Drilling through incompetent shales, loose sands, and dolomites can be a very troublesome process because of numerous sloughing, caving-ins, and collapse of wellbores’ walls. These troubles are addressed, as a rule, by numerous hole reaming jobs involving increase of drillstring rotational speed and injection of high-viscosity and heavy-weight drilling fluid. These operations can last for two weeks in some cases, increasing NPT and translating into high costs. Casing-while-drilling has been proved to lower drilling costs due to elimination of tripping events for hole reaming, for trouble zones are isolated immediately after drilling out. TatNIPIneft Institute in cooperation with Perekryvatel OOO, have designed a drillable PDC bit to be used in the casing-while-drilling process. Tests using the inhouse test jig have been successfully performed. In the test jig, the PDC bit was tested for drillability using a 142.9-mm PDC bit. Field tests using the PDC drillable bit with a cementing port were performed in Well No. 11378, Chernoozerskoye field. The 168-mm casing pipes with thread connections TMK UP CWB were used. After cementing, the bit was drilled out for 4.5 minutes. A similar 220.7-mm bit was run on expandable profile liner OLKSB-220.7. In this case, the bit was drilled out using a PDC SSP 142.9 DHD 513 bit. The process took 7 minutes. The successful tests of drillable alloy bits open up opportunities for further development of the casing-while-drilling process as an efficient drilling technology.
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