Application of sulfonated and oil-mixed positive gel polymer drilling fluid in the horizontal well with long open hole

Due to the long sections of open hole in the development horizontal wells of Tarim oilfield, as well as the problems of collapsing formations, thief zones and stuck pipe, different drilling fluid systems were used for drilling different intervals. In the upper formation, the positive gel polymer drilling fluid was used to prevent the dispersing and mud making in the soft mudstone, as well as differential pipe stuck. Positive gel polysulfonated drilling fluid was used in the lower formation, to ensure the best drilling fluid performances in HPHT condition, and formation isolation was also achieved with the combination use of stabilizing agent, this ensured the a stabilized hole condition in the long open hole. During drilling the hor- izontal interval, sulfonated and oil mixed positive gel drilling fluid was used. By using this drilling fluid system, ROP was improved and the soaking time of open hole was minimized, while such problems as forming of cutting bed, poor rheology, insufficient hydraulic horse power and pressure drop were effectively solved; with the combination use of reservoir protection agent and super fine calcium carbonate, the mud cake quality was improved and the temporary plugging was also formed, and this effectively protected the oil and gas reservoirs. Field applications in 50 wells of long open hole horizontal wells showed that this set of drilling fluid system has stable performance, strong inhibition, good cuttings transportation and suspension. The drilling operations were safe and smooth and no stuck pipes were encountered, at the same time good economic benefits were obtained as huge amount of cost on casing was saved.