Shale Vs Sand: Pretty Basic Stuff? -- June 12, 2016

Disclaimer: in a long note like this, there will be typographical an factual errors. This post started out because I was trying to sort out the EIA graph on this page, but then that took me to Saudi Arabia, which is far afield of where I started.

Two things have come out of this exercise: I have a better understanding of "tight" and "shale." Lay people like me commonly (and incorrectly) use "tight" and "shale" synonymously. Experts often use "tight" without the entire phrase "tight sands" but it appears that "tight" and "tight sands" are synonymous and both correctly and interchangeably used, whereas no one would ever be caught dead at an oil and gas cocktail party and talk about "tight shale." In the graph below, for example, it's "shale" vs "tight." The word "sands" is not seen. "Tight" = "tight sands." Pretty basic and I should not be covering this again after 9 years of blogging about the Bakken but there is it.

Oh, I almost forgot. The second thing that came out of this exercise: unless Prince Salman can use salt water to frack, he has major challenges when it comes to fracking. It also explains recent article suggesting Saudi Arabia may begin to import natural gas; it may make economic sense.

Okay, done with the disclaimer and the private comments, let's get started.

I don't think I've ever really sorted this out or talked about it much. I know I've used the terms interchangeable and incorrectly.

But the EIA graph below brings the importance of differentiating the terms "tight" and "shale."

I will assume that most of us have a "general understanding" of the difference between "conventional" and "unconventional" when used in the oil and gas industry.

"Tight" and "shale" are both components of "unconventional."

Here's the graph, which has been tweeted several times by EIA (I'm glad the EIA is into tweeting but has anyone asked why the EIA tweets?):

This is what caught my attention: the growth of natural gas production from "tight gas" plays is projected to actually decrease or stay flat. The growth of natural gas production in the US is projected to be incredible and will come almost entirely from "shale gas and tight oil" plays.

Now to sort out "shale" vs "tight." A google search begins.

Here a few sites that seem reasonable.

The oilprice article is perhaps one of the best.

• 2014; it begins:

The recent news that Saudi Arabia has not found natural gas to be as available as it had thought from its shale deposits, and is shifting to exploring for gas in their tight sand formations has not caught a lot of attention.

But it is worth considering some of the aspects of this – and hence this post.

The Oil and Gas Journal define (sic) tight sands in this way: The term tight gas sands refers to low-permeability sandstone reservoirs that produce primarily dry natural gas. A tight gas reservoir is one that cannot be produced at economic flow rates or recover economic volumes of gas unless the well is stimulated by a large hydraulic fracture treatment and/or produced using horizontal wellbores. . . . . . . . . Tight sands produce about 6 tcf of gas per year in the United States, about 25% of the total gas produced.

The production of natural gas from tight sands is different to that from shale sources, for, as the Canadian Center for Energy notes: initial production rates are low; however, productivity is long lived.

• And then goes on to explain why. This is an article one may want to archive in case it "disappears."

The agilegeoscience article is pretty basic, but a start; dated 2011; note the comment about number of stages of multi-stage fracking; the reader thought 10 - 20 stages was incredible; the writer makes a comment that the importance of differentiating "shale" from "tight sands" has to do with exploration. To the extent that's accurate, it explains Slawson's early attempts to explore both the upper Bakken and the middle Bakke. Sand is sand-like; shale is clay-like.

This is an incredibly cool site, exploreshale: the Marcellus is shale, as is the Utica.

So, now back to the graph. Unconventional natural gas is going to be produced from shale, not sand, in the US, going forward, as least as forecast by the EIA. It would be wise to remember that the presumptive Democratic presidential nominee is on record as opposing fracking in the US, though apparently she favors it elsewhere.

One can see why newbies (including me) get confused. In an article posted this year, this statement:

Bakken shale consists of three layers, an upper layer of shale rock, a middle layer of sandstone/dolomite, and a lower layer of shale rock. The middle sandstoen (sic) layer is what is commonly drilled and fracked.

Obviously that's incorrect. What has just been described is not "Bakken shale," but rather, the Bakken formation. The article does get it right at the beginning by referring to the Bakken formation, but when suggesting that the "Bakken shale consists of three layers" ..... well, you get the point.  [By the way, the linked site is a "sourcewatch" site; be advised. It looks like a "wiki" site but is not.]

Somehow I get the feeling there's a whole lot more to this but I don't want to get too far into the weeds.

But that's interesting, isn't it? The EIA projects natural gas is going to be produced from shale, not sand, in the US but the oilprice article began with "the recent news that Saudi Arabia has not found natural gas to be as available as it had thought from its shale deposits, and is shifting to exploring for gas in their tight sand formations has not caught a lot of attention."

