Monday, March 15, 2010

Drilling Down Deep Over Offshore Oil.

The Economist has published an excellent article (link below) on the subject of deep-sea drilling. The first offshore oil well completely out of sight of land was drilled in 1947, 17 km off the Louisiana coast in the Gulf of Mexico. The platform of the drilling rig was no larger than a tennis court and was supplemented by several refurbished naval barges remaining from WWII which provided both space for storage and for the crew to sleep. The seabed was a mere 15 feet below, but now far greater depths of water are being fathomed.

In 2008, Shell's 22,000 tonne Perdido spar was towed from Finland where it was constructed to a spot 320 km off the coast of Texas, where it was chained to the seabed 2,400 metres below. This is connected to subsea wells in yet deeper water at 2,900 metres. Such offshore drilling operations are attended with daunting physical challenges. Since a longer and heavier drill string is required in deeper water, the supporting platform must be more heavily engineered. The interlocking sections of pipe are heavy, at around 30 kg/metre.

Since conventional onshore oil is held in countries that are unstable in regard to their political amenability to the West, offshore drilling is forcing private companies to look for oil further afield, in more inhospitable locations, and increasingly in deep water. The pressure of water increases by one atmosphere for each 10 meters of depth, and at almost 3 km, is close to 300 times normal atmospheric pressure, or around 4,500 pounds (2 tonnes) per square inch. The consequent pressure on the seafloor makes it more difficult to pump the oil up to the surface.

Hitting the right spot is a feat in its own right, and Robin Walker, of the oil-services company WesternGeco, uses the following analogy. "Imagine a large offshore oil rig as a matchbox. Next, imagine the matchbox on top of a two-storey building, with the upper floor filled with water and the lower floor filled with rock, sand and, in some cases, salt. Striking an oil reservoir with a drill pipe is then like hitting a coin at the base of the building with a strand of human hair." If the hit is in the wrong place, the costs are enormous, and an industry rule of thumb is that drilling a deepwater "dry hole" - a well with no oil - is around $100 million. BP says it can be as much as $200 million.

To avoid any errors, complex geophysical measurements are necessary including multi-dimensional seismic imaging, where a rough 3-D image is created of the subsurface rocks. Despite the difficulties, a number off major deepwater finds have been identified recently: Tupi, off the coast of Rio de Janieiro is thought to hold 8 billion barrels of oil, but this lies underneath 2,000 metres of water, 3,000 metres of sand and rock and a 2,000 metre layer of salt. Other "ultra-deepwater" discoveries, defined as those under 1,500 metres or more of water, have been made off the coasts of Angola, Sierra Leone and Nigeria, along with several more in the Gulf of Mexico.

Obtaining images of commingled salt and rock poses difficulties because the waves emitted from seismic sources travel faster through salt than in rock. When there is a mixture of reflected and refracted waves present, constructing an image of the subsurface from a normal sonar survey is not readily accomplished. Thus, rather than collecting seismic data in two dimensions, using streamers and them using computational processing to get a 3-D image, an actual 3-D data acquisition was done, using hydrophones and multiple seismic sources from three of four vessels moving in parallel, called a "wide-azimuth" survey. The accuracy can be honed further by passing over the same region a number of times from different angles ("multi-azimuth" survey).

The greatest challenge, however, is processing the data. When the surveys indicate there is a high probability that oil is down there, an exploratory well is drilled. This involves pumping a liquid called "mud" through the drill string to remove borehole cuttings and to cool the drill-bit and maintain pressure at the base of the well. As the drill cuts through the rock and sand under the seabed, the pressure of the "mud" in the drill must be kept within defined limits: if it is too low, the pressure of underground fluids and gases ("pore pressure") on the well wall will drive it to collapse, but if it is too high, the mud can accentuate and expand existing fractures in the surrounding rock which causes a loss in circulation as the mud leaks out into the newly formed fissures.

This is a simple overview, but all in all, the discovery and successful production of oil from these reservoirs offshore will depend on continual advances in technology and computation.

Related Reading.
"Plumbing the Depths."

Saturday, March 13, 2010

Coffee-Powered Car Does What it Says on the Tin.

When I heard of a coffee-powered car I envisaged the tank being filled with the liquid beverage from a cafetiere. This is not what is meant, however, and the fuel is ground coffee combusted in a fluidised bed as a form of biomass. "Why choose coffee?" you might ask. However, a BBC presenter was left stranded on the M1 when Britain's first coffee-powered car broke down there. It was intended that the car would make a 210 mile journey from London to Manchester, but it ground to a halt outside Birmingham. The vehicle in fact broke down four times, which delayed the journey while the engine was cleaned.

