The problems of low drilling efficiency and low core recovery due to borehole collapse were solved with pulling in casing while drilling through using combined BHA with casing.

采用组合钻具进行跟管钻进，通过随钻跟入的套管保护孔壁，解决因钻孔垮塌导致钻探效率和岩心采取率低等技术难题。

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Increased core rate and to maintain borehole stability obtained is crucial to fully evaluate the oil shale.

提高取心率与保持井壁稳定性是对油页岩充分评价的关键性技术。

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During course of in situ stress measurement, some problems such as core discing, minification and caving of borehole due to horizontal stress are appeared, and their mechanism is studied.

在现场地应力测量过程中发现了岩芯饼裂、钻孔径缩和钻孔破碎塌孔等现象，分析了这些现象的力学机理。

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