Efficiency of reamers in the course of underwater passage construction by directional drilling

This paper addresses the issue of selecting a rock cutting tool to ream a pilot bore of an underwater passage as applicable to soil physics and mechanics and reaming techniques. Engineering challenges arising from the use of various cutting tools for reaming are also highlighted.
Materials and methods
Comparative method of correlation of geotechnical construction conditions as applicable to directional drilling.
Results
Thus, ineffective soil drilling, poor cleaning of the bottomhole and the drill string, i.e. settling of cuttings in the hole, and well caving in slow down the rate of penetration on certain drilling intervals. Eventually, all this points to the fact that the drilling technique applied is not effi ient. Thisincludes issues related to operation of rock cutting tools, hole cleaning and drilling mud parameters.
Сonclusions
Evaluation of geological and drilling conditions, drilling problems and failures, as well as their correlation with achieved volumetric soil cutting rate (Tab. 2) [2] and rate of penetration (Tab. 1) suggest the following:
1. Failure of drilling equipment flags poor performance of drill pipes and shows that the rock cutting tool was unable to efficiently cut the soil under applied load. Further this allows us to speak of drilling equipment being inadequate towards the soil drilled as well as of design flaws.
2. Operating problems and failures resulting from wells caving in are not only indicative of poor stabilizing properties of the drilling fluid but they also show that the rock cutting tool is not capable of compacting and stabilizing uncemented rock by transferring loads from the drill string onto the bottomhole.
3. Comparison of results, given in Tab. 1 and 2, reveals another factor that supports criticism of applied reamers. Soils found in the 2nd and 3rd groups of passages are lithologically similar.However rates of hole construction in given conditions vary by 2-3 times. This problem gets significantly worse with the enlargement of a drilled wellbore. We may therefore assert that construction of passages through directional drilling is still associated with lack of efficient1000+ mm reamers to be used in medium and high complexity rocks as well asin soft formations with highly abrasive inclusions.
4. A high efficiency rock cutting tool helps to improve performance indicators for passage construction and effectiveness of directional drilling method.
That said, we deem it necessary to further review current views on selection of drilling equipment and design of rock cutting tools in the form of reamers.