US 12,203,365 B2
Method for evaluating rock drillability by nano-indentation test on rock cutting
Zizhen Wang, Qingdao (CN); Xianbo Lei, Qingdao (CN); Weidong Zhou, Qingdao (CN); Chengwen Wang, Qingdao (CN); Ruihe Wang, Qingdao (CN); Xian Shi, Qingdao (CN); Luopeng Li, Qingdao (CN); Hongjian Ni, Qingdao (CN); and Rui Zhang, Qingdao (CN)
Assigned to CHINA UNIVERSITY OF PETROLEUM (EAST CHINA), Qingdao (CN)
Filed by CHINA UNIVERSITY OF PETROLEUM (EAST CHINA), Qingdao (CN)
Filed on Aug. 9, 2022, as Appl. No. 17/883,616.
Claims priority of application No. 202210057803.5 (CN), filed on Jan. 19, 2022.
Prior Publication US 2023/0228189 A1, Jul. 20, 2023
Int. Cl. E21B 49/02 (2006.01); G01N 3/42 (2006.01)
CPC E21B 49/02 (2013.01) [G01N 3/42 (2013.01); G01N 2203/0019 (2013.01); G01N 2203/0286 (2013.01)] 5 Claims
OG exemplary drawing
 
1. 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:

OG Complex Work Unit Math
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:

OG Complex Work Unit Math
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.