Unconventional Natural Gas Resources

Exploration and production companies explore for these deposits by using complex technologies to identify prospective drilling locations. Once extracted, the natural gas is processed to eliminate other gases, water, sand, and other impurities. Some hydrocarbon gases, such as butane and propane, are captured and marketed separately. Once it has been processed, the cleaned natural gas is distributed through a system of pipelines across thousands of miles (USEIA, 2007). It is through these pipelines that natural gas is transported to its endpoint for residential, commercial, and industrial use. 

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Near term options include primarily the unconventional natural gas resources (Western tight gas sands, Eastern Devonian gas shales, geopressured aquifers, and methane from coal deposits). Mid-term options include coal gasification (peat... 

Research to date has shown that a significant resource base exists in what is commonly called Unconventional Natural Gas Resources. These resources differ in geological formation and geographical location and are typically categorized as follows o Western Tight Gas Sands... 

Presently, abundantly available natural gas on the North Slope has no market and most of the produced gas is reinjected. Continued reinjection will ultimately result in high gas/oil ratio in the reservoir thus causing gas recycling problem and production decline. The purpose of this paper is to review the available conventional and unconventional natural gas resources of northern Alaska and their potential uses. 

Commercial natural gas occurrence can be broadly classified into two categories, conventional and unconventional. The conventional category includes natural gas found as associated and non-associated or free gases, including dissolved or solution. The unconventional natural gas resource includes, (1) deep gas, (2) coal bed methane, (3) gas hydrates and (4) gas In shales, (5)... 

NaturalGas.org. (2011). Overview of Natural Gas Unconventional Natural Gas Resources, http / / naturalgas.org / overview / unconvential ng resource.asp. 

The Beaufort-Mackenzie Basin hosts immense unconventional natural gas hydrate reserves that are often co-located with conventional petroleum resources. Osadetz et al. (2005) reported that the conventional resources are co-located with an immense gas hydrate resource estimated between 2.4 x 1012 and 87 x 1012 m3 of raw natural gas. Because the expected decline in conventional natural gas production from the Western Canada Sedimentary Basin cannot be replaced by conventional production from frontier regions alone, this immense hydrate resource offers a solution to replace the expected decline in conventional gas reserves. 

Potential resource bases and the economic benefits of using the resource are being determined for unconventional natural gas sources. Numerous assessments have been performed by DOE, the gas industry, and other groups. The ranges of resource estimates from these assessments are summarized below. 

Trofimuk, A.A., Cherskii, N.V., Makogon, Y.F., Tsarev, V.P., presented at 11th ASA Conference on Conventional and Unconventional World Natural Gas Resources, Laxenburg, Austria, June 3-4 (1980). 

The proven reserves of natural gas in northern Alaska are estimated to be 47 trillion standard cubic feet (TSCF) and represent approximately 25% of the total U.S. reserves. The undiscovered recoverable conventional natural gas resources are estimated to 89 TSCF and additional 500 TSCF are deposited as unconventional gas hydrates. The hydrates are mostly found along the North Slope and adjacent shelf. 

Table III represents the northern Alaska natural gas resource summary for conventional as well as unconventional resources. It should be noted that the undiscovered unconventional resource of natural gas in the form of gas hydrates Is only a rough estimate.

Resource estimates and current production Natural gas from coal is present wherever coal is found and, as coal is found in great quantities throughout the world (see Section 3.5), natural gas from coal may represent a large energy source. As for all types of unconventional gas, the published reserve and resource figures show great variations and are often based on estimations from incomplete data. In addition, as... 

To represent the range of estimates of the EUR of natural gas, a very pessimistic estimate of 283 Tm3 by Laherrere (2004a) and a very optimistic estimate of 558 Tm3 by Chabrelie (2002) have been selected. For comparison, the USGS (2000) estimates the P95 EUR of natural gas at 301 Tm3, theP5 EUR at 604 Tm3 and the mean at 436 Tm3. The estimate of the Federal Institute for Geosciences and Natural Resources (BGR, 2007) of 466 Tm3 is in the middle. As for unconventional gas, only reserves have been taken into account, owing to the large uncertainties related to unconventional gas occurrences. As of today, 81 Tm3 of natural gas have already been produced. 

Naturally occurring clathrate hydrates are found in marine sediments and in permafrost. Because they contain a large amount of methane, they are thought to have potential as an unconventional energy resource. At the same time, however, clathrate hydrates are a serious problem for the gas and oil industries, because they form easily under suitable conditions at the sites of natural gas production, transportation, and processing. The inhibition and control of hydrates in pipelines adds tremendously to gas production costs. ... 

Lei, Q. 2008 Status Analysis and Advices on Exploration and Development of Unconventional Hydrocarbon Resources. Natural Gas Industry 28(12) 7-10 (In Chinese). 

The use of unconventional to describe a gas resource is open to interpretation as technology advances and discrete reservoirs become limited, the reserves considered unconventional a few decades ago are more commonly viewed as conventional by modern standards (Santoro et al., 2011). In this book, conventional refers specifically to discrete reservoirs of associated or unassociated natural gas, and unconventional refers to tight-gas formations. 

Until recently, many oil and gas companies considered natural gas locked in tight, impermeable shale uneconomical to produce. Advanced drilling and reservoir stimulation methods have dramatically increased gas production from unconventional shales. The Barnett Shale formation in Texas has experienced the most rapid development. The Marcellus Shale formation of the Appalachian basin, in the northeastern United States, potentially represents the largest unconventional gas resource in the United States. Other shale formations, such as the Haynesville Shale, straddling Texas and Louisiana, have also attracted interest, as have some formations in Canada. The resource potential of these shales has significantly increased the natural gas reserve estimates in the United States (Andrews, 2009). 

Note, however, that unconventional sources of natural gas, in addition to obviously higher costs of production, differ from traditional sources by much lower production rate, short duration of active life (the production capacity of shale gas wells falls particularly rapidly during the 1st year (Fig. 12.16)), and spread over huge areas. In addition, a significant portion of these resources is located in remote regions, including Arctic. Even in the United States with its highly developed system of pipelines, more than half of potential resources are out of reach of the gas transportation system. 

A world atlas, giving sites with evidence of hydrate deposits, both onshore and offshore, is presented in Chapter 7, Figure 7.2. Since each volume of hydrate can contain as much as 184 volumes of gas (STP), hydrates are currently considered a potential unconventional energy resource. Table 1.4 lists the milestones accomplished to further our knowledge on naturally occurring hydrates. 

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