Both oil and gas are less dense than water, so they generally tend to rise upward through water-saturated rock and sediment.

石油和天然气的密度都比水小，所以二者通常会浮在被水浸泡的岩石和沉积物的表层。

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The eruption seems to have started with the volcano spitting out lumps of rock up to 2 metres across, before releasing an enormous pyroclastic flow - a fast-moving gush of hot gas and rock.

火山似乎在释放出巨大的火山碎屑流(一种热的气体和岩石快速移动的喷流)之前，从开始吐出2米宽度的岩石块而开始爆发。

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Shale traps gas more tightly than other rock.

页岩比其他岩石将燃气困得更紧。

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Companies are developing gas supplies trapped in shale rock two to three thousand meters underground.

VOA: special.2009.10.23

This causes the rock to break, or fracture,releasing the gas.

VOA: special.2009.10.23

In cases where the mass is known, scientists can determine the density, ultimately hinting at the internal structure (gas, rock and so on).

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The drilling technique, which uses sand, water and chemicals under high pressure to extract oil and natural gas from rock formations, has helped Eagle Ford oil production grow by 184% last year compared with 2011, according to the Railroad Commission of Texas, which regulates the state's oil and gas exploration and production.

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At first glance, it might seem obvious that it was through the action of flowing water (fluvial), but the Curiosity team needs to rule out the possibility that these rocks were deposited by the wind (aeolian) or by some kind of surge, such as the fast-moving clouds of gas and rock that will often plummet down the sides of particular types of volcano (a pyroclastic surge).

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