With the development of highly deviated and horizontal wells, new techniques for running logging tools have been developed, in addition to the wireline method, for conveying logging tools in wells. Five techniques are now operational: the wireline method, the measurement-while-drilling (MWD) method, the information and measuring systems in horizontal wells (Simphor TM) method, the pumpdown stinger method, and the coiled-tubing method.
Logging by wireline is naturally restricted to well inclinations up to 65 degrees. Because they use drillpipes, Simphor and MWD techniques are theoretically capable of covering all conventionally drilled wells, whatever their deviation or horizontal development. With the use of a telescopic stinger, only small-diameter or production tools can be used. The relative fragility of coiled tubing limits its use to deviated wells with standard tools and to short horizontal drainholes with lighter tools. The last two methods offer the advantage of being operable without a drilling rig.
In addition to horizontal wells, these methods naturally lend themselves to all highly deviated or difficult wells where wireline working is not possible, thus adapting to a wide range of applications.
In vertical or slightly deviated wells, logging tools are traditionally lowered by gravity on a wireline. With the development of wells with horizontal boreholes, where gravity can no longer assist in moving the logging tools and where the drain lengths in the reservoir to be logged are no longer expressed in tens of meters but in hundreds of meters, new ways to convey the instruments down to the bottom of the hole had to be found.
Four new principles of running in probes are now operational to meet this need. The first uses the drillstring as a rigid link between the tools and the surface (the Simphor method); the second is based on the principle of the telescopic tube (pumpdown stinger); the third uses a coiled tubing. For these three techniques, the data vector is the cable. The fourth way of taking bottomhole measurements in highly deviated or horizontal wells is the MWD method, where drillpipe is used as a means of displacement, but where the data are sent through the drilling fluid and no longer by cable.
The purpose of this paper is to recall the principles of these different techniques, to study their advantages and disadvantages, and with the experience gained in horizontal wells, to indicate the ranges of use of each, in terms of well conditions, inclination, or horizontal development. All these methods have been successfully tested, either in openhole wells or in cased holes for logs with standard or production tools.
Naturally, all these methods do not involve the same logging tools. We remind the reader, however, that we are dealing here with means of conveying the probes and not the quality of the tools. It is also known that the working conditions and responses of certain tools are heavily influenced by the position of the drain relative to the layers and give rise to specific difficulties in interpretation. This matter is also left aside in this paper.