EXTENDED-REACH COMPOSITE-MATERIALS DRILLPIPE

This paper presents a new composite drillpipe design that allows for a n increase in the drilling reach of high-angle, directional wells. Hor izontal reach is greatly limited by resisting friction forces that are created by the interaction between the drillstring and the lower side of the borehole. As the drillstring is advanced further into a highly directional borehole, the resisting friction forces give rise to ever -increasing applied-torque and axial (push)-force requirements. The gr avitational forces (i.e., drillstring weight) dominate the buoyancy fo rces in nearly all modem drillstring designs that are currently used i n highly directional drilling operations. These dominating gravitation al forces create reaction forces between the drillpipe and the borehol e wall. The reaction forces, when multiplied by the coefficient of fri ction between the drillstring and the borehole, yield tangential surfa ce forces on the drillstring (normal to, and parallel with, the pipe a xis). These forces resist the applied torque that rotates the drillstr ing and the applied axial (push) force that advances the drillstring. The new composite drillpipe design discussed in this paper reduces the specific weight of the drillpipe so that it will have nearly neutral buoyancy in 15.4-lbm/gal drilling muds. With this reduction in drillpi pe specific weight, a drillstring with this new design will have great ly reduced gravitational forces and, in turn, greatly reduced resistin g friction forces. This design feature allows the applied torque and a xial force to be more effective, thus allowing greater extended-reach capabilities. It is estimated that the current extended horizontal-rea ch approximate limit of IO km could be increased to 15 km or more with the application of this new composite drillpipe design. Such an incre ase in reach would have an important impact on the development of oil and gas fields that are economically dependent on advanced directional drilling technologies. This new composite drillpipe technology has be en extensively bench and field tested and has been successfully used i n short-radius drilling operations. The design features of the propose d light-weight composite drillpipe are discussed and compared to curre nt horizontal drilling operational requirements (using a steel drillpi pe). The new light-weight designs can be used with either steel or tit anium tool joints (with a filament-wound composite-tube body structure between the tool joints). The drillpipe may be fabricated in either 3 0- or 42-ft lengths. Engineering feasibility studies have shown that t his new light-weight composite drillpipe will be economical to fabrica te and should provide significant economic advantages in the developme nt of oil and gas fields requiring extensive directional drilling oper ations.