| "A Study on Sidetracking Slim-hole Reaming " is a key technique to improve the longevity of the sidetracking wells in Liaohe Oilfield. This paper illustrates the study on the problems of small annular clearance, casing centralization and poor cementing existing in the sidetracking slim-hole by analyzing the reason for the short life of the sidetracking wells as well as by combining the slim-hole drilling experiences both at home and abroad. Theoretically, the proper annular clearance and reaming process for the sidetracking slim-hole are discussed, and the preferred clearance of φ152.4 mm and φ118 mm is finalized. The analysis on annular clearance optimization showed that increasing the compressive resistance of cement was a better way to improve the bearing capacity of cement sheath and casing. Considering the hanging ability, seal performance and two-phase fluid driving efficiency of the cement, that is, not only should the cement have high compressive resistance and shear bonding strength, and low interface permeability, it should also have good displacement efficiency and high bearing capacity, the optimal thickness of the cement sheath should be around 1". On the basis of sidetracking slim-hole reaming study, the slim-hole reaming tools which are suitable for different formations are developed, and they are further improved and perfected through field test, φ152.4 mm and φ 118 mm reaming tools are developed. The borehole reamed by the reaming tools is uniform and successive, which eliminates the non-uniform borehole caused by hole collapse during sidetracking operation, improving cementing quality. As for the reaming hole increases the thickness and improves the impact resistance of the cement sheath, the damaging degree is greatly decreased during perforation, workover, production and steam stimulation, prolonging the life time of the sidetracking wells. After reaming, the big annular clearance between borehole and casing as well the less circulating resistance will contribute to decreasing invasion depth of the drilling fluid and slurry, therefore, formation damage caused by drilling fluid and slurry is also reduced. Compared with drilling, reaming operation will shorten the drilling fluid soak time because of the rapid reaming process, as a result, the formed mud cake is less consolidated and is much easier to be washed out during cementing, therefore the second interface cementing can be improved, also the hold down pressure of water applied onto reservoir will be reduced, improving the well productivity. The narrow clearance cementing problem is solved by changing the slim-hole narrow clearance into wide clearance conventional cementing. φ152.4 mm and φ118 mm reaming tools are suitable for the sedimentary formation such as sandstone and shale. In the field test, a new reaming technique is recommended according to the borehole characteristic, that is, φ152.4 mm borehole is enlarged to 170-180mm, φ118 mm to 140-150 mm, the minimum well depth is 875m, and the maximum depth is 2935m, all the reaming holes are successive and smooth. After reaming, the slim-hole cementing is greatly improved, with thepremium rate of more than 90%. According to the information abroad, the average life time of sidetracking wells after reaming can be prolonged by 30%. In the middle or late period of the field, the sidetracking wells are critical to improve the development potential of old blocks and keep stable production, while the reaming technique is the most effective technique to prolong the longevity of the sidetracking wells.
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