Calcium Nitrate Treated Polyamine Drilling Fluid Technology

In the marine sedimentary area in southeast Ecuador,formations drilled are young,unconsolidated,ready-to-disperse and highly mud making,especially theChalcanaand Orteguaza layers,where long sections of formations with more than 80% shales and with interbeded coal seams are found.These formations,having poor diagenetic grade and strong water absorption capacity,are very unstable and downhole troubles have long been encountered during drilling operations.A calcium nitrate treated polyamine drilling fluid has been engineered to drill these formations.This drilling fluid has stable properties and strong inhibitive capacity,and the rate of linear expansion of shale cores is only 0.47 mm after immersing 16 h in the drilling fluid,and the primary recovery of shale cuttings on hot rolling test is 96%,the secondary recovery of shale cuttings 88%.Tolerance to clay contamination is 6% and tolerance to cuttings contamination is 8%.This drilling fluid has low corrosion to drilling tools (corrosion rate is 0.058,5 mm/a),and is non-toxic and easy to degrade.Field application has demonstrated that this drilling fluid is highly inhibitive,has good hole cleaning capacity and cuttings carrying capacity.Good lubricity of the drilling fluid helped minimize bit balling.Borehole stabilization and safe drilling have been realized,and drilling time saved.The running of φ339.7 mm casing string has been completely successful.