The Gas Research Institute (GRI) initiated a data acquisition and analysis project in 1990 with the goal of evaluating the applicability of horizontal well completions In various gas-productive reservoirs. One of the target gas reservoirs in this study was the Mancos B interval of the Mancos Shale located in the Southwest Rangely Field in northwest Colorado. The overall objectives of the project were to determine reservoir characteristics from a vertical well, model the reservoir, design an appropriate horizontal well completion and compare the production economics of the horizontal well to the economics of the standard vertical well completion.Data were initially acquired from a vertical well completion in the Mancos B to evaluate the extent and strike of natural fractures, insitu stress magnitude and direction, log-derived reservoir characteristics, pre-and post-frac production rates and hydraulic fracture dimensions. A horizontal well was subsequently designed to intersect the interpreted primary set of natural fractures in the Mancos B. The horizontal well was air-drilled and intersected approximately 1,500 ft of the Mancos B "main porosity zone."Borehole image log data indicated that no significant natural fractures were intersected by the horizontal wellbore. A 4-1/2-in. liner was cemented in the well to facilitate hydraulic fracturing after only minimal gas was produced from the open-hole during a 3-week production test. Reservoir modeling and economic forecasting Indicated that 2 hydraulic fracture treatments over the 1 ,500-ft interval would be the most economical. Two fracture treatments were attempted but both resulted in screenouts during the early sand stages. The early screenouts were believed to be directly related to the higher than normal in-situ stresses that were observed during breakdowns and injection tests. Due to the limited vertical extent of natural References and illustrations at end of paper.fractures and the lack of vertical permeability, horizontal well completions in this area of the Mancos B reservoir do not appear to be a viable completion alternative to hydraulically fractured vertical wells.

Our main task was to prepare and seek the adoption of a design which was bound to be a compromise between the dictates of conflicting interests.128. A comprehensive quality control system was organized by the project engineer (my co-Author) covering inspection and testing at the various steel producing works, fabricating shops and works providing all other materials, and also specialized inspection and testing at the assembly and erection sites. Progress of the reconstruction was governed mainly by the rate at which approximately 5000 tons of steel in grades and sizes normally required for bridge work could be rolled and delivered from the three rolling mills to the three fabricating shops working on the approach spans and main arches.129. Collaboration between British Rail and the Welsh Office achieved approval of a secondary proposal for an upper road deck on which construction work is steadily proceeding. On completion, the upper deck, three lanes wide, will form part of a scheme already designed, by which the Holyhead road will by-pass Bangor and also the Telford suspension bridge, the life of which should thereby be greatly extended. M r R. W. HusbandAt the beginning of the job it was thought that considerable use could be made of the old tubes in construction of the new bridge. Undoubtedly they made excellent access ways both for men and materials, but before the work had progressed far the nuisance value of both tubes and towers became apparent. 131. Lifting of members in the top of the arches and in the approach spans was restricted by the presence of the underside of the ironwork. The bulk of the tubes meant that the travelling gantries for the erection of the arch units had to be considerably larger than required for their prime purpose, and the sag in the tubes dictated that certain members in the top of the arches had to be initially set lower than required until the tubes had been dismantled. At the top of the towers the sandstone and brickwork had spalled badly, leaving few square and flat surfaces to work to.132. From the outset the Contractor was faced with a daunting task and we would like to acknowledge the considerable ingenuity and innovation used throughout the job to overcome the large number of expected and unexpected problems that arose.