Barnett spars with Hugoton for top US gas field

Newark East field in North Texas, center of the Mississippian Barnett shale play, was Texas's largest gas-producing field in 2006 and could become the largest in terms of ultimate recovery in the Lower 48.

By OGJ editors
HOUSTON, May 8 -- Newark East field in North Texas, center of the Mississippian Barnett shale play, was Texas's largest gas-producing field in 2006 and could become the largest in terms of ultimate recovery in the Lower 48.

The field ranked third in the nation in reserves, after the entire San Juan basin in New Mexico and Colorado and Pinedale field in the Green River basin in Wyoming, and second in the nation in terms of production after San Juan.

Eleven articles totaling more than 220 pages describe numerous aspects of the Barnett shale formation in the April 2007 issue of the American Association of Petroleum Geologists Bulletin.

One article states, "Several individuals who have worked the Barnett play believe that the greater Newark East field will eventually surpass the Hugoton field of Kansas, Oklahoma, and Texas as the largest onshore gas field in the conterminous US."

The Kansas and Oklahoma portions of Hugoton have produced 35 tcf of gas from two conventional formations and could have another 20 tcf recoverable, a recent study said (OGJ Online, Apr. 27, 2007).

The US Geological Survey in 2004 estimated the Barnett's potential at 26.2 tcf of undiscovered recoverable gas, excluding possible increased recovery as a result of horizontal drilling.

The 26.2 tcf applies to an area of more than 4 million acres. The play is considered to have 3-4 tcf of proved reserves, leading to a total resource of more than 30 tcf as most recently envisioned.

How the play grew
Discovered by the former Mitchell Energy Corp. in 1981 in Wise County, Newark East field attracted the drilling of only 100 wells between 1981 and 1990, wrote David F. Martineau, Pitts Oil Co. LLC, Dallas, in the AAPG lead article.

The field has been divided into the original core area where the Barnett overlies the Ordovician Viola limestone and the expansion area where it sets atop the Ordovician Ellenburger Group. The early drilling was in Wise and Denton counties, and development has now spread to more than 30 counties underlain by the Fort Worth basin and Bend arch.

Federal tax credits that expired in 1993 for gas produced from tight sands and state severance tax relief that continues today helped spur Barnett shale gas development.

Numerous other Barnett shale field names include JMG Mag field in Jack County, Cleburne field in Johnson County, and St. Joe Ridge field in Montague County.
The field(s) had produced 2.3 tcf and was making 2 bcfd of gas as of July 2006, Montague wrote.

Operators completed more than 6,200 wells through September 2006, more than 5,800 wells were on production, and hundreds of others were drilled, completed, or awaiting a pipeline.

Technology advances
The main technology improvements have been shale gas-in-place evaluation, geologic relationships, wellbore designs, and completion techniques, Martineau wrote.

Canister desorption tests in the late 1990s-early 2000s on wells with nearly identical total organic carbon values indicated that gas recovery from the Barnett shale would be more than double what was previously thought. Also, the formation has an above-normal pressure gradient in the core area that reaches 0.54 psi/ft.

Operators have used 3D seismic surveys since 2001 mostly outside the core area where the size and strike of the faults and number and size of karsts are more random.
Mitchell Energy began pursuing the Barnett shale in the early 1980s. The company had a large acreage position in Boonsville (Bend Conglomerate) field, which had produced 1.67 tcf of gas in 30 years. The field's decline left infrastructure that needed a new play to remain economic.

Mitchell produced 1.35 bcf in 24 years from its first 1981 Barnett shale completion, which Martineau described as a "supposedly original noncommercial well."

Vertical drilling was the primary drilling method until 2002. More than 1,900 horizontal wells have been drilled. Hydraulic fracturing advanced through several generations until the onset in 2006 of the "simo-frac," in which an operator simultaneously fracs two parallel horizontal well bores 500-1,000 ft apart.

It remains to be seen whether the Barnett will be economic in areas where it thins to 100-150 ft.

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