Application of a Low Activity High Calcium Content Polyamine Drilling Fluid on Well Zhunbei101

The geological structure of the Zhunbei block is complex and volatile. Coexistence of several fractured zones and fracture development in this block have frequently resulted in severe borehole wall instability. A low activity high calcium content polyamine drilling fluid was developed to deal with these problems. The drilling fluid has calcium content of 3.0% at most the activity of the drilling fluid can be adjusted to less than 0.95, and the membrane efficiency of the drilling fluid can be maintained above 0.2; all these properties are beneficial to borehole wall stabilization. Application of this drilling fluid on the well Zhunbei101 showed that, between well depth of 2000 m and 4200 m, the activity of the drilling fluid was kept at below 0.95, the Ca²⁺ concentration was maintained at above 6000 mg/L. No mud loss and borehole wall collapse happened throughout the whole drilling operation. The average rate of hole enlargement of the second interval was 6.96%, and that of the third interval was 0.59%. The drilled cutting content of the drilling fluid was reduced by optimizing the solids control equipment. The lubricity of the drilling fluid was improved using drilling lubricant. The use of the drilling fluid has provided a reliable guarantee to the efficient development of the reservoirs in the north of Junggar Basin.