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For purposes of this discussion, microsystems are those systems or subsystems that represent a quantum leap in the size and/or capability of currently available systems. Interest in these systems is tied to the interest in “smart” drilling and the demand for increased information and reliability. Reliability can often be defined as simplicity. Smaller systems that require less power or are passive measurement devices can be of great benefit in building more complicated sensory and communication networks.
With the incorporation of "interferometry" technology into fiber-optic systems, it has become possible to talk about extremely small packages suitable for harsh environments,  such as a drilling environment. Fig. 1 shows an example of a pressure sensor developed for a stationary measurement environment, such as a well completion. With the advent of composite drillpipe and the capability to embed such systems into the wall of the pipe, using much more sophisticated information systems for drilling is very possible.
If it were possible to reduce drilling cost to the point that it could be considered a part of “predrill” prospect development, a significant capability would exist for improving the economics of developing today’s fractured, unconventional resource. That feasibility is being investigated (Fig. 2) at Los Alamos Natl. Laboratory under a grant through the Department of Energy’s (DOE) National Gas and Oil Technology Partnership Program. The project is called microdrilling. The first enabling technologies were the microelectromechanical systems (MEMS) that made feasible a complete “rethink” of new economies possible for exploration drilling. It is possible to talk about smart drilling systems drilling 2⅜-in.-diameter and smaller boreholes with drill rigs that do not look at all like today’s conventional rigs. The MEMS technologies also make possible downhole systems that are essential for steering and formation evaluation.
To be successful, microdrilling cannot simply be an expensive, smaller form of “slimhole” technology. The MEMS technology will allow a significant reduction in the size of drill rigs and drilling systems. However, the key will be to reduce total well cost. Such concepts as the monoborehole, resulting from expandable tubular technology, must be part of the complete microdrilling capability. In addition, high rate of penetration (ROP) drilling tools will need to be investigated.
Of significant potential to all coiled-tubing drilling is the development program for a high-pressure coiled-tubing drilling system. Maurer Technology developed and tested this system with financial assistance from the DOE. Instantaneous ROPs as high as 1,400 ft/hr were recorded during surface testing in limestone. The system incorporates a special moineau-type, positive-displacement motor with high-pressure (10,000 psi) housing. The motor drives a special polycrystalline diamond cutter (PDC) bit with high-pressure jets to etch the rock ahead of the bit. Thus, the bit only needs to break up the remaining rock not cut by the jet.
Such systems are excellent for coiled-tubing operations because they offer the potential for high ROPs without significant drilling torque.
- Ruan, H., Chen, Y., Liu, Y. et al. 2001. Optical Fiber Logging System for Multiphase Profile Analysis in Steam Injection Wells. Presented at the SPE Western Regional Meeting, Bakersfield, California, 26-30 March. SPE-68807-MS. http://dx.doi.org/10.2118/68807-MS.