05.07.2009

The slow movement of water through the pore spaces of a solid material

Shale gas is natural gas produced from the fractures, pore spaces and physical matrix of shales. Shale gas plays are considered area plays since shale gas, similar to coal bed methane is often found over large contiguous areas. Most shales have low matrix permeabilities and require the presence of extensive natural fracture systems to sustain commercial gas production rates. In North America, the drilling boom for shale gas got under way after advanced techniques — horizontal drilling combined with hydraulic fracturing — allowed companies to tap gas trapped in huge shale beds that had been out of reach just a decade earlier. Shale fracs however require significant greater quantities of water than sand fracs

Problems with shale gas drilling include: over usage of water which is problematic (very true of China where water is needed for rice growing and using it for shale gas could lead to hunger); fugitive emissions could mean that shale gas is less environmentally friendly than coal; fracking or fracturing has been said to cause problems such as the possibility of small earthquakes (stills needs further study). The geological conditions in China are very different to those in the US in that the reservoirs are believed to be very deep so conditions are very difficult

A sill is rock that has intruded between older layers of sedimentary rock. The sill does not cut across pre-existing rocks in contrast to dikes, which do cut across older rocks. Sills are always parallel to layers of the surrounding rock. Usually they are in a horizontal orientation, although tectonic processes can cause rotation of sills into near vertical orientations.

A technique that stimulates production of a tight formation by setting off charges downhole that crack open the formation.

Sendout capacity is the amount of natural gas a facility can put into the pipeline system a day.

LNG sendout expresses the amount of gas flowing out of LNG terminals into pipelines

A well is shut down when initial drilling ceases for one reason or another

This is the cable that is towed directly behind a survey vessel (2D, 3D). The cable is the listening device and registered signals are fed through the cables and routed to the instrument room of the vessel, where the signals are converted and stored on data tapes for further analyses.

A cable towed behind the vessel conducting the seismic survey and containing hydrophones that record the pressure changes. 2D surveys use a single cable and 3D surveys use up to 12 cables.

In parallel with the registration and data storage, an onboard quality control and preliminary data view is carried out locally onboard by the onboard Geophysicist.

Seismic cables have a slight positive buoyancy and will float to the surface if they are left with no tension in water. The cable has to be balanced to operate at a constant certain depth of 7m below the sea surface; this is achieved by pre-survey adjustments (adding/removing ballast or streamer fluid) and maintained during operations by means of cable control device (cable levelers or birds) positioned typically every 300m along the cables. Ideally, the cables should be towed straight behind the vessel. If this is not possible due to currents and influence by the environment, the streamer may be expected to ’feather’ up to 10 degrees.

Continuous information about how the shape of the cables changes and where they are located are achieved through cable mounted compasses, and GPS receivers on the tail buoys of the cables. A total picture of positions and behavior of the cables are at all times presented on various displays onboard the vessel. Should there be an emergency situation, the crew have the possibility to quickly (10 minutes) dive the cables to safe depth > 20m using the depth controlling birds, This usually has to be done only if there are ships traveling on a collision course with the cables and the crew and the assistant vessel are not able to get in contact with this ship to ask for a change of course.

The substance produced from the treatment of kerogen, that hydrocarbon found in some shales, which is difficult and costly to extract. Shale is a dense rock formation common in many parts around the world which has long been known to contain natural gas. Production, however was impractical when the price of oil was low because the rock is not porous enough for the gas to flow. In the 1990s, however, companies figured out how to crack the shale using pressurized water, thus releasing the gas, with the technique being perfected in the Barnett Shale, a massive shale-gas field around Fort Worth, Texas which produces in 2008 about 4 bcf of natural gas per day. US shale plays could hold as much as 840 trillion cubic feet of gas, the equivalent of more than 140 billion barrels of oil, more than half the proven reserves of Saudi Arabia, but the amounts produced could eventually definitely be lower and production will require billions of dollars of drilling. Limited availability of drilling rigs, oil-field workers and pipelines as well as environmental and regulatory constraints will restrict how fast production will advance. The discovery however of this new source of natural gas has increased production and could change the supply and demand equilibrium