Date of Award

1987

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Andrzej K. Wojtanowicz

Abstract

The phenomenon of mechanical friction in the oil well borehole was investigated. Immediate application of such a study is to improve casing design in directional wells. An additional application is the prediction of reciprocating loads in directional wells for cementing purposes, that is recognized to be an effective method to avoid cement channeling through efficient mud displacement. Field studies on the borehole friction coefficient revealed its insensitivity to depth, various well trajectories, size of pipe and its surface configuration, leading to the conclusion that one value of the borehole friction factor can represent a single well. Also there was good agreement between 2-D and 3-D model predictions for drag-weight ratios above 25%, and spatial irregularities retained at minimum above the kick-off point. The prediction of surface axial loads at the planning stage of the well using the 2-D model was also investigated. It showed that surface running loads can be planned for in advance as long as surface irregularities are kept within reasonable limits, and a good estimate of the borehole friction factor is made. Minimum design factors for the borehole friction factor and predicted running loads are estimated for this research. The results suggest the inclusion to the design process of casing strings in directional wells. Laboratory experiments were also conducted on an instrument with dynamic filtration and friction factor evaluation capabilities, using 6 in. rock cores. Seven water base and three oil base drilling fluids were used. The results showed that most of the friction factor values fell within the range of 0.2 to 0.3, and for most cases these values were insensitive to lubricant addition. It was found that its effect can be significant in areas of low contact pressures and high filtration rates. Such conditions are associated with the long slant hole section of directional wells. A new method for casing design in directional wells was developed. The method is based on determination of maximum axial pulling loads. The criteria of minimum cost of casing string is used for selection of the combination casing string. The calculation procedure is based on the dynamic programming technique.

Pages

274

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