Tuesday, September 24, 2019

Tight Oil Chapter 3

The most notable tight oil plays in North America include the Bakken shale, the Niobrara formation, the Barnett shale, the Eagle Ford shale, and the Miocene Monterey play of California's San Joaquin Basin in the United States, and the Cardium play in Alberta. In many of these tight formations, the existence of large quantities of oil has been known for decades and efforts to commercially produce those resources have occured sporadically with typically disappointing results. However, starting in the mid-2000s, advancements in well-drilling and stimulation technologies combined with high oil prices have turned tight oil resources into one of the most actively explored and produced targets in North America. 

Furthermore, of the tight oil plays, perhaps the best understood is the Bakken which straddles the border between Canada and the United States in North Dakota, Montana, and Saskatchewan. Much of what is known about the exploitation of tight oil resources comes from industry experiences in the Bakken and the prediction of future tight oil resource development described in this study are largely based on that knowledge. The Bakken tight oil play historically  includes three zones, or members, within the Bakken Formation. 

The upper and lower members of the Bakken are organic-rich shales which serve as oil source rocks, while the rocks of the middle member may be siltstone formations, sandstone formations, or carbonate formations that are also typically characterized by low permeability and high oil content. Since 2008 the Three Forks Formation, another tight oil-rich formation which directly underlies the lower Bakken shale, has also yielded highly productive oil wells. Drilling, completion, and stimulation strategies for wells in the Three Forks Formation are similar to those in the Bakken and the light, sweet crude oil that is produced from both plays has been geochemically determined to be essentially identical. Generally, the Three Forks Formation is considered to be part of the Bakken play, though the authors of published works will sometimes refer to it as the Bakken-Three Forks play.

Other known tight formations (on a worldwide basis) include the R'Mah Formation in Syria, the Sargelu Formation in the northern Persian Gulf region, the Athel Formation in Oman, the Bazhenov formaiton and Achimov Formation in West Siberia, Russia, the Coober Pedy in Australia, the Chicontepex formation in Mexico, and the Vaca Muerta field in Argentina (US EIA, 2011, 2013). However, tight oil formations are heterogeneous and vary widely over relatively short distances. Thus, even in a single horizontal drill hole, the amount of oil recovered may vary as may recovery within a field or even between adjacent wells. This makes evaluation of shale plays and decisions regarding the profitability of wells on a particular lease difficult and a tight reservoir which contains only crude oil (without natural gas as the pressurizing agent) cannot be economically produced (US EIA, 2011, 2013).

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