Development and Field Applications of a New Anti-Sloughing Drilling Fluid System in Daniudi Gas Field

In the Daniudi Gas Field, the Ordos Basin, borehole collapse tends to occur during the drilling of the Shiqianfeng and Shihezi Formations, resulting in complex downhole situations, where drilling operation can not be carried out smoothly. This paper presents the results of developing and applying a new type of anti-sloughing drilling fluid system which was prepared by adding a gel-type cuttings carrying agent into the original drilling fluid. After developing the new product, it was then used in the Daniudi Gas Field. In the new system, the plugging agent was composed of the newly developed anti-sloughing sealer PAS-5 and the cationic asphalt powder YK-H, and the dosage of anti-high temperature filtrate reducer was increased. Laboratory experiments demonstrated that the new type of drilling fluid system performed well overall with better rheological properties, temperature resistance and suppression, and its rolling recovery rate was greater than 96.0% and plugging rate was up to 91.3%. The new type of anti-sloughing drilling fluid system was applied on site to four wells in the Daniudi Gas Field. The wells were drilled without complications, and were done so in a manner that was safe, fast, and with high quality. The hole enlargement rate was less than 6.0%, and the average ROP (rate of penetration) of target layer significantly increased. Results demonstrated that the wellbore instability of Shiqianfeng and Shihezi Formations in Daniudi Gas Field could be solved effectively by using the new type of anti-sloughing drilling fluid.