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Abstract
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Maroon Field with 67 km of length and 7 km of width is one of the largest crude oil reservoirs in southwest of Iran. This asymmetric anticline reservoir along the North-West to South-East is in alignment with adjacent fields and is located in southeast of Ahvaz. This field was discovered in 1343 and its development begun since 1348. Gachsaran’s high-pressure conditions along with the complex features of its formation in Maroon Field during drilling and production processes requires the analysis of problems from different perspectives. A significant number of damages to the casings and liners of Maroon oil wells of Gachsaran’s high pressure formation have been reported, which makes the investigation of casing collapce and its causes along with solutions to prevent this phenomenon, a necessary and vital task. This thesis extensively investigated the casing collapse of oilfields around the world and in southwest of Iran. The causes were diagnosed to be high pressure formations, formation bending and drifting, poor quality of cover-cement of casing, poor distribution of tensions and geotectonic movements, reservoir compressibility, and thermal operations. Also a wide variety of information, of the referred oilfields have been presented. Upon full investigation of the wells in the aforementioned field which were affected by collapse and analysis of the data collcted from the field and formations movements, the geotectonic movements due to the Arabia-Eurasia plate convergence was found out to be the main cause. Formation convergence and casing collapse were simulated and they matched the with the field’s and its data. According to mentioned analysis, double casing along with proper cementing using high quality cement, is the best method to prevent premature casing collapse, and it can approximately double the lifetime of the well. Using 9 5/8” casing, N-80, 43.5 lb/ft until the first layer of Gachsaran, and then using 7” casing, P-110, 35 lb/ft till entering the reservoir
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