FORT WORTH, Texas -- Advances in technology have transformed the Spraberry/Wolfcamp fields in the Delaware Basin of West Texas — once dismissed as the most uneconomic oil field in the U.S — to the most active stacked fields in the country, an oil industry executive said recently.

Scott Sheffield, chairman and chief executive of Pioneer Natural Resources Co. (NYSE: PXD), told attendees at the recent DUG Permian Basin conference in Fort Worth, Texas, that the field is undergoing an important renaissance, but its future was not always that rosy.

Activity in the region dates to 1943, when oil was found from an unnamed formation drilled from a farm owned by Abner Spraberry in Dawson County, Texas. The formation was named in his honor and production soon flowed. By 1951, Time magazine declared it the most active field in the U.S. Two years later, however, production dropped off precipitously and it was declared the most uneconomic oil field in the country. The Texas Railroad Commission shut the field in for several months, Sheffield said.

The majors dominated exploration and production in the 1950s, primarily Texaco, Phillips 66 and Mobil. By the 1990s, the independents had become the dominant players in the two fields. A typical Spraberry/Wolfcamp well in the Midland Basin has about 70% to 75% oil and about 15% from gas.

The formation has multiple layers of shales with high total organic content, each about 250 to 500 feet thick. The technology that allows producers to draw oil from shale has led to its latest renaissance, Sheffield said.

Today the Spraberry and the underlying Wolfcamp, located in the Midland Basin of the Permian, are the two most active fields in the U.S. by rig count, 264, according to figures from Baker Hughes.

Pioneer Natural Resources (NYSE: PXD) is third largest oil producer in Texas. It has about 900,000 acres in the Spraberry/Wolfcamp formations, where it is the largest producer and acreage holder. It currently has with 24 rigs operating (nine horizontal and 15 vertical) and 7,000 producing wells.

Pioneer is currently producing 89,000 barrels of oil equivalent (BOE) per day from the Spraberry/Wolfcamp. Other operators in the Spraberry/Wolfcamp include Apache Corp. (NYSE: APA), Concho Resources Inc. (NYSE: CXO), Endeavor International Corp. (NYSE: END), Laredo Petroleum Inc. (NYSE: LPI), Fasken, EOG Resources Inc. (NYSE: EOG), Crownquest Operating LLC, Energen and Linn Energy (NYSE: LINE).

The two plays are estimated to have recoverable reserves in the range of 50 billion BOE, making it the largest in the U.S. and the second largest in the world, only trailing the Ghawar Field in Saudi Arabia, Sheffield said.

Overall production from the two plays fluctuated between 50,000 bbl per day to 100,000 bbl per day from 1956 through 2009, when the production began to spike dramatically as operators learned how to tap into the shale reserves in the formations. From 2009 to 2012, the number of vertical wells rose abruptly and production rose to around 450,000 bbl per day. Since 2012, the increase in production was driven by horizontal activity.

The Spraberry/Wolfcamp horizontal growth trajectory is similar to the Bakken and Eagle Ford, although it is earlier in its growth phase. Today, the increase in production is driven largely by horizontal wells. The horizontal wells were only 4% of the total in the region only two years ago. Today, about 23% of the wells are horizontal, and Sheffield predicted that in the next three to five years about half of the rigs in the region will be horizontal.

“The vertical rigs will continue to decline as we open up more and more intervals. At some point in time there will be very little vertical drilling in the Spraberry Trend field,” Sheffield said.

“There is a huge potential for that (region) moving forward,” he said. Production could grow to as much as 2.5 million BOE per day by 2033 if well activity increases from 60 horizontal rigs in 2013 to about 170 per year in 2013 and thereafter.

Pioneer Natural Resources is based in Irving, Texas.