Well logging technology for highly deviated and horizontal wellbores

Abstract With the Dresser Atlas pipe-conveyed logging system for highly deviated wells, i.e., the Slant-hole Express, the logging instruments are guided to the bottom of the borehole through the protection of the drillpipe. A wireline guide placed at the end of the drillstring assembly, facilitates the re-entry of the logging instruments into the drillstring after completion of the open-hole logging run. The significant difference in the Slant-hole Express operation and conventional through-drillpipe pump-down operations is in the use of a sidedoor wireline entry-sub properly placed within the drillstring. Casing depth and placement of the sub, which should stay within the protective casing during the logging operation, then defines the length of the open-hole logging run per trip in the borehole. A significant advantage of the Slant-hole Express system is that no special “wet” electrical cable connector is required for mating to the logging instrumentation. In order to overcome downhole problems due to friction of logging instruments, insufficient weight, rigidity of long instrument assemblies, and the possibility of the bull plug sticking at small obstructions in highly deviated wellbores, a number of mechanical devices are available. These include sinker bars, swivels, knuckle joints, side-and-through-rollers, and nose guides. In the horizontal portion of a borehole, the use of coiled tubing has proven successful in “pushing” the logging instrumentation toward the bottom (end) of the borehole. The basic concepts, considerations, observations, and field experiences with this technology are discussed and illustrated in this paper.