There are roughly 36,000 shale wells in the five major shale basins in the United States that have produced nearly 23 Tcf of natural gas and 682 million barrels of oil and condensate, according to a tally gleaned from state regulatory records by Powell Shale Digest, a weekly newsletter specializing in North American shale news and research.

About half the total number of wells, 17,980, were drilled in the granddaddy Barnett Shale from June 1982 through May 2012, producing nearly 12 Tcf of gas and 40 million barrels of oil.

“The first well in the Barnett, drilled by George Mitchell in 1981, is still producing today for Devon Energy. It’s probably been refracked, but it’s producing and it’s not a stripper well,” said Powell Shale Digest Managing Editor Will Brackett.

The Haynesville Shale in Texas and Louisiana was the next top gas producer with 2,199 wells producing nearly 6 Tcf in a four year (Louisiana) to six year (Texas) period ending in April-May 2012. The Fayetteville Shale in Arkansas produced 2.5 Tcf from 3,730 wells from May 2001 through November 2011. Marcellus Shale production was split between Pennsylvania, which recorded 1.5 Tcf from 2,312 wells in the 2.4 years ending in December 2011 and West Virginia, which produced about 122 Bcf from 1,515 wells from July 2009 through December 2011.

The largest oil and condensate producing shale was the Bakken/Three Forks in North Dakota and Montana with 419 million liquid barrels from 7,374 wells from 1986 through June 2012. Next was the Eagle Ford in Texas with 3,597 wells producing 120.6 million BO/BC in the last seven years ending in May 2012.

Brackett said Shale Digest, which was founded by Michael E. (Gene) Powell Jr. in 2003 as Powell Barnett Shale Newsletter, attempted to put a number on shale production in response to a question from a newspaper in Paris, France. They published their findings in connection with a three-day program focused on shale that Shale Digest developed in the Dallas-Fort Worth area for eight international energy journalists visiting under a U.S. State Department educational program.

Shale Digest made a basic presentation on “Evolution of Shale Plays in the United States.” The international journalists also were briefed by editors from the Dallas Morning News and the Forth Worth Star Telegram.

As to its shale totals, Brackett said the endeavor was “a challenge. We did the best we could with the available records and think we achieved a reasonable degree of accuracy.” Shale Digest gleaned the data from state regulatory records, which have been maintained for various time periods with various methodologies and with varied consistency. It helped that he has a staff well-versed in shale and able to read some of the more obscure tea leaves, but in the end “it’s just an estimate.”

Brackett said state record-keeping is improving, partly because so many people are asking them for information. “Pennsylvania now updates its wells every six months. It used to be every five years.” In earlier times producers feared competition if their wells were identified. Now companies are claiming bragging rights over new wells, finding that reporting results “makes them look good and sell themselves.”

As to future production, Brackett took issue with analysts who see shale wells as heavy producers early on, then quickly heading for stripper well oblivion. As the wells decline, “I think they’ll go back in and frack again. They’re getting — what? — 15-20% of the reserves in place; that could be 50%” with new technology. “They’re not doing it now because they have too much on their plate already, but engineers are working right now to figure out how to go back in and frack again” without destroying the well.