Study on Strong Inhibition Compound-salt Plugging Drilling Fluid and Its Application in Offshore Drilling Practices

Well-bore instability problems often occurred when drilling in the formations of Dongying Group and Shahejie Group in Block Chengbei of Shengli Offshore in the past, which led to various down-hole complex problems and seriously affected the comprehensive benefits. In view of this situation, a seawater compound-salt plugging drilling fluid system is developed. The system is obviously superior to the traditional polysulfonate system in rheology, inhibition, high temperature resistance, bentonite contamination resistance and lubricity, and the temperature resistance can reach more than 180°C. The application results of more than ten wells on several platforms in Shengli offshore show that the drilling fluid system has stable performance, convenient maintenance, strong clay inhibition, plugging and collapse prevention, the average well diameter swelling rate of all wells is less than 8.0%, and the cementing quality qualification rate is 100%. It can effectively control the formation mud making, and the waste drilling fluid is only 1/3~1/4 of the conventional water-based drilling fluid. After well completion, the plug can be removed by acidizing, which has achieved good formation damage controlling effect