High density drilling fluid research and applicationin Borehole DZShen021 at SichuanTibet Railway

Abstract:

Borehole DZShen021 at SichuanTibet Railway is a tectonics investigation hole where the stratum is very complex. During drilling, water gushing, sand gushing, falling stones and borehole shrinkage occurred. The high density drilling fluid was researched and used to balance downhole pressure to prevent mud and sand from flowing into the drilling string, so that the inner tube of the core barrel can be landed in place smoothly. Through selection and concoction of the strong inhibitive and low water loss drilling fluid, borehole collapse and shrinkage in mudstone were reduced. The drill bit diameter was also increased, hence the annulus to allow drilling cuttings to be discharged smoothly; thus the circulating pump pressure can be reduced, which was conducive to the stability of the hole wall in the fault gouge section. The screen pipe was used over the broken section to divert some water inflow so as to reduce the damage to drilling fluid performance. By strengthening the control of drilling parameters, disturbance to the borehole wall was reduced and the borehole wall was maintained as stable as possible. Finally, the borehole was drilled to the designed depth, achieving the purpose of engineering investigation.