Test of compound drilling with the torsional impactor in hot dry rock geothermal wells

Abstract:

The torsional impactor which can increase drilling rate and efficieny has seen wide use in oil and gas drilling industry. But hot dry rock drilling is quite different, where many difficulties such as high temperature, high pressure,hard rock, strong abrasiveness,deep and ultra-deep wells, are encountered. Specific design has been made on the torsional impactor in regard to these issues and trial use was conducted. A series of drilling tests were conducted on the torsional impactor with different drilling tool combinations in hard-extremely hard rock strata during two drilling trips to study its influence on drilling efficiency.The test results show that the torsional impactor can eliminate the lateral vibration of PDM caused by centrifugal inertia force， which verifies the feasibility of the combined application of the torsional impactor and PDM. ROP increased by 29.59% from the well section where the torsional impactor was not used.In addition， the roller cone bit had higher drilling advantages over the PDC bit in the combined drilling mode of the torsional impactor+PDM+the rotary table in terms of the rock fragmentation mechanism and the formation adaptability. The test results can provide theoretical basis for both the study of the matching between the torsional impactor and the cone bit and that for the coupling between the torsional impactor and PDM.

Key words:torsional impactor;compound drilling;dry hot rock drilling;drilling efficiency