The Trenton-Black River (TBR for short) is a deep oil and natural gas formation found underneath New York State and stretching to the southwest as far as West Virginia. In New York the TBR has gas-rich pockets that lay under the Utica shale in western New York and parts of the Southern Tier of the State. The Finger Lakes district is its most productive area. There is also potential for TBR in Kentucky, West Virginia, Ohio, Michigan and as far north as the Saint Lawrence Lowlands in the Province of Quebec, Canada.
From a geologic standpoint, TBR consists of two distinct sedimentary layers of limestone--Black River, a carbonate layer overlain by the Trenton formation, a clay-limestone or cement rock, e.g. argillaceous limestone. Historically, the former is formed in shallow waters, and the latter in much deeper ones.
In the pay zones of this play, the Black River carbonate tends to be partially replaced by magnesium, or dolomitized by hot flows of magnesium-rich water flowing up through faults or fracture systems from a heat source below.
TBR consists of large pockets of natural gas from 7,000 to 11,800 feet deep, but averaging around 10,000; that is approximately two miles below the surface. The gas occurs in long narrow structures. These can be up to 10 miles long and 1/2 mile wide typically in places where the native limestone in the Black River formation has, through faulting, been replaced with hydrothermal dolomite. These structures are readily visible on 2D and 3D seismic. Seismic markers for natural gas deposits include:
- Depressions over the dolomitized area.
- Vertical displacement in the basement surface.
- Any change in the nature of seismic data within a dolomitized region.
Reservoirs typically are bounded by impervious limestones. Lows or slumps in the seismic can indicate a dolomitized zone.
The porosity of these structures is quite variable. On a statistical basis, horizontal drilling can increase the production and reserves of TBR reservoirs by traversing from the lower porosity to the higher porosity sections of the deposit.
Drilling hotspots in the Trenton-Black River include:
- Chautauqua County, New York
- Chemung County, New York
- Steuben County, New York
- Saint Lawrence Lowlands, Quebec, Canada
- Hillsdale County, Michigan (oil)
- Roane County, West Virginia
For example in Steuben County the formation has been under development for many years. The majority of drilling in the deposit is near Corning and Caton, New York.
In New York State, annual TBR production has grown from 1.6 bcf in 1998 to over 40 bcf/year between 2005 and 2007. By 2008, production receded somewhat to 34.8 bcf/year. In that year, 100 TBR wells produced 69% of the State's total natural gas production. That came from only 100 wells with one very prolific TBR well alone producing roughly 2 bcf/year.