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Anisotropy on the ductile-to-brittle transition for rock in process of drilling

He Mingming, Wang Jing, Yuan Zhuoya, Wang Haoteng, Ma Xudong, Luo Bo

Acta Geophysica

2023

Vol. 71, no. 5

2107--2124

Anisotropy is an inherent property of rocks. It refers to the different response of the rock properties in each direction. Understanding the anisotropy characteristics of rock failure by drilling has practical applications in improving drilling efficiency, especially for engineering applications. In this paper, a criterion is established to clarify the ductile-to-brittle transition in the drilling process of rock. Moreover, a new anisotropy index has been proposed to evaluate the effect of anisotropy on the critical state of the ductile-to-brittle transition. The digital drilling tests are conducted on six types of rock to study the drilling mechanical performance in the X, Y, and Z directions. The anisotropy characteristics of drilling parameters and mechanical specific energy (MSE) are analysed at the critical state of ductile–brittle failure. The results show that the critical state of ductile–brittle failure is manifested as an inflection point of the depth of cut. The evolution of MSE is fitted as two linear functions, which corresponds to the two stages. The order of anisotropy in MSE is obtained as: gneiss > slate > red sandstone > granite > argillaceous sandstone > sandstone. The anisotropy in the uniaxial compressive strength and MSE for different rock types has the same sequences. The advantages of the proposed method in determining rock anisotropy are illustrated.

Total Specific Energy (TSE) as a new indicator of drilling efficiency

Toczek P., Wiśniowski R., Stryczek S., Ziaja J., Mazur C.

AGH Drilling, Oil, Gas

2017

Vol. 34, no. 3

715--729

Knowing the data from drilling works which had been carried out in a given area gives the opportunity to develop the next borehole with great precision. An important element of the design is to analyze and interpret data in detail, which can be used during the following drilling process. Based on a literature analysis, certain methods of the selection of drill bits have been indicated. Mechanic specific energy curves of drill bits applied in drilling works in northern Poland have been compared. The drilling works took place in the Precambrian platform. The compared mechanic specific energy curves were calculated with the use of R. Teale and H. Rabia equations. A relation between mechanical specific energy and pressure loss in polycrystalline diamond compact drill bits was determined. New drilling ratio TSE - Total Specific Energy which considers hydraulic power energy in the nozzles of the drill bit was calculated.