Coring technology in gravel layer in longgang and jiulongshan structure

The lithology of Longgang,Jiulongshan structure is mainly coarse quartz sandstone and sandy conglomerate. Because the unique characteristics of the gravel is hard,brittle,and poor drilability,the coring bit and coring tool are easily be damage. Based on the different drilling time,the hardness of the gravel was divided into three different ones. During coring,the working condition of coring bit in gravel with different hardness was not easy to determine. Based on the comparative analysis of gravel coring in well Longgang 117 and 167 well,and lithological characters,the coring difficulties were put forward,coring bit was optimized and selected,the drilling parameters and coring methods suited for the gravel coring were researched.