Techniques for Mud Loss Control in Drilling Fractured Formations in Shi-202 Well Zone

Mud losses mainly took place in the upper part of the N₁ and E₃² formations in the Shi-202 well zone. The N1 formation is full of fractures and the E₃² formation is a double-medium reservoir full of fractures and solution vugs. Low formation pressure bearing capacity, long open hole, multiple lose zones in the hole and coexistence of high pressure and low pressure in the same open hole section have made it difficult to deal with the mud losses. A flaky particle material, NTS, with high compressive strength and being able to roll over when going into mud loss channels, was introduced to drilling fluid to stop and control mud losses. Based on the rates of mud losses, three mud loss control slurries were formulated through laboratory experiment:1) active mud+1.0% NT-DS+(2%-3%) NTS (fine)+(1%-3%) walnut shell (0.1-1 mm)+(1%-3%) SDL+(1%-3%) SQD-98. The total concentration of these additives was 12%-13%. 2) base mud+2% NTS (fine)+3% walnut shell (1-3 mm)+(3%-4%) walnut shell (0.5-1 mm)+1%NT-DS+3% SDL+3% SQD-98. The total concentration of these additives was 15%-16%. 3) base mud+3% NTS (medium:fine=1:2)+(3%-5%) walnut shell (1-3 mm)+(3%-5%) walnut shell (0.5-1 mm)+(1%-2%) NT-DS+3% SDL+5% SQD-98. The total concentration of these additives was about 25%. Operational program for the use of these mud loss control slurries was also developed and tried on 4 wells in the Shi-202 well zone. Good results have been obtained using the mud loss control slurries and mud losses were 100% under control. Pressure bearing capacity of the targeted formation was enhanced, widening the safe drilling window of the formation. The success of the mud loss control has satisfied the requirements of subsequent operations.