Shales and the gas within them

This is Sunday, so this is a technical talk about getting fossil fuel out of the ground. While some previous posts have dealt with sandstone and carbonate deposits I’m going to be talking about getting gas out of shale for a couple of weeks, and so, before I started talking about Horizontal Wells, we’d better chat for a minute or so about shale. And when I don’t give an alternate reference for the information, I am likely quoting from the Primer on Natural Gas in Shale, from the Department of Energy.

Folk who live near rivers, or along their outlet to the sea are familiar with the large mud flats that can develop around the outlet. These flats, which extend out into the sea, can cover large areas. When I was in school at Lancaster in the UK, we went to Morecambe Bay when my parents came to visit, and the large areas exposed when the tide ebbed remain a lasting memory. Through geological time these beds of mud have lain under large stretches of water, and so, at the algae that float in the water died, so they fell, and were caught in the mud. The mud is largely made up of clays, which in very small sizes are shaped a bit like a plate, and so as they settle, capturing and covering the algae remains, they tend to create layers (which can later tell us some of the conditions at the time they were deposited). When conditions are right – generally with a relatively warm sea containing a lot of nutrients – the sea can host vast colonies of algae, and over geological time the death of these algae built up considerable organic matter in the mud on the sea bed.

The main gas shale deposits in North America are in the Barnett shale, the Fayetteville, the Woodford, the Haynesville, and the Marcellus while, in Canada, the large fields are in the Horn River and Montney deposits. Not that there are not others, but these are the ones that the Oil and Gas Journal calls “The Magnificent Seven.” As an example the Barnett shale was deposited during the Mississippian Epoch, itself part of the Carboniferous Era, between 315 and 350 million years ago. At that time the map of the Earth looked at bit like this ) .

Shape of the Land and Seas at the time of the Mississippean Epoch

However not all the shales were deposited at that time. The Haynesville, for example is much younger, having been laid down in Jurassic Era, (remember the dinosaurs of Jurassic Park?) which was some140 to 200 million years or so ago, and when the globe looked a bit more familiar.

The map of the earth some 195 million years ago during the Jurassic

The mud that was deposited grew to be very thick – even after it was compressed by the weight of overlying additional sediments that turned into rock, the Barnett shale still can measure between 50 and 600 ft thick.

The individual particles that made up the mud were quite small, so that, as the material was compressed, the resulting rock became relatively impervious. Thus if the gas-generating algal remains were trapped, they were held in the shale, but dispersed throughout it, rather than concentrated in larger pore spaces, such as are found in sandstones. And, to be economic, there still needs to be a significant amount trapped within the pore space, which needs to be at least in the 5 – 12% range to hold enough gas to be worthwhile. Putting this into a different context, the Barnett, for example, is estimated to hold about 325 scf (cubic feet at a standard defined temperature and atmospheric pressure) of natural gas per ton of rock – or in about 13 cubic feet of rock. (Needless to say deep in the ground the gas is very compressed).

As the rock was buried deeper, so the temperature and the pressure also rose, gradually “cooking” the organic material over time. Depending on how deep the rock was buried, and the temperature, the material either turned into an oil, or if it were buried deeper and at a hotter temperature, it would turn into a gas. The relative conditions that set these bounds are sometimes referred to as the oil and gas windows for rock, and can be illustrated with a graph.

Geothermal gradients defining the oil and gas windows as a function of depth and temperature. (From WVU)

The current reservoir depths at which the different shales are now found can differ quite significantly from those at which the gas or oil was first formed, with depths for the Fayetteville being as little as 3,000 ft (0.9 km) to the Haynesville which can be at more than 14,000 ft. (4.3 km). The Barnett is around 6 - 8,000 ft (2.4 km).

Permeability, or the ease with which gas, oil or water can flow through a rock is measured in a unit called a Darcy, but it is sufficiently large that most rock permeabilities are measured in thousandths of a Darcy, or millidarcies (Md). As a point of reference for a rock with a good permeability such as the Ghawar oilfield in Saudi Arabia, Greg Croft quotes values in the 600 Md range.

A microdarcy is one thousandth of the value of a millidarcy, and it is this unit that the permeability of gas shales are often measured. Thus the permeability of the Marcellus shale can be around 20 microdarcy and the Barnett around 10 microdarcy. The density of the rock can be seen from the sample pieces shown at the Chesapeake Web site.

Illustration of gas shales from the Chesapeake web site.

These fine-grained rocks with low permeabilities mean that the producer has to rely on other paths within the rock to allow the gas to escape. Originally this was just the natural fractures that can be found in the rock. As the rock compresses vertical fractures often generate within the rock. These fractures can be quite consistent, though in contrast to the bedding, they normally occur vertically.

Shale fractures from Geology.com

The problem is that conventional vertical wells don’t intersect a lot of these fractures, and thus, when the gas shales were first drilled the production was very low, and often uneconomic.

However when horizontal wells were developed it became easier to intersect a lot of these fractures as the well moved along the reservoir, and so it is time to introduce horizontal wells in the next post.