The car was a modified 1988 Volkswagon Sirocco that had been intended to be scrapped, and it is said it ran on the equivalent of 10,000 espressos, rated that at 1 mile on 56 espressos giving it a maximum speed of 60 miles per hour. There is no need for criticism, however, since the aim of the project was to raise awareness about the use of energy as demonstrated by the car, which has been dubbed "car-puccino". Ouch!

The stunt is part of The Big Bang: Young Scientists and Engineers Fair, in Manchester. This is on through March 11th - 13th and there are over 15,000 students between the ages of 9 and 19 registered to attend it, so far. The BBC programme Bang Goes the Theory will present its roadshow at the fair, of which an episode is to be broadcast on May 3rd entitled "Car-puccino".

I applaud all means to raise awareness about the issues and practicalities of energy, especially to the up and coming generation, and to coin a modern expression the coffee-powered car has thus "done what it says on the tin".

Related Reading.
"Bang goes the theory! TV presenter stranded on M1 when coffee-powered car runs out of caffeine."

Friday, March 12, 2010

Mining for Gas may Set-Off Earthquakes.

It is concluded that a "plausible cause" of a series of small earthquakes in Texas during 2008 - 2009 is saltwater pumped deep into the earth to recover natural gas, though this explanation is not definitive. In a process known as "hydraulic fracturing", shale layers are cracked by injecting water mixed with sand under high pressure, in order to liberate trapped natural gas. According to the USGS (United States Geological Survey), there may be 200 trillion cubic feet of gas trapped in shale across America.

Seismologist, Brian Slump of the Southern Methodist University, analysed data from 11 earthquakes and by a process of triangulation managed to place the origin to around one tenth of a mile south of Dallas-Fort Worth airport, on top of a geological fault located about 15,000 feet below the surface. Slump commented that although this is an old fault, stresses upon it remain that could trigger earthquakes.

Since 2002, 13 fracture wells have been drilled in proximity to it, but the study led by Slump found that the epicentre is almost exactly on the point of a reinjection well into which 9,000 barrels of seawater/day were pumped at a depth of 10,000 - 14,000 feet. The saline "flowback" water was then pumped to the surface and disposed of by injecting it into deep rock formations, in order to avoid further treatment.

Caution has been advised by Shaopeng Huang, from Michigan University, who said that: "a causal link between a given earthquake with a particular borehole is debatable," considering the huge amount of energy implicit in even small quakes. Slump stresses that his team are saying merely that such a link is "plausible not definitive", while noting that since the cessation of saltwater injection following a third set of tremors in June, the quakes have stopped.

I am reminded of a Swiss Geothermal energy project, in which the injection of water into naturally hot rock to recover heat, also caused quakes. Evidently, one should proceed with some trepidation in mixing geology with water that is not naturally part of it.

Related Reading.
"Texas earthquakes may be linked to wells for gas mining," By Dan Vergano, USA Today.

Thursday, March 11, 2010

Shell and PetroChina Bid for Australian Coal-Seam Gas Reserves.

Arrow Energy, the owner of the biggest reserves of gas trapped in seams of Australian coal, has been offered £2 billion by Royal Dutch Shell and PetroChina. The gas, principally methane, is a cleaner fuel than either coal or oil and has a much higher calorific output per unit mass at 57 GJ/tonne, compared with around 29 GJ/tonne for anthracitic coal and 42 GJ/tonne for oil. Shares for Arrow are up by around 50% on the Sydney Stock Exchange, promoted by the expectation of a higher bid from the two giants.

Arrow Energy also owns the Fisherman's Landing liquefied natural gas project in Queensland, one of ten of its type in Australia, and the Territorial government has predicted around 50 billion Australian Dollars in investment as a global competition ensues among companies keen to export the fuel to growing markets in Asia.

China has announced its intention to increase the use of gas as a fuel three-fold to provide around 10% of its total energy by 2020, as part of an aim to curb its use of coal. PetroChina is the greatest producer of oil and gas in China, and its CEO has said that it will make efforts to increase its holdings of liquid natural gas, including that derived from gas physically trapped in coal.

A Shanghai-based energy analyst, Shi Yan is quoted as saying: "It appears that this bid is in its early stages, but it's part of China's efforts to sure supply." And this is true of all sources of energy, in nations across the world.

Related Reading.
"Shell and PetroChina swoop on Arrow Energy for its gas reserves."