Method for evaluating rock drillability by nano-indentation test on rock cutting

A method for evaluating a rock drillability by a nano-indentation test on a rock cutting, comprising the following steps:

• (1) conducting a nano-indentation test comprising of a plurality of indentation points on a rock cutting sample, and calculating a micro-hardness of each of indentation points of the rock cutting sample:
• wherein, the micro-hardness of each of the indentation points under the nano-indentation test on the rock cutting sample is calculated as follows:
• H
• n
• =
• P
• m
• A
• c
• (
• 1
• )
• A
• c
• =
• 24.56
• h
• c
• 2
• (
• 2
• )
• wherein, Hn denotes the micro-hardness of each of the indentation points under the nano-indentation test on the rock cutting sample, Pascal (Pa);
• Pm denotes a maximum indentation load applied in the nano-indentation test, Newton (N);
• Ac denotes a projected area of a contact zone between an indenter and the rock cutting sample, meter square (m2);
• and he denotes an indentation depth, meter (m);
• (2) calculating a proportion of each of mineral components of the rock cutting sample, and establishing a transformation relationship between the micro-hardness of each of indentation points of the rock cutting sample under the nano-indentation test and a macro-hardness, wherein the rock cutting sample is a combination of the mineral components in different proportions, and the micro-hardness of each of indentation points of the rock cutting sample varies at different indentation points based on the different proportions of the mineral components under the nano-indentation test on the rock cutting sample;
• the macro-hardness of the rock cutting sample is calculated as follows:
• H
• =
• ∑
• i
• =
• 1
• p
• ρ
• i
• ⁢
• H
• i
• (
• 3
• )
• wherein, H denotes the macro-hardness of the rock cutting sample, Pa;
• p denotes a category number of the mineral components constituting the rock cutting sample;
• ρi denotes a weight of an i-th mineral component of the mineral components;
• and Hi denotes a micro-hardness of the i-th indentation points under the nano-indentation test on the rock cutting sample, Pa;
• and
• (3) establishing a regression model between the calculated micro-hardness of the rock cutting sample under the nano-indentation test and a rock drillability based on a relationship between the macro-hardness of the rock cutting sample, the micro-hardness under the nano-indentation test, and the rock drillability;
• wherein a regression model between the macro-hardness of the rock cutting sample and the rock drillability is as follows:
• kd=aH+b (4)
• wherein, kd denotes the rock drillability for a roller cone bit;
• H denotes the macro-hardness of the rock cutting sample, Mega Pascal (MPa);
• and a and b denote regression coefficients.