As usual this has been a very short description of a relatively complex topic, and so questions, and comments are appreciated.

P57. Pick Points

Over at The Oil Drum, Jon Friese has a guest post with an interesting plot of the relative drilling activity in the four major gas shale fields. It shows that while drilling in the Fayetteville and Woodford shale has remained relatively stable, there has been considerably more activity in the Haynesville shale, and a rapid drop-off in rig count in the Barnett. Overall the number of rigs drilling in gas shale has held remarkably constant over recent months at around 230 rigs, though this is down from the peak of 311 rigs last December. This is happening just as a new pipeline extension is connecting into the Barnett field. The Sherman extension to the Enterprise Texas Intrastate connector will carry up to 1 bcf out to markets as far apart as the North East and Florida. The Barnett had increased production in 2008 to nearly 1.4 tcf, and had 10,500 wells with 222 companies operating. But over the last few months the rig count had fallen 57% from 214 rigs to 91. With an average of 25 people per rig this is a loss of some 3,000 jobs. Meanwhile Exxon Mobil has leases on 19,400 acres in the Marcellus shale.


Oh, and in the great game of Azerbaijani natural gas, the Russians are now trying to get the gas that might go West to Turkey, to go instead North to Russia (who could then sell it into Europe). It is part of the ongoing struggle over supplies for the Nabucco pipeline. Gazprom is also trying to raise $500 million on the Eurobond market. Further East, the pipeline from Turkmenistan to China should have the Turkmen leg finished this year. Gas should reach peak flow (30 bcm per year) in 2011. And the Turkmen are still talking about possibly piping natural gas down to India and Pakistan. It is needed since even exports of goods from Pakistan are now being reduced due to shortages of natural gas. India, meanwhile is bringing new gas on stream and using natural gas increases from current fields to improve fertilizer production.

While Mt Redoubt is relatively quiet today, there are signs of new eruptions from a volcano in the Congo that last erupted in 2002, nearly destroying the nearby town of Goma.

Financing for wind power in the UK appears to be rapidly fading

Despite the fact that the UK has richer ambient energy resources than any other country in Europe, the government managed to beat its target for renewable power down to 15% of total energy supply, rather than the 20% adopted across the EU. Even so, this means that by 2020 35% of our electricity must be produced by wind, hydro, wave, tidal, solar or biomass generators. The technology that could be most widely deployed is wind power, but investment is melting away faster than an Andean glacier.

Shell has pulled out completely. Centrica, E.ON and BT are reviewing their plans. Sun Microsystems has suspended its projects. The Spanish company Iberdrola is cutting its investment in the UK by 40%. Scores of smaller firms are going bust.

On the other hand the British government has just offered increased financial support in order to get production closer to target.

The government is also planning to sign contracts with companies by the end of the year to develop up to 25 gigawatts of offshore wind power that will be awarded from its Round 3 development phase.

But developers are anxious about financing the investments, which, at about GBP3 million a megawatt, are roughly double that of onshore wind.

The recent banking crisis has also made project finance difficult to come by and more expensive.

P43. Pick Points

I mentioned in Monday’s post that I have an interest in algae, and so I will put up a couple of items that caught my attention this weekend. The first deals with the possibility of using wind power to provide some of the energy that algae need to foster growth Some of the European wind farms have been up for a while, and one in Denmark, that was installed in 1990, is looking at using some of the extra power to encourage algae growth. The algae, through the generation of biofuel, would thus act as a form of “battery” for the wind. One problem, however, is to ensure biological security, since the escape of algae species into a favorable place, such as in Hawaii, can have negative results, and require costly capture and remediation. The use of algae for flue gas cleanup has inspired a number of efforts, from Israel to MIT (who use it to make hydrogen), to Missouri . There is also the blog Oilgae, which carries the MIT report on the topic.


Developers of the Shtokman project are talking about using CCS as part of the strategy for development at the site. There is anticipation that the cost of the project will decline with the poor economy. More details of the loan from China to encourage a pipeline and oil supply to that nation are now emerging. The change in investment strategy has the advantage of getting a good price now for the oil, and securing it into the future. Russia is also trying to find a way to improve the efficient use of energy, with planning for a new law on the way, and an example of how it might be done, comes from a dairy. In the United States homeowners can look at the Home Energy Rating System which compares the energy use of a house with a standard. Based on the result that you get different approaches may be needed to lower the number (a 200 means you use twice the standard). Oregon is moving to have the state provide loans to encourage upgrading of homes in a way that would make them more energy efficient. As I noted in Monday’s post, this is something that we are seeing in an increasing number of states.

