Abstract This paper offers a study of a new model of articulated downhole motor assembly for short radius horizontal drilling. Theoretical analysis of this model and relationships among acting forces, deformations, structure, borehole geometry and operating parameters are given. Design principles of the assembly configuration and main conclusions are also presented.
Introduction To meet the increasing demand of petroleum resources, since 1970's the short radius horizontal well drilling technology has been improved fastly. Now this technology has become the important technical way to enhance oil recovery of old wells.
Drilling tool is the key equipment in the drilling of short radius horizontal wells. Since 1930's, several companies have engaged in a series of research work and developed several kinds of short radius horizontal well drilling system. Hundreds of wells were then successfully drilled. Among the existing systems, the articulated downhole motor assembly is the most interesting one, because of its excellent technical performance and promising future development.
The articulated downhole motor assembly consists of a lower and an upper sections (Fig. 1). The lower section is a specially configurated motor assembly. It can be classified into two kinds, i.e. Angle-Build and Angle-Hold, depending on the application. The upper section is a flexible collar string connected by specially designed knuckle joints.
The function of the lower section is to drill the borehole (curved short radius section or horizontal section), while the upper one merely follows the curvature produced by the lower's and keeps the drilling continuously.
Although there are many published papers introducing the basic concepts, configurations and applications of the assemblies, the authors of this paper didn't find any one of them to deal with a mechanical constructions and its design principle. Very important theoretical works on the proper design of such assembly is to meet its engineering requirements. This paper, presenting the author's main works at mechanical analysis and design principle of the above mentioned assembly, may fulfill the deficiency in this domain.
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