Analysis of energy for rotary drilling in weathered granite formation

Abstract

Rotary drilling is a dominant way in geotechnical engineering borehole surveying. Based on the principle of conversation of energy, the energy for rotary drilling has been analyzed. Besides, a hydraulic rotary drill R-20 instrumented with a drilling process monitoring (DPM) system has been used for site investigation on weathered granite formation-, and drilling energy is further analyzed based on the monitored data. The result shows that the penetrating energy in drilling is mainly kinetic energy dependant. The distribution of energy for rock failure is related with the strength characteristics of the penetrated formation. The kinetic energy is more than 98 percent and energy from effective thrust force is less than 2 percent when drilling in slightly weathered rock or fresh rock. However, the energy from the effective thrust force reaches to more than 22 percent, apparently increases with the increase in weathered degree of rock when drilling in soil or very strongly weathered rock. It shows that kinetic energy of drilling system and energy of effective thrust force can reflect the characteristics of the penetrated formation, which can provide theoretical foundation for identification of formation using penetrating energy in real-time.

旋轉鉆進是巖土工程鉆探的主要鉆進方式,從能量守恒原理出發,對旋轉鉆進的能量進行分析。同時,在R-20液壓式回轉鉆機上安裝數字式鉆孔過程監測(DPM)系統,在風化花崗巖地基工程中進行試驗,并在監測數據的基礎上對鉆進能量進行分析計算。研究結果表明,鉆進過程中用于破碎巖石的能量主要來自鉆進系統的動能,鉆進系統用于破碎巖石的能量分配與地層強度特性有關。在風化程度較低或新鮮巖層中鉆進時,破碎巖石98%以上的能量來自系統的動能,而軸壓力推動鉆頭位移所給出的能量不到2%;在土層或全風化巖層中,軸壓力所做的功達到22%以上,且明顯隨風化程度的增高而增大,說明鉆進系統動能與軸力功可用以表征地層的可鉆性,這為實時鉆進能量用于地層的識別提供理論依據。