St Mary Land and Exploration is drilling horizontal wells into the Woodford, and Haynesville shale and while cutting the number of rigs back to 7, from 16 at the peak of last year, one or two of the rigs will shuttle between the Haynesville, the Eagle Ford and the Marcellus shale sites. The lateral section of the well is around 3,300 ft, and with 10 slick-water fracs will use some 3,000,000 lb of resin coated sand proppant. There is some move in Pennsylvania to require that drilling records for the Marcellus be made public (including production data) every six months. Other states such as Louisiana and Wyoming post such production on Web sites. Chesapeake, who is drilling both Marcellus and Hanesville is currently getting a favorable press. With natural gas prices projected as perhaps falling as low as $2 per MMBtu due to lack of demand and overproduction, this years prospects don’t look good for the industry.

Scotland is looking for new ways to develop marine energy, the target being some 60,000 MW. The current projects are based in Orkney, and the European Marine Energy Centre. The current targets are sites around Britain and Ireland that are capable of producing more than 1,000 MW each, largely from wave and tidal energy.

The State Governors are asking Presidential help in promoting biofuels hoping to see approval, for example, of ethanol blends above 10% and as high as 30%. (This was something Dr Chu was asked about last week).

Because of the global financial problems Russia and Kazakhstan are considering slowing the development of the Karachanganak project (which is reputed to have 47 trilion cubic ft of gas).

P30 Pick Points

Half-a-dozen or so stories of interest:

Moving to undo some of the last actions of the Bush Administration Interior Secretary Salazar has cancelled the lease agreements that had earlier been approved (but then delayed when the government did not cash the checks) in Utah for oil and natural gas. At the same time, in Wyoming some sales are proceeding, while other leases have been withdrawn at the Governor’s request.

Adding additional numbers to the costs for drilling wells in the gas shales, Encore Acquisition have stated that their goal this year, in the Bakken, is to reduce costs from $5 million per well to $4 million. They are also planning refracs of some of the wells. These are done some 9 – 18 months after initial completion, and at a cost of $500,000 each can increase reserves by up to 80,000 boe. Over in the Woodford, Newfield Exploration have lowered (on a lateral foot basis) the cost of drilling wells by some 38% and are hoping to continue this trend by drilling longer wells (out to 5,000 ft from 4,436 ft last year and 2,700 ft in 2007.) Lease rates in the Marcellus were reported to be up to $4,000 an acre and 17.5% royalty, prior to the slackening of demand.

Public relations in the Barnett still appear to be becoming more difficult, as an application for a compressor station has just been withdrawn. Without the dramatic reductions in well costs, and without an increase in gas prices unlikely in the present glut of gas, the current economics of many operations are being further questioned by Arthur Berman.

Royal Dutch Shell said that the cost of producing oil from the oil sands of Alberta rose to $38 a barrel last year. Their production dropped last year to 80,000 bd falling 7,000 bd from 2007, while costs rose by $9 a barrel. More than $60 billion worth of projects have now been delayed, including the expansion of the Shell output to 250,000 bd, which was scheduled for next year. Meanwhile Marathon has written down the $1.4 billion cost of its oil sand operation. Canadian Oil Sands trust, the largest shareholder in Syncrude Canada cut its dividend 80% because of the drop in oil prices. Meanwhile BP and Husky have not yet gone forward with their investment on the Sunrise assets in Alberta. Yet the prospects are such that a firm that specializes in the construction side of the development has just been taken over by Aecon. They, however, do not have to deal with the stronger environmental rules that are now being applied to the tailings ponds.

Merrill Lynch says non-OPEC oil production has peaked, expecting that such production will be in the 49-50 mbd range by next year, while the IEA were predicting last summer that the peak would be next year at around 51 mbd. The Merrill Lynch projection is based on an increase in field decline rates which they set at 4.5% against the IEA figure of 4.2%. The IEA recognizes that the decline rate will rise to 4.7% in the next seven years, but this will slow, not stop increases in production. In contrast ML argue that some of the decline will come from the loss in capital availability and this will carry decline above 5% (and perhaps as high as 6%). Should this happen then within a year oil prices will be back where they were earlier last year. A year ago CERA were saying that a 4.5% rate was typical but they were saying this as rumors and reports of figures already above 5% were starting to circulate.

It looks as though Croatia is going to be the next meal for Gazprom as plans for the Pan European Pipeline start to collapse, and their experts head off to Moscow. With Nabucco also still not having enough gas commitment to be viable and Gazprom is making promises to Turkey about providing natural gas their dominance becomes more evident. With the upcoming North and South Stream deliveries giving Russia the chance to provide for 50% of Western European gas needs (up from the current 25%), the only question becomes where does Gazprom get all the money to fund these developments? It must find $10 billion in debt payments by the end of July, and just lost up to $2 billion in the dispute with Ukraine. As a result they are sweetening their stock offers, even as their production of natural gas falls 14% y-o-y . On the other hand, as deliveries through the Baku-Tblitsi-Ceyhan rise, those through the Baku-Novorossisk pipeline are falling.

Over at the European Tribune Luis has just finished his 3-part review of the plan to Secure the Energy Future of the EU, with earlier posts on the Action Plan and an Introduction. Given the outreaching hand of Gazprom, it is worth getting to know this background, before it gets more serious.

More stories can be found at The Energy Bulletin and Drumbeat at The Oil Drum