Advanced prediction for field strength parameters of rock using drilling operational data from impregnated diamond bit

Field drilling can be a continuous, fast, and reliable technology to predict the cohesion, internal friction angle, and unconfined compressive strength (UCS) of rock in petroleum engineering. Herein, a theoretical model is established in an impregnated diamond bit considering some effective parameters including friction parameter, crushed zone, and bit geometry parameter. A novel method is proposed to determine field strength parameters including the cohesion, internal friction angle, and UCS of four types of rock using drilling logging data. Many drilling experiments in the field are conducted using a drilling process monitoring apparatus to obtain drilling logging data (thrust force, torque, penetration rate, and rotation speed). Experimental results on weak, medium-strong, and strong rock show that drilling with an impregnated diamond core bit includes two fully dependent and simultaneous processes: rock cutting and frictional contact, the dominant role of which is dependent on the cutting point. The cohesion, internal friction angle, and UCS estimated from the proposed method for the four types of rocks are close to those from standard laboratory tests. This practical method can provide practical, fast, and reliable estimation for field strength parameters of rock and should be highly beneficial to field applications in rock engineering.