“Yessir!” says David Ruffin as he takes yet another question about the drilling process on the busy well-pad in the Pinedale Anticline natural gas field in the US state of Wyoming.
While the industry has a reputation of attracting tough, hard men who, in movies at least, communicate mostly in sharp, blunt, exchanges, Ruffin – a tall, imposing figure in blue denim jeans and the mandatory hard hat – is unfailingly polite.
He is energy multinational Shell’s on-site supervisor at the Mesa 5-26 well-pad, which is among scores that dot the rich Pinedale Anticline gas field in Sublette County in the west-central part of the prairie state.
It is expertise like his that will have to be imported to South Africa should our government – in the face of vehement opposition from a substantial body of locals – sanction shale gas exploration and exploitation in the Karoo.
There are fundamental differences between the western region of Wyoming and the Karoo, notably relating to the key issue of water.
The prairie is also arid with a low annual rainfall but, because of the snow-covered surrounding mountain ranges and the presence of sufficient groundwater, water availability was not listed as one of the nine key concerns about the Pinedale Anticline gas field (although its impact on both surface and groundwater is).
Also, although the prairie looks superficially similar to the Karoo, it is not as biologically diverse – and particularly the Succulent Karoo which is one of the world’s biodiversity “hotspots”.
Another difference is that fracking (hydraulic fracturing) in Wyoming is done in vertical wells, whereas the Karoo proposal is for horizontal fracking. This is because the US operation taps gas from what is called a discontinuous reservoir sandstone, or “tight sands”, formation that, in cross-section, can be likened to a bag of chips, requiring vertical directional drilling.
Until fairly recently, the Pinedale Anticline project area of about 250km² was the third largest natural gas field in the US. But with this booming industry chasing new discoveries, it now probably ranks “only” in the top five, with reserves estimated at some 40 trillion cubic feet, of which 20-to-25 trillion is recoverable. This could provide enough energy to power 10 million homes for 30 years.
It’s much smaller but proportionately more productive neighbour, the Jonah gas field to the south, ranks seventh and is estimated to contain 10.5 trillion cubic feet of natural gas in its productive area of just 85km².
The Pinedale Anticline gas field was discovered in 1938 and unsuccessful attempts were made to exploit it over the next decades – including a proposal to use nuclear devices – before drilling started in earnest in the early 21st century.
Gas exploration and exploitation in the US is managed in terms of a 2008 environmental Record of Decision by the federal Bureau of Land Management, also the major landowner with close to 80% of the surface areas of the field. To date, some 1 700 individual wells have been drilled of which just over 400 are Shell’s – the smallest share of the three lessees that exploit this field. But the wells of the energy giant alone produce some 12.7 million cubic metres of gas a day.
Clusters of wells are consolidated in drill pads which can contain as many as 64 wells. This reduces the required infrastructure like roads and the environmental footprint of the drilling which is done with mobile diesel-electric-powered rigs operated by a sub-contracting company.
Ruffin explains that a well is begun with a 50cm conductor pipe inserted to a depth of about 30m. Then a different rig is brought in to drill a 28cm-wide hole into which a steel casing is inserted, to a depth of 750m. This is followed by an 21cm intermediate hole lined with 17cm casing to 2 450m, and the final, deep production, section below that – up to 4 300m – is a 15cm hole with 11cm steel casing.
Cement is pumped between the well wall and the casing to enforce the seal, and wells are pressure-tested to ensure integrity. Wells take between 14 days and 17 days to drill. The deepest well in this field is 4 450m. Drill bits, which weigh about 20kg and cost R274 000 each, last around 50 hours.
The cost of drilling each well in this field is some $3 million (R25m) – “If there are no problems”. Then there are all the other costs of associated production infrastructure like roads, pipelines, compressor facility sites and the central production facilities.
The fracking to open cracks in the rock formation and free the natural gas is done by a separate sub-contractor, and can take from two to five days per well to complete.
There can be as many as 14 fracking “stimulations” per well, each requiring some 20 000 barrels (119 litres a barrel) of fracking fluid. This consists mainly of freshwater (around 90 percent) and various kinds of sand (about 9.5 percent) which keep the cracks apart, as well as chemicals (0.5 percent) like gelling agents, friction reducers, guar gum, disinfectants and scale inhibitors. Mixtures differ according to individual wells.
Huge compressor trucks pump the fracking fluid down the well at a rate of about 45-to-50 barrels a minute and a pressure of up to 10 000 psi (pounds per square inch).
Once the fracking operation has been completed, the downward pressure is released and the natural underground pressure forces much of the used fracking fluid back up the well, followed by condensate and gas. The well is capped for production.
Wells in this field are expected to have a production life of some 40 years, while the entire project is estimated at 60 years from the drilling of the first well until all wells have been plugged and abandoned and the habitat rehabilitated.
* John Yeld visited Wyoming as a guest of Shell. - Sunday Argus