Correlation study of cuttings and formation during tunnel geological investigation using HDD technology

Abstract

To improve the accuracy of formation inversion by cuttings during tunnel geological investigation using horizontal directional drilling technology, this study focuses on the correlation of cutting transportation features and formation spatial locations based on a tunnel geological investigation project. This study mainly draws the following conclusions: The different cuttings' migration modes are determined according to the cutting's migration settling velocity, Fei Xiangjun's critical velocity theory, and Larsen's minimum return velocity theory. The migration of cuttings in the annulus is bedload, a small number of cuttings are suspended load, and the little remaining is cutting's bed. The newly generated cuttings at the drill bit tooface would come out as suspended load first with drilling fluid in the field. The cutting suspended moving mode was established based on the material transportation theory, the freesuspension, and the movement equations of cutting particles. According to the recorded data of carbonaceous slate cuttings and quartz schist cuttings, the resistance coefficient of the intact borehole wall during cutting movement is obtained, while the resistance coefficient of the fault zone is 2.72 times that of the intact zone. Then, the final suspended moving speeds of cuttings in the annulus for Φ140 mm and Φ168 mm drill rods are calculated, and finally, the correlation analysis calculation model for cuttings and formation is established.

Keywords

• horizontal directional drilling
• tunnel geological investigation
• cuttings transportation
• formation inversion