|
Barnett Shale, Shale Gas Plays:
The Barnett Shale is similar in many of its geochemical characteristics to the Antrim, Woodford, and Bakken shales. They are derived from similar depositional environments and organic matter assemblages. Gas shale well productivity varies widely by basin, due to variations in the natural fracturing, richness of the shale, net thickness, and initial rates. The major change has been in well completion and operating methods, which have led to increase per well reserves. Currently, the deep hrizontal (7000'-8000') wells with 2000'plus legs in the Barnett shale are the most prolific, showing initial daily production rates of 1,500-2,500 Million CFPD.
The Antrim Shale is an organic-rich, black shale deposited during the Devonian and Mississippian ages in an area of approximately 30,000 square miles of Michigan and northern Indiana. The shale is found at depths ranging from 1,000' - 2,000'. Antrim's gas in place equals to 10 - 20 BCF/square mile and initial flow rates of 100-200 MCFPD. There have been over 7,000 wells drilled in the Antrim play.
In comparison,the Barnett Shale is an organic-rich, black shale of a thick deposit of Mississippian age strata. Because the shale has considerable thickness, the resource concentration is high, on the order of 25 ~ 40 BCF/square mile with some estimates of 80 BCF long term, and initial flow rates of 1,500 - 2,500 MCFPD. The retention of hydrocarbons in the Barnett is due to its high carbon content and lithofacies. Various maturity levels can be mapped across the Barnett area using a kerogen decomposition model that accurately describes dry gas, wet gas, light oil, and heavy oil generation.
The presence of gas in the other zones such as the conglomerate gives secondary target potential along with the caddo and marble falls/forrestberg limes.
.
The most prospective areas are where the Barnett rests on the Viola or Simpson rock formation. Horizontal drilling and completions have mitigated the Ellenburger absent the viola limestone risk, in areas where the aquifer becomes a problem. The organic-rich shale is a reservoir target of over 40 BCF/square mile in place.
Regional Setting:
During the collision of the North American and the South American/North African tectonic plates, the Fort Worth Basin formed and remained a subsiding basin throughout the development of the super-continent called Pangaea. The Barnett Shale was one of the sediment deposits in this basin. The extreme eastern margin of the Fort Worth Basin is obscured by metamorphic, overthrust rocks of the Ouachita foldbelt. This orogeny was initiated in Late Mississippian time and is approximately contemporaneous with the deposition of the Barnett Shale. The sea inundated this shelf area and the southern Oklahoma aulacogen.
The dark organic muds and a few thin limestones of the Barnett were depositied along this adjacent shelf area to the aulacogen. The shale thickens to the northeast and east toward the aulacogen. Note the project area is on regional depositional strike with the Newark, East Field in Wise/Denton area.
:
Increased drilling in the Barnett Shale has been spurred by a reduction in completion cost as a result of using light sand water fracs, good gas prices, and multiple refracing opportunities of productive zones. Recent horizontal drilling of the tight gas shale is testing the limits of the field area and is expected to continue. The testing of the Barnett Shale in these areas could open up the potential of large reserves. These formations have a high potential for producible hydrocarbons at relatively lower risk to other drilling areas.
Rick Boyle, President, Boyle Oil Corp.
mail contact
|