I guess this is the importance of differentiating between shale and sand:

• where one looks when looking for oil and/or natural gas; it may vary across the globe
• how one extracts oil and/or natural gas from shale or sand; there may be differences, such as type and amount of water; type and amount of proppant; alternatives to water, sand, ceramic
• whether initial production and decline rates differ between sand and shale

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Saudi Aramco And Unconventional Natural Gas

From epmag, 2012:

Saudi Aramco divides its unconventional resources into two categories – shale gas and tight-sand reservoirs. The exploration will focus on three areas within the country.

“The first area is in the northwest part of Saudi Arabia,” Saleh told participants in the 2012 CWC Third World Shale Oil and Gas Conference, Sept. 21, in Houston.

 The second area is South Ghawar. The Ghawar field is the largest oil field in Saudi Arabia. This area is a tight-gas sand opportunity, he noted. The area is close to infrastructure. There is a large amount of geological data available from the development of the oil field, which can be used to define the tight-gas sands.

The third area is in southern Saudi Arabia in the Rub Al-Khali. This would be shale. The source rock is primarily Jurassic and Cretaceous.

Now, where's that article that says SA was disappointed in shale gas results and is turning to tight sands natural gas?

From the Journal of Petroleum Technology:

The company’s unconventional ambitions are focused on three different areas in Saudi Arabia.

The first is located in the northern part of the country. The target formation is called the Qusaibia Hot Shale and is found at a depth between 6,000 ft to 8,000 ft. The shale is considered to be relatively shallow and is the source rock for conventional gas fields in the area. The gas produced from this area will support a major mining project still under construction and a new power plant.

The other two plays are in the eastern province and located along the periphery of the Ghawar oil field, the largest conventional oil field in the world. These two areas will benefit from their proximity to existing infrastructure and the large amount of geological data already collected from the development of Ghawar.

The play located to the south of Ghawar is a deep tight sandstone formation where five appraisal gas wells have been drilled so far.

Sitting just east of Ghawar is the third play where Saudi Aramco is targeting a tight carbonate formation called the Tuwaiq Mountain—the source rock for the giant oil field. The company believes this field is comparable in many respects to the Eagle Ford Shale in Texas. “Sometimes, it is better than the Eagle Ford in terms of the permeability and porosity,” Almomen said.

The Tuwaiq Mountain formation is split into two tiers. The upper tier has nearly double the total organic content of the Eagle Ford while the lower tier is about the same. A pilot well drilled in the Tuqaiq Mountain formation had an average 30-day initial production rate of 3 MMscf/D of gas and 1,800 B/D of oil.

In addition to core samples and openhole logs, sonic logging tools and ­diagnostic fracture injection testing are being used to make key determinations about each formation’s permeability, pore pressure, and in-situ stress state. Using this information, completion engineers are placing as many as 16 fracture stages along the laterals. They are placing the stages only in the areas that appear to have the best production characteristics and are avoiding areas with poor reservoir quality. Based on production logs, Almomen said this strategy has resulted in 95% of the perforation clusters contributing to production in some of the best cases.

The company’s plans include using microseismic surveys and chemical tracers to better characterize fracture networks and to determine how cluster stages are contributing to production. The company is also investigating technologies to overcome the challenges involved with hydraulic fracturing in the middle of the Arabian Desert. “We are experimenting with local sand and we’re doing some research on water management, testing, and trying to create a decent frac fluid using sewage water, seawater, and other fluids,” said Almomen.

Nope, that's not it. I'm still looking for that article that says SA was disappointed in shale gas results and is turning to tight sands natural gas.

Ah, this might be it, from 2014. From Shale Gas International: Saudi Arabia concentrates on tight gas as Shell abandons shale exploration .

Saudi Arabia is focusing on developing its tight gas deposits to compete with U.S. shale. It also seeks to satisfy its domestic energy needs with gas to free its crude reserves for export.

As Bloomberg reported on Monday, state-owned oil and gas company Saudi Aramco is now targeting a cost of $2 to $3 per thousand cubic feet of tight gas.

Saudi Aramco is drilling in tight sands reservoirs where permeability and porosity is greater than that of shale formations but below that of conventional oil and gas bearing sands.

At 645 trillion cubic feet of technically recoverable shale gas, Saudi Arabia holds fifth largest shale gas deposits in the world, but water scarcity makes extraction difficult.

Shale gas exploration requires the use of a technique called fracking which requires up to 2.5 and 5 million gallons water per well. Also on Monday, Reuters reported that Royal Dutch Shell decided to end its investments in a gas development project in Saudi Arabia.