Month: July 2009

Transporter who holds himself out to the general public for the transportation of goods (such as gas) over a definite route and according to a regular schedule. Transmission system is a common carrier

An element in a two-part pricing method used in capacity transactions (energy charge is the other element). The capacity tariff is calculated based on the amount of capacity being purchased

The mixing of one producer’s generated supply of electric energy or natural gas with another utility’s generated supply within a transmission system

To turn coal into liquid fuel is a very intensive process requiring much coal, water and a lot of money (the price of a plant is estimated at $4 billion). The coal must be fired up to 1,000 degrees and mixed with water. Then the gas that’s created is transformed into fuel that can be used in cars and jets. To wean the US off of just 1 million barrels of the 21 million barrels of crude oil consumed daily, an estimated 120 million tons of coal would need to be mined each year. In addition, the extensive use of CTL substantially increases carbon emissions

High viscosity liquid product resulting from the carbonization of coal (the heating of coal in the absence of air at temperatures ranging from about 900° to 1,200° C). Many commercially important compounds are derived from coal tar. Low-temperature tars result when coal, peat, lignite, or wood are carbonized at temperatures not exceeding 700° C

The primary energy source of natural gas is a substance called methane (CH4). Coal bed methane (CBM) is simply methane found in coal seams. It is produced by non-traditional means, and therefore, while it is sold and used the same as traditional natural gas, its production is very different. CBM is generated either from a biological process as a result of microbial action or from a thermal process as a result of increasing heat with depth of the coal.

CSG is methane gas that is trapped in coal deposits; it is a natural gas formed as a by-product during the coalification process whereby organic matter is turned into coal. To extract the gas a hole is drilled down into the coal seam and is cased. The coal seam is perforated which then enables the gas to flow to the surface, where it is gathered and processed as required. Unlike conventional natural gas reservoirs, where gas is trapped in the pores or void spaces of a rock such as sandstone or limestone, methane trapped in coal is adsorbed onto the coal surface (cleats and joints) or micropores and held in place by reservoir and (water) pressure. Hence the coal is the source and the reservoir for the methane. To extract the CSG wells are drilled into the coal seams – the water is pumped out and the CSG is then released (desorbed) from the coal. If the pressure within the seam is high enough the gas may flow to the surface unaided, if not the gas must be pumped. Various techniques have been developed to enhance the rate of desorbtion, including the pumping of carbon dioxide underground to increase field pressure (which leads some CSG promoters to describe it as a form of “clean coal”). Like shale gas, seam gas is often called unconventional gas. In the past though this gas was viewed as more of a hazard to miners than a benefit. The micropore surface area of coal is very large, and can potentially hold significantly more methane per unit volume than most conventional reservoirs. The amount of gas trapped in the coal is a function of coal rank, pressure and temperature. Coal generally has lower permeabilities than conventional reservoirs so the rates of production are usually lower. In order to achieve optimal production rates, one method used is to stimulate the coal reservoirs by hydraulic fracturing. Newer drilling techniques like surface to in-seam (SIS) make fracturing unnecessary and also increase productivity. CSG is naturally an odorless gas that is used just like any other form of conventional gas

In order to produce CSG, a well is typically drilled to a depth of between 500m–1,000m to intersect the gas bearing coal seams. Steel casing is cemented into the well bore to isolate the hole from all surrounding stratigraphy and to seal it from the surrounding environment. The casing is then perforated at the depth of the coal seam, to further isolate the gas extraction zone. Hydraulic fracture stimulation is where a sand and water mixture is pumped into the coal seam through the perforations at the target zone at high pressure until the coal structurally cracks. Fractures propagate horizontally from the well bore, typically in two directions. These fractures, deep in the coal seam, have no effect on the ground surface. The injected sand is used as a proppant to prevent the fractures from fully closing. Essentially the sand is squashed by the coal seam and the sand in the coal establishes a porous pathway, enabling previously trapped gas to flow into the well bore. After the fracture stimulation, a work-over rig installs production tubing in the well, a pump (if required) and surface facilities (well head, piping and instrumentation, etc). The water pump may be required for a short time to extract excess water from the coal seam. The gas extracted from a completed well that is in production flows through a gathering line network, under its own pressure. Gas production is dependent on many factors. These typically include the thickness of coal gas content, permeability (ability for the gas to flow), depth of the coal seam and purity of the gas. CSG is typically found at depths ranging between 400m – 1,000m. These shallower depths make it possible to use smaller, more mobile, truck-mounted drilling rigs than those used for conventional gas. This reduces the surface foot print of the activity and improves exploration cost efficiencies.