一旦到达油层，石油就会由于地下巨大压力涌到地面上来，这种巨大压力来自地下天然气或水。

Once we get down to the oil, it usually flows to surface because great pressure, either from gas or water, is pushing it.

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且常发生井漏、气侵、坍塌性卡钻、井涌与井喷等井下复杂问题，导致机械钻速低与钻井事故频发。

Low penetration as well as drilling incidents of high frequency resulted from problems caused by leakage, gas migration, collapsing sticking, well kick, blowout and so forth.

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