Drillpipe structures to accommodate downhole testing

A drill collar structure to facilitate measurement-while-drilling (MWD) techniques while at the same time having sufficient rigidity to facilitate the drilling operation is disclosed. In some embodiments, a metal structure involving openings such as slots, preferably oriented longitudinally along its axis, but also in other configurations, are disclosed to allow sufficient strength while at the same time allowing exit and entrance of electromagnetic energy. A composite structure is also disclosed which, for given layers, has adjacent fibers such as glass and carbon, so that when the layers are overlapped, glass areas overlap glass areas throughout the radial thickness of the composite tube to create "windows" for the entrance and exit of electromagnetic energy. In yet other embodiments, the drill collar can be made of a metallic frame structure with a multiplicity of openings which are filled with a composite material. The metallic frame structure provides structural rigidity while the openings, filled with composite material which are attached to the metal structure, form a fluid-tight cohesive structure sufficient to withstand the rigors of drilling, while at the same time allow the measurements of the formation to be taken through the windows or by making use of sensors embedded in the windows. In another alternative composite structure, carbon fibers can be used if they are electrically insulated in the areas where electromagnetic energy is to enter and exit the structure. Another composite alternative is to alternate carbon and glass fibers in particular sequences or to use insulated carbon fibers to facilitate the operation of instruments which can be mounted in the structure whose operation could be negatively affected by conductivity in the wall in an azimuthal direction.