In Hongqiling nickel mine area, there were four holes had been abandoned, which took Sichuan Huafeng
Drilling Engineering Co. LTD a painful cost. The mining exploration borehole is designed about 1300m deep,
where 0~23 m is topsoil, 23~260 m is water sensitive altered amphibolite, 260~1200m is altered, loose and strong
water sensitive stratums which soapstone, chlorite and hornblende-limestone appear irregularly and alternately,
below 1200m is stable granitic gneiss. Construction difficulties focused on altered chlorite zone. Dealing with water
sensitive stratums, "dry drilling" can be used, which no water need to pump while drilling, but, for drilling a deep
hole , it is high risk and labour intensity, low efficiency. In order to enable rope core drilling goes on smoothly, KP
copolymer low solids mud, double polymer mud, PAB solidfree mud, vegetable gum mud, low solid sulfonated mud
had been tried. But, all of them failed to effectively inhibit hydration swelling of fracture zone, which resulting in
hole’s wall collapse and pump blocked, furthermore, the borehole cannot be swept down to the bottom. Even though
repeatedly cementing, the hole’s wall stable result is still not satisfactory. Along with the temperature was very low,
although the laboratory experiment performances of the drilling fluid was good, due to the harsh construction
environment, drilling fluid performance was hard to be guaranteed. Therefore, to select a new suitable drilling fluid
system had to be rethought.