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.
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。
3
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.