Drilling fluid wall protection for the comprehensive geological survey Borehole LS01 for the Lingwu and Ciyaobao map sheets in Ningxia

Abstract:

The LS01 hole for comprehensive geological survey of Lingwu and Ciyaobao has a designed depth of 800.00m. During the drilling process, more than 200 meters of Quaternary unconsolidated loose strata was encountered, mainly gravel (boulder)-coarse sand-medium sand-fine sand were interbeded. It was difficult to drill and protect the borehole wall, and prone to have blockage and collapse incidents which made difficult coring. When entering the Tertiary system, the purple mudstone of Qingshuiying formation was met, and the stratum was slippery and produced mud; when entering the Cretaceous Yijun gravel formation, drilling encountered 365.91m broken conglomerate, loose and broken, prone to leading to sticking, high rotatory resistance, less footage per run, and slow advance. In reference to similar borehole drilling data and formation conditions, the film-forming wall-protecting drilling fluid was finally adopted. During the drilling process, the film-forming wall flushing fluid played a good role in drilling through multi-layers of complex strata and provided good wall protection over the broken conglomerate hole section without falling stones and hole collapse accidents. The overall core recovery rate reached 95.89%, meeting the requirements of geological design, which saved casing material. The final hole depth was 800.00 meters, and the final hole diameter was 124.00mm.