could involve the use of longer horizontal laterals, more intensive well completions, increased drilling efficiencies, and lower operating costs. Kuuskraa said advances in technology can lead to lower unit costs and improve resource recovery efficiency, significantly expanding the technically recoverable shale and tight sand resource